Nature and Human Society: The Quest for a Sustainable World (1997)
Chapter: Countryside Biogeography and the Provision of Ecosystem Services
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Countryside Biogeography and the Provision of Ecosystem Services
Humanity has become a dominant force on Earth, altering important characteristics of the atmosphere, oceans, and terrestrial systems. One of the many consequences of these alterations is the extinction of populations and species, which is projected to drive biodiversity to its lowest level since humanity came into being (Ehrlich and Ehrlich 1981; Wilson 1992). A crucial set of policy questions is when, where, and how to direct societal activities to soften or reverse their effect on biodiversity.
In addressing these questions, one is immediately confronted with a set of trade-offs in the allocation of resources (such as land and water) to competing uses, to competing individuals and groups of people, and ultimately to competing value systems. These tradeoffs are becoming increasingly vexing from both ethical and practical perspectives. They involve our most important ideals (such as ensuring a prosperous future for our children), our oldest tensions (such as between individual and societal interests), and sometimes our bloodiest tendencies (such as using genocide as a convenient way of gaining control over resources). Society is poorly equipped to handle these tradeoffs, and they are appearing everywhere; the well-being of current and future generations hinges on how the tradeoffs are dealt with.
The short-term benefits of alteration of habitats, the primary cause of loss of biodiversity, are typically clear and allow relatively small groups of immediate beneficiaries to exert great influence on the political process in favor of short-term exploitation. In contrast, the arguments for conservation tend to be diverse and difficult to measure, and the benefits of any single decision about conservation are
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diffused over very large numbers of people. The arguments for conservation typically are drawn from any of four distinct lines of reasoning: ethical, aesthetic, direct economic, and indirect economic (Heywood 1995; Hughes and others 2000; Ehrlich and Ehrlich 1992). Ethical reasoning involves the conviction that, as the dominant species on the planet, humanity has the responsibility of stewardship toward “The Creation,” its only known living companions in the universe. This moral responsibility exists independent of the perceived value of nonhuman organisms to human well-being. The other three classes of argument rest on the benefits that humanity derives from other organisms, which I collectively refer to here as “ecosystem services.”
The reasons for stemming the loss of biodiversity thus range in character from the intangible, the spiritual and philosophical, to the purely anthropocentric and pragmatic (for a nice overview, see Goulder and Kennedy 1997). One might say they span the spectrum from things that make life worth living to things that make life possible at all. Clearly, both ends of the spectrum are important, although the significance ascribed to each varies considerably with social context and understanding. Lack of public understanding of societal dependence on natural ecosystems is a major hindrance to the implementation of policies needed to bring the human economy into balance with the capacity of Earth's life-support systems to sustain it.
The purpose of this paper is to explain this dependence briefly, to describe how recognition of it can help resolve the tradeoffs that society now faces, and to indicate where society could invest profitably in broadening and deepening the scientific understanding of ecosystem services. First, I briefly characterize ecosystem services in biophysical and economic terms. Then, I indicate how the concept provides a framework that, if supported with appropriate institutions and policies, allows us to incorporate ecosystem-service values into decision-making. Finally, I turn to a key underlying biological issue: the capacity of human-dominated landscapes to support biodiversity and sustain ecosystem services. My emphasis throughout is on the anthropocentric and pragmatic.
Life on the Moon.
Society derives a wide array of life-support benefits from biodiversity and the natural ecosystems within which it exists. These benefits are captured in the term “ecosystem services”, the conditions and processes through which natural ecosystems, and the species that are a part of them, sustain and fulfill human life (Daily 1997; Holdren and Ehrlich 1974). These services include the production of ecosystem goods, such as seafood, timber, forage, and many pharmaceuticals, which represent an important and familiar part of the economy.
Perhaps the easiest way to appreciate the importance of biodiversity in supplying life-support goods and services is by way of a thought experiment that removes the familiar backdrop of Earth. Imagine trying to set up a happy life on the moon. Assume for the sake of argument that the moon miraculously already had some of the basic conditions for supporting human life, such as an atmosphere, a climate, and a physical soil structure similar to those on Earth. After packing one's
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possessions and coaxing one's family and friends into coming along, the big question would be, Which of Earth's millions of species would be needed to make the sterile moonscape habitable?
One could choose first from among all the species used directly for food, drink, spices, fiber, timber, pharmaceuticals, and industrial products, such as waxes, rubber, and oils. Even if one were selective, this list could amount to hundreds or even thousands of species. And one would not have begun considering the species needed to support those used directly: the bacteria, fungi, and invertebrates that recycle wastes and help make soil fertile; the insects, bats, and birds that pollinate flowers; and the herbaceous plants, shrubs, and trees that hold soil in place, nourish animals, and help control the gaseous composition of the atmosphere that influences Earth's climate. No one knows exactly how many or which combinations of species would be required to support human life. So, rather than listing individual species, one would have to list instead the life-support services required by the lunar colony and try to choose groups of species able to perform them. A partial list of such services includes the following (Daily 1997):
• production of a wide variety of ecosystem goods;
• purification of air and water;
• mitigation of flood and drought;
• detoxification and decomposition of wastes and cycling of nutrients;
• generation and preservation of soils and renewal of their fertility;
• pollination of crops and natural vegetation;
• dispersal of seeds;
• control of the vast majority of agricultural pests;
• maintenance of biodiversity;
• protection from the sun's harmful ultraviolet rays;
• partial stabilization of climate;
• moderation of weather extremes and their effects; and
• provision of aesthetic beauty and intellectual stimulation that lift the human spirit.
The closest attempt to carry out this experiment here on Earth was the first Biosphere 2 “mission” (Cohen and Tilman 1996). A facility was constructed on 3.15 acres in Arizona that sealed off its inhabitants as much as possible from the outside world; eight people were meant to live inside for 2 years without the transfer of materials in or out. The experimenters had to decide which species to use to populate the closed ecosystem. They moved in tons of soil (with its huge abundance and variety of little-known fungi, arthropods, worms, and microorganisms), added numerous other animals and plants, and fueled the system with sunlight (through transparent walls) and electricity (at an annual cost of about $1 million). Biosphere 2 featured agricultural land and elements of a variety of natural ecosystems, such as forest, savanna, desert, and even a miniature ocean.
In spite of an investment of $200 million in the design, construction, and operation of this model Earth, it proved impossible to supply the material and physical needs of the eight “Biospherians” for the intended stay. Many unexpected and
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unpleasant problems arose, including a drop in the concentration of oxygen from 21% to 14%, a level normally found at an elevation of 17,500 ft; skyrocketing concentrations of carbon dioxide with large daily and seasonal fluctuations; high concentrations of nitrous oxide to the point where brain functioning can be impaired; extinction of 19 of 25 vertebrate species; extinction of all pollinators (thereby dooming most of the plant species to eventual extinction); population explosions of aggressive vines and crazy ants; and failure of water-purification systems.
The basic conclusion from this experiment is that there is no demonstrated alternative to maintaining the viability of “Biosphere 1,” Earth (Cohen and Tilman 1996). Ecosystem services operate on such a grand scale and in such intricate and little-explored ways that most could not be replaced by technological means (Ehrlich and Mooney 1983). They existed for millions or billions of years before humanity evolved, making them easy to take for granted and hard to imagine disrupting beyond repair. Yet escalating effects of human activities on natural ecosystems now imperil the delivery of these services. The primary threats are changes in the uses of lands, causing loss of biodiversity and facilitating biotic invasion, and synergisms of these with alteration of biogeochemical cycles, release of toxic substances, possible rapid change of climate, and depletion of stratospheric ozone (Daily 1997b).
Management of Natural Capital
Maintaining Earth as a suitable habitat for Homo sapiens will require society to begin to recognize natural ecosystems and their biodiversity as capital assets, which, if properly managed, will yield a flow of benefits over time. Relative to physical capital (buildings, equipment, and so on), human capital (skills, knowledge, health, and so on, embodied in the labor force), and financial capital, natural capital is poorly understood, little valued, scarcely monitored, and undergoing rapid depletion. Sustainable management of ecosystem services will require a systematic characterization of the services, in biophysical, economic, and other terms along with the development of financial mechanisms and policy institutions to provide the means of monitoring and safeguarding them.
Characterization involves an explicit cataloging of important services on a variety of scales. In other words, which ecosystems supply what services? For a given location, which are supplied locally, which are imported, and which are exported? Characterization also involves finding answers to other questions (Costanza and Folke 1997; Daily 1997c; Holdren 1991), such as, what is the effect of alternative human activities on the supply of services?
The administration of New York City first considered replacing its natural water-purification system (the Catskill Mountains) with a filtration plant but found that it would cost an estimated $6–8 billion in capital plus $300 million per year to operate. The high costs prompted investigation of an alternative solution, namely restoring and safeguarding the natural purification services of the Catskills. That would involve purchasing land in and around the watershed to protect it and subsidizing several changes on privately owned land: upgrading sewage-treat-
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ment plants; improving practices on dairy farms and undertaking “environmentally sound” economic development. The total cost of this option was estimated at about $1.5 billion (Revkin 1997).
Thus, New York City had a choice of investing in $6–8 billion in physical capital or $1.5 billion in natural capital. It chose the latter option, raising an environmental bond issue to fund its implementation. This financial mechanism captured the important economic and public-health values of a natural asset (the watershed) and distributed them to those assuming the responsibilities of stewardship for the asset and its services.
The Catskills supply many other valuable services, such as control of flooding, sequestration of carbon, conservation of biodiversity, and, perhaps above all, beauty, serenity, and spiritual inspiration. Moreover, these services benefit others besides consumers of water in New York City. It would be absurd to try to express the full value of the ecosystem services provided by the Catskills in dollars. In this case, fortunately, there was no reason to try: even a lower estimate of the value of the natural asset was sufficient to induce adopting a policy of conservation.
The challenge is to extend this model to other geographic locations and to other services. The US Environmental Protection Agency recently estimated that treating, storing, and delivering safe drinking water to the United States without taking this approach would require an investment in physical capital of $138.4 billion over the next 20 years. More than 140 municipalities in the United States now are considering watershed protection, an option that aligns market forces with the environment, as a more cost-effective option than building artificial treatment facilities (The Trust for the Public Land 1997). Indeed, interest is growing worldwide in adopting watershed conservation. Rio de Janeiro and Buenos Aires, for example, are investigating this option; both have highly threatened watersheds of enormous biotic value (Chichilnisky and Heal 1998).
Extending this model to other services requires that an ecosystem meet two conditions. First, it must supply at least one good or service to which a commercial value can be attached. Second, some of that value must be appropriable by the steward of the ecosystem (Chichilnisky and Heal 1998). Public goods and services are difficult to privatize: if provided for one, they are provided for all, so their providers typically cannot appropriate all the value of the good or service. Natural water purification is a public service, but access to the resulting high-quality water is excludable; thus, the case of a watershed works by bundling a public service with a private good. Private capital could be mobilized in this cause to the benefit of both individual investors and society at large (Chichilnisky and Heal 1998).
In principle, this approach could be made to work for other ecosystem goods and services, such as for realizing and safeguarding biodiversity, ecotourism, and carbon-sequestration values. With appropriate institutional support (such as that needed for the management of common property resources), mechanisms for safeguarding sources of flood control, pollination, and pest-control services also may be developed. This is an important subject for further interdisciplinary investigation by persons from academe, government, and the private sector.
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Countryside Biogeography
Attaining the ultimate goal of sustainably managing natural capital will require a deeper understanding of the relative effects of alternative activities on biodiversity and ecosystem services. A key question is, Where do critical thresholds lie in the relationships between the condition and extent of an ecosystem and the quality of the services that it supplies? Let us explore this issue from the perspective of the modification of ecosystems by agricultural activities.
Food production is arguably humanity's most important activity. It is also the most important proximate cause of the loss of biodiversity worldwide, involving major direct and indirect effects, including conversion of natural habitat to agricultural use, facilitation of biotic invasion through trade (thereby increasing the rate of introduction of exotic species) and alteration of habitat (thereby increasing the susceptibility of native communities to invasion), and application of chemical fertilizers and pesticides.
In the face of such effects, the fates of organisms that once made their homes in unbroken expanses of natural habitat range along a broad continuum. At one end is the decline of population to local and eventually global extinction; at the other end is expansion into human-controlled landscapes. Biologists have paid considerable attention to the status of the biotas of fragments of natural habitat, such as forest patches, and comparably little attention (outside the context of pest management) to the organisms that occupy the highly disturbed matrix in which those fragments occur. One reason for this emphasis is undoubtedly the crisis nature of extinction: given the justified panic to save remaining natural habitat, it is taking some time to appreciate a complementary opportunity, namely, to enhance the hospitability of agricultural landscapes for biodiversity. The emphasis traces to other factors, including the prominence of the theories of island biogeography and the island paradigm in conservation biology; the assumption that a very small fraction of species is capable of persisting outside of “islands” of natural habitat, that is, in human-controlled habitats; and the frequent (although often subconscious) projection of disdain for humanity's destruction of natural habitat onto the organisms that profit from it.
The organisms that can take advantage of countryside, rural and suburban landscapes devoted primarily to human activities, deserve more attention for a series of reasons. First, it is unlikely that many large, relatively undisturbed tracts of natural habitat will remain in the face of projected growth in the size, food needs, and environmental effects of the human population. Second, the potential for conserving many species might rest on preserving or enhancing some aspects of rural landscapes that contain remnants of native habitat in lieu of protecting large tracts of undisturbed habitat, which is generally much less feasible socioeconomically. Third, the supply of some important ecosystem servicessuch as pest control, pollination, and water purificationwill depend in many instances on the biodiversity that occurs locally, in the vicinity of human habitation, in countryside habitats. Finally, a growing interest in restoration also will require comparing the conservation value of alternative sites for the establishment and succession of desired community assemblages.
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Countryside biogeography is the study of the diversity, abundance, conservation, and restoration of biodiversity in rural and other human-dominated landscapes. Broad issues in this area pertain to the future course, societal consequences, and appropriate policy responses to the mass extinction currently under way. They include the following sorts of questions.
• What is the relationship between levels of agricultural intensification and biodiversity in countryside landscapes? Measures of agricultural intensification include the frequency distribution of clearing sizes, the ratio of clearing to hedgerow areas, the spatial configuration and relative coverage of native and human-dominated habitats within the countryside landscape, the diversity of crops under cultivation, modification of the hydrological cycle, and the levels and types of chemical fertilizers and pesticides applied.
• Which species traits confer an advantage for survival in the face of tropical deforestation and other major alterations of habitat?
• Are these traits distributed randomly across taxa, or are some groups of organisms especially resistant and others especially prone to extinction? In other words, will the current episode of extinction nip off the buds of the evolutionary tree of life relatively uniformly, or will it eliminate some major limbs, dramatically reshaping the future diversity and evolution of life?
• Can simple mathematical theory be developed to predict patterns of persistence of biodiversity in countryside landscapes?
• How accurately can patterns of biodiversity in countryside habitats be predicted on the basis of remotely sensed information on land use (for example, with images from satellites)?
• How effectively can countryside biotas perform ecosystem services?
• What practical measures can be taken to enhance the capacity of countryside habitats to sustain biodiversity and ecosystem services as well as human activities?
This is not the place for a comprehensive review of work addressing those issues. I offer instead a few illustrative findings to date:
• In Europe, more than 50% of the land area with high conservation value is under low-intensity farming. Examples of these habitat types include blanket bog, northern Atlantic wet heath, lowland hay meadow, heather moorlands, wood pasture, alpine pasture, and nonirrigated cereal steppe (Bignal and McCracken 1996). Intensification of farming practices in recent decades has resulted in declining populations of many species of birds throughout Europe. For instance, nine of the 11 species of waders listed in the Red Data Book that occur in Sweden are seriously threatened by changes in farming practices there (Johansson and Blomqvist 1996).
• Recent studies are beginning to illuminate the strength and type of biotic control over the functioning of ecosystems (Chapin and others 1997). Greater richness of species can enhance the stability of the ecosystem. In species-poor plots of grassland in Minnesota, for example, a severe drought caused a reduction
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in productivity of more than 90% from predrought levels, whereas productivity in species-rich plots was reduced by 50% (Tilman 1994). Alterations in habitat that change the functional diversity and composition of plant species appear especially likely to have major effects on various properties of ecosystems (Hooper and Vitousek 1997; Tilman and others 1997).
• In the vicinity of Las Cruces in southern Costa Rica, a significant fraction of the native avian species appear to be persisting, at least temporarily, in open countryside habitats in a mixed-agricultural landscape that retains 27% of its once-continuous forest cover. Of possible original totals in the 33 species of birds under consideration, it appears that 1–9% have become extinct locally, 50–54% are restricted to habitats of forested countryside, and 36–40% occur in habitats of open countryside that are as far as 6 km from the nearest large tracts (at least 200 hectares) of forest (Daily and others in review).
• Some systems of cultivation used in coffee production appear to have high potential for conserving birds and other elements of the native biota. Systems of cultivation that use shade trees, plantations with tall canopy cover, diverse stratification, little pruning, and low levels of insecticides are especially rich in birds, including both resident and neotropical migrant species (Greenberg and others 1997). Strikingly high abundances of arthropods and richness of species have also been found. For example, fogging of shade trees with pyrethrins in a Costa Rican coffee plantation in formerly upland-rainforest habitat yielded a richness of coleopteran and hymenopteran species comparable with that of samples from trees in upland rainforests in Peru and Brazil (Perfecto and others 1996).
• Nocturnality might confer an advantage of dispersal and possibly of survival in the face of tropical deforestation. Surveys of the diversity of diurnal birds and butterflies and nocturnal beetles and moths in forested patches reveal the classic island biogeographic pattern for birds and butterflies (in other words, fewer in smaller patches) but similarly high diversities of moths and beetles among forested patches of all sizes (0.1–225 hectares). A possible mechanism explaining this apparent advantage is that typically the movement of nocturnal species occurs when the conditions of thermal, humidity, and solar radiation are similar between native forest and cleared areas; during the day, the hot, dry, and bright conditions in open areas might impede dispersal seriously for many organisms (Daily and Ehrlich 1996).
Ideally, further effort in empirical and theoretical research on issues of countryside biogeography eventually will allow us to predict patterns of biodiversity in human-dominated landscapes worldwide (White and others 1997). This would be an important step toward characterizing and monitoring the effects of humans on ecosystems and the services they supply.
Conclusions
The human population and its standards of living are maintained by a steady depletion of natural capital assets, including renewable-resource stocks and waste sinks that, if they were safeguarded, could sustain a flow of ecosystem goods and
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services through time. In our collective behavior, there is little recognition or systematic accounting, let alone nurturing, of these critical capital assets.
Tremendous payoff could result from further research on managing Earth's life-support systems. Such research should be oriented toward developing the following:
• a broader and deeper understanding of the functioning of Earth's life-support systems and the effects of humanity on them, especially in countryside habitats;
• systematic accounting and monitoring of the condition of these systems;
• ways of quantifying the importance of ecosystems at the margin, from biophysical, economic, and cultural (aesthetic and spiritual) perspectives, that is, ways of determining, for instance, how much importance should be attached to the preservation or destruction of the next unit of habitat;
• ways of incorporating these values into a framework for decision-making; and
• ways of creating appropriate institutions and policies to allow the individuals or societies that safeguard life-support systems for the public good to realize the value of their stewardship.
In the market-driven culture that prevails today, the concept of ecosystem services offers a new way to approach actions of conservation by confronting market forces on their own terms. This concept has promise because it integrates biophysical and social dimensions of managing the biosphere; it offers rational, practical solutions to tradeoffs in allocation of resources to competing uses and people; and it is adaptable to different economic and cultural circumstances. Similarly, countryside biogeography can reveal new strategies for preserving biodiversity and ecosystem services in the context of some of humanity's most important activities. Nevertheless, these frameworks are just two tools to complement the many others required for protecting biodiversity (Raven 1990; Raven and Wilson 1992). In our quest to safeguard the systems that make life possible, it is critical that we not lose sight of what makes life worth living.
Acknowledgments
I am grateful for insightful comments from Scott Daily, Michael Dalton, Paul Ehrlich, Geoffrey Heal, and Jennifer Hughes. This work was supported by the generosity of Peter and Helen Bing, the Pew Charitable Trusts, and the Winslow Foundation.
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