Abstract

Planetary boundary science defines key thresholds in the Earth System's ecological conditions that precede local or global ecosystem collapse and threaten human well-being. Terrestrial ecosystems enter into the nine originally defined planetary boundaries only indirectly, through boundaries such as biodiversity and land use. This observational study and literature review aggregate what is known regarding the quantity and quality of terrestrial ecosystems - particularly old-growth and primary forests - necessary to sustain the biosphere. The study seeks to answer the question: what extent of landscapes, bioregions, continents, and the global Earth System must remain as connected and intact core ecological areas and agroecological buffers to sustain local ecosystem services as well as the biosphere commons? Two preeminent considerations are connectivity of large ecosystem patches, enabling them to persist as the matrix for the landscape, and critical collapse of the dominant large habitat patch – or "percolating cluster" – into smaller, more isolated habitats, in a sea of human development. This transition, which has been found to occur at about 40% habitat loss in landscapes and bioregions, is likely to be similar at a continental and global scale. An example of the importance of connected ecosystems is illustrated by the effort to maintain Asian elephants as a viable umbrella species in the Western Ghats bioregion of India. Elephants moving across landscapes are emblematic examples of the myriad types of flows on a connected landscape that make life possible.

A new planetary boundary threshold is proposed: that across scales 60% of terrestrial ecosystems must remain, setting the boundary at 66% as a precaution. It is concluded that sustaining the biosphere requires that natural and semi-natural ecosystems, and their biogeochemical flows, must remain the context for human endeavors. This in turn requires large core ecological areas and geographically well-connected ecosystem processes and patterns as the majority of the global and fractal landscape matrix. Further, again based on ecology's percolation theory, two-thirds of the 66% of terrestrial ecosystems to be maintained must be protected as ecological core areas, for the ecological patterns and processes of the other third - composed of human managed ecosystems - to be sustained as buffer and transition zones. Thus strict protection is proposed for 44% of global land, 22% as agro-ecological buffers, and 33% as zones of sustainable human use. Because humanity is now the major force shaping the biosphere, up to 50% of Earth's land surface has already been transformed from mostly wild to mostly anthropocentric; thus the biosphere may already have lost its global percolating cluster. If so, with diminished connectivity, the global ecosystem now exists as islands of nature within a sea of humanity, and it is urgent to protect large, relatively intact terrestrial ecosystems that remain, especially old-growth and primary forests. To ensure global ecological sustainability, it will be necessary to re-connect matrices of intact ecosystems across scales, so that globally the biosphere can percolate back to connected nature as the provider of context to all life. Otherwise, it is hypothesized the global biosphere may collapse, and Earth System perish.

*Version 1.1 making edits to shorten for publication from paper presented at Kerala Eco-Conference.

From Malthus (1798), through Aldo Leopold's land ethic (1949), to Limits of Growth (Meadows et al. 1972), through the Millennium Ecosystem Assessment (2005), and finally to current planetary boundary and global change science (Rockström et al. 2009, 2009b); a common strand of concern has been expressed regarding human growth's impacts upon Earth's biophysical systems – terrestrial ecosystems in particular – and an interest in requirements for global ecological sustainability, while avoiding biosphere collapse. Our biosphere is composed of Earth's thin mantle of life present at, and just above and below, the Earth's surface. Some have indicated human impacts upon the biosphere are analogous to a large, uncontrolled experiment, which threatens its collapse (Trevors et al. 2010). Little is known what collapse of the biosphere would look like, how long it would take, what are its ecosystem and spatial patterns, and whether it is reversible or survivable. But it is becoming more widely recognized that Earth's ecosystems services depend fundamentally upon holistic, well-functioning natural systems (Cornell 2009).

Accelerating human pressures on the Earth System are exceeding numerous local, regional, and global thresholds; with abrupt and possibly irreversible impacts upon the planet's life-support functions (UNEP 2012). Planetary boundaries provide a framework to study these phenomena, by defining a "safe operating space for humanity with respect to the Earth System" (Rockström et al. 2009). The study of planetary boundaries seeks to set control variable values that are a safe distance from thresholds that avoid cessation of key biophysical processes that determine the planet's ability to self-regulate to maintain conditions conducive to life (Rockström et al. 2009b). This builds upon landmark efforts by Meadows et al. (1972) to first define global limits to growth. They concluded that key resource scarcities would emerge, predictions which have proven remarkably accurate (Turner 2008), albeit delayed – but not avoided – through the advent of computer technology. Ecological and economic warnings since at least Malthus have called attention to economies' dependence upon natural resources. The conclusion that near-exponential growth of human population and economic activity cannot be sustained, far from being disproven, is more valid than ever (Brown et al. 2011).

The initial planetary boundary exercise identified nine global scale processes, including climate change, rate of biodiversity loss (terrestrial and marine), nitrogen and phosphorus cycles, ozone depletion, ocean acidification, freshwater, land use change, chemical pollution, and atmospheric aerosol loading. Thresholds were established for seven of these, and three – rate of biodiversity loss, climate change, and the nitrogen cycle – were found to already have surpassed a preliminary assessment of the safe planetary boundary threshold (Rockström et al. 2009). Many of these changes occur in a nonlinear and abrupt manner, while others are more incremental and subtle, yet both types of change threaten the viability of contemporary human societies by diminishing or destroying ecological life-support systems. If one or more of these boundaries are crossed, it could be "deleterious of even catastrophic" as nonlinear and abrupt environmental change occurs at the continental to planetary scale (Rockström et al. 2009b).

Figure 1: Rockström et al. 2009

Setting boundaries of course requires normative decisions on risk and uncertainty. Planetary boundary details and methodology are not without critics, as they are in themselves an imperfect social construct, prone towards bias and political boundaries favoring the rich. Yet there is no escaping the observation that humans have become a powerful agent in Earth System evolution (Biermann 2012). It has been noted that setting thresholds may in itself prolong the risk of continued degradation on the false premise that there is time and it is safe to do so (Schlesinger 2009). Nonetheless, given the well-documented plethora of environmental decline, there appears to be little question that quantifying as best you can based upon science when these changes become dangerous – however uncertain and problematic – and what can be done to avoid possible human extinction and biosphere collapse – remains a valid and valuable field of inquiry.

Earth has gone through many changes, yet for the last 10,000 years of the Holocene epoch there has been a remarkable period of stability – with temperature, freshwater, and biogeochemical flows staying in a relatively narrow range. Yet humanity's largely deleterious activities upon ecosystems have become a force of nature, impacting Earth System functioning (Zalasiewicz et al. 2011). It is increasingly acknowledged that human activities, including use of fossil fuel and industrial agriculture, are destroying ecosystems and changing the climate, threatening this stability.

It is generally accepted that humanity is in ecological overshoot, which means we have already surpassed planetary limits upon sustainability, with lags in full impacts yet to be realized. A growing human population takes goods and services from the Earth System at a rate that erodes its capacity to support us (Steffen et al. 2011). And it is clear that civilization depends upon humanity remaining within thresholds (Folke 2011).

Some have proposed that this human dominance signals a new geological epoch that could supplant the Holocene; it has been dubbed the Anthropocene (Crutzen 2002; Steffen et al. 2011). As we move further into the Anthropocene, humanity risks driving the Earth into "hostile states from which we cannot easily return" (Steffen et al. 2011). Humans depend upon the biosphere – the global Earth System which integrates life and its relationships – for the human life-support system. Human development and advancement are often not perceived as being connected with the biosphere and ecosystem services. Given human domination of the biosphere, ecology must more fully incorporate human behavior (Peterson 2000).

There is a strong consensus that human activities are influencing the Earth's climate (IPCC 2007). Yet an understanding of the impacts of loss and diminishment of natural ecosystems – whether terrestrial, aquatic, or marine; expressed at various scales, and examined using numerous ecological criteria including genetic, organism, species, plant community, and landscape perspectives – remains more elusive. The scale and magnitude, the sheer momentum behind biological impoverishment of the planet is in this researcher's opinion not well understood. And it seems clear that worst-case scenarios of global ecological collapse are not being given their just and prudent consideration.

In fact climate science – as one example – has been described as alarmist, but studies have found instead that it is often conservative in its predictions, erring on the side of less dramatic impacts (Brysse 2012). Rahmstorf and colleagues (2007) found in comparing IPCC’s Third Assessment Report (TAR) with subsequent observations in the science, that the IPCC had underestimated the change in global mean temperature, sea level rise, and atmospheric carbon dioxide concentration. Hansen and colleagues (2012b) found that extreme heat during the summertime is occurring at three times the standard deviation of historical climatology, with extreme heat anomalies such as that in the American southwest in 2011 and Moscow in 2010 having gone from covering 1% to 10% of Earth's surface at any time. The increased probability of such events is compared to "loaded dice."

In short, scientists may be significantly underestimating future impacts, magnitude, and rate of anthropogenic climate change. The same scientific bias in favor of avoiding emotion and maintaining an objective tone – when faced with what may turn out to be an unprecedented and poorly understood global ecological emergency – is likely to be present in assessments of ecosystems, biodiversity, and the state of the biosphere. Up to one half of Earth's land surface has already been transformed by human action, and no ecosystems are free of human influence (Vitousek et al. 1997). While the scientific literature is replete with ecological warnings – such as Folke and colleagues (2011) cautioning of a need to "avoid tipping into a new undesirable Earth System state" – there is a lack of specificity about what exactly this means.

Planetary boundaries represent tipping points where Earth's subsystems react in a nonlinear, abrupt fashion. The approach focuses on key biogeochemical processes that determine planetary self-regulation and make the Earth System highly analogous to other scales of life from the cell to organisms and ecosystems. It connects traditional environmentalism with Earth System science and what is known of ecological resilience. If further developed and moved downscale to key subsystems, a planetary boundary perspective could serve as a framework for prescriptive ecological policy and inform radical social, legal, and political change required for a sustainable society in relation to the ecosystems that are its underpinning.

Our era's remarkable scouring of Earth's naturally evolved ecosystems has become commonplace, barely noticed by most, as it is thought that destroying natural systems is a normal development process. Yet the Millennium Ecosystem Assessment (2005) found that, of 24 global ecosystem processes – ranging from direct food provisioning to more indirect services – 15 are being degraded or used unsustainably. Climate change is expected in the next decades to place enormous strain upon the survival and integrity of important ecoregions – and their species and ecosystems (Beaumont et al. 2010). Initial planetary boundary research indicates that climate is already past safe levels (Rockström et al. 2009b). There is concern that climate may be approaching or even reaching a point of no return, such that even without additional forcing from anthropogenic climate change, warming will continue out of control, driven by feedbacks such as forest dieback and polar ice and permafrost melt (Hansen et al. 2008).

This loss of biodiversity and ecosystems is problematic enough, yet in conjunction with the planetary boundary of possible looming abrupt and runaway climate change, terrestrial ecosystem loss can only be described as catastrophic. Loss of the panoply of life so rapidly and completely within only a few centuries represents the wholesale dismantling of the biosphere. Terrestrial ecosystems are the nodes in interactions between oceans, air, and water. They are the energy pumps cooling Earth and cycling water, nutrients, and energy. The destruction and diminishment of ecosystems, together with climate change, mean loss of the context within which humanity exists and loss of the environmental top-down regulatory system that makes life possible.

There is increased interest in challenges facing global ecology and equitable advancement for humanity. Recently a group of leading ecological and development luminaries called the Blue Planet Laureates (Brundtland et al. 2012) noted the almost certain impossibility of achieving global ecological sustainability without addressing related issues of poverty, inequity, and injustice. They noted again – what is deeply contested but should be obvious, because nothing grows forever – that infinite growth on a finite planet is not possible. Kosoy et al. (2012) go so far as to say the dominant economic system is delusional, not acknowledging that economies must live within Earth's biogeochemical constraints, and grow by accumulating ever-increasing ecological debt. The dominant economic model, which emphasizes industrial growth, is based upon a mechanistic worldview that destroys its own life support system through failure to see the essence of interrelated social and ecological systems (Taylor 2007), as all growth-based development is ultimately unsustainable (Daly 2005).

The dominant economic model is misconceived, based upon metaphysics devoid of scientific support. Industrial capitalism has not been systematically reviewed in light of 200 years of science (Kovoy et al. 2012), much less recent findings of threats to global ecological sustainability. Economic systems should meet all human needs and not destroy biodiversity and ecosystems. Our natural habitat and life-support systems are being treated like a commodity, on the false premise that they can be replaced with technology. Thus, the global economy is almost certainly profoundly unsustainable.

It is increasingly recognized that economic and social ills are deeply entwined with these limits and cumulatively pose a threat to the biosphere, that the social economy is a subset of the global ecological system, and that a need exists for courageous leaders to speak the difficult truths, and for all to educate and act on these matters (Cairns 2010). Our health and well-being depend upon complex ecosystems that support life on our planet, yet we are consuming the biophysical foundation of civilization. Efforts to systematically assess the long-term, aggregate impact of human activities upon environmental life support systems are lacking (Kosoy et al. 2012). We will either transform ourselves away from these planetary boundaries or enter a series of escalating crises until collapse. It is quite possible that as a result of degraded ecosystems and resource shortages, we are going to witness collapse of the world socio-political-economic system (Taylor 2007), some sort of biosphere collapse, and perhaps death of the Earth System.

The global nature of challenges facing the biosphere and humanity is unique, transcending national boundaries and cultures. This global ecological emergency is occurring during times of high levels of material comfort for some while others suffer extreme depredations, but all alike are facing an eroded planetary life support system (Steffen et al. 2011). Natural scientists must overcome the propensity to ignore the politics of human societies (Peterson 2000). These observations illustrate that efforts to sustain the biosphere cannot help but be political, and if humanity is to survive, much less thrive, scientists who are experts on these issues had best be willing to make prescriptive recommendations that may well prove controversial. Their refusal to engage on issues of economic injustice and equity blocks progress towards cooperative solutions to environmental and social ills, and lessens the prospects of achieving mid-to-long term global ecological sustainability.

Terrestrial ecosystems are not among the nine originally defined planetary boundaries directly, except peripherally through other boundaries, such as biodiversity and land use. This is unfortunate, as landscape ecology and global change inform us regarding the importance of large, connected natural ecosystems – where the flows of genes, species, nutrients, energy water occurs across scale and ecological criteria – in a process of life begetting life. A key indicator of bioregional sustainability is habitat areas for large, wide-ranging species – who, when their habitat is protected, provide an umbrella for the continued provision of local and global ecosystem services. We know shockingly little about how many terrestrial ecosystems must be left standing to maintain a habitable world and to guarantee biosphere sustainability.

Planetary boundary literature may not be adequately accounting for the integrative, keystone nature of terrestrial ecosystems in maintaining the biosphere. Preserving large and connected, intact, naturally evolved terrestrial ecosystems – i.e., both new core global ecological preserves along with restored buffers and transition zones – may be required for global ecological sustainability. Wildlife corridors to maintain connectivity across scales from genes to ecosystems are important to counter habitat fragmentation (Jones et al. 2012). Core protected areas that are large and configured to minimize edge effects and maximize interior habitat are critical to maintaining landscapes where nature remains the matrix, providing top-down ecological constraint upon ecosystem pattern and process (Soulé and Terborgh 1999; Noss et al. 1999). Recent findings indicate that edge effects can increase in fragmented forests through continuous diminishment even with relatively little new loss of habitat (Riitters and Wickham 2012).

The question of how many terrestrial ecosystems are required to sustain the biosphere needs to be investigated further, given the wholesale clearance that is occurring of natural plant communities and wildlife populations arrayed in ecosystems across landscapes and whole bioregions. This is a review paper in political ecology, a discipline that seeks to integrate natural and social science approaches to understanding the relationship between ecosystems and people (Peterson 2000). Political ecology is firmly rooted in geography and first emerged in the 1970s to link community ecology, cybernetics, system theory, and cultural adaptation to address ecology and political economy concerns (Walker 2005). Through this initial literature review and observational study, I hope to begin answering this question and laying out a research program to continue to establish and refine an agreed upon, relatively clear, and defensible terrestrial ecosystem loss planetary boundary.

Political ecology has been accused of lacking ecology (Walker 2005). Here I am going to propose an ecologically rich revision to the planetary boundary framework – while not ignoring politics – to more fully measure the importance of intact terrestrial ecosystems for ecological processes required to sustain ecology and maximize life's well-being. And I am going to do so within the illustrative land-use decisions being made in the Western Ghats and Kerala, India, in pursuit of regional ecological sustainability, including the conservation of viable Asian elephant populations. It is not unscientific to discuss the political implications of ecology and trends in ecosystem loss.

Planetary boundaries as now conceived provide little guidance to on-the-ground development decisions such as those being made in Kerala under the planning process for Western Ghats ecologically sensitive areas. Yet we know critical thresholds of landscape pattern – such as the provision for adequate Asian elephant habitat and corridors – are an ongoing discussion there. To be useful as more than an academic exercise, planetary boundaries need to inform action now. What is needed is that extra layer of detail at the subsystem level, using landscape to bioregional approaches. We need to identify key ecological metrics across scales in terrestrial ecosystems which, when breached, lead to system instability and crash, and intervene appropriately to avoid and mitigate.

The gravest shortcomings to planetary boundary thought are this glaring lack of a terrestrial ecosystem boundary and the anthropocentric focus, in essence writing off other life forms that don't keep humanity "safe." It will also be suggested that planetary boundaries must be less anthropocentric and seek to determine thresholds to maintain all life, including the biosphere as a whole. Planetary boundary thinking needs to further elucidate thresholds and boundaries for naturally evolved ecosystems – particularly terrestrial – as a safe space not just for humanity but for all life and the continuation of natural evolutionary processes within a living biosphere.

Biodiversity and Old-Growth Forest Loss, Abrupt Climate Change, and Ecosystem Collapse

Humanity dominates the Earth to such an extent that there is unknown potential for Earth to be transformed rapidly and irreversibly into a previously unknown state (Barnosky et al. 2012). Solar energy accumulating in plants through photosynthesis drives essentially all the Earth’s food chains. Agriculture, forestry, and urbanization are transforming major biogeochemical cycles, changing global climate and the structure and function of terrestrial ecosystems. The Earth System has undergone remarkable biological change in a short geological time frame. Some one-third to one-half of global ecosystem production is now used by humans, and agricultural systems by various estimates now cover 40-50% of the land surface (Foley et al. 2005; Mooney et al. 2009). Human appropriation of the net primary production of Earth's terrestrial ecosystems has been estimated to be 23.8%, with some 53% of this harvest for use, 40% due to land-use productivity changes, and 7% the result of human-caused fires (Haberl et al. 2007). An earlier estimate placed human use of Earth's biological production at 50% (Vitousek 1997).

It is likely that such major land-use shifts undermine the capacity of the Earth to provide food, freshwater, forest resources, and a relatively stable climate. Humanity faces the enormous challenge of managing trade-offs of meeting immediate human needs (and seemingly endless desires) against maintaining the biosphere’s ability to provide such goods and services in the long-run (Foley et al. 2005). Like all organisms, humans are subject to natural laws, one being fundamental energetic constraints (Brown et al. 2011). Such massive changes in land use not only transform Earth's terrestrial surface but also change biogeochemical processes, reducing the ability of ecosystems to provide services necessary for human well-being (Haberl et al. 2007).

Given such rapid change in the fundamental structure, composition, and function of the biosphere, there has not been enough consideration of worst-case ecological scenarios. This failure is true even as evident impacts of abrupt climate change and ecosystem collapse continue to exceed predictions of just several years ago. It is difficult to respond to an emergency of any type if you don't fully understand its scale and severity. It is worthwhile to review this global ecological change playing out across Earth's terrestrial ecosystems and what it means for prospects for long-term global ecological sustainability.

Forests today cover some 30% of the Earth's land surface, storing some 45% of terrestrial carbon (Bonan 2008). Deforestation represents the final elimination of a forest. It describes the cutting, clearing, and removal of forest and subsequent conversion into anthropogenic ecosystems such as pasture or cropland (Kricher 1997). Humans have altered the terrestrial biosphere for some 8,000 years, yet the destruction has notably intensified over the past century, estimated by some to have crossed a critical threshold with 50% of the terrestrial biosphere transformed to anthropocentric non-natural systems by the mid-20th century. As of 2000, various estimates are that 29% to 75% of nature has been lost to land-use changes (Ellis 2011).

Around half of the world's three billion hectares of forests that originally covered the Earth prior to being impacted significantly by humans have been completely deforested over the past 80 centuries (Bryant and Bailey 1997). During the 1990s clearance of natural tropical forests was as high as 152,000 km2 annually (Bonan 2008). In addition to deforestation, the ecological value of much of the world’s remaining forests has been significantly diminished through various types of overuse. While over half of the world’s original forests remain, most have been heavily impacted by humans and can no longer be considered primary, old-growth forests or wilderness. Estimates are that less than one-fifth of Earth's original forests remain in large, relatively intact and undiminished natural primary forest ecosystems (Bryant et al. 1997). We need better and updated estimates to show how many old, mostly ecologically intact forests remain.

These large, connected primary and old-growth forests maintain natural ecological and evolutionary patterns and processes while providing ecosystem services that make the planet habitable. Remaining tropical wilderness areas in particular are major repositories of biodiversity, contain major watersheds, fill a crucial role in stabilizing the climate, and are also of great economic and strategic importance. Conversion of forests and other natural ecosystems to agriculture has averaged 0.8% annually over the past 40–50 years and is the major force reducing terrestrial ecosystems (Millennium Ecosystem Assessment 2005).

Numerous assessments indicate the area of the world’s forests is shrinking. Williams (2003) puts the parameters of possible annual deforestation rates at 7.5 to approximately 20 million hectares (ha) per year. Some 70% of the land that was deforested was changed to agricultural land (UNEP 2002). At current rates of deforestation, tropical forests will not persist outside protected areas 35 years from now. While tropical forest loss is widely recognized, the rate of loss or degradation shows little indication of appreciable slowing (Terborgh and van Schaik 1997).

Loss of forest habitat is problematic in its own right. Yet fragmentation results when a single forest is divided into a number of smaller habitat patches. Fragmentation is a type of forest diminishment, and biologists generally agree fragmentation, habitat loss, and degradation are major sources of decline in biodiversity and ecosystem functionality (Ehrlich and Ehrlich 1981; Diamond 1984; Wilson 1985; Soule 1991; Noss and Cooperrider 1994). Forest fragmentation leads to significant changes in ecological conditions. Some changes are abiotic: patches tend to be drier and more prone to windthrows. Others are biotic; forest fragments have fewer forest interior species and are more likely to undergo invasion by exotic weedy species.

As the proportion of suitable habitat in a landscape decreases, reduced area and isolation start to limit the population of species (Harris 1984; Franklin and Forman 1987; Noss and Cooperrider 1994). Fragmentation also reduces the capacity of forests to sequester carbon (Dobson et al. 1999). Many of these changes are due to increased edge effects: amplified biotic interactions and significant abiotic changes at the periphery of a forest patch.

Biodiversity and natural ecosystems provide ecosystem services that make the Earth habitable (Ehrlich and Ehrlich 1981; Noss and Cooperrider 1994). Widespread loss of biodiversity could be diminishing the Earth System's ability to regulate key biological processes and feedbacks (Steffen et al. 2011). Ecological systems constitute a life-support system upon which all life on Earth is dependent and without which human civilization may perish (Lubchenco 1998). Ecosystem functions include nutrient cycling and energy flows, disturbance regimes and recovery processes (succession), hydrological cycles, weathering and erosion, decomposition, herbivory, predation, pollination, and seed and animal dispersal (Noss 1992). Kareiva and Marvier (2003) add plant biomass production and drought resistance to the list. Deforestation diminishes the functioning of ecological systems and reduces the output of ecosystem services (Lubchenco 1998).

The richness of species found in ecosystems provides for resilience of ecosystem processes (Rockström 2009). There is growing evidence that biodiversity sustains ecosystems, preventing them from tipping into undesired states (Folke et al. 2004). Species loss affects the functioning of species and their ability to respond and adapt to changing conditions (Rockström et al. 2009b). Species extinction rates already exceed background rates by 100–1000 times what has been typical over Earth's history (Millennium Ecosystem Assessment 2005).

Connectivity is essentially the opposite of fragmentation. Corridors preserve existing connections (Noss and Cooperrider 1994). Retaining habitat connectivity can provide for recolonization of habitat core areas following local extirpation and allow for daily and seasonal movements and normal dispersal of animals (Dobson et al. 1999). Providing for increased landscape connectivity helps alleviate the impacts of habitat fragmentation (Schumaker 1996), including by maintaining dispersal routes and links between habitat patches.

Most existing protected areas are small, isolated, and fragmented (Soule and Terborgh 1999). In cases where connectivity is lost, it can be restored. This approach has been called “rewilding” (Soule and Noss 1998). Soule and Terborgh (1999) argue that the restoration of ecological connectivity must be a ubiquitous conservation activity in both temperate and tropical regions and must focus upon large-scale, top-down processes such as those provided by large, keystone species like Asian elephants. It has been shown that tropical forests in particular show a remarkable degree of resilience, and once land-use pressures destroying and diminishing them are removed or reduced, they can recover relatively rapidly (Bhagwat et al. 2012), albeit to a reduced state if critical thresholds in composition, structure, function, and dynamics were surpassed.

Earth's life is being dramatically reduced, particularly large animals and trees. Large old trees – which often play a critical ecosystem role, including storing carbon, cycling water, providing food to wildlife, and otherwise providing rich micro-environments – are rapidly declining worldwide as they are logged, face elevated mortality, and reduced recruitment. By themselves, large trees increase landscape connectivity as well by attracting seed dispersers and pollinators, and providing stepping stones across a landscape (Lindenmayer et al. 2012). The loss of large-bodied wildlife, also termed apex consumers, cascades through ecosystems worldwide, and may be humanity's most pervasive impact upon the natural world. Loss of apex consumers shortens food chains, and alters the intensity of herbivory and thus plant abundance and composition. As top-down forcing is lost, ecosystem regime shift often occurs (Estes et al. 2011). This loss of keystone species has led to increasingly simplified and less stable ecological networks and patterns of connectivity (Barnosky et al. 2011).

Primary and other types of old-growth forests (terms used inter-changeably while meaning all old forests) have been found to be irreplaceable for sustaining tropical biodiversity, which cannot be protected without effective protected areas and curtailed demand for old-growth timber (Gibson et al. 2011). Primary old tropical forests transpire large amounts of water, cooling the microclimate, bioregion, and planet. Changes in forest cover both cause and are caused by changes in climate – as vegetation cover is tightly coupled to Earth's climate through biogeophysical feedbacks. (Brovkin et al. 2009). As well as storing large amounts of carbon dioxide, old-growth forests have been found to continue removing carbon dioxide from the atmosphere, and accumulating it in their biomass and soils (Luyssaert et al. 2008). Habitat fragmentation in conjunction with climate change causes elevated tree mortality along forest edges, altering canopy dynamics, community composition, biomass accumulation and carbon storage (Laurance 2003).

Agriculture has been a driving force behind primary forest loss, and agricultural expansion in intact terrestrial ecosystem must end if they are to be maintained (Foley et al. 2011). However, the processes driving primary tropical forest deforestation and diminishment have shown a recent shift towards major industries (rather than poor farmers) such as commercial-scaled logging, oil and gas, and plantations as the most frequent cause of forest loss (Butler and Laurance 2008). Given the first priority for conservation must be habitat preservation (Fahrig 2001), it is likely that primary and other old-growth forests must be fully protected and expanded if the biosphere is to be maintained. International efforts to protect the world's forests have been made more difficult by a lax definition of forests, which equates old-growth with tree plantations, which are quite different ecologically (Sasaki and Putz 2009).

Mass extinction occurs when Earth loses more than three-quarters of its species, which is believed to have occurred five times in the past half-billion years. Yet each time, except the Cretaceous meteorite event, this occurred over hundreds of thousands to millions of years (Barnosky et al. 2011). It is widely believed that humans are causing a sixth mass extinction event, particularly through climate change and habitat fragmentation. It is possible that species diversity will not reradiate following such events – particularly if the biosphere is rapidly damaged past key thresholds, and the Earth System has collapsed or perhaps in key aspects even died.

It is very difficult to predict with any certainty how terrestrial ecosystems will interact with other global environmental change, though it is virtually certain they will be more simple structurally, with more early successional vegetation (Walker and Steffen 1997). Large ecosystems can shift abruptly and irreversibly in state when forced across thresholds. Recently there has been much research into such catastrophic shifts in ecosystems, and under what conditions they shift dramatically to other conditions. It is believed that some complex ecosystems can exist in alternative stable states. Shifts between these states can cause large losses in ecosystem patterns and processes, including an end to continued provision of economic benefits (Scheffer et al. 2011).

There is evidence that the global ecosystem as a whole can exhibit planetary transition as humans push Earth past tipping points and as the result of cumulative small-scale events. This is evident as human population growth and resulting resource use and depletion cause more of Earth's surface to be transformed and fragmented. Human population growth of about 77 million people a year drives these global changes, as human population has quadrupled in the past century to over seven billion. Areas that once housed natural biodiversity and ecosystems which power the Earth System now contain only a few species (Barnosky 2012).

Concurrently there has been an effort to determine early warning signals for such critical transitions, to determine tipping points where ecosystems make a sudden shift to a new dynamic regime (Drake and Griffen 2010; Carpenter et al. 2011). Certain generic aspects of an ecosystem approaching a critical point and undergoing phase shift have been noted, including bifurcations, flickering between states, a critical slowdown in system processes, and autocorrelation in these processes (Scheffer et al. 2009). In other instances, it is noted that for some complex natural systems for which there are multiple outcomes to a phase shift, there is likely to be no warning of regime changes. Drastic changes can appear in nature without warning (Hastings and Wysham 2010), and even when indicators of ecosystem regime shift are detected, it is often too late to avert them (Biggs et al. 2009).

While it is of academic interest to know when such phase shifts may occur, given lack of political commitment to avoiding ecosystem deterioration, it is not at once clear what benefit is provided by advance warning of a tipping point immediately before it occurs. There is no indication that human governance is capable of making such dramatic changes as would be required in ecosystem management just before collapse. More general predictive powers are needed to know earlier that a system is in trouble. Clearly there exists a need to not only deepen our understanding of such ecosystem change but ensure social science governance issues are integrated into pursuit of sustainability (Reid et al. 2010). Underlying drivers that push ecosystems towards thresholds – such as habitat loss and fragmentation which are ubiquitous in today's economic activity – must be slowed and addressed well before thresholds are reached (Biggs et al. 2008).

Abrupt climate change that was large-scale and widespread have occurred many times as the Earth has moved past thresholds in the past, yet stabilizing feedbacks operating at a long-term scale have kept Earth within a relatively narrow band of liquid-water conditions conducive to life for almost 4 billion years (Alley et al. 2003). Yet, within this band, within the span of a few decades global temperature can rapidly increase by more than a dozen degrees Celsius (Schultz 2012). Human activities can potentially push the Earth system past critical tipping points into different qualitative states (Lenton et al. 2008). Climate change is often perceived as a smooth, gradual process, when in fact it could pass tipping points and become abrupt and potentially runaway (Lenton et al. 2008). With human climate forcing, climate impacts may be "big, fast, and patchy" at a regional scale; triggering abrupt crashes of ecosystems (Breshears et al. 2011). Synergistic climate and landscape vegetational changes are likely to induce profound shifts in the societies living there (Heyder et al. 2011), whose success depends upon meeting critical thresholds to physiological human needs.

There is growing concern that science has consistently underestimated the rate and intensity of climate change. This illustrates the difficulty of addressing what could conceivably be apocalyptic-scale threats within the staid and conservative scientific tradition. We are witnessing long-term and abrupt climate changes already in Arctic sea ice melt, loss of ice mass in Greenland and West Antarctica, a shift of subtropical regions towards the poles, bleaching and death of coral reefs, large floods, weakening of the ocean carbon sink (Rockström 2009b), and an increase in extreme weather events (Hansen 2012b).

It is generally accepted that given a climate sensitivity of about 3 degrees Celsius for doubled carbon dioxide equivalency, atmospheric concentration of CO2 must be reduced from its current almost 400ppm to 350ppm, if humanity is to maintain the relative Holocene climate stability within which civilization has evolved (Hansen et al. 2008). To maintain such an Earth System it is critically important to rapidly reduce fossil fuel emissions (Hansen and Sato 2012). Recovering from present overshoot would require the phasing out of coal, an end to all fossil fuels unless carbon is sequestered, and use of agriculture and forest practices to resequester carbon (Hansen et al. 2008). It has been suggested that slowing population growth rates could account for 19-29% of the emissions reductions necessary by 2050 to avoid the most dangerous impacts of climate change (O' Neill et al. 2010).

The current rate of warming caused by increased greenhouse gas emissions is almost certainly unprecedented in the last 10,000 years (Beaumont et al. 2010). Climate change processes unleashed through release of carbon dioxide are largely irreversible for thousands of years (Solomon et al. 2008). In general, it is believed that biotic feedback considerably extends the lifespan of the biosphere by maintaining low atmospheric carbon dioxide levels (as well as other processes such as silicate rock weathering) (Lenton and Blow 2001). Projected loss of biodiversity is likely to be underestimated when land use and climate change are examined in isolation (Chazal and Rounsevell 2008), as these systems are tightly coupled and synergistic.

There is much evidence that climate change is causing major alterations in biological systems (Rosenzweig et al. 2008). Climate change is a threat to all levels of biodiversity (Maclean and Wilson 2011), causing changes in vegetation communities large enough to impact the integrity of biomes, and contribute to a sixth mass extinction (Bellard 2012). Malcolm et al. (2006) consider global warming to be one of the most serious threats to biodiversity, and losses of 39–43% of endemic species from 25 major biodiversity hotspots to be possible.

Climate change has been found to impact biological systems – and their phenology, distribution of species, morphology, and net primary productivity – including the "Global 200" ecoregions of exceptional biodiversity (Olson and Dinerstein 2002). Terrestrial ecosystems cycle ten times the annual amount of carbon released by fossil fuels and altered land use. And climate change may severely impact these processes, restructuring the terrestrial biosphere at the continental scale (Heyder et al. 2011). Yet tropical forests in particular are vulnerable to a warmer, drier climate (Bonan 2008). Ecosystems exert influence upon climate through changes in the water, energy and greenhouse gas balance (Chapin et al. 2008).

Climate change affects forests by altering the frequency, timing, duration, and intensity of naturally occurring disturbance patterns including fires, drought, insects and pathogens, introduced species, hurricanes, and extreme weather (Dale et al. 2001). Shifting in rainfall and precipitation patterns associated with climate change are expected to intensify the severity of droughts, gravely impacting forests and causing further forest decline (Choat et al. 2012). Some studies have shown that forest cover plays a far greater role in determining rainfall than has generally been appreciated (Sheil and Murdiyarso 2009). Largely as a result of drought, it is possible the Amazon rainforest, facing climate change–induced extreme warming and drying, may die back to all but refugia, releasing carbon dioxide in a massive positive feedback (Cox et al. 2004; Nepstad et al. 2007). This threat almost certainly faces smaller natural old forests as well. The land-to-ocean pressure gradient driving the southwest Indian Summer monsoon has been shown to be reduced due to albedo changes associated with land use changes, including old forest loss, as well as aerosol pollution (Lenton et al. 2008).

Mean global temperatures by 2070 or earlier will be higher than they have ever been since the human species evolved (Barnosky et al. 2011). Evident global warming of just under 1 degree Celsius will almost certainly be added to by additional warming already in the pipeline, including as the result of vegetational changes (Hansen et al. 2008). By the end of the century we can expect virtually all ecoregions to be under climate stress caused by heat and precipitation patterns that are well outside recent variability patterns. It is expected in the next 20 years that monthly temperatures will be beyond 2 standard deviations of the 20th century baseline, and substantial variation in precipitation may threaten the survival of biologically important ecoregions worldwide. This increase in temperatures relative to natural variability is expected to be particularly pronounced in the tropics, impacting spatial distribution of both organisms and ecosystems (Beaumont et al. 2010).

It is likely that human land-use changes increase the vulnerability of tropical forests to climate change and may be as important as abiotic changes in their decline, as synergies magnify habitat loss and fragmentation (Brodie et al. 2011). To allow vegetation to adapt the best it can to climate change, it is thought to be important to maintain and enhance landscape connectivity so species can migrate. Protected areas are identified both because they allow biodiversity and ecosystems to migrate and otherwise adjust as best they can to climate change and because their vegetation is an important component in minimizing warming (Hannah et al. 2007). Landscapes that display fractal qualities such as non-uniform forest edges have been found to be more tolerant of habitat destruction (Hill and Caswell 1999).

Other than protecting as much habitat a possible, wildlife corridors offer another means to maintain ecosystem processes and viability of isolated populations across human-impacted landscapes. Yet habitat corridors continue to be lost across the world, critically undermining the connectivity of ecosystems on scales from the local landscape through bioregional to global. While the pros and cons – including greater spreading of disease – have been weighed, the evidence generally supports habitat corridors as a means to maintain landscape connectivity (Williams and Snyder 2005).

One approach to studying the effects of habitat loss and fragmentation upon landscapes has been percolation theory, which shows that some aspects of structural habitat fragmentation may change rapidly below critical proportions of habitat (Swift and Hannon 2009). At 40% of a landscape's habitat loss, many linear landscape measures such as edge density, contagion, distance to nearest neighbor, and fractal dimension show a 50% probability of an abrupt change to non-linear responses (Hargis et al. 1998). As habitats are dissected into smaller parcels, landscape connectivity – the functional linkage between habitat patches – becomes disrupted (With and Crist 1995).

Percolation models that simulate landscapes have found that when habitat covers less than 59% (0.59275) of the landscape, the largest habitat patch decreases abruptly and no longer spans the entire landscape (Gustafson and Parker 1992; Andren 1994; Bascompte and Sole 1996). A percolating cluster exists when a path exists across a landscape from one side to the other, regardless of scale. If a percolating cluster exists, organisms as well as flows of energy and other materials including species can move from one edge of the landscape through a path of habitat cells to the other. When connectivity is defined on the basis of the nearest neighbor, a critical threshold exists near 60% whereby the probability of a percolating cluster is 50%. Below this level percolating clusters rarely exist, and even 2% above this threshold the likelihood becomes very high (Williams and Snyder 2005).

Figure 2: Williams et al. 2005

Another critical landscape threshold in relationship to habitat loss that occurs across scales is that at about 40% of habitat retention (60% loss), the distance between patches increases rapidly (Gustafson and Parker 1992; Andren 1994), and at 30% habitat patch numbers peak. These fragmentation thresholds may represent a positive feedback mechanism with potential to drive irreversible regime shift in ecosystem functions across fragmented landscapes (Pardini et al. 2010). At greater spatial scales of analysis, these may aggregate to critical breaks in ecosystem connectivity and thus sustainability at the continental and biosphere scales.

When a percolating cluster exists, the landscape is connected and characterized by a few large habitats. Below this threshold of ~59% the landscape is characterized by many small and disconnected habitats. This is a remarkable characteristic of landscapes across scale (Wu 2004) and represents a direct phase shift between connectivity and nonconnectivity. Below this level of connectivity, the likelihood of critical transitions increases – that is, once this amount of Earth's ecosystems have been transformed, the remainder can change rapidly (Barnosky et al. 2011). Critically, this percolation and resultant lack of connectivity also aligns with the landscape shifting from habitats surrounding humanity, to human works surrounding islands of habitat.

Throughout history, human settlements were islands that existed within the sea of nature; now as a result of habitat fragmentation, at most scales this has largely been reversed (Janzen 1986). This matrix of intact terrestrial ecosystems is being lost across bioregions, continents, and the global biosphere as a whole as landscapes are percolating, losing connectivity and the ability to provide their ubiquitous top-down regulation and provisioning of human and other natural processes. Solutions to habitat loss and fragmentation require the popular embrace and implementation of basic conservation biology principles including the need to protect large core areas, establish agroecological buffers and transition zones, and have these larger core areas connected as the matrix for sustainable human societies.

Most of the research into thresholds for terrestrial ecosystems has looked at extinction of species or progressive dismantling of a landscape-sized ecosystem. Other researchers have begun to look at continental-scale conservation and noted the importance of top-down regulation provided by intact ecological matrixes across large scales (Soulé and Noss 1998; Soulé and Terborgh 1999, 1999b). Yet it is possible to go even further upscale and view the biosphere as a big landscape. Viewing terrestrial ecosystems in space and time as changing patterns of patch and matrix is not scale dependent; one explicitly states the scale for which an ecosystem and landscape perspective is taken. Findings regarding critical levels of connectivity for biodiversity in ecosystems taking a landscape perspective are almost certainly as valid as viewing continental ecosystem and landscape patterns aggregating to the biosphere, though further research is necessary.

We do not yet know with certainty at a global scale how much land must be transformed before there is a planetary shift, but various studies and theory suggest that numerous critical thresholds exist between 50% and 90%. What is clear is that beyond thresholds, ecosystem services undergo state shift, destabilize, and begin to degrade as networks of ecological connectivity begin to disassemble. By 2025, it is predicted we can expect that 50% of Earth's land will have undergone state shifts, as human population reaches 8.2 billion; and 70% of Earth's land could be shifted to human use with populations of 11.5 billion by 2060 (Barnosky et al. 2011). As mentioned, various measurements of human usurpation of land mass for agricultural and net primary productivity place the level at 50%.

As well as the 40% loss associated with loss of a percolating cluster and thus landscape and ecosystem connectivity, 50% habitat loss appears to be a critical value, where remaining natural systems are transformed to new states through large-scale forcing in atmospheric chemistry, nutrient, and energy cycling changes. At or near this point, ecosystems flip from being the landscape matrix to being islands, further isolating and disconnecting ecosystems. Our ability to know that critical thresholds are near or have been crossed is complicated by lag times; moreover, it is not immediately known whether an ecosystem or even the entire biosphere has crossed a critical transition, and it is almost certainly not possible to know except in retrospect (Barnosky et al. 2011).

Natural vegetational communities and animal populations – whose ecosystem outputs are likely critical sources of biosphere stability – are simultaneously being reduced by habitat loss, fragmentation, and abrupt climate change. To survive and thrive, humanity may be well advised by the state of current science to protect and restore natural, large, and connected ecosystems and to cut fossil fuel emissions. Species extinction from climate change is expected to be a nonlinear power function of global warming; therefore minimizing global warming is a major biodiversity conservation goal (Hansen et al. 2010). Entire tropic networks will be affected, and ecosystem functioning is expected to be significantly reduced (Bellard et al. 2012).

Over recent decades, most governments and conservation organizations have called for 10–12% protection of each type of ecosystem, a target which relegates terrestrial ecosystems to being isolated, unconnected remnants in a sea of human development and could prove inadequate to meet human needs and maybe even crash the biosphere. Some 13% of Earth's total land area is now covered with protected areas (UNEP 2012) – with about half providing adequate protections (Laurance et al. 2012). At the 2010 Nagoya Conference on the Convention on Biological Diversity, a 17% protected area goal for terrestrial ecosystems was put forth (Noss et al. 2011). These values appear to be largely arbitrary. They accept that virtually all unprotected lands, particularly in the tropics, will be industrially developed and that with 90% habitat loss, some 50% of species will go extinct from habitat loss alone (Soulé and Sanjyan 1998). This level of terrestrial ecosystem protection virtually ensures the lack of a percolating cluster, and thus inadequate landscape connectivity to mediate critical ecosystem flows for sustainability.

As tropical deforestation quickens, protected areas are often the only places where natural ecosystems and biodiversity can persist. Yet protected areas in the tropics are especially vulnerable to human encroachment and other environmental stresses. Laurance et al. (2012) found that about half of tropical reserves are losing biodiversity across taxonomic and functional groupings, and 80% of reserves show some signs of decline. In many cases this was found to be due to landscapes around reserves being under threat, the lack of buffers and transition zones, their small size, and lack of connectivity with the broader landscape. If even protected areas cannot persist, where in the future shall our and the biosphere's ecosystem services upon which we depend be derived?

Others such as Noss et al. (2011) are also calling for "bolder conservation," offering the more biocentric proposal that some 25–75% be managed for biodiversity conservation and stating frankly that "Nature needs at least 50%, and it is time we said so." Percolation theory's insights into ecological connectivity applied across scales makes the case for doing so, not only for the sake of biodiversity and ecosystems, but for sustainability of continents and the biosphere – and of people, who require ecosystems as their context as well. Critical to the efficacy of protected areas is sizable buffer and transition zones around reserves, maintaining connectivity to other forest areas, and low-impact community based land uses around reserves (Laurance et al. 2012).

Convincing evidence is emerging that industrial logging in tropical forests that is both sustainable and profitable is impossible (Zimmerman and Kormos 2012). There are questions whether repeated harvests can truly sustain natural ecosystems (Nasi and Frost 2009). Logging generally removes large trees where most of the forest's carbon is stored (Vieira et al. 2005). Despite these concerns, humanity continues to clear what old native forest vegetation still exists. Despite significant science, the myth of "sustainable forest management" in old-growth forests continues, supported by a diverse cast of characters ranging from Greenpeace to the World Bank.

Small-scale community ecoforestry has proven to lead to reasonable protection of intact tropical forest ecosystems (Bray et al. 2003). Limited logging at low intensities, such as might occur under small-scale community ecoforestry, with few if any roads, and which generally removes less than five trees per hectare in tropical forests and does not open the canopy and disturb the soil, in theory may maintain old growth's key structure and species composition. Yet this is generally not what is occurring: most old-growth forests are logged industrially at two to three times higher intensity than their rate of recovery (Zimmerman and Kormos 2012), with roads left behind that enable further diminishment.

It is useful for this study to understand that biological systems can be investigated at any scale. The Gaia hypothesis holds that the Earth system is in some ways analogous to a living, self-regulating organism – with air, land, soil, and oceans as her organs; plants and animals as cells; and water as blood, cycling nutrients and energy to be alive. Formulated by James Lovelock (1979), the Gaia hypothesis noted the role of biology in promoting homeostasis in the Earth System; that is, life maintains the conditions for life. Coordinated activity between individual species and the environment is similar to interactions between cells and organs in multicellular organisms (Kondrat'ev 2001).

According to this and similar theories of the biotic regulation of the environment, living systems have the capacity to actively maintain environmental conditions that sustain life. There is a need to focus upon the sustainability of Gaia – the global ecosystem – based upon what is known about sustaining biodiversity, ecosystems, and landscapes across scales. Very little is known regarding the requirements for sustainability of the global biosphere and what aspects of terrestrial ecosystems in terms of quality and placement are necessary to do so. This researcher concurs fully with Soule and Terborgh (1999) that "science and advocacy must become allies in the defense of nature."

Terrestrial Ecosystem Loss as a Planetary Boundary

Planetary boundaries have not well characterized the impacts of terrestrial ecosystem loss, and thresholds for human and the biosphere's safety are not well known. Simply, how many intact terrestrial ecosystems are required to maintain operable biosphere? More broadly, how can ecosystem collapse be avoided and global ecological sustainability achieved? While progress has been made in identifying fossil fuel emissions as a threat to our biosphere and thus human well-being, relatively less urgency has been assigned to quantifying the threat posed by terrestrial ecosystem loss at a continental and global scale.

It is worrying that terrestrial ecosystem loss and diminishment are not more prominent in their own right within the initial conception of planetary boundaries. It may prove to be an ominous oversight. Not many are asking how many terrestrial ecosystems are required to maintain a livable biosphere for humanity and all species. It is not clear how such an obvious boundary could have been missed, except perhaps that land clearance, in what may be overdeveloped countries where most science occurs, is so ubiquitous that it is taken to be the natural condition.

Running (2012) made an initial, independent effort to explicitly define a measurable planetary boundary for terrestrial ecosystems based upon plant net primary productivity. While such a boundary does recognize terrestrial ecosystem loss, integrating well primary aspects of global ecosystem sustainability, it remains problematic in focusing merely upon biomass production, while not assessing critical spatial and scale-dependent ecosystem processes in cycles provided by fully intact and connected natural ecosystems.

What is sought here is the first iteration of a less arbitrary terrestrial ecosystem loss threshold value and precautionary boundary. This needs to be more inclusive of the full range of ecological services provided by intact, large, and connected ecosystems and more rooted in scientific phenomena relating to the loss of habitat and profound dismantling of ecological connectivity resulting from habitat fragmentation.

A planetary boundary for terrestrial ecosystem loss would go well beyond the current planetary boundary proposal's land system change and biodiversity loss and deal with ecological processes and patterns – the integrative services – provided by land still covered with intact natural vegetation. Clearly the scouring away of complex plant and animal life (arrayed across landscapes in complex ecosystems; integrated with water, climate, and oceans; and aggregating to bioregions, continents, and ultimately the one, shared biosphere; which can now be mapped and analyzed in detail using satellites and computers) can be conceived in terms of a planetary boundary. A proposed terrestrial ecosystem planetary boundary may well be more rigorously defined than some others, providing guidance to bioregional and landscape decision-making processes as well.

The current conception of a planetary boundary measuring land and natural vegetation is inadequate. It is not enough to assess the quality of land and its intact ecosystems only in terms of how much land is under agricultural development. The current land-use boundary only partially gets at the tremendous loss of ecosystem processes such as pollution absorption, pollination, and soil development, and ecological patterns such as naturally evolved plant community assemblages that are lost with the decay or disappearance of terrestrial ecosystems.

Terrestrial ecosystems are rooted in geography to a far greater extent than the other boundaries, so there is no excuse for not crafting a boundary based upon their position and quality. A bioregional and continental terrestrial ecosystem boundary for global ecological sustainability could be measured based upon what we know about landscape pattern and percolation states at various thresholds of natural plant community coverage and about critical thresholds, regime shifts, and different basins of attraction for ecosystems at the plant community and landscape criterion. A planetary boundary for terrestrial ecosystem loss would draw upon computerized mapped data, aggregating conditions of natural habitats across scale, capturing the full complexity of land-based ecological thresholds.

Other planetary boundaries refer to terrestrial ecosystems in scattered and haphazard ways, but in fact, persistent large, connected, and naturally evolving ecosystems are a central organizing principle of a living biosphere, in fact, of life itself. Like the land-use planetary boundary, terrestrial ecosystem loss is tightly coupled with other boundaries. The spatial distribution of this loss across scales is critically important to ensuring that continental-scale land-cover thresholds are not crossed.

When ~39% of variously scaled ecological systems viewed as landscapes are destroyed (60% habitat remains), the landscape is said to percolate. As reviewed earlier, at this point in habitat loss we see critical collapse of a dominant large habitat patch, the percolating cluster – constituting the matrix of the landscape – into smaller, more isolated habitat, in a sea of human development. This critical deterioration of habitat connectivity continues so that at or near 50% loss of bioregional and landscape natural vegetation, the natural habitat percolates from people within ecosystems, to natural islands surrounded by human works. This is likely to be similar at continental and global scales, which can be viewed independent of scale as landscapes themselves.

A new planetary boundary threshold is proposed that 60% of terrestrial ecosystems must remain intact with the boundary set at 66% as a precaution. This is seen as necessary to provide a safe space not only for humanity, but for all life, including the Earth System. It is hypothesized that loss and diminishment of terrestrial ecosystems aggregates from the local and regional scale, yet disrupts planetary process with this global scale threshold, just as it does across local landscapes. Ensuring that natural ecosystems and their biogeochemical flows remain the context for human endeavors is hypothesized to be a requirement to sustain the biosphere long term. Doing so requires large core ecological areas – and the critical connectivity of ecosystem processes and patterns – as the global landscape matrix.

It is further proposed on the basis of ecology's percolation theory that two-thirds of the 66% of terrestrial ecosystems must be protected as ecological core areas, to ensure the ecological integrity of the semi-natural agroecological landscapes, by encompassing them within a matrix of intact nature. Avoiding fragmentation and providing for core ecological areas, throughout a mixed-use landscape, is the challenge of terrestrial ecosystem ecology. Thus a terrestrial ecosystem loss planetary boundary is proposed in sum that protects 44% of the global land mass remaining as intact ecological cores, with 22% as agroecological, agroforestry and managed forest buffers, and transition zones. Buffer zones are multiple-use areas that can serve as habitat for some species and insulate core reserves from human activities (Soulé and Terborgh 1999).

Recommendations for a terrestrial ecosystem loss planetary boundary align closely with Soulé and Sanjayan's (1998) scientific review that to represent and protect most biodiversity, particularly wide-ranging species, 50% habitat protection is required. Noss and colleagues (2012) note the timidity of conservation targets and bemoan the acceptance that viable populations of native species and ecosystem services are willfully not maintained, also calling for 50% landscape protection. Earth needs a new class of connected global ecological preserves to sustain key core ecosystems required for an operable biosphere, regional ecological sustainability, and sustainable human advancement.

This guidance is perhaps most useful for the last large wildernesses found in South America, Northern Canada and Russia, the Congo Basin, and Papua New Guinea and East Asia. There land clearing thought necessary to improve human well-being can seek to maintain large and connected core ecological areas as the landscape matrix. In Earth's remaining wildlands, this planetary boundary can guide ecosystem and land-use decisions, as some portion of the bioregion is altered to meet human needs, while maintaining the bioregion's contribution to biosphere sustainability.

Humanity is near or has recently surpassed allowable terrestrial ecosystem loss within a sustainable biosphere. Given that as much as 50% of Earth's biological production may already be dominated by humans (Vitousek 1997), and as much as 33–40% of biospheric production has been coopted by humans (Vitousek 1986; Running 2012), there is an urgency to the terrestrial ecosystem loss boundary. Like the climate change, biodiversity, and nitrogen cycle boundaries, it is quite likely humanity has already crossed the planetary boundary for how many terrestrial ecosystems can be lost.

Extensive extractive land-use patterns found in most populated areas are already well beyond proposed planetary boundaries for loss and diminishment of terrestrial ecosystems in virtually every continent and bioregion. There, as well as across nearly fully modified landscapes, the intent can be to allow remnants to expand, by means including targeted restoration. Some habitat with some connectivity is better than none of either. It can thus be equally telling, as a restoration ecology goal through deliberate land-use planning decisions, to grow core ecological areas and their connectivity. Remnants like the Western Ghats old growth and their elephant herds must be enlarged and reconnected, so that continued ecosystem services may flow to Kerala and neighboring states.

It is going to be difficult in many parts of the world to get back to 66% natural ecosystem cover, and 44% of Earth's surface as fully intact, old terrestrial ecosystems. Agroecological systems, suggested here as minimally across 22% of the land mass, are going to have a play a part in reestablishing an ecological context and top-down constraint upon humanity (Dalgaard et al. 2003; Francis et al. 2003). It is thought that agroecological systems that better mimic natural processes can provide limited ecosystem services, while buffering core ecological areas (Ericksen et al. 2009). Agriculture as it is now practiced has numerous harmful effects, including pollution and habitat destruction, yet there are efforts to incorporate agriculture flows more fully with the flows of plants, animals, nutrients, and water that flow across landscapes. Agroforestry is long established and now being augmented by innovations in permaculture, organic gardening, restoration ecology, and re-wilding.

The key threshold is that at these levels, across continents and the biosphere, natural and semi-natural ecosystems remain the context for human endeavors. And within this ecosystem matrix, intact core ecological reserves constitute the intact, encompassing matrix for agroecological patches. The critical increase in fragmentation and reduction in habitat connectivity and ecological cores can be avoided by maintaining nature as the context for human activities. The potential for natural ecosystems to continue their unimpeded evolutionary development based on the full array of genetic materials is also maximized.

There exists great potential to target the restoration of key areas on landscapes – such as critical gaps in habitat corridors – to improve the connectivity of a landscape or even a bioregion. Emphasis should be upon reestablishing key natural disturbance regimes and promoting the movement of species between habitat fragments (Soulé and Terborgh 1999). Restoring corridors between isolated habitat patches can mitigate or reverse the impacts of fragmentation (Williams and Snyder 2005). The intent would be to identify the most important corridors historically, as well as using computer mapping technologies, to regain a percolating cluster across the landscape and thus reestablish habitat connectivity. Such connectivity can be reestablished first within existing protected areas and then increased in size to neighboring protected and unprotected habitat.

Humanity desperately needs a predictive science of the biosphere if we are to avoid its collapse or even death (Moorcroft 2006). It is critical that humanity reconnect with the biosphere, both to make our dependence upon the biosphere more visible and to link efforts to achieve global ecological sustainability to goals for justice, equity, and rights (Folke 2011). The public, policymakers, and ecological scientists alike need to acknowledge and respond to the fact that humanity has surpassed the carrying capacity of Earth's climate, ecosystems, and biosphere – that we are well into overshoot, and that fact, in view of lags in the system, without rapid changes in trends driven by changes in human behavior, can only result in global ecological collapse and the end of being. There is a glaring need for research agenda to understand at what point the biosphere may perish and Earth die and to configure ecosystems and other boundary conditions to prevent her from doing so.

It is vital to both the biosphere and human advancement that what is known about healthy terrestrial ecology be united with a legal framework to pursue local, regional, and global sustainability goals at scale. We must get at the keystone role that large, intact, naturally evolved ecosystems have as an ecological element in the function of the Earth System.

Elephants in India's Western Ghats as an Umbrella Species and Indicator of Local and Global Ecosystem Sustainability

To have meaning in guiding global ecological sustainability policy, these continental and global observations and the proposed 66% / 44% boundary for terrestrial ecosystem loss must be grounded in real-life landscape and bioregional conservation considerations such as efforts to maintain continued viable populations of Asian elephant in Kerala, India. The Asian elephant is an umbrella species which requires extensive and adequate natural habitat to ensure its survival as well as provide for water, clean air, soil, pollinators, and other ecosystem services. An expansive, cutting-edge, and rigorous ecological science–based ecosystem and land-use mapping exercise has occurred in Kerala, but it faces organized resistance from extractive industries, and the legal structure is not yet in place to embed its requirements for local and regional sustainability.

There is little doubt that habitat fragmentation and climate change of the type reviewed here are fundamentally altering India's remaining terrestrial ecosystems, especially in the Western Ghats and Kerala, and impacting their continued provision of local, bioregional, and Earth System ecological process and pattern. Much natural habitat has been lost in India. The deforestation rate for India as a whole from 1981 to 1990 was estimated at 0.60% annually (United Nations Food and Agriculture Organization 1993). Jha and colleagues (2000) found using satellite data that the southern part of the Western Ghats lost 25.6% of forest cover in the 22 years between 1973 and 1995, much of it to an increase in plantations and agriculture. Menon and Bawa (1998) estimated the rate of deforestation in the Western Ghats to be 0.57% from 1920 to 1990. These high rates of deforestation do not include the often deleterious effects of habitat fragmentation and forest degradation.

India, like much of the world, is already being impacted strongly by climate change. Malcolm and colleagues (2006) predict that, depending on biome definitions and the amount of habitat connectivity and thus migration, 12–57% of Indian habitat will be lost to global warming, and that India's biomes would need to migrate from 230 to 1,228 meters per year to remain in favorable climatic conditions, an impossibility which highlights the degree of threat climate poses to India's terrestrial ecosystems, and vice versa. Ravindranath and colleagues projected that by 2085, between 68 and 77% of India's forests are likely to shift in type as a result of climate change. They note the impact this will have on the 200,000 forest villages dependent upon forest resources.

The Western Ghats is one of the original 34 hotspots of global biodiversity (Myers 2003) and because of its distinctiveness and irreplaceability is recognized as one of the "Global 2000" ecoregions (Olson and Dinerstein 2002). The region serves as a water tower for Peninsular India, catching and storing monsoonal rains (Western Ghats Ecology Expert Panel 2011). The region's variable topography and precipitation result in a wide range of vegetation types, including both wet and dry forest types, as well as 4,000 species of flowering plants, 1,600 of which are endemic (Jha et al. 2000). Dry forest types provide crucial habitats for wide ranging species such as tigers (Panthera tigris) and the Asian elephant (Elephas maximas), whose presence greatly enhances ecosystem health through their top-down regulation (Das et al. 2006).

It is thought that from 1920 to 1990 about 40% of the vegetation of the southern region of the Western Ghats was lost (Menon and Bawa 1997). It is estimated that 6.8% of the Western Ghats' original primary vegetation remains (Myers et al. 2000), though larger areas of secondary forest persist. Some 15% of the Ghats is under some form of protected area status (Western Ghats Ecology Expert Panel 2011). In 1978, Gadgil and Vartak reported upon the existence of "sacred groves" – community preserved forests sometimes as large as 20 hectares – that were maintained traditionally in a near-virgin condition. It is not clear to what extent if any these persist, yet all old growth could offer important genetic resources and baseline data on plant community assemblages that will prove critical to forest restoration so that the bioregion can be reconnected and better withstand escalating climate change.

It is urgent to the future well-being of the Western Ghats' peoples and ecology that all old-growth forests are identified; their situation is stabilized, and they are given full protection and used as locally evolved seed sources. They can also provide baseline community assemblage data for natural regeneration and assisted restoration. Doing so is critical for the continued provision of ecosystem services and to ensure that progress is made to reconnect ecosystems at both landscape, bioregional, and continental scales. Crucial to doing so will be ending the encroachment of plantation agriculture, mining, and residential sprawl upon protected and unprotected remaining natural terrestrial ecosystems.

Populations of Asian elephants are estimated to be 30,000–50,000, with 60% in India. As an umbrella species, when protected, Asian elephants preserve large tracts of habitats rich in other species as well as ecosystem processes such as water retention, soil creation, and pollination essential to people. The Asian elephant is listed as endangered on the Red List of Threatened Species compiled by IUCN. Habitat loss is the primary threat facing the existence of Asian elephants in the heavily populated Western Ghats (Riddle et al. 2010). The estimated original range of Asian elephants was 9 million square kilometers, of which only about 500,000 remain (Sukumar 2003). It has been suggested in the case of African elephants, that above 50% human use of the landscape, they essentially disappear (Riddle et al. 2010).

There is ample evidence that natural ecosystems in the Western Ghats are urgently threatened, and protected areas must be enlarged (Gunawardene et al. 2007) and better connected to maintain habitat for elephants, tigers, and people. There has been an observed weakening in the Indian Summer Monsoon patterns which provide much of the Western Ghats and India's water, almost certainly linked to this loss of widespread and connected habitat, and aerosol air pollution. It is thought that past certain thresholds the monsoon system could become less regular, bifurcating between a weak and strong monsoon state, or even collapse (Lenton et al. 2008). Loss of forest cover in the Western Ghats is almost certainly going to lead to increased drought and lack of drinking water (Sheil and Murdiyarso 2009).

The umbrella species concept would suggest that by recognizing the Asian elephant's rights to exist, and by ensuring adequate habitat and corridor connectivity to maintain viable populations, the peoples of the Western Ghats can also ensure their own survival and well-being. There are reasons India's elephants and humans have coexisted and find themselves alive on the same landscapes; they may be co-evolved and need each other. Maintaining and expanding elephant habitat through restoration, with an emphasis on buffers, transition zones, and particularly habitat corridors – while difficult and costly – and given deserved compensation, would also provide for ecological services for Kerala's population, potentially in perpetuity to all classes of people, while meeting responsibilities of all locales to contribute to maintenance of our shared biosphere through ample land-use and ecosystem planning. Traditional peoples were almost certainly more aware that healthy elephant and other wildlife populations ensured their well-being too, and awareness of this coevolution is necessary now.

Kerala and the wider region's remaining relatively large populations of Asian elephants – and tigers as well – are a testament to its high level of human development. Yet this does not come without a price. There is a large loss of agricultural crops to elephants, and in India as a whole, 100–200 people are killed each year in human–elephant conflicts (Jayson and Christopher 2008). Much of the remaining elephant habitat in the Western Ghats is surrounded by rural populations that depend on forests for their habitat too (Riddle et al. 2010). Yet while the Asian elephant as an umbrella species requires extensive and adequate natural habitat for its survival, it also provides for water, clean air, soil, pollinators, and other ecosystem services. The continued existence of Western Ghats remnant forest fragments – with viable populations of elephants as well as tigers as top predators – is an indicator of both global and local ecological sustainability. Yet under current habitat loss trends, this important ecological base and heritage will be lost in the relative near term if not granted more effective protections.

The Western Ghats Ecology Panel has presented a report to the Ministry of the Environment and Forests, Government of India, which is a worthy starting point for the type of land-use planning exercises that must be carried out in the Western Ghats if ecosystem collapse is to be avoided and ecological sustainability with continued human advancement achieved. The exercise sought to identify, at a coarse scale, ecologically sensitive areas (ESAs) and how to manage them (Gadgil et al. 2011; Western Ghats Ecology Expert Panel 2011). Sensitive areas with low levels of resilience were identified, as were ecologically significant areas. Lack of essential corridors for connectivity between certain protected areas was identified as an additional area of concern.

The mapping exercise used a straightforward "weight and rate" geographic information system approach – of the type published by the author in his native bioregion of the United States northern hardwood forests (Barry et al. 2001), overlaying various geographic data regarding biological, culture, and geoclimatic features, following established and best global practices for doing so. Such factors as species biological richness, rarity in terms of distribution and taxonomy, habitat richness, productivity, resilience, cultural significance, topography, and climate were thus overlaid and able to be viewed cumulatively as a surface to see where they aligned and identify significant ecologically sensitive areas at a scale for bioregional planning (but perhaps not for landscape planning). One primary advantage of such an approach is that various maps can be generated weighing the factors differently, depending upon different assumptions and questions.

This Western Ghats Ecology Expert Panel identified three zones of ecological sensitivity and suitability. Quite interestingly and independently, the total of most important priority areas (referred to as ESZ1), along with existing protected areas, was chosen to be 60% of the landscape, aligning closely with the present study's finding that this is the threshold where critical bioregional connectivity is maintained. These ESZ1 and protected areas, along with ESZ2 areas, are set for 75% of the landscape, allowing for buffers and transition zones which are critically lacking in the region. This exercise is pursuing exactly what is recommended herein to ensure network connectivity of landscapes, bioregions, and the global biosphere. This leaves a full 25% of the landscape to ESZ3 zones, where urban, industrial, and monoculture agriculture could continue to reside within an intact ecological matrix. This may be how landscape sustainability across bioregions is achieved, and continental to biosphere level ecological collapse avoided.

It is likely that opposition to such farsighted ecological planning is largely based upon economic self-interest rather than any legitimate concerns with the science or methods used. The ESA findings need to be tied to laws to bring about requirements for local and regional sustainability. Despite technological advancements, if ecological decisions – when faced with local and global ecological threats – are made for political reasons, a disconnect will continue between the needs of the biosphere, needs of natural habitat for charismatic megafauna such as the Asian elephant, and human needs and desires.

With a large grain of grids of 9 x 9 km suitable for bioregional ESA mapping, it would still be beneficial to do additional landscape planning mapping at perhaps a 1 km or smaller grain (if suitable satellite data is available), particularly to identify key elephant habitats and corridors, tiger reserves, and remnant old growth and to assess the habitat connectivity of existing protected areas at a more detailed resolution. With fewer than 7% of the Western Ghats remaining as old growth, more focus upon where old growth exists, where it may be unprotected, and where it could be targeted for expansion through ecological restoration and natural regeneration would be appropriate and essential to the region's ecological sustainability – from the biosphere to monsoonal climate criteria. This could also make possible more explicit emphasis in the existing bioregional assessment upon the known habitat of Asian elephants and tigers, as both are keystone species who play critical roles in top-down ecological regulation, which will be lost if viable and connected populations are not maintained.

There have been other landscape planning exercises that preliminarily mapped Western Ghats' natural vegetation and landscape patterns to make various recommendations. Das et al. (2006) identified what they called "areas of high conservation values" using a systematic conservation planning approach. They found that wide-ranging mammals were highly correlated with threatened and endemic species richness, and overall animal and habitat quality, indicating that elephants and tigers may be an effective umbrella focal species whose conservation would protect other biodiversity. They also found that more than half of their identified priority areas were reserve forests that had not yet been granted protected status, though reserve forests often bordered existing protected forests.

To ensure ecological sustainability, Kerala and other Western Ghats states clearly need to identify gaps in existing habitat cover that will reconnect the landscape. Maintaining habitat for Asian elephant populations and seeking to reconnect the landscape may prove to be the best way of doing so. A similar landscape planning exercise in Tanzania documented a similar loss of habitat connectivity in regard to African elephants, assessed its root causes, and explored restoration options and priority conservation goals (Jones 2012). A similar plan to protect and restore necessary corridors is needed in Kerala and throughout the Western Ghats.

Whether the Western Ghats Ecology Expert Panel is accepted and implemented or not, the Western Ghats' landscapes and bioregion faces a crying need for land-use and ecosystem planning. As the most visible manifestation of a connected ecosystem, Indian elephants are both the means of securing local ecosystems and development potential as well as serving the needs of the biosphere.

Continued viable populations of Asian elephant in Kerala, India, are an indicator of potential for both global and local ecological sustainability. This umbrella species requires extensive and connected natural habitat for its survival, which also provides for water, clean air, soil, pollinators, and other ecosystem services. Persistence of elephants imposes limits upon human activity to ensure continued maintenance of ecosystem services. Maintaining viable populations of the umbrella species Asian elephant will go a long way towards local and global ecological sustainability.

Major educational activities must build awareness of the importance of ecosystems to both lasting local advancement and global sustainability of our one shared biosphere (Riddle et al. 2010). By recognizing the Asian elephants' rights to exist, and ensuring adequate habitat, the people of Kerala and the wider Western Ghats bioregion can also ensure their own survival and well-being.

It is vitally important to Kerala’s and the Western Ghats' prospects for global ecological sustainability that the Western Ghats Ecology Expert Panel findings are accepted and their recommendations carried out. The current bioregional scale planning must be built upon at a finer scale to allow decisions about protecting and expanding old natural forests, their core ecological habitats, and necessary large corridors for elephant movement. These protection efforts and restoration can continue for all time. The need for elephant and tiger habitat protection align closely with India's habitat protection measures necessary to maintain ecosystems and achieve climate goals. If can’t be done in Kerala, with its high level of ecology and human development, it can’t be done anywhere.

We need to find landscape configurations in places like Kerala that provide local ecological sustainability and community advancement while also proving adequate to contribute proportionally to maintaining regional ecosystem processes necessary – when aggregated across continents – to sustain our one shared biosphere. It is vital for global ecological sustainability that natural old-growth forests and other terrestrial ecosystems are fully protected and helped to expand and mature.

Kerala's elephants are a staggeringly valuable asset, providing a means to envision habitat requirements as an umbrella for human and biosphere sustainability. As a real world example, elephants moving across landscapes are emblematic and widely visible examples of the types of flows that continue on a connected landscape, and are required for local and global ecological sustainability. As go Kerala's Asian elephants and their habitat, so shall go the biosphere.

Blunt, Biocentric Discussion on Avoiding Global Ecosystem Collapse and Achieving Global Ecological Sustainability

Science needs to do a better job of considering worst-case scenarios regarding continental- and global-scale ecological collapse. The loss of biodiversity, ecosystems, and landscape connectivity reviewed here shows clearly that ecological collapse is occurring at spatially extensive scales. The collapse of the biosphere and complex life, or eventually even all life, is a possibility that needs to be better understood and mitigated against. A tentative case has been presented here that terrestrial ecosystem loss is at or near a planetary boundary. It is suggested that a 66% of Earth's land mass must be maintained in terrestrial ecosystems, to maintain critical connectivity necessary for ecosystem services across scales to continue, including the biosphere. Yet various indicators show that around 50% of Earth's terrestrial ecosystems have been lost and their services usurped by humans. Humanity may have already destroyed more terrestrial ecosystems than the biosphere can bear. There exists a major need for further research into how much land must be maintained in a natural and agroecological state to meet landscape and bioregional sustainable development goals while maintaining an operable biosphere.

It is proposed that a critical element in determining the threshold where terrestrial ecosystem loss becomes problematic is where landscape connectivity of intact terrestrial ecosystems erodes to the point where habitat patches exist only in a human context. Based upon an understanding of how landscapes percolate across scale, it is recommended that 66% of Earth's surface be maintained as ecosystems; 44% as natural intact ecosystems (2/3 of 2/3) and 22% as agroecological buffer zones. Thus nearly half of Earth must remain as large, connected, intact, and naturally evolving ecosystems, including old-growth forests, to provide the context and top-down ecological regulation of both human agroecological, and reduced impact and appropriately scaled industrial activities.

Given the stakes, it is proper for political ecologists and other Earth scientists to willingly speak bluntly if we are to have any chance of averting global ecosystem collapse. A case has been presented that Earth is already well beyond carrying capacity in terms of amount of natural ecosystem habitat that can be lost before the continued existence of healthy regional ecosystems and the global biosphere itself may not be possible. Cautious and justifiably conservative science must still be able to rise to the occasion of global ecological emergencies that may threaten our very survival as a species and planet.

Those knowledgeable about planetary boundaries – and abrupt climate change and terrestrial ecosystem loss in particular – must be more bold and insistent in conveying the range and possible severity of threats of global ecosystem collapse, while proposing sufficient solutions. It is not possible to do controlled experiments on the Earth system; all we have is observation based upon science and trained intuition to diagnose the state of Earth's biosphere and suggest sufficient ecological science–based remedies.

If Gaia is alive, she can die. Given the strength of life-reducing trends across biological systems and scales, there is a need for a rigorous research agenda to understand at what point the biosphere may perish and Earth die, and to learn what configuration of ecosystems and other boundary conditions may prevent her from doing so. We see death of cells, organisms, plant communities, wildlife populations, and whole ecosystems all the time in nature – extreme cases being desertification and ocean dead zones. There is no reason to dismiss out of hand that the Earth System could die if critical thresholds are crossed. We need as Earth scientists to better understand how this may occur and bring knowledge to bear to avoid global ecosystem and biosphere collapse or more extreme outcomes such as biological homogenization and the loss of most or even all life. To what extent can a homogenized Earth of dandelions, rats, and extremophiles be said to be alive, can it ever recover, and how long can it last?

The risks of global ecosystem collapse and the need for strong response to achieve global ecological sustainability have been understated for decades. If indeed there is some possibility that our shared biosphere could be collapsing, there needs to be further investigation of what sorts of sociopolitical responses are valid in such a situation. Dry, unemotional scientific inquiry into such matters is necessary – yet more proactive and evocative political ecological language may be justified as well. We must remember we are speaking of the potential for a period of great dying in species, ecosystems, humans, and perhaps all being. It is not clear whether this global ecological emergency is avoidable or recoverable. It may not be. But we must follow and seek truth wherever it leads us.

Planetary boundaries have been quite anthropocentric, focusing upon human safety and giving relatively little attention to other species and the biosphere's needs other than serving humans. Planetary boundaries need to be set that, while including human needs, go beyond them to meet the needs of ecosystems and all their constituent species and their aggregation into a living biosphere. Planetary boundary thinking needs to be more biocentric.

I concur with Williams (2000) that what is needed is an Earth System–based conservation ethic – based upon an "Earth narrative" of natural and human history – which seeks as its objective the "complete preservation of the Earth's biotic inheritance." Humans are in no position to be indicating which species and ecosystems can be lost without harm to their own intrinsic right to exist, as well as the needs of the biosphere. For us to survive as a species, logic and reason must prevail (Williams 2000).

Those who deny limits to growth are unaware of biological realities (Vitousek 1986). There are strong indications humanity may undergo societal collapse and pull down the biosphere with it. The longer dramatic reductions in fossil fuel emissions and a halt to old-growth logging are put off, the worse the risk of abrupt and irreversible climate change becomes, and the less likely we are to survive and thrive as a species. Human survival – entirely dependent upon the natural world – depends critically upon both keeping carbon emissions below 350 ppm and maintaining at least 66% of the landscape as natural ecological core areas and agroecological transitions and buffers. Much of the world has already fallen below this proportion, and in sum the biosphere's terrestrial ecosystem loss almost certainly has been surpassed, yet it must be the goal for habitat transition in remaining relatively wild lands undergoing development such as the Amazon, and for habitat restoration and protection in severely fragmented natural habitat areas such as the Western Ghats.

The human family faces an unprecedented global ecological emergency as reckless growth destroys the ecosystems and the biosphere on which all life depends. Where is the sense of urgency, and what are proper scientific responses if in fact Earth is dying? Not speaking of worst-case scenarios – the collapse of the biosphere and loss of a living Earth, and mass ecosystem collapse and death in places like Kerala – is intellectually dishonest. We must consider the real possibility that we are pulling the biosphere down with us, setting back or eliminating complex life.

The 66% / 44% / 22% threshold of terrestrial ecosystems in total, natural core areas, and agroecological buffers gets at the critical need to maintain large and expansive ecosystems across at least 50% of the land so as to keep nature connected and fully functional. We need an approach to planetary boundaries that is more sensitive to deep ecology to ensure that habitable conditions for all life and natural evolutionary change continue. A terrestrial ecosystem boundary which protects primary forests and seeks to recover old-growth forests elsewhere is critical in this regard. In old forests and all their life lie both the history of Earth's life, and the hope for its future. The end of their industrial destruction is a global ecological imperative.

Much-needed dialogue is beginning to focus on how humanity may face systematic social and ecological collapse and what sort of community resilience is possible. There have been ecologically mediated periods of societal collapse from human damage to ecosystems in the past (Kuecker and Hall 2011). What makes it different this time is that the human species may have the scale and prowess to pull down the biosphere with them. It is fitting at this juncture for political ecologists to concern themselves with both legal regulatory measures, as well as revolutionary processes of social change, which may bring about the social norms necessary to maintain the biosphere. Rockström and colleagues (2009b) refer to the need for "novel and adaptive governance" without using the word revolution. Scientists need to take greater latitude in proposing solutions that lie outside the current political paradigms and sovereign powers.

Even the Blue Planet Laureates' remarkable analysis (Brundtland et al. 2012), which notes the potential for climate change, ecosystem loss, and inequitable development patterns neither directly states nor investigates in depth the potential for global ecosystem collapse, or discusses revolutionary responses. UNEP (2012) notes abrupt and irreversible ecological change, which they say may impact life-support systems, but are not more explicit regarding the profound human and ecological implications of biosphere collapse, or the full range of sociopolitical responses to such predictions. More scientific investigations are needed regarding alternative governing structures optimal for pursuit and achievement of bioregional, continental, and global sustainability if we are maintain a fully operable biosphere forever. An economic system based upon endless growth that views ecosystems necessary for planetary habitability primarily as resources to be consumed cannot exist for long.

Planetary boundaries offer a profoundly difficult challenge for global governance, particularly as increased scientific salience does not appear to be sufficient to trigger international action to sustain ecosystems (Galaz et al. 2012). If indeed the safe operating space for humanity is closing, or the biosphere even collapsing and dying, might not discussion of revolutionary social change be acceptable? Particularly, if there is a lack of consensus by atomized actors, who are unable to legislate the required social change within the current socioeconomic system. By not even speaking of revolutionary action, we dismiss any means outside the dominant growth-based oligarchies.

In the author's opinion, it is shockingly irresponsible for Earth System scientists to speak of geoengineering a climate without being willing to academically investigate revolutionary social and economic change as well. It is desirable that the current political and economic systems should reform themselves to be ecologically sustainable, establishing laws and institutions for doing so. Yet there is nothing sacrosanct about current political economy arrangements, particularly if they are collapsing the biosphere. Earth requires all enlightened and knowledgeable voices to consider the full range of possible responses now more than ever.

One possible solution to the critical issues of terrestrial ecosystem loss and abrupt climate change is a massive and global, natural ecosystem protection and restoration program – funded by a carbon tax – to further establish protected large and connected core ecological sustainability areas, buffers, and agro-ecological transition zones throughout all of Earth's bioregions. Fossil fuel emission reductions must also be a priority. It is critical that humanity both stop burning fossil fuels and destroying natural ecosystems, as fast as possible, to avoid surpassing nearly all the planetary boundaries.

In summation, we are witnessing the collective dismantling of the biosphere and its constituent ecosystems which can be described as ecocidal. The loss of a species is tragic, of an ecosystem widely impactful, yet with the loss of the biosphere all life may be gone. Global ecosystems when connected for life's material flows provide the all-encompassing context within which life is possible. The miracle of life is that life begets life, and the tragedy is that across scales when enough life is lost beyond thresholds, living systems die.

We simply must learn to live in a manner that does not destroy our habitat – in a globalized world, our biosphere – or we all may needlessly die, perhaps taking all life with us. We had best start looking in more earnest at the land around us and the life and processes it sustains as a measure of societal and biosphere well-being. While addressing all planetary boundaries, there is a particular need to immediately begin the end of fossil fuels and to empower and invest in the restoration and protection of natural ecosystems, as two of the most vitals paths to global ecological sustainability

Global ecological sustainability depends critically upon maintaining connectivity of ecosystem processes. The movement of massive elephants across landscapes is hard to ignore, but at numerous ecological scales, less visible movements of life, energy, water and nutrients are what keeps Earth alive. Political ecology has the potential to provide the needed framework to integrate human needs for just, equitable advancement with the needs of the biosphere to avoid collapse, and the required sufficient policies and available political structures to do so. Let's make it so.

* Dr. Glen Barry would like to acknowledge research assistance provided by Dr. Tom Rooney, and editing by Paul Hawley, which proved critical to the successful completion of this paper. And to thank Nagaraj Narayanan of Kerala Law Academy for making the conference possible, to Jeff Berkson of AnchorBank for gainfully employing me, and acknowledge the love and support of my wife Julie and daughter Talita who sustain me. And my goofy golden retriever Ginger deserves mention too, just for being there. All errors and omissions of course remain my own.

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Proposing a planetary boundary for terrestrial ecosystem loss

By Dr. Glen Barry, December 16, 2012

Paper presented at the Kerala Law Academy International Law Conference on Conservation of Forests, Wildlife and Ecology, December 15-17, 2012

Theme - The Legal Regime and Measures for Conservation of Bio Diversity and Protection of Ecological Balance of Western Ghats

“Earth provides enough to satisfy every man's need, but not every man's greed.” – Mahatma Gandhi

"How wonderful it is that nobody need wait a single moment before starting to improve the world." – Anne Frank

*Version 1.0, not yet peer reviewed, or final edits for publication in conference proceedings. Here is the most recent version entitled "Terrestrial Ecosystem Loss and Biosphere Collapse" being readied for publication.

Review Paper Abstract

Planetary boundary science continues the study of requirements to avoid ecosystem collapse and to achieve global ecological sustainability, by defining key thresholds in the Earth System's ecological conditions that threaten human well-being. Terrestrial ecosystems do not enter into the nine originally defined boundaries ranging from climate change to water availability, except peripherally through other boundaries such as land use and biodiversity. A rigorous research agenda is necessary to determine what quantity and quality of terrestrial ecosystems are required across landscapes so as to sustain the biosphere. This includes a spatially explicit way of indicating what extent of a landscape, bioregion, continent and global Earth System must remain in the form of connected and intact core ecological areas and semi-natural agroecological buffers, in order to sustain local ecosystem services as well as the biosphere commons. Connectivity of large ecosystem patches which remain the matrix for the landscape is a preeminent consideration. When ~60% of a natural ecosystem habitat remains, after just under 40% of the ecosystem has been destroyed, the landscape is said to percolate, and we see critical collapse of the "percolating cluster" – the dominant large habitat patch constituting the matrix of the landscape – into smaller, more distant habitat, in a sea of human development. This critical deterioration of habitat connectivity continues so that at or near 50% loss of a landscape or bioregon's natural vegetation, the natural habitat percolates from people within ecosystems, to natural islands surrounded by human works. This transition is likely to be similar at a continental and global scale.

A new planetary boundary threshold is proposed: that 60% of terrestrial ecosystems must be maintained across scales – with the boundary set at 66% as a precaution – as a safe space not only for humanity but for all life and to maintain the long-term viability of the biosphere. It is thought that loss and diminishment of terrestrial ecosystems aggregates from the local and regional scale, yet disrupts planetary process with this global scale threshold. It is hypothesized that ensuring natural ecosystems and their biogeochemical flows remain the context for human endeavors is a requirement to sustain the biosphere for the long term, and that fundamentally this requires large core ecological areas, and the critical connectivity of ecosystem processes and patterns, as the global and fractal landscape matrix. It is further proposed on the basis of ecology's percolation theory that two-thirds of the 66% of terrestrial ecosystems must be protected as ecological core areas (in total 44% of the global land mass as intact ecological cores, 22% as agroecological, agroforestry and managed forest buffers, and transition zones), to ensure the ecological integrity of the semi-natural agroecological landscapes, to maintain critical ecosystem connectivity across scales, and encompass semi-natural landscapes and bioregions within a matrix of intact nature to ensure that their own ecological patterns and processes are sustainable. Up to 50% of Earth's land surface has already been transformed from mostly wild to mostly anthropocentric, so the biosphere is likely to have already lost its global percolating cluster. If indeed bioregional and global scaled landscapes are similar to landscape and bioregional pattern, terrestrial ecosystem connectivity is already critically lacking, and the global ecosystem now exists as patches of nature within a sea of humanity. It is urgent to protect most of what remains and to begin reconstructing connected ecological landscape matrixes of intact ecosystems across scales, so that globally the biosphere can percolate back to connected nature as the provider of top-down context to human and all life.

To have meaning in guiding global ecological sustainability policy, these continental and global observations – and proposed 66% presence / 44% protected – planetary boundary for terrestrial ecosystem loss must be grounded in real-life landscape and bioregional conservation considerations. An example are efforts to achieve ecological sustainability, including maintaining continued viable populations of Asian elephants in the Western Ghats bioregion of India, particularly within Kerala state, as an umbrella species. The Asian elephant requires extensive and adequate natural habitat for its survival, and the Western monsoon depends upon forest-dependent pressure gradients – and thus the provision of both provides for water, clean air, soil, pollinators, and other ecosystem services for the region, nation, and biosphere. An initial expansive regional ecosystem mapping exercise that seeks to identify natural gradients in ecological importance has taken place in Kerala, but its largely top-down processes have faced organized socio-political resistance, it is not clear the scientifically valid mapping processes have enough understanding and support, and the legal structure is not in place to tie its requirements for local and regional sustainability to laws. As a real-world example, elephants moving across landscapes are emblematic and widely visible examples of the myriad types of flows that continue on a connected landscape, making life possible. It is suggested that as go the Western Ghats' and Kerala's Asian elephants and their habitat, so shall go the biosphere, and that it is crucial to build awareness that healthy ecosystems are essential to both local advancement and global sustainability. On the basis of taking such an ecosystem and landscape approach to the needs of Earth System sustainability, and given pernicious trends of ecosystem loss and decline, it is concluded that more attention is needed to prevent worst-case outcomes including biosphere collapse and a lifeless Earth, particularly because of abrupt climate change and ecosystem loss. A massive and global program to protect and restore natural ecosystems – funded by a carbon tax on fossil fuels – is presented as the sort of policy approach necessary at this time to avoid biosphere collapse. Humanity is now the major force shaping the biosphere, which, if current trends in ecological loss and diminishment continue, may collapse or die as a result.

Introduction to Planetary Boundaries

From Malthus (1798), through Aldo Leopold's land ethic (1949), to Limits of Growth (Meadows et al. 1972), through the Millennium Ecosystem Assessment (2005), and finally to current planetary boundary and global change science (Rockström et al. 2009, 2009b); a common strand of concern has been expressed regarding human growth's impacts upon Earth's biophysical systems – terrestrial ecosystems in particular – and an interest in requirements for global ecological sustainability, while avoiding biosphere collapse. Our biosphere is composed of Earth's thin mantle of life present at, and just above and below, the Earth's surface. Some have indicated human impacts upon the biosphere are analogous to a large, uncontrolled experiment, which threatens its collapse (Trevors et al. 2010). Little is known what collapse of the biosphere would look like, how long it would take, what are its ecosystem and spatial patterns, and whether it is reversible or survivable. But it is becoming more widely recognized that Earth's ecosystems services depend fundamentally upon holistic, well-functioning natural systems (Cornell 2009).

Accelerating human pressures on the Earth System are exceeding numerous local, regional, and global thresholds; with abrupt and possibly irreversible impacts upon the planet's life-support functions (UNEP 2012). Planetary boundaries provide a framework to study these phenomena, by defining a "safe operating space for humanity with respect to the Earth System" (Rockström et al. 2009). The study of planetary boundaries seeks to set control variable values that are a safe distance from thresholds that avoid cessation of key biophysical processes that determine the planet's ability to self-regulate to maintain conditions conducive to life (Rockström et al. 2009b). This builds upon landmark efforts by Meadows et al. (1972) to first define global limits to growth. They concluded that key resource scarcities would emerge, predictions which have proven remarkably accurate (Turner 2008), albeit delayed – but not avoided – through the advent of computer technology. Ecological and economic warnings since at least Malthus have called attention to economies' dependence upon natural resources. The conclusion that near-exponential growth of human population and economic activity cannot be sustained, far from being disproven, is more valid than ever (Brown et al. 2011).

The initial planetary boundary exercise identified nine global scale processes, including climate change, rate of biodiversity loss (terrestrial and marine), nitrogen and phosphorus cycles, ozone depletion, ocean acidification, freshwater, land use change, chemical pollution, and atmospheric aerosol loading. Thresholds were established for seven of these, and three – rate of biodiversity loss, climate change, and the nitrogen cycle – were found to already have surpassed a preliminary assessment of the safe planetary boundary threshold (Rockström et al. 2009). Many of these changes occur in a nonlinear and abrupt manner, while others are more incremental and subtle, yet both types of change threaten the viability of contemporary human societies by diminishing or destroying ecological life-support systems. If one or more of these boundaries are crossed, it could be "deleterious of even catastrophic" as nonlinear and abrupt environmental change occurs at the continental to planetary scale (Rockström et al. 2009b).

Setting boundaries of course requires normative decisions on risk and uncertainty. Planetary boundary details and methodology are not without critics, as they are in themselves an imperfect social construct, prone towards bias and political boundaries favoring the rich. Yet there is no escaping the observation that humans have become a powerful agent in Earth System evolution (Biermann 2012). It has been noted that setting thresholds may in itself prolong the risk of continued degradation on the false premise that there is time and it is safe to do so (Schlesinger 2009). Nonetheless, given the well-documented plethora of environmental decline, there appears to be little question that quantifying as best you can based upon science when these changes become dangerous – however uncertain and problematic – and what can be done to avoid possible human extinction and biosphere collapse – remains a valid and valuable field of inquiry.

Earth has gone through many changes, yet for the last 10,000 years of the Holocene epoch there has been a remarkable period of stability – with temperature, freshwater, and biogeochemical flows staying in a relatively narrow range. Yet humanity's largely deleterious activities upon ecosystems have become a force of nature, impacting Earth System functioning (Zalasiewicz et al. 2011). It is increasingly acknowledged that human activities, including use of fossil fuel and industrial agriculture, are destroying ecosystems and changing the climate, threatening this stability.

It is generally accepted that humanity is in ecological overshoot, which means we have already surpassed planetary limits upon sustainability, with lags in full impacts yet to be realized. A growing human population takes goods and services from the Earth System at a rate that erodes its capacity to support us (Steffen et al. 2011). And it is clear that civilization depends upon humanity remaining within thresholds (Folke 2011).

Some have proposed that this human dominance signals a new geological epoch that could supplant the Holocene; it has been dubbed the Anthropocene (Crutzen 2002; Steffen et al. 2011). As we move further into the Anthropocene, humanity risks driving the Earth into "hostile states from which we cannot easily return" (Steffen et al. 2011). Humans depend upon the biosphere – the global Earth System which integrates life and its relationships – for the human life-support system. Human development and advancement are often not perceived as being connected with the biosphere and ecosystem services. Given human domination of the biosphere, ecology must more fully incorporate human behavior (Peterson 2000).

There is a strong consensus that human activities are influencing the Earth's climate (IPCC 2007). Yet an understanding of the impacts of loss and diminishment of natural ecosystems – whether terrestrial, aquatic, or marine; expressed at various scales, and examined using numerous ecological criteria including genetic, organism, species, plant community, and landscape perspectives – remains more elusive. The scale and magnitude, the sheer momentum behind biological impoverishment of the planet is in this researcher's opinion not well understood. And it seems clear that worst-case scenarios of global ecological collapse are not being given their just and prudent consideration.

In fact climate science – as one example – has been described as alarmist, but studies have found instead that it is often conservative in its predictions, erring on the side of less dramatic impacts (Brysse 2012). Rahmstorf and colleagues (2007) found in comparing IPCC’s Third Assessment Report (TAR) with subsequent observations in the science, that the IPCC had underestimated the change in global mean temperature, sea level rise, and atmospheric carbon dioxide concentration. Hansen and colleagues (2012b) found that extreme heat during the summertime is occurring at three times the standard deviation of historical climatology, with extreme heat anomalies such as that in the American southwest in 2011 and Moscow in 2010 having gone from covering 1% to 10% of Earth's surface at any time. The increased probability of such events is compared to "loaded dice."

In short, scientists may be significantly underestimating future impacts, magnitude, and rate of anthropogenic climate change. The same scientific bias in favor of avoiding emotion and maintaining an objective tone – when faced with what may turn out to be an unprecedented and poorly understood global ecological emergency – is likely to be present in assessments of ecosystems, biodiversity, and the state of the biosphere. Up to one half of Earth's land surface has already been transformed by human action, and no ecosystems are free of human influence (Vitousek et al. 1997). While the scientific literature is replete with ecological warnings – such as Folke and colleagues (2011) cautioning of a need to "avoid tipping into a new undesirable Earth System state" – there is a lack of specificity about what exactly this means.

Planetary boundaries represent tipping points where Earth's subsystems react in a nonlinear, abrupt fashion.  The approach focuses on key biogeochemical processes that determine planetary self-regulation and make the Earth System highly analogous to other scales of life from the cell to organisms and ecosystems. It connects traditional environmentalism with Earth System science and what is known of ecological resilience. If further developed and moved downscale to key subsystems, a planetary boundary perspective could serve as a framework for prescriptive ecological policy and inform radical social, legal, and political change required for a sustainable society in relation to the ecosystems that are its underpinning.

Our era's remarkable scouring of Earth's naturally evolved ecosystems has become commonplace, barely noticed by most, as it is thought that destroying natural systems is a normal development process. Yet the Millennium Ecosystem Assessment (2005) found that, of 24 global ecosystem processes – ranging from direct food provisioning to more indirect services – 15 are being degraded or used unsustainably. Climate change is expected in the next decades to place enormous strain upon the survival and integrity of important ecoregions – and their species and ecosystems (Beaumont et al. 2010). Initial planetary boundary research indicates that climate is already past safe levels (Rockström et al. 2009b). There is concern that climate may be approaching or even reaching a point of no return, such that even without additional forcing from anthropogenic climate change, warming will continue out of control, driven by feedbacks such as forest dieback and polar ice and permafrost melt (Hansen et al. 2008).

This loss of biodiversity and ecosystems is problematic enough, yet in conjunction with the planetary boundary of possible looming abrupt and runaway climate change, terrestrial ecosystem loss can only be described as catastrophic. Loss of the panoply of life so rapidly and completely within only a few centuries represents the wholesale dismantling of the biosphere. Terrestrial ecosystems are the nodes in interactions between oceans, air, and water. They are the energy pumps cooling Earth and cycling water, nutrients, and energy. The destruction and diminishment of ecosystems, together with climate change, mean loss of the context within which humanity exists and loss of the environmental top-down regulatory system that makes life possible.

There is increased interest in challenges facing global ecology and equitable advancement for humanity. Recently a group of leading ecological and development luminaries called the Blue Planet Laureates (Brundtland et al. 2012) noted the almost certain impossibility of achieving global ecological sustainability without addressing related issues of poverty, inequity, and injustice. They noted again – what is deeply contested but should be obvious, because nothing grows forever – that infinite growth on a finite planet is not possible. Kosoy et al. (2012) go so far as to say the dominant economic system is delusional, not acknowledging that economies must live within Earth's biogeochemical constraints, and grow by accumulating ever-increasing ecological debt. The dominant economic model, which emphasizes industrial growth, is based upon a mechanistic worldview that destroys its own life support system through failure to see the essence of interrelated social and ecological systems (Taylor 2007), as all growth-based development is ultimately unsustainable (Daly 2005).

The dominant economic model is misconceived, based upon metaphysics devoid of scientific support. Industrial capitalism has not been systematically reviewed in light of 200 years of science (Kovoy et al. 2012), much less recent findings of threats to global ecological sustainability. Economic systems should meet all human needs and not destroy biodiversity and ecosystems. Our natural habitat and life-support systems are being treated like a commodity, on the false premise that they can be replaced with technology. Thus, the global economy is almost certainly profoundly unsustainable.

It is increasingly recognized that economic and social ills are deeply entwined with these limits and cumulatively pose a threat to the biosphere, that the social economy is a subset of the global ecological system, and that a need exists for courageous leaders to speak the difficult truths, and for all to educate and act on these matters (Cairns 2010). Our health and well-being depend upon complex ecosystems that support life on our planet, yet we are consuming the biophysical foundation of civilization. Efforts to systematically assess the long-term, aggregate impact of human activities upon environmental life support systems are lacking (Kosoy et al. 2012). We will either transform ourselves away from these planetary boundaries or enter a series of escalating crises until collapse. It is quite possible that as a result of degraded ecosystems and resource shortages, we are going to witness collapse of the world socio-political-economic system (Taylor 2007), some sort of biosphere collapse, and perhaps death of the Earth System.

The global nature of challenges facing the biosphere and humanity is unique, transcending national boundaries and cultures. This global ecological emergency is occurring during times of high levels of material comfort for some while others suffer extreme depredations, but all alike are facing an eroded planetary life support system (Steffen et al. 2011). Natural scientists must overcome the propensity to ignore the politics of human societies (Peterson 2000). These observations illustrate that efforts to sustain the biosphere cannot help but be political, and if humanity is to survive, much less thrive, scientists who are experts on these issues had best be willing to make prescriptive recommendations that may well prove controversial. Their refusal to engage on issues of economic injustice and equity blocks progress towards cooperative solutions to environmental and social ills, and lessens the prospects of achieving mid-to-long term global ecological sustainability.

Terrestrial ecosystems are not among the nine originally defined planetary boundaries directly, except peripherally through other boundaries, such as biodiversity and land use. This is unfortunate, as landscape ecology and global change inform us regarding the importance of large, connected natural ecosystems – where the flows of genes, species, nutrients, energy water occurs across scale and ecological criteria – in a process of life begetting life. A key indicator of bioregional sustainability is habitat areas for large, wide-ranging species – who, when their habitat is protected, provide an umbrella for the continued provision of local and global ecosystem services. We know shockingly little about how many terrestrial ecosystems must be left standing to maintain a habitable world and to guarantee biosphere sustainability.

Planetary boundary literature may not be adequately accounting for the integrative, keystone nature of terrestrial ecosystems in maintaining the biosphere. Preserving large and connected, intact, naturally evolved terrestrial ecosystems – i.e., both new core global ecological preserves along with restored buffers and transition zones – may be required for global ecological sustainability. Wildlife corridors to maintain connectivity across scales from genes to ecosystems are important to counter habitat fragmentation (Jones et al. 2012). Core protected areas that are large and configured to minimize edge effects and maximize interior habitat are critical to maintaining landscapes where nature remains the matrix, providing top-down ecological constraint upon ecosystem pattern and process (Soulé and Terborgh 1999; Noss et al. 1999). Recent findings indicate that edge effects can increase in fragmented forests through continuous diminishment even with relatively little new loss of habitat (Riitters and Wickham 2012).

The question of how many terrestrial ecosystems are required to sustain the biosphere needs to be investigated further, given the wholesale clearance that is occurring of natural plant communities and wildlife populations arrayed in ecosystems across landscapes and whole bioregions. This is a review paper in political ecology, a discipline that seeks to integrate natural and social science approaches to understanding the relationship between ecosystems and people (Peterson 2000). Political ecology is firmly rooted in geography and first emerged in the 1970s to link community ecology, cybernetics, system theory, and cultural adaptation to address ecology and political economy concerns (Walker 2005). Through this initial literature review and observational study, I hope to begin answering this question and laying out a research program to continue to establish and refine an agreed upon, relatively clear, and defensible terrestrial ecosystem loss planetary boundary.

Political ecology has been accused of lacking ecology (Walker 2005). Here I am going to propose an ecologically rich revision to the planetary boundary framework – while not ignoring politics – to more fully measure the importance of intact terrestrial ecosystems for ecological processes required to sustain ecology and maximize life's well-being. And I am going to do so within the illustrative land-use decisions being made in the Western Ghats and Kerala, India, in pursuit of regional ecological sustainability, including the conservation of viable Asian elephant populations. It is not unscientific to discuss the political implications of ecology and trends in ecosystem loss.

Planetary boundaries as now conceived provide little guidance to on-the-ground development decisions such as those being made in Kerala under the planning process for Western Ghats ecologically sensitive areas. Yet we know critical thresholds of landscape pattern – such as the provision for adequate Asian elephant habitat and corridors – are an ongoing discussion there. To be useful as more than an academic exercise, planetary boundaries need to inform action now. What is needed is that extra layer of detail at the subsystem level, using landscape to bioregional approaches. We need to identify key ecological metrics across scales in terrestrial ecosystems which, when breached, lead to system instability and crash, and intervene appropriately to avoid and mitigate.

The gravest shortcomings to planetary boundary thought are this glaring lack of a terrestrial ecosystem boundary and the anthropocentric focus, in essence writing off other life forms that don't keep humanity "safe." It will also be suggested that planetary boundaries must be less anthropocentric and seek to determine thresholds to maintain all life, including the biosphere as a whole. Planetary boundary thinking needs to further elucidate thresholds and boundaries for naturally evolved ecosystems – particularly terrestrial – as a safe space not just for humanity but for all life and the continuation of natural evolutionary processes within a living biosphere.

Biodiversity and Old-Growth Forest Loss, Abrupt Climate Change, and Ecosystem Collapse

Humanity dominates the Earth to such an extent that there is unknown potential for Earth to be transformed rapidly and irreversibly into a previously unknown state (Barnosky et al. 2012). Solar energy accumulating in plants through photosynthesis drives essentially all the Earth’s food chains. Agriculture, forestry, and urbanization are transforming major biogeochemical cycles, changing global climate and the structure and function of terrestrial ecosystems. The Earth System has undergone remarkable biological change in a short geological time frame. Some one-third to one-half of global ecosystem production is now used by humans, and agricultural systems by various estimates now cover 40-50% of the land surface (Foley et al. 2005; Mooney et al. 2009). Human appropriation of the net primary production of Earth's terrestrial ecosystems has been estimated to be 23.8%, with some 53% of this harvest for use, 40% due to land-use productivity changes, and 7% the result of human-caused fires (Haberl et al. 2007). An earlier estimate placed human use of Earth's biological production at 50% (Vitousek 1997).

It is likely that such major land-use shifts undermine the capacity of the Earth to provide food, freshwater, forest resources, and a relatively stable climate. Humanity faces the enormous challenge of managing trade-offs of meeting immediate human needs (and seemingly endless desires) against maintaining the biosphere’s ability to provide such goods and services in the long-run (Foley et al. 2005). Like all organisms, humans are subject to natural laws, one being fundamental energetic constraints (Brown et al. 2011). Such massive changes in land use not only transform Earth's terrestrial surface but also change biogeochemical processes, reducing the ability of ecosystems to provide services necessary for human well-being (Haberl et al. 2007).

Given such rapid change in the fundamental structure, composition, and function of the biosphere, there has not been enough consideration of worst-case ecological scenarios. This failure is true even as evident impacts of abrupt climate change and ecosystem collapse continue to exceed predictions of just several years ago. It is difficult to respond to an emergency of any type if you don't fully understand its scale and severity. It is worthwhile to review this global ecological change playing out across Earth's terrestrial ecosystems and what it means for prospects for long-term global ecological sustainability.

Forests today cover some 30% of the Earth's land surface, storing some 45% of terrestrial carbon (Bonan 2008). Deforestation represents the final elimination of a forest. It describes the cutting, clearing, and removal of forest and subsequent conversion into anthropogenic ecosystems such as pasture or cropland (Kricher 1997). Humans have altered the terrestrial biosphere for some 8,000 years, yet the destruction has notably intensified over the past century, estimated by some to have crossed a critical threshold with 50% of the terrestrial biosphere transformed to anthropocentric non-natural systems by the mid-20th century. As of 2000, various estimates are that 29% to 75% of nature has been lost to land-use changes (Ellis 2011).

Around half of the world's three billion hectares of forests that originally covered the Earth prior to being impacted significantly by humans have been completely deforested over the past 80 centuries (Bryant and Bailey 1997). During the 1990s clearance of natural tropical forests was as high as 152,000 km2 annually (Bonan 2008). In addition to deforestation, the ecological value of much of the world’s remaining forests has been significantly diminished through various types of overuse. While over half of the world’s original forests remain, most have been heavily impacted by humans and can no longer be considered primary, old-growth forests or wilderness. Estimates are that less than one-fifth of Earth's original forests remain in large, relatively intact and undiminished natural primary forest ecosystems (Bryant et al. 1997). We need better and updated estimates to show how many old, mostly ecologically intact forests remain.

These large, connected primary and old-growth forests maintain natural ecological and evolutionary patterns and processes while providing ecosystem services that make the planet habitable. Remaining tropical wilderness areas in particular are major repositories of biodiversity, contain major watersheds, fill a crucial role in stabilizing the climate, and are also of great economic and strategic importance. Conversion of forests and other natural ecosystems to agriculture has averaged 0.8% annually over the past 40–50 years and is the major force reducing terrestrial ecosystems (Millennium Ecosystem Assessment 2005).

Numerous assessments indicate the area of the world’s forests is shrinking. Williams (2003) puts the parameters of possible annual deforestation rates at 7.5 to approximately 20 million hectares (ha) per year. Some 70% of the land that was deforested was changed to agricultural land (UNEP 2002). At current rates of deforestation, tropical forests will not persist outside protected areas 35 years from now. While tropical forest loss is widely recognized, the rate of loss or degradation shows little indication of appreciable slowing (Terborgh and van Schaik 1997).

Loss of forest habitat is problematic in its own right. Yet fragmentation results when a single forest is divided into a number of smaller habitat patches. Fragmentation is a type of forest diminishment, and biologists generally agree fragmentation, habitat loss, and degradation are major sources of decline in biodiversity and ecosystem functionality (Ehrlich and Ehrlich 1981; Diamond 1984; Wilson 1985; Soule 1991; Noss and Cooperrider 1994). Forest fragmentation leads to significant changes in ecological conditions. Some changes are abiotic: patches tend to be drier and more prone to windthrows. Others are biotic; forest fragments have fewer forest interior species and are more likely to undergo invasion by exotic weedy species.

As the proportion of suitable habitat in a landscape decreases, reduced area and isolation start to limit the population of species (Harris 1984; Franklin and Forman 1987; Noss and Cooperrider 1994). Fragmentation also reduces the capacity of forests to sequester carbon (Dobson et al. 1999). Many of these changes are due to increased edge effects: amplified biotic interactions and significant abiotic changes at the periphery of a forest patch.

Biodiversity and natural ecosystems provide ecosystem services that make the Earth habitable (Ehrlich and Ehrlich 1981; Noss and Cooperrider 1994). Widespread loss of biodiversity could be diminishing the Earth System's ability to regulate key biological processes and feedbacks (Steffen et al. 2011). Ecological systems constitute a life-support system upon which all life on Earth is dependent and without which human civilization may perish (Lubchenco 1998). Ecosystem functions include nutrient cycling and energy flows, disturbance regimes and recovery processes (succession), hydrological cycles, weathering and erosion, decomposition, herbivory, predation, pollination, and seed and animal dispersal (Noss 1992). Kareiva and Marvier (2003) add plant biomass production and drought resistance to the list. Deforestation diminishes the functioning of ecological systems and reduces the output of ecosystem services (Lubchenco 1998).

The richness of species found in ecosystems provides for resilience of ecosystem processes (Rockström 2009). There is growing evidence that biodiversity sustains ecosystems, preventing them from tipping into undesired states (Folke et al. 2004). Species loss affects the functioning of species and their ability to respond and adapt to changing conditions (Rockström et al. 2009b). Species extinction rates already exceed background rates by 100–1000 times what has been typical over Earth's history (Millennium Ecosystem Assessment 2005).

Connectivity is essentially the opposite of fragmentation. Corridors preserve existing connections (Noss and Cooperrider 1994). Retaining habitat connectivity can provide for recolonization of habitat core areas following local extirpation and allow for daily and seasonal movements and normal dispersal of animals (Dobson et al. 1999). Providing for increased landscape connectivity helps alleviate the impacts of habitat fragmentation (Schumaker 1996), including by maintaining dispersal routes and links between habitat patches.

Most existing protected areas are small, isolated, and fragmented (Soule and Terborgh 1999). In cases where connectivity is lost, it can be restored. This approach has been called “rewilding” (Soule and Noss 1998). Soule and Terborgh (1999) argue that the restoration of ecological connectivity must be a ubiquitous conservation activity in both temperate and tropical regions and must focus upon large-scale, top-down processes such as those provided by large, keystone species like Asian elephants. It has been shown that tropical forests in particular show a remarkable degree of resilience, and once land-use pressures destroying and diminishing them are removed or reduced, they can recover relatively rapidly (Bhagwat et al. 2012), albeit to a reduced state if critical thresholds in composition, structure, function, and dynamics were surpassed.

Earth's life is being dramatically reduced, particularly large animals and trees. Large old trees – which often play a critical ecosystem role, including storing carbon, cycling water, providing food to wildlife, and otherwise providing rich micro-environments – are rapidly declining worldwide as they are logged, face elevated mortality, and reduced recruitment. By themselves, large trees increase landscape connectivity as well by attracting seed dispersers and pollinators, and providing stepping stones across a landscape (Lindenmayer et al. 2012). The loss of large-bodied wildlife, also termed apex consumers, cascades through ecosystems worldwide, and may be humanity's most pervasive impact upon the natural world. Loss of apex consumers shortens food chains, and alters the intensity of herbivory and thus plant abundance and composition. As top-down forcing is lost, ecosystem regime shift often occurs (Estes et al. 2011). This loss of keystone species has led to increasingly simplified and less stable ecological networks and patterns of connectivity (Barnosky et al. 2011).

Primary and other types of old-growth forests (terms used inter-changeably while meaning all old forests) have been found to be irreplaceable for sustaining tropical biodiversity, which cannot be protected without effective protected areas and curtailed demand for old-growth timber (Gibson et al. 2011). Primary old tropical forests transpire large amounts of water, cooling the microclimate, bioregion, and planet. Changes in forest cover both cause and are caused by changes in climate – as vegetation cover is tightly coupled to Earth's climate through biogeophysical feedbacks. (Brovkin et al. 2009). As well as storing large amounts of carbon dioxide, old-growth forests have been found to continue removing carbon dioxide from the atmosphere, and accumulating it in their biomass and soils (Luyssaert et al. 2008). Habitat fragmentation in conjunction with climate change causes elevated tree mortality along forest edges, altering canopy dynamics, community composition, biomass accumulation and carbon storage (Laurance 2003).

Agriculture has been a driving force behind primary forest loss, and agricultural expansion in intact terrestrial ecosystem must end if they are to be maintained (Foley et al. 2011). However, the processes driving primary tropical forest deforestation and diminishment have shown a recent shift towards major industries (rather than poor farmers) such as commercial-scaled logging, oil and gas, and plantations as the most frequent cause of forest loss (Butler and Laurance 2008). Given the first priority for conservation must be habitat preservation (Fahrig 2001), it is likely that primary and other old-growth forests must be fully protected and expanded if the biosphere is to be maintained. International efforts to protect the world's forests have been made more difficult by a lax definition of forests, which equates old-growth with tree plantations, which are quite different ecologically (Sasaki and Putz 2009).

Mass extinction occurs when Earth loses more than three-quarters of its species, which is believed to have occurred five times in the past half-billion years. Yet each time, except the Cretaceous meteorite event, this occurred over hundreds of thousands to millions of years (Barnosky et al. 2011). It is widely believed that humans are causing a sixth mass extinction event, particularly through climate change and habitat fragmentation. It is possible that species diversity will not reradiate following such events – particularly if the biosphere is rapidly damaged past key thresholds, and the Earth System has collapsed or perhaps in key aspects even died.

It is very difficult to predict with any certainty how terrestrial ecosystems will interact with other global environmental change, though it is virtually certain they will be more simple structurally, with more early successional vegetation (Walker and Steffen 1997). Large ecosystems can shift abruptly and irreversibly in state when forced across thresholds. Recently there has been much research into such catastrophic shifts in ecosystems, and under what conditions they shift dramatically to other conditions. It is believed that some complex ecosystems can exist in alternative stable states. Shifts between these states can cause large losses in ecosystem patterns and processes, including an end to continued provision of economic benefits (Scheffer et al. 2011).

There is evidence that the global ecosystem as a whole can exhibit planetary transition as humans push Earth past tipping points and as the result of cumulative small-scale events. This is evident as human population growth and resulting resource use and depletion cause more of Earth's surface to be transformed and fragmented. Human population growth of about 77 million people a year drives these global changes, as human population has quadrupled in the past century to over seven billion. Areas that once housed natural biodiversity and ecosystems which power the Earth System now contain only a few species (Barnosky 2012).

Concurrently there has been an effort to determine early warning signals for such critical transitions, to determine tipping points where ecosystems make a sudden shift to a new dynamic regime (Drake and Griffen 2010; Carpenter et al. 2011). Certain generic aspects of an ecosystem approaching a critical point and undergoing phase shift have been noted, including bifurcations, flickering between states, a critical slowdown in system processes, and autocorrelation in these processes (Scheffer et al. 2009). In other instances, it is noted that for some complex natural systems for which there are multiple outcomes to a phase shift, there is likely to be no warning of regime changes. Drastic changes can appear in nature without warning (Hastings and Wysham 2010), and even when indicators of ecosystem regime shift are detected, it is often too late to avert them (Biggs et al. 2009).

While it is of academic interest to know when such phase shifts may occur, given lack of political commitment to avoiding ecosystem deterioration, it is not at once clear what benefit is provided by advance warning of a tipping point immediately before it occurs. There is no indication that human governance is capable of making such dramatic changes as would be required in ecosystem management just before collapse. More general predictive powers are needed to know earlier that a system is in trouble. Clearly there exists a need to not only deepen our understanding of such ecosystem change but ensure social science governance issues are integrated into pursuit of sustainability (Reid et al. 2010). Underlying drivers that push ecosystems towards thresholds – such as habitat loss and fragmentation which are ubiquitous in today's economic activity – must be slowed and addressed well before thresholds are reached (Biggs et al. 2008).

Abrupt climate change that was large-scale and widespread have occurred many times as the Earth has moved past thresholds in the past, yet stabilizing feedbacks operating at a long-term scale have kept Earth within a relatively narrow band of liquid-water conditions conducive to life for almost 4 billion years (Alley et al. 2003). Yet, within this band, within the span of a few decades global temperature can rapidly increase by more than a dozen degrees Celsius (Schultz 2012). Human activities can potentially push the Earth system past critical tipping points into different qualitative states (Lenton et al. 2008). Climate change is often perceived as a smooth, gradual process, when in fact it could pass tipping points and become abrupt and potentially runaway (Lenton et al. 2008). With human climate forcing, climate impacts may be "big, fast, and patchy" at a regional scale; triggering abrupt crashes of ecosystems (Breshears et al. 2011). Synergistic climate and landscape vegetational changes are likely to induce profound shifts in the societies living there (Heyder et al. 2011), whose success depends upon meeting critical thresholds to physiological human needs.

There is growing concern that science has consistently underestimated the rate and intensity of climate change. This illustrates the difficulty of addressing what could conceivably be apocalyptic-scale threats within the staid and conservative scientific tradition. We are witnessing long-term and abrupt climate changes already in Arctic sea ice melt, loss of ice mass in Greenland and West Antarctica, a shift of subtropical regions towards the poles, bleaching and death of coral reefs, large floods, weakening of the ocean carbon sink (Rockström 2009b), and an increase in extreme weather events (Hansen 2012b).

It is generally accepted that given a climate sensitivity of about 3 degrees Celsius for doubled carbon dioxide equivalency, atmospheric concentration of CO₂ must be reduced from its current almost 400ppm to 350ppm, if humanity is to maintain the relative Holocene climate stability within which civilization has evolved (Hansen et al. 2008). To maintain such an Earth System it is critically important to rapidly reduce fossil fuel emissions (Hansen and Sato 2012). Recovering from present overshoot would require the phasing out of coal, an end to all fossil fuels unless carbon is sequestered, and use of agriculture and forest practices to resequester carbon (Hansen et al. 2008). It has been suggested that slowing population growth rates could account for 19-29% of the emissions reductions necessary by 2050 to avoid the most dangerous impacts of climate change (O' Neill et al. 2010).

The current rate of warming caused by increased greenhouse gas emissions is almost certainly unprecedented in the last 10,000 years (Beaumont et al. 2010). Climate change processes unleashed through release of carbon dioxide are largely irreversible for thousands of years (Solomon et al. 2008). In general, it is believed that biotic feedback considerably extends the lifespan of the biosphere by maintaining low atmospheric carbon dioxide levels (as well as other processes such as silicate rock weathering) (Lenton and Blow 2001). Projected loss of biodiversity is likely to be underestimated when land use and climate change are examined in isolation (Chazal and Rounsevell 2008), as these systems are tightly coupled and synergistic.

There is much evidence that climate change is causing major alterations in biological systems (Rosenzweig et al. 2008). Climate change is a threat to all levels of biodiversity (Maclean and Wilson 2011), causing changes in vegetation communities large enough to impact the integrity of biomes, and contribute to a sixth mass extinction (Bellard 2012). Malcolm et al. (2006) consider global warming to be one of the most serious threats to biodiversity, and losses of 39–43% of endemic species from 25 major biodiversity hotspots to be possible.

Climate change has been found to impact biological systems – and their phenology, distribution of species, morphology, and net primary productivity – including the "Global 200" ecoregions of exceptional biodiversity (Olson and Dinerstein 2002). Terrestrial ecosystems cycle ten times the annual amount of carbon released by fossil fuels and altered land use. And climate change may severely impact these processes, restructuring the terrestrial biosphere at the continental scale (Heyder et al. 2011). Yet tropical forests in particular are vulnerable to a warmer, drier climate (Bonan 2008). Ecosystems exert influence upon climate through changes in the water, energy and greenhouse gas balance (Chapin et al. 2008).

Climate change affects forests by altering the frequency, timing, duration, and intensity of naturally occurring disturbance patterns including fires, drought, insects and pathogens, introduced species, hurricanes, and extreme weather (Dale et al. 2001). Shifting in rainfall and precipitation patterns associated with climate change are expected to intensify the severity of droughts, gravely impacting forests and causing further forest decline (Choat et al. 2012). Some studies have shown that forest cover plays a far greater role in determining rainfall than has generally been appreciated (Sheil and Murdiyarso 2009). Largely as a result of drought, it is possible the Amazon rainforest, facing climate change–induced extreme warming and drying, may die back to all but refugia, releasing carbon dioxide in a massive positive feedback (Cox et al. 2004; Nepstad et al. 2007). This threat almost certainly faces smaller natural old forests as well. The land-to-ocean pressure gradient driving the southwest Indian Summer monsoon has been shown to be reduced due to albedo changes associated with land use changes, including old forest loss, as well as aerosol pollution (Lenton et al. 2008).

Mean global temperatures by 2070 or earlier will be higher than they have ever been since the human species evolved (Barnosky et al. 2011). Evident global warming of just under 1 degree Celsius will almost certainly be added to by additional warming already in the pipeline, including as the result of vegetational changes (Hansen et al. 2008). By the end of the century we can expect virtually all ecoregions to be under climate stress caused by heat and precipitation patterns that are well outside recent variability patterns. It is expected in the next 20 years that monthly temperatures will be beyond 2 standard deviations of the 20th century baseline, and substantial variation in precipitation may threaten the survival of biologically important ecoregions worldwide. This increase in temperatures relative to natural variability is expected to be particularly pronounced in the tropics, impacting spatial distribution of both organisms and ecosystems (Beaumont et al. 2010).  

It is likely that human land-use changes increase the vulnerability of tropical forests to climate change and may be as important as abiotic changes in their decline, as synergies magnify habitat loss and fragmentation (Brodie et al. 2011). To allow vegetation to adapt the best it can to climate change, it is thought to be important to maintain and enhance landscape connectivity so species can migrate. Protected areas are identified both because they allow biodiversity and ecosystems to migrate and otherwise adjust as best they can to climate change and because their vegetation is an important component in minimizing warming (Hannah et al. 2007). Landscapes that display fractal qualities such as non-uniform forest edges have been found to be more tolerant of habitat destruction (Hill and Caswell 1999).

Other than protecting as much habitat a possible, wildlife corridors offer another means to maintain ecosystem processes and viability of isolated populations across human-impacted landscapes. Yet habitat corridors continue to be lost across the world, critically undermining the connectivity of ecosystems on scales from the local landscape through bioregional to global. While the pros and cons – including greater spreading of disease – have been weighed, the evidence generally supports habitat corridors as a means to maintain landscape connectivity (Williams and Snyder 2005).

One approach to studying the effects of habitat loss and fragmentation upon landscapes has been percolation theory, which shows that some aspects of structural habitat fragmentation may change rapidly below critical proportions of habitat (Swift and Hannon 2009). At 40% of a landscape's habitat loss, many linear landscape measures such as edge density, contagion, distance to nearest neighbor, and fractal dimension show a 50% probability of an abrupt change to non-linear responses (Hargis et al. 1998). As habitats are dissected into smaller parcels, landscape connectivity – the functional linkage between habitat patches – becomes disrupted (With and Crist 1995).

Percolation models that simulate landscapes have found that when habitat covers less than 59% (0.59275) of the landscape, the largest habitat patch decreases abruptly and no longer spans the entire landscape (Gustafson and Parker 1992; Andren 1994; Bascompte and Sole 1996). A percolating cluster exists when a path exists across a landscape from one side to the other, regardless of scale. If a percolating cluster exists, organisms as well as flows of energy and other materials including species can move from one edge of the landscape through a path of habitat cells to the other. When connectivity is defined on the basis of the nearest neighbor, a critical threshold exists near 60% whereby the probability of a percolating cluster is 50%. Below this level percolating clusters rarely exist, and even 2% above this threshold the likelihood becomes very high (Williams and Snyder 2005).

Another critical landscape threshold in relationship to habitat loss that occurs across scales is that at about 40% of habitat retention (60% loss), the distance between patches increases rapidly (Gustafson and Parker 1992; Andren 1994), and at 30% habitat patch numbers peak. These fragmentation thresholds may represent a positive feedback mechanism with potential to drive irreversible regime shift in ecosystem functions across fragmented landscapes (Pardini et al. 2010). At greater spatial scales of analysis, these may aggregate to critical breaks in ecosystem connectivity and thus sustainability at the continental and biosphere scales.

When a percolating cluster exists, the landscape is connected and characterized by a few large habitats. Below this threshold of ~59% the landscape is characterized by many small and disconnected habitats. This is a remarkable characteristic of landscapes across scale (Wu 2004) and represents a direct phase shift between connectivity and nonconnectivity. Below this level of connectivity, the likelihood of critical transitions increases – that is, once this amount of Earth's ecosystems have been transformed, the remainder can change rapidly (Barnosky et al. 2011). Critically, this percolation and resultant lack of connectivity also aligns with the landscape shifting from habitats surrounding humanity, to human works surrounding islands of habitat.

Throughout history, human settlements were islands that existed within the sea of nature; now as a result of habitat fragmentation, at most scales this has largely been reversed (Janzen 1986). This matrix of intact terrestrial ecosystems is being lost across bioregions, continents, and the global biosphere as a whole as landscapes are percolating, losing connectivity and the ability to provide their ubiquitous top-down regulation and provisioning of human and other natural processes. Solutions to habitat loss and fragmentation require the popular embrace and implementation of basic conservation biology principles including the need to protect large core areas, establish agroecological buffers and transition zones, and have these larger core areas connected as the matrix for sustainable human societies.

Most of the research into thresholds for terrestrial ecosystems has looked at extinction of species or progressive dismantling of a landscape-sized ecosystem. Other researchers have begun to look at continental-scale conservation and noted the importance of top-down regulation provided by intact ecological matrixes across large scales (Soulé and Noss 1998; Soulé and Terborgh 1999, 1999b). Yet it is possible to go even further upscale and view the biosphere as a big landscape. Viewing terrestrial ecosystems in space and time as changing patterns of patch and matrix is not scale dependent; one explicitly states the scale for which an ecosystem and landscape perspective is taken. Findings regarding critical levels of connectivity for biodiversity in ecosystems taking a landscape perspective are almost certainly as valid as viewing continental ecosystem and landscape patterns aggregating to the biosphere, though further research is necessary.

We do not yet know with certainty at a global scale how much land must be transformed before there is a planetary shift, but various studies and theory suggest that numerous critical thresholds exist between 50% and 90%. What is clear is that beyond thresholds, ecosystem services undergo state shift, destabilize, and begin to degrade as networks of ecological connectivity begin to disassemble. By 2025, it is predicted we can expect that 50% of Earth's land will have undergone state shifts, as human population reaches 8.2 billion; and 70% of Earth's land could be shifted to human use with populations of 11.5 billion by 2060 (Barnosky et al. 2011). As mentioned, various measurements of human usurpation of land mass for agricultural and net primary productivity place the level at 50%.

As well as the 40% loss associated with loss of a percolating cluster and thus landscape and ecosystem connectivity, 50% habitat loss appears to be a critical value, where remaining natural systems are transformed to new states through large-scale forcing in atmospheric chemistry, nutrient, and energy cycling changes. At or near this point, ecosystems flip from being the landscape matrix to being islands, further isolating and disconnecting ecosystems. Our ability to know that critical thresholds are near or have been crossed is complicated by lag times; moreover, it is not immediately known whether an ecosystem or even the entire biosphere has crossed a critical transition, and it is almost certainly not possible to know except in retrospect (Barnosky et al. 2011).

Natural vegetational communities and animal populations – whose ecosystem outputs are likely critical sources of biosphere stability – are simultaneously being reduced by habitat loss, fragmentation, and abrupt climate change. To survive and thrive, humanity may be well advised by the state of current science to protect and restore natural, large, and connected ecosystems and to cut fossil fuel emissions. Species extinction from climate change is expected to be a nonlinear power function of global warming; therefore minimizing global warming is a major biodiversity conservation goal (Hansen et al. 2010). Entire tropic networks will be affected, and ecosystem functioning is expected to be significantly reduced (Bellard et al. 2012).  

Over recent decades, most governments and conservation organizations have called for 10–12% protection of each type of ecosystem, a target which relegates terrestrial ecosystems to being isolated, unconnected remnants in a sea of human development and could prove inadequate to meet human needs and maybe even crash the biosphere. Some 13% of Earth's total land area is now covered with protected areas (UNEP 2012) – with about half providing adequate protections (Laurance et al. 2012). At the 2010 Nagoya Conference on the Convention on Biological Diversity, a 17% protected area goal for terrestrial ecosystems was put forth (Noss et al. 2011). These values appear to be largely arbitrary. They accept that virtually all unprotected lands, particularly in the tropics, will be industrially developed and that with 90% habitat loss, some 50% of species will go extinct from habitat loss alone (Soulé and Sanjyan 1998). This level of terrestrial ecosystem protection virtually ensures the lack of a percolating cluster, and thus inadequate landscape connectivity to mediate critical ecosystem flows for sustainability.

As tropical deforestation quickens, protected areas are often the only places where natural ecosystems and biodiversity can persist. Yet protected areas in the tropics are especially vulnerable to human encroachment and other environmental stresses. Laurance et al. (2012) found that about half of tropical reserves are losing biodiversity across taxonomic and functional groupings, and 80% of reserves show some signs of decline. In many cases this was found to be due to landscapes around reserves being under threat, the lack of buffers and transition zones, their small size, and lack of connectivity with the broader landscape. If even protected areas cannot persist, where in the future shall our and the biosphere's ecosystem services upon which we depend be derived?

Others such as Noss et al. (2011) are also calling for "bolder conservation," offering the more biocentric proposal that some 25–75% be managed for biodiversity conservation and stating frankly that "Nature needs at least 50%, and it is time we said so." Percolation theory's insights into ecological connectivity applied across scales makes the case for doing so, not only for the sake of biodiversity and ecosystems, but for sustainability of continents and the biosphere – and of people, who require ecosystems as their context as well. Critical to the efficacy of protected areas is sizable buffer and transition zones around reserves, maintaining connectivity to other forest areas, and low-impact community based land uses around reserves (Laurance et al. 2012).

Convincing evidence is emerging that industrial logging in tropical forests that is both sustainable and profitable is impossible (Zimmerman and Kormos 2012). There are questions whether repeated harvests can truly sustain natural ecosystems (Nasi and Frost 2009). Logging generally removes large trees where most of the forest's carbon is stored (Vieira et al. 2005). Despite these concerns, humanity continues to clear what old native forest vegetation still exists. Despite significant science, the myth of "sustainable forest management" in old-growth forests continues, supported by a diverse cast of characters ranging from Greenpeace to the World Bank.

Small-scale community ecoforestry has proven to lead to reasonable protection of intact tropical forest ecosystems (Bray et al. 2003). Limited logging at low intensities, such as might occur under small-scale community ecoforestry, with few if any roads, and which generally removes less than five trees per hectare in tropical forests and does not open the canopy and disturb the soil, in theory may maintain old growth's key structure and species composition. Yet this is generally not what is occurring: most old-growth forests are logged industrially at two to three times higher intensity than their rate of recovery (Zimmerman and Kormos 2012), with roads left behind that enable further diminishment.

It is useful for this study to understand that biological systems can be investigated at any scale. The Gaia hypothesis holds that the Earth system is in some ways analogous to a living, self-regulating organism – with air, land, soil, and oceans as her organs; plants and animals as cells; and water as blood, cycling nutrients and energy to be alive. Formulated by James Lovelock (1979), the Gaia hypothesis noted the role of biology in promoting homeostasis in the Earth System; that is, life maintains the conditions for life. Coordinated activity between individual species and the environment is similar to interactions between cells and organs in multicellular organisms (Kondrat'ev 2001).

According to this and similar theories of the biotic regulation of the environment, living systems have the capacity to actively maintain environmental conditions that sustain life. There is a need to focus upon the sustainability of Gaia – the global ecosystem – based upon what is known about sustaining biodiversity, ecosystems, and landscapes across scales. Very little is known regarding the requirements for sustainability of the global biosphere and what aspects of terrestrial ecosystems in terms of quality and placement are necessary to do so. This researcher concurs fully with Soule and Terborgh (1999) that "science and advocacy must become allies in the defense of nature."

Terrestrial Ecosystem Loss as a Planetary Boundary

Planetary boundaries have not well characterized the impacts of terrestrial ecosystem loss, and thresholds for human and the biosphere's safety are not well known. Simply, how many intact terrestrial ecosystems are required to maintain operable biosphere? More broadly, how can ecosystem collapse be avoided and global ecological sustainability achieved? While progress has been made in identifying fossil fuel emissions as a threat to our biosphere and thus human well-being, relatively less urgency has been assigned to quantifying the threat posed by terrestrial ecosystem loss at a continental and global scale.

It is worrying that terrestrial ecosystem loss and diminishment are not more prominent in their own right within the initial conception of planetary boundaries. It may prove to be an ominous oversight. Not many are asking how many terrestrial ecosystems are required to maintain a livable biosphere for humanity and all species. It is not clear how such an obvious boundary could have been missed, except perhaps that land clearance, in what may be overdeveloped countries where most science occurs, is so ubiquitous that it is taken to be the natural condition.

Running (2012) made an initial, independent effort to explicitly define a measurable planetary boundary for terrestrial ecosystems based upon plant net primary productivity. While such a boundary does recognize terrestrial ecosystem loss, integrating well primary aspects of global ecosystem sustainability, it remains problematic in focusing merely upon biomass production, while not assessing critical spatial and scale-dependent ecosystem processes in cycles provided by fully intact and connected natural ecosystems.

What is sought here is the first iteration of a less arbitrary terrestrial ecosystem loss threshold value and precautionary boundary. This needs to be more inclusive of the full range of ecological services provided by intact, large, and connected ecosystems and more rooted in scientific phenomena relating to the loss of habitat and profound dismantling of ecological connectivity resulting from habitat fragmentation.

A planetary boundary for terrestrial ecosystem loss would go well beyond the current planetary boundary proposal's land system change and biodiversity loss and deal with ecological processes and patterns – the integrative services – provided by land still covered with intact natural vegetation. Clearly the scouring away of complex plant and animal life (arrayed across landscapes in complex ecosystems; integrated with water, climate, and oceans; and aggregating to bioregions, continents, and ultimately the one, shared biosphere; which can now be mapped and analyzed in detail using satellites and computers) can be conceived in terms of a planetary boundary. A proposed terrestrial ecosystem planetary boundary may well be more rigorously defined than some others, providing guidance to bioregional and landscape decision-making processes as well.

The current conception of a planetary boundary measuring land and natural vegetation is inadequate. It is not enough to assess the quality of land and its intact ecosystems only in terms of how much land is under agricultural development. The current land-use boundary only partially gets at the tremendous loss of ecosystem processes such as pollution absorption, pollination, and soil development, and ecological patterns such as naturally evolved plant community assemblages that are lost with the decay or disappearance of terrestrial ecosystems.

Terrestrial ecosystems are rooted in geography to a far greater extent than the other boundaries, so there is no excuse for not crafting a boundary based upon their position and quality. A bioregional and continental terrestrial ecosystem boundary for global ecological sustainability could be measured based upon what we know about landscape pattern and percolation states at various thresholds of natural plant community coverage and about critical thresholds, regime shifts, and different basins of attraction for ecosystems at the plant community and landscape criterion. A planetary boundary for terrestrial ecosystem loss would draw upon computerized mapped data, aggregating conditions of natural habitats across scale, capturing the full complexity of land-based ecological thresholds.

Other planetary boundaries refer to terrestrial ecosystems in scattered and haphazard ways, but in fact, persistent large, connected, and naturally evolving ecosystems are a central organizing principle of a living biosphere, in fact, of life itself. Like the land-use planetary boundary, terrestrial ecosystem loss is tightly coupled with other boundaries. The spatial distribution of this loss across scales is critically important to ensuring that continental-scale land-cover thresholds are not crossed.

When ~39% of variously scaled ecological systems viewed as landscapes are destroyed (60% habitat remains), the landscape is said to percolate. As reviewed earlier, at this point in habitat loss we see critical collapse of a dominant large habitat patch, the percolating cluster – constituting the matrix of the landscape – into smaller, more isolated habitat, in a sea of human development. This critical deterioration of habitat connectivity continues so that at or near 50% loss of bioregional and landscape natural vegetation, the natural habitat percolates from people within ecosystems, to natural islands surrounded by human works. This is likely to be similar at continental and global scales, which can be viewed independent of scale as landscapes themselves.

A new planetary boundary threshold is proposed that 60% of terrestrial ecosystems must remain intact with the boundary set at 66% as a precaution. This is seen as necessary to provide a safe space not only for humanity, but for all life, including the Earth System. It is hypothesized that loss and diminishment of terrestrial ecosystems aggregates from the local and regional scale, yet disrupts planetary process with this global scale threshold, just as it does across local landscapes. Ensuring that natural ecosystems and their biogeochemical flows remain the context for human endeavors is hypothesized to be a requirement to sustain the biosphere long term. Doing so requires large core ecological areas – and the critical connectivity of ecosystem processes and patterns – as the global landscape matrix.

It is further proposed on the basis of ecology's percolation theory that two-thirds of the 66% of terrestrial ecosystems must be protected as ecological core areas, to ensure the ecological integrity of the semi-natural agroecological landscapes, by encompassing them within a matrix of intact nature. Avoiding fragmentation and providing for core ecological areas, throughout a mixed-use landscape, is the challenge of terrestrial ecosystem ecology. Thus a terrestrial ecosystem loss planetary boundary is proposed in sum that protects 44% of the global land mass remaining as intact ecological cores, with 22% as agroecological, agroforestry and managed forest buffers, and transition zones. Buffer zones are multiple-use areas that can serve as habitat for some species and insulate core reserves from human activities (Soulé and Terborgh 1999).

Recommendations for a terrestrial ecosystem loss planetary boundary align closely with Soulé and Sanjayan's (1998) scientific review that to represent and protect most biodiversity, particularly wide-ranging species, 50% habitat protection is required. Noss and colleagues (2012) note the timidity of conservation targets and bemoan the acceptance that viable populations of native species and ecosystem services are willfully not maintained, also calling for 50% landscape protection. Earth needs a new class of connected global ecological preserves to sustain key core ecosystems required for an operable biosphere, regional ecological sustainability, and sustainable human advancement.

This guidance is perhaps most useful for the last large wildernesses found in South America, Northern Canada and Russia, the Congo Basin, and Papua New Guinea and East Asia. There land clearing thought necessary to improve human well-being can seek to maintain large and connected core ecological areas as the landscape matrix. In Earth's remaining wildlands, this planetary boundary can guide ecosystem and land-use decisions, as some portion of the bioregion is altered to meet human needs, while maintaining the bioregion's contribution to biosphere sustainability.

Humanity is near or has recently surpassed allowable terrestrial ecosystem loss within a sustainable biosphere. Given that as much as 50% of Earth's biological production may already be dominated by humans (Vitousek 1997), and as much as 33–40% of biospheric production has been coopted by humans (Vitousek 1986; Running 2012), there is an urgency to the terrestrial ecosystem loss boundary. Like the climate change, biodiversity, and nitrogen cycle boundaries, it is quite likely humanity has already crossed the planetary boundary for how many terrestrial ecosystems can be lost.

Extensive extractive land-use patterns found in most populated areas are already well beyond proposed planetary boundaries for loss and diminishment of terrestrial ecosystems in virtually every continent and bioregion. There, as well as across nearly fully modified landscapes, the intent can be to allow remnants to expand, by means including targeted restoration. Some habitat with some connectivity is better than none of either. It can thus be equally telling, as a restoration ecology goal through deliberate land-use planning decisions, to grow core ecological areas and their connectivity. Remnants like the Western Ghats old growth and their elephant herds must be enlarged and reconnected, so that continued ecosystem services may flow to Kerala and neighboring states.

It is going to be difficult in many parts of the world to get back to 66% natural ecosystem cover, and 44% of Earth's surface as fully intact, old terrestrial ecosystems. Agroecological systems, suggested here as minimally across 22% of the land mass, are going to have a play a part in reestablishing an ecological context and top-down constraint upon humanity (Dalgaard et al. 2003; Francis et al. 2003). It is thought that agroecological systems that better mimic natural processes can provide limited ecosystem services, while buffering core ecological areas (Ericksen et al. 2009). Agriculture as it is now practiced has numerous harmful effects, including pollution and habitat destruction, yet there are efforts to incorporate agriculture flows more fully with the flows of plants, animals, nutrients, and water that flow across landscapes. Agroforestry is long established and now being augmented by innovations in permaculture, organic gardening, restoration ecology, and re-wilding.

The key threshold is that at these levels, across continents and the biosphere, natural and semi-natural ecosystems remain the context for human endeavors. And within this ecosystem matrix, intact core ecological reserves constitute the intact, encompassing matrix for agroecological patches. The critical increase in fragmentation and reduction in habitat connectivity and ecological cores can be avoided by maintaining nature as the context for human activities. The potential for natural ecosystems to continue their unimpeded evolutionary development based on the full array of genetic materials is also maximized.

There exists great potential to target the restoration of key areas on landscapes – such as critical gaps in habitat corridors – to improve the connectivity of a landscape or even a bioregion. Emphasis should be upon reestablishing key natural disturbance regimes and promoting the movement of species between habitat fragments (Soulé and Terborgh 1999). Restoring corridors between isolated habitat patches can mitigate or reverse the impacts of fragmentation (Williams and Snyder 2005). The intent would be to identify the most important corridors historically, as well as using computer mapping technologies, to regain a percolating cluster across the landscape and thus reestablish habitat connectivity. Such connectivity can be reestablished first within existing protected areas and then increased in size to neighboring protected and unprotected habitat.

Humanity desperately needs a predictive science of the biosphere if we are to avoid its collapse or even death (Moorcroft 2006). It is critical that humanity reconnect with the biosphere, both to make our dependence upon the biosphere more visible and to link efforts to achieve global ecological sustainability to goals for justice, equity, and rights (Folke 2011). The public, policymakers, and ecological scientists alike need to acknowledge and respond to the fact that humanity has surpassed the carrying capacity of Earth's climate, ecosystems, and biosphere – that we are well into overshoot, and that fact, in view of lags in the system, without rapid changes in trends driven by changes in human behavior, can only result in global ecological collapse and the end of being. There is a glaring need for research agenda to understand at what point the biosphere may perish and Earth die and to configure ecosystems and other boundary conditions to prevent her from doing so.

It is vital to both the biosphere and human advancement that what is known about healthy terrestrial ecology be united with a legal framework to pursue local, regional, and global sustainability goals at scale. We must get at the keystone role that large, intact, naturally evolved ecosystems have as an ecological element in the function of the Earth System.

Kerala's Elephants in India's Western Ghats as an Umbrella Species and Indicator of Local and Global Ecosystem Sustainability

To have meaning in guiding global ecological sustainability policy, these continental and global observations and the proposed 66% / 44% boundary for terrestrial ecosystem loss must be grounded in real-life landscape and bioregional conservation considerations such as efforts to maintain continued viable populations of Asian elephant in Kerala, India. The Asian elephant is an umbrella species which requires extensive and adequate natural habitat to ensure its survival as well as provide for water, clean air, soil, pollinators, and other ecosystem services. An expansive, cutting-edge, and rigorous ecological science–based ecosystem and land-use mapping exercise has occurred in Kerala, but it faces organized resistance from extractive industries, and the legal structure is not yet in place to embed its requirements for local and regional sustainability.

There is little doubt that habitat fragmentation and climate change of the type reviewed here are fundamentally altering India's remaining terrestrial ecosystems, especially in the Western Ghats and Kerala, and impacting their continued provision of local, bioregional, and Earth System ecological process and pattern. Much natural habitat has been lost in India. The deforestation rate for India as a whole from 1981 to 1990 was estimated at 0.60% annually (United Nations Food and Agriculture Organization 1993). Jha and colleagues (2000) found using satellite data that the southern part of the Western Ghats lost 25.6% of forest cover in the 22 years between 1973 and 1995, much of it to an increase in plantations and agriculture. Menon and Bawa (1998) estimated the rate of deforestation in the Western Ghats to be 0.57% from 1920 to 1990. These high rates of deforestation do not include the often deleterious effects of habitat fragmentation and forest degradation.

India, like much of the world, is already being impacted strongly by climate change. Malcolm and colleagues (2006) predict that, depending on biome definitions and the amount of habitat connectivity and thus migration, 12–57% of Indian habitat will be lost to global warming, and that India's biomes would need to migrate from 230 to 1,228 meters per year to remain in favorable climatic conditions, an impossibility which highlights the degree of threat climate poses to India's terrestrial ecosystems, and vice versa. Ravindranath and colleagues projected that by 2085, between 68 and 77% of India's forests are likely to shift in type as a result of climate change. They note the impact this will have on the 200,000 forest villages dependent upon forest resources.

The Western Ghats is one of the original 34 hotspots of global biodiversity (Myers 2003) and because of its distinctiveness and irreplaceability is recognized as one of the "Global 2000" ecoregions (Olson and Dinerstein 2002). The region serves as a water tower for Peninsular India, catching and storing monsoonal rains (Western Ghats Ecology Expert Panel 2011). The region's variable topography and precipitation result in a wide range of vegetation types, including both wet and dry forest types, as well as 4,000 species of flowering plants, 1,600 of which are endemic (Jha et al. 2000). Dry forest types provide crucial habitats for wide ranging species such as tigers (Panthera tigris) and the Asian elephant (Elephas maximas), whose presence greatly enhances ecosystem health through their top-down regulation (Das et al. 2006).

It is thought that from 1920 to 1990 about 40% of the vegetation of the southern region of the Western Ghats was lost (Menon and Bawa 1997). It is estimated that 6.8% of the Western Ghats' original primary vegetation remains (Myers et al. 2000), though larger areas of secondary forest persist. Some 15% of the Ghats is under some form of protected area status (Western Ghats Ecology Expert Panel 2011). In 1978, Gadgil and Vartak reported upon the existence of "sacred groves" – community preserved forests sometimes as large as 20 hectares – that were maintained traditionally in a near-virgin condition. It is not clear to what extent if any these persist, yet all old growth could offer important genetic resources and baseline data on plant community assemblages that will prove critical to forest restoration so that the bioregion can be reconnected and better withstand escalating climate change.

It is urgent to the future well-being of the Western Ghats' peoples and ecology that all old-growth forests are identified; their situation is stabilized, and they are given full protection and used as locally evolved seed sources. They can also provide baseline community assemblage data for natural regeneration and assisted restoration. Doing so is critical for the continued provision of ecosystem services and to ensure that progress is made to reconnect ecosystems at both landscape, bioregional, and continental scales. Crucial to doing so will be ending the encroachment of plantation agriculture, mining, and residential sprawl upon protected and unprotected remaining natural terrestrial ecosystems.

Populations of Asian elephants are estimated to be 30,000–50,000, with 60% in India. As an umbrella species, when protected, Asian elephants preserve large tracts of habitats rich in other species as well as ecosystem processes such as water retention, soil creation, and pollination essential to people. The Asian elephant is listed as endangered on the Red List of Threatened Species compiled by IUCN. Habitat loss is the primary threat facing the existence of Asian elephants in the heavily populated Western Ghats (Riddle et al. 2010). The estimated original range of Asian elephants was 9 million square kilometers, of which only about 500,000 remain (Sukumar 2003). It has been suggested in the case of African elephants, that above 50% human use of the landscape, they essentially disappear (Riddle et al. 2010).

There is ample evidence that natural ecosystems in the Western Ghats are urgently threatened, and protected areas must be enlarged (Gunawardene et al. 2007) and better connected to maintain habitat for elephants, tigers, and people. There has been an observed weakening in the Indian Summer Monsoon patterns which provide much of the Western Ghats and India's water, almost certainly linked to this loss of widespread and connected habitat, and aerosol air pollution. It is thought that past certain thresholds the monsoon system could become less regular, bifurcating between a weak and strong monsoon state, or even collapse (Lenton et al. 2008). Loss of forest cover in the Western Ghats is almost certainly going to lead to increased drought and lack of drinking water (Sheil and Murdiyarso 2009).

The umbrella species concept would suggest that by recognizing the Asian elephant's rights to exist, and by ensuring adequate habitat and corridor connectivity to maintain viable populations, the peoples of the Western Ghats can also ensure their own survival and well-being. There are reasons India's elephants and humans have coexisted and find themselves alive on the same landscapes; they may be co-evolved and need each other. Maintaining and expanding elephant habitat through restoration, with an emphasis on buffers, transition zones, and particularly habitat corridors – while difficult and costly – and given deserved compensation, would also provide for ecological services for Kerala's population, potentially in perpetuity to all classes of people, while meeting responsibilities of all locales to contribute to maintenance of our shared biosphere through ample land-use and ecosystem planning. Traditional peoples were almost certainly more aware that healthy elephant and other wildlife populations ensured their well-being too, and awareness of this coevolution is necessary now.

Kerala and the wider region's remaining relatively large populations of Asian elephants – and tigers as well – are a testament to its high level of human development. Yet this does not come without a price. There is a large loss of agricultural crops to elephants, and in India as a whole, 100–200 people are killed each year in human–elephant conflicts (Jayson and Christopher 2008).  Much of the remaining elephant habitat in the Western Ghats is surrounded by rural populations that depend on forests for their habitat too (Riddle et al. 2010). Yet while the Asian elephant as an umbrella species requires extensive and adequate natural habitat for its survival, it also provides for water, clean air, soil, pollinators, and other ecosystem services. The continued existence of Western Ghats remnant forest fragments – with viable populations of elephants as well as tigers as top predators – is an indicator of both global and local ecological sustainability. Yet under current habitat loss trends, this important ecological base and heritage will be lost in the relative near term if not granted more effective protections.

The Western Ghats Ecology Panel has presented a report to the Ministry of the Environment and Forests, Government of India, which is a worthy starting point for the type of land-use planning exercises that must be carried out in the Western Ghats if ecosystem collapse is to be avoided and ecological sustainability with continued human advancement achieved. The exercise sought to identify, at a coarse scale, ecologically sensitive areas (ESAs) and how to manage them (Gadgil et al. 2011; Western Ghats Ecology Expert Panel 2011). Sensitive areas with low levels of resilience were identified, as were ecologically significant areas. Lack of essential corridors for connectivity between certain protected areas was identified as an additional area of concern.

The mapping exercise used a straightforward "weight and rate" geographic information system approach – of the type published by the author in his native bioregion of the United States northern hardwood forests (Barry et al. 2001), overlaying various geographic data regarding biological, culture, and geoclimatic features, following established and best global practices for doing so. Such factors as species biological richness, rarity in terms of distribution and taxonomy, habitat richness, productivity, resilience, cultural significance, topography, and climate were thus overlaid and able to be viewed cumulatively as a surface to see where they aligned and identify significant ecologically sensitive areas at a scale for bioregional planning (but perhaps not for landscape planning). One primary advantage of such an approach is that various maps can be generated weighing the factors differently, depending upon different assumptions and questions.

This Western Ghats Ecology Expert Panel identified three zones of ecological sensitivity and suitability. Quite interestingly and independently, the total of most important priority areas (referred to as ESZ1), along with existing protected areas, was chosen to be 60% of the landscape, aligning closely with the present study's finding that this is the threshold where critical bioregional connectivity is maintained. These ESZ1 and protected areas, along with ESZ2 areas, are set for 75% of the landscape, allowing for buffers and transition zones which are critically lacking in the region. This exercise is pursuing exactly what is recommended herein to ensure network connectivity of landscapes, bioregions, and the global biosphere. This leaves a full 25% of the landscape to ESZ3 zones, where urban, industrial, and monoculture agriculture could continue to reside within an intact ecological matrix. This may be how landscape sustainability across bioregions is achieved, and continental to biosphere level ecological collapse avoided.

It is likely that opposition to such farsighted ecological planning is largely based upon economic self-interest rather than any legitimate concerns with the science or methods used. The ESA findings need to be tied to laws to bring about requirements for local and regional sustainability. Despite technological advancements, if ecological decisions – when faced with local and global ecological threats – are made for political reasons, a disconnect will continue between the needs of the biosphere, needs of natural habitat for charismatic megafauna such as the Asian elephant, and human needs and desires.

With a large grain of grids of 9 x 9 km suitable for bioregional ESA mapping, it would still be beneficial to do additional landscape planning mapping at perhaps a 1 km or smaller grain (if suitable satellite data is available), particularly to identify key elephant habitats and corridors, tiger reserves, and remnant old growth and to assess the habitat connectivity of existing protected areas at a more detailed resolution. With fewer than 7% of the Western Ghats remaining as old growth, more focus upon where old growth exists, where it may be unprotected, and where it could be targeted for expansion through ecological restoration and natural regeneration would be appropriate and essential to the region's ecological sustainability – from the biosphere to monsoonal climate criteria. This could also make possible more explicit emphasis in the existing bioregional assessment upon the known habitat of Asian elephants and tigers, as both are keystone species who play critical roles in top-down ecological regulation, which will be lost if viable and connected populations are not maintained.

There have been other landscape planning exercises that preliminarily mapped Western Ghats' natural vegetation and landscape patterns to make various recommendations. Das et al. (2006) identified what they called "areas of high conservation values" using a systematic conservation planning approach. They found that wide-ranging mammals were highly correlated with threatened and endemic species richness, and overall animal and habitat quality, indicating that elephants and tigers may be an effective umbrella focal species whose conservation would protect other biodiversity. They also found that more than half of their identified priority areas were reserve forests that had not yet been granted protected status, though reserve forests often bordered existing protected forests.

To ensure ecological sustainability, Kerala and other Western Ghats states clearly need to identify gaps in existing habitat cover that will reconnect the landscape. Maintaining habitat for Asian elephant populations and seeking to reconnect the landscape may prove to be the best way of doing so. A similar landscape planning exercise in Tanzania documented a similar loss of habitat connectivity in regard to African elephants, assessed its root causes, and explored restoration options and priority conservation goals (Jones 2012). A similar plan to protect and restore necessary corridors is needed in Kerala and throughout the Western Ghats.

Whether the Western Ghats Ecology Expert Panel is accepted and implemented or not, the Western Ghats' landscapes and bioregion faces a crying need for land-use and ecosystem planning. As the most visible manifestation of a connected ecosystem, Indian elephants are both the means of securing local ecosystems and development potential as well as serving the needs of the biosphere.

Continued viable populations of Asian elephant in Kerala, India, are an indicator of potential for both global and local ecological sustainability. This umbrella species requires extensive and connected natural habitat for its survival, which also provides for water, clean air, soil, pollinators, and other ecosystem services. Persistence of elephants imposes limits upon human activity to ensure continued maintenance of ecosystem services. Maintaining viable populations of the umbrella species Asian elephant will go a long way towards local and global ecological sustainability.

Major educational activities must build awareness of the importance of ecosystems to both lasting local advancement and global sustainability of our one shared biosphere (Riddle et al. 2010).  By recognizing the Asian elephants' rights to exist, and ensuring adequate habitat, the people of Kerala and the wider Western Ghats bioregion can also ensure their own survival and well-being.

It is vitally important to Kerala’s and the Western Ghats' prospects for global ecological sustainability that the Western Ghats Ecology Expert Panel findings are accepted and their recommendations carried out. The current bioregional scale planning must be built upon at a finer scale to allow decisions about protecting and expanding old natural forests, their core ecological habitats, and necessary large corridors for elephant movement. These protection efforts and restoration can continue for all time. The need for elephant and tiger habitat protection align closely with India's habitat protection measures necessary to maintain ecosystems and achieve climate goals. If can’t be done in Kerala, with its high level of ecology and human development, it can’t be done anywhere.

We need to find landscape configurations in places like Kerala that provide local ecological sustainability and community advancement while also proving adequate to contribute proportionally to maintaining regional ecosystem processes necessary – when aggregated across continents – to sustain our one shared biosphere. It is vital for global ecological sustainability that natural old-growth forests and other terrestrial ecosystems are fully protected and helped to expand and mature.

Kerala's elephants are a staggeringly valuable asset, providing a means to envision habitat requirements as an umbrella for human and biosphere sustainability. As a real world example, elephants moving across landscapes are emblematic and widely visible examples of the types of flows that continue on a connected landscape, and are required for local and global ecological sustainability. As go Kerala's Asian elephants and their habitat, so shall go the biosphere.

Blunt, Biocentric Discussion on Avoiding Global Ecosystem Collapse and Achieving Global Ecological Sustainability

Science needs to do a better job of considering worst-case scenarios regarding continental- and global-scale ecological collapse. The loss of biodiversity, ecosystems, and landscape connectivity reviewed here shows clearly that ecological collapse is occurring at spatially extensive scales. The collapse of the biosphere and complex life, or eventually even all life, is a possibility that needs to be better understood and mitigated against. A tentative case has been presented here that terrestrial ecosystem loss is at or near a planetary boundary. It is suggested that a 66%  of Earth's land mass must be maintained in terrestrial ecosystems, to maintain critical connectivity necessary for ecosystem services across scales to continue, including the biosphere. Yet various indicators show that around 50% of Earth's terrestrial ecosystems have been lost and their services usurped by humans. Humanity may have already destroyed more terrestrial ecosystems than the biosphere can bear. There exists a major need for further research into how much land must be maintained in a natural and agroecological state to meet landscape and bioregional sustainable development goals while maintaining an operable biosphere.

It is proposed that a critical element in determining the threshold where terrestrial ecosystem loss becomes problematic is where landscape connectivity of intact terrestrial ecosystems erodes to the point where habitat patches exist only in a human context. Based upon an understanding of how landscapes percolate across scale, it is recommended that 66% of Earth's surface be maintained as ecosystems; 44% as natural intact ecosystems (2/3 of 2/3) and 22% as agroecological buffer zones. Thus nearly half of Earth must remain as large, connected, intact, and naturally evolving ecosystems, including old-growth forests, to provide the context and top-down ecological regulation of both human agroecological, and reduced impact and appropriately scaled industrial activities.

Given the stakes, it is proper for political ecologists and other Earth scientists to willingly speak bluntly if we are to have any chance of averting global ecosystem collapse. A case has been presented that Earth is already well beyond carrying capacity in terms of amount of natural ecosystem habitat that can be lost before the continued existence of healthy regional ecosystems and the global biosphere itself may not be possible. Cautious and justifiably conservative science must still be able to rise to the occasion of global ecological emergencies that may threaten our very survival as a species and planet.

Those knowledgeable about planetary boundaries – and abrupt climate change and terrestrial ecosystem loss in particular – must be more bold and insistent in conveying the range and possible severity of threats of global ecosystem collapse, while proposing sufficient solutions. It is not possible to do controlled experiments on the Earth system; all we have is observation based upon science and trained intuition to diagnose the state of Earth's biosphere and suggest sufficient ecological science–based remedies.

If Gaia is alive, she can die. Given the strength of life-reducing trends across biological systems and scales, there is a need for a rigorous research agenda to understand at what point the biosphere may perish and Earth die, and to learn what configuration of ecosystems and other boundary conditions may prevent her from doing so.  We see death of cells, organisms, plant communities, wildlife populations, and whole ecosystems all the time in nature – extreme cases being desertification and ocean dead zones. There is no reason to dismiss out of hand that the Earth System could die if critical thresholds are crossed. We need as Earth scientists to better understand how this may occur and bring knowledge to bear to avoid global ecosystem and biosphere collapse or more extreme outcomes such as biological homogenization and the loss of most or even all life. To what extent can a homogenized Earth of dandelions, rats, and extremophiles be said to be alive, can it ever recover, and how long can it last?

The risks of global ecosystem collapse and the need for strong response to achieve global ecological sustainability have been understated for decades. If indeed there is some possibility that our shared biosphere could be collapsing, there needs to be further investigation of what sorts of sociopolitical responses are valid in such a situation. Dry, unemotional scientific inquiry into such matters is necessary – yet more proactive and evocative political ecological language may be justified as well. We must remember we are speaking of the potential for a period of great dying in species, ecosystems, humans, and perhaps all being. It is not clear whether this global ecological emergency is avoidable or recoverable. It may not be. But we must follow and seek truth wherever it leads us.

Planetary boundaries have been quite anthropocentric, focusing upon human safety and giving relatively little attention to other species and the biosphere's needs other than serving humans. Planetary boundaries need to be set that, while including human needs, go beyond them to meet the needs of ecosystems and all their constituent species and their aggregation into a living biosphere. Planetary boundary thinking needs to be more biocentric.

I concur with Williams (2000) that what is needed is an Earth System–based conservation ethic – based upon an "Earth narrative" of natural and human history – which seeks as its objective the "complete preservation of the Earth's biotic inheritance." Humans are in no position to be indicating which species and ecosystems can be lost without harm to their own intrinsic right to exist, as well as the needs of the biosphere. For us to survive as a species, logic and reason must prevail (Williams 2000).

Those who deny limits to growth are unaware of biological realities (Vitousek 1986). There are strong indications humanity may undergo societal collapse and pull down the biosphere with it. The longer dramatic reductions in fossil fuel emissions and a halt to old-growth logging are put off, the worse the risk of abrupt and irreversible climate change becomes, and the less likely we are to survive and thrive as a species. Human survival – entirely dependent upon the natural world – depends critically upon both keeping carbon emissions below 350 ppm and maintaining at least 66% of the landscape as natural ecological core areas and agroecological transitions and buffers. Much of the world has already fallen below this proportion, and in sum the biosphere's terrestrial ecosystem loss almost certainly has been surpassed, yet it must be the goal for habitat transition in remaining relatively wild lands undergoing development such as the Amazon, and for habitat restoration and protection in severely fragmented natural habitat areas such as the Western Ghats.

The human family faces an unprecedented global ecological emergency as reckless growth destroys the ecosystems and the biosphere on which all life depends. Where is the sense of urgency, and what are proper scientific responses if in fact Earth is dying? Not speaking of worst-case scenarios – the collapse of the biosphere and loss of a living Earth, and mass ecosystem collapse and death in places like Kerala – is intellectually dishonest. We must consider the real possibility that we are pulling the biosphere down with us, setting back or eliminating complex life.

The 66% / 44% / 22% threshold of terrestrial ecosystems in total, natural core areas, and agroecological buffers gets at the critical need to maintain large and expansive ecosystems across at least 50% of the land so as to keep nature connected and fully functional. We need an approach to planetary boundaries that is more sensitive to deep ecology to ensure that habitable conditions for all life and natural evolutionary change continue. A terrestrial ecosystem boundary which protects primary forests and seeks to recover old-growth forests elsewhere is critical in this regard. In old forests and all their life lie both the history of Earth's life, and the hope for its future. The end of their industrial destruction is a global ecological imperative.

Much-needed dialogue is beginning to focus on how humanity may face systematic social and ecological collapse and what sort of community resilience is possible. There have been ecologically mediated periods of societal collapse from human damage to ecosystems in the past (Kuecker and Hall 2011). What makes it different this time is that the human species may have the scale and prowess to pull down the biosphere with them. It is fitting at this juncture for political ecologists to concern themselves with both legal regulatory measures, as well as revolutionary processes of social change, which may bring about the social norms necessary to maintain the biosphere. Rockström and colleagues (2009b) refer to the need for "novel and adaptive governance" without using the word revolution. Scientists need to take greater latitude in proposing solutions that lie outside the current political paradigms and sovereign powers.

Even the Blue Planet Laureates' remarkable analysis (Brundtland et al. 2012), which notes the potential for climate change, ecosystem loss, and inequitable development patterns neither directly states nor investigates in depth the potential for global ecosystem collapse, or discusses revolutionary responses. UNEP (2012) notes abrupt and irreversible ecological change, which they say may impact life-support systems, but are not more explicit regarding the profound human and ecological implications of biosphere collapse, or the full range of sociopolitical responses to such predictions. More scientific investigations are needed regarding alternative governing structures optimal for pursuit and achievement of bioregional, continental, and global sustainability if we are maintain a fully operable biosphere forever. An economic system based upon endless growth that views ecosystems necessary for planetary habitability primarily as resources to be consumed cannot exist for long.

Planetary boundaries offer a profoundly difficult challenge for global governance, particularly as increased scientific salience does not appear to be sufficient to trigger international action to sustain ecosystems (Galaz et al. 2012). If indeed the safe operating space for humanity is closing, or the biosphere even collapsing and dying, might not discussion of revolutionary social change be acceptable? Particularly, if there is a lack of consensus by atomized actors, who are unable to legislate the required social change within the current socioeconomic system. By not even speaking of revolutionary action, we dismiss any means outside the dominant growth-based oligarchies.

In the author's opinion, it is shockingly irresponsible for Earth System scientists to speak of geoengineering a climate without being willing to academically investigate revolutionary social and economic change as well. It is desirable that the current political and economic systems should reform themselves to be ecologically sustainable, establishing laws and institutions for doing so. Yet there is nothing sacrosanct about current political economy arrangements, particularly if they are collapsing the biosphere. Earth requires all enlightened and knowledgeable voices to consider the full range of possible responses now more than ever.

One possible solution to the critical issues of terrestrial ecosystem loss and abrupt climate change is a massive and global, natural ecosystem protection and restoration program – funded by a carbon tax – to further establish protected large and connected core ecological sustainability areas, buffers, and agro-ecological transition zones throughout all of Earth's bioregions. Fossil fuel emission reductions must also be a priority. It is critical that humanity both stop burning fossil fuels and destroying natural ecosystems, as fast as possible, to avoid surpassing nearly all the planetary boundaries.

In summation, we are witnessing the collective dismantling of the biosphere and its constituent ecosystems which can be described as ecocidal. The loss of a species is tragic, of an ecosystem widely impactful, yet with the loss of the biosphere all life may be gone. Global ecosystems when connected for life's material flows provide the all-encompassing context within which life is possible. The miracle of life is that life begets life, and the tragedy is that across scales when enough life is lost beyond thresholds, living systems die.

We simply must learn to live in a manner that does not destroy our habitat – in a globalized world, our biosphere – or we all may needlessly die, perhaps taking all life with us. We had best start looking in more earnest at the land around us and the life and processes it sustains as a measure of societal and biosphere well-being. While addressing all planetary boundaries, there is a particular need to immediately begin the end of fossil fuels and to empower and invest in the restoration and protection of natural ecosystems, as two of the most vitals paths to global ecological sustainability

Global ecological sustainability depends critically upon maintaining connectivity of ecosystem processes. The movement of massive elephants across landscapes is hard to ignore, but at numerous ecological scales, less visible movements of life, energy, water and nutrients are what keeps Earth alive. Political ecology has the potential to provide the needed framework to integrate human needs for just, equitable advancement with the needs of the biosphere to avoid collapse, and the required sufficient policies and available political structures to do so. Let's make it so.

* Dr. Glen Barry would like to acknowledge research assistance provided by Dr. Tom Rooney, and editing by Paul Hawley, which proved critical to the successful completion of this paper. And to thank Nagaraj Narayanan of Kerala Law Academy for making the conference possible, to Jeff Berkson of AnchorBank for gainfully employing me, and acknowledge the love and support of my wife Julie and daughter Talita who sustain me. And my goofy golden retriever Ginger deserves mention too, just for being there. All errors and omissions of course remain my own.

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