3. Ecosystem services, trade-offs, and biodiversity
5. Substituting for ecosystem services
6. Ecosystem services and conservation
Ecosystem services are defined as “the multiple benefits provided by ecosystems to humans” (The Millennium Ecosystem Assessment, 2005). In other words, ecosystem services are only services to the extent that they support human well-being and are thus an inherently anthropocentric construct. Analysts cannot understand how the delivery of ecosystem services has changed over time solely from a purely natural science analysis of ecological patterns, processes, or functions. They must also understand what people value and how much they value it. Ecological dynamics could remain constant, but the services people derive from ecosystems could still change as people’s values or circumstances change. Ecosystems could degrade, from a purely ecological perspective, but that degradation of ecological systems could still support an enhanced flow of services from humanity’s perspective. Any adequate assessment of the flow of ecosystem services, or any assessment of how best to manage ecological systems to maximize the benefits people receive from them, must join ecological and social analyses.
However, this is a guide to ecology, and therefore, this section primarily contains contributions by ecologists. Ecologists obviously have much to contribute to an understanding of ecosystem services. In this section, various authors cover issues of scale (Scholes, chapter VI.1), biodiversity–ecosystem functioning relationships (Naeem, chapter VI.2), and critical aspects of ecological organization (Norberg, chapter VI.3), among other things. Authors examine ecosystem services in agroecosystems (Power et al., chapter VI.4), forests (Solórzano and Páez-Acosta, chapter VI.5), grasslands (Downs and Sala, chapter VI.6), and marine ecosystems (Baskett and Halpern, chapter VI.7). Other authors analyze different types of services, from tangible and consumable goods such as fresh water (Palmer and Richardson, chapter VI.8) to the more intangible and esoteric cultural or spiritual services provided by the world’s ecological systems, and other services in between (Daszak and Kilpatrick on regulating services in chapter VI.9; Per-gams and Kareiva on genetic diversity in chapter VI. 10). But ultimately, the ecological analyses are just the starting point—knowing how ecological functions are changing, although relevant to adequate comprehension and appropriate management of ecosystem services, is not enough. The social value placed on those services— the human desires that translate a mere ecosystem function into a beneficial service—are half the equation. I have thus chosen to close this section with two nonecological chapters (which obviously can not do full justice to the second half of the equation): one focuses on the economics of ecosystem services (Perrings, chapter VI.11) and the other on how technological innovation has altered the need for, and therefore value placed on, various services (Goklany, chapter VI.12). This section closes with an exploration of how a focus on ecosystem services, rather than species richness per se, might alter conservation practices and outcomes (Rodríguez, chapter VI.13). I return to many of these issues—on the interplay between the social and ecological components of ecosystem services—in the topics I highlight below.
The recognition that ecological systems benefit humans must, in some sense, be as old as humanity itself—every culture or social group that I know of has developed rituals aimed at influencing Nature and her bounty. Even the more scientific assessment of ecological services has a deep history; Plato, for instance, recognized the connection among deforestation, erosion, and the drying of springs in his native Greece. Similarly, the connection between Nature’s services and the value humans place on those services was made, perhaps not first but certainly eloquently, by David Ricardo in 1817, when he wrote:
The labour of nature is paid, not because she does much, but because she does little. In proportion, as she becomes niggardly in her gifts, she extracts a greater price for her work. Where she is munificently beneficent, she always works gratis. (Ricardo, D., and F. W. Kolthammer. 1817. The Principles of Political Economy and Taxation. Mineola, NY: Courier Dover Publications, reprinted 2004)
In other words, humans will value most those services that are most scarce.
More frequent scientific and economic assessments of the benefits of ecological systems, however, only began in earnest in the latter part of the twentieth century. Mooney and Ehrlich (1997) provide a more thorough history than what follows, a history that starts with Marsh in 1864 and runs through to the present day; they themselves contributed a seminal paper in 1983 (Ehrlich and Mooney, 1983). The Beijer Institute of Ecological Economics launched a biodiversity program that ran from 1991 to 1993 with the specific purpose of valuing the full range of the benefits of ecosystems as opposed to individual environmental stocks, which had been the dominant approach in the preceding 25 years. The Global Biodiversity Assessment (Heywood, 1995) addressed questions of the value of goods and services delivered by biodiversity to society, among other things. That study, combined with Gretchen Daily’s volume on Nature’s Services, released in 1997, firmly established the need to make an assessment of ecosystem services a prominent part of the scientific agenda.
More recently, The Millennium Ecosystem Assessment (MA), a globally comprehensive assessment and synthesis of the consequences of ecosystem change for human well-being, involving more than 1300 experts worldwide and focusing on both global and more regional trends, was released (MA, 2005). The MA established a consensus framework for categorizing ecosystem services (see figure 1), which included support services, provisioning services, regulating services, and cultural services. Provisioning services are those tangible and consumable items humans derive from ecosystems—food, fiber, fuel, and fresh water, to name a few. Regulating services encompass the ecological patterns and processes that contain Nature’s dynamics within certain bounds; reducing, for instance, the probability of massive landslides, pandemic disease outbreaks, or catastrophic climate excursions. Cultural services are the largely intangible and “unconsumed” services that ecosystems provide (unconsumed in the sense that enjoyment by one does not preclude enjoyment by another)—these are services such as recreation, aesthetic appeal, or a spiritual communion with nature. Supporting services are critical to the maintenance of all other ecosystem services and include such things as nutrient cycling, primary production, and soil formation. These supporting services are largely not used or valued directly by people; their value is indirect because they are an essential prerequisite to the provisioning of all other services. As a result, they are generally treated differently than the other three categories of services (as they are in this volume), being more akin to ecosystem functions or processes than to ecosystem services.
Given the comprehensive treatment of ecosystem services provided by the MA, we made no such effort here. Instead, this section of The Princeton Guide to Ecology is intended to highlight how one might assess and enhance ecosystem services in particular ecosystem types (chapters VI.8–VI.11), or understand some of the difficulties inherent in managing particular services (chapters VI.5–VI.7). These and other chapters also emphasize some of the future scientific challenges to an improved understanding of ecosystem services.
In the remaining sections of this chapter, I emphasize what I think are the biggest challenges for scientists trying to demonstrate the benefits that ecosystems provide to humans and the biggest challenges to effective management of ecosystem services. These include (1) our inability, as of yet, to adequately anchor the flow of services to particular ecological configurations, including levels of biodiversity; (2) the challenges introduced by the multiple scales over which ecosystem services are produced and consumed; (3) the possibility of substitutions for some ecosystem services with human-made technologies and capital; and (4) what all of this might mean for formulating a more positive agenda for conservation. This is certainly not the first or last word on these issues; they find voice in many of the other chapters in this section and in the numerous articles now appearing concerning ecosystem services. Nonetheless, if we are to make the framework introduced by the MA—connecting ecosystem services to human well-being—operational, they are issues the academy must attack, and soon.
Not all ecosystem services can be simultaneously maximized. There are some simple examples of this— high-yielding agricultural systems, for instance, are generally extremely simplified systems, often monocultures, and the dramatic increase in food provisioning attained by these agricultural systems comes at the cost of other services, such as maintenance of genetic diversity, freshwater provisioning, or recreational opportunities. (See Power et al., chapter VI.4, however, for some management strategies that at least enhance the delivery of nonprovisioning services in agricultural systems.) Similarly, wilderness areas maintained for recreational, spiritual, or aesthetic reasons may enhance some services, such as water regulation, while detracting from others, such as provisioning of fodder. Often maintaining the resilience of a system—its capacity to maintain ecosystem services at a particular level despite changing conditions—means reducing the overall average provisioning of services within that system. These issues of trade-off are covered in many of the chapters dealing with specific ecosystems or services, but they are a particular focus of chapter VI.1 by Scholes.
Figure 1. A conceptual framework showing the division of ecosystem services into supporting, provisioning, regulating, and cultural services and showing the connections between these service categories and human well-being. (Adapted from the Millennium Ecosystem Assessment, http://www.millenniumassessment.org/en/GraphicResources.aspx.)
A corollary to this is that each service requires different ecological attributes or configurations. If the same ecological attribute were implicated each time— if the provisioning of all ecosystem services, for instance, increased with increasing species richness— then no such trade-offs would occur. All ecosystem services could be maximized by maximizing species richness. Some environmentalists assert something very close to this—that saving biological diversity (by which they often mean species richness or habitat diversity) enhances the delivery of ecosystem services. But some ecosystem services, such as food provisioning, require reductions in biodiversity if they are to be delivered effectively. Others, such as carbon sequestration, will depend on species richness only to an extent—a handful of different tree species may suffice to maximize carbon sequestration. Still others may depend on attributes of the system that are relatively unrelated to species number or identity. Erosion control, for instance, depends most directly on vegetative cover; although cover may be enhanced by having a mix of species present, species richness itself may have only a second- or third-order effect on erosion control.
Ecologists have studied the relationship between biodiversity (most often species richness or functional diversity) and ecosystem functioning. In many, but not all, cases there is a positive relationship between the two. The functions most often studied—net primary production, nutrient cycling or retention—map most directly to the supporting services described by the MA. Other functions studied—such as invasion resistance—might map more directly to regulating services. But ecologists have not, as yet, as thoroughly studied the connection between biodiversity and the broader suite of ecosystem services described in the MA. These issues of which species or ecological attributes contribute to ecosystem–service provisioning are covered in chapters VI.2 by Naeem and VI.3 by Norberg.
Of course, if one is managing for a whole suite of ecosystem services, either on a patch or across the landscape, then many different species or patches with different traits and attributes will have to be present. But managing for, say, species richness will largely not ensure maximum delivery of other services. Societal preferences and values should ultimately determine which ecosystem services are enhanced and which are allowed to degrade (informed by the constraints of possible ecological outcomes), and it will be these preferences and values that ultimately dictate our treatment of the species with whom we share the planet. Of course, the moral (“we think other species have the right to exist”), religious (“God will judge us based on how we treat the birds of the field”), and aesthetic (“there is something wondrous about an Andean Condor in flight”) values come into play here, and although they may be of great importance in many decisions, they are still only part of what is driving decisions about converting, protecting, or managing the world’s biodiversity. Other ecosystem services may be equally or even more valuable, particularly in the places where we live (e.g., urban areas) or in places of great poverty. The ecosystem services framework, then, delivers some particular challenges to conservation activities; these are discussed in chapter VI.10 by Pergams and Kareiva and in chapter VI.13 by Rodríguez.
Of critical importance in the understanding and management of ecosystem services—indeed any ecological process—is the matter of scale (see, e.g., Levin, 1999). For some ecosystem services, the ecological configurations underpinning those services must be replicated in many sites in order to ensure adequate delivery to the world’s inhabitants. Examples would include freshwater provisioning (given a limited ability to transport freshwater supplies around the globe); storm regulation (because it does local residents little good to have storm regulation a half-world or even kilometers away); or, for those residents with limited mobility, aesthetically pleasing or recreationally popular sites. Other ecosystem services may be locally located but deliver global benefits. Examples in this category would include unique and confined species that provide spiritual or medicinal benefit; or areas of high carbon sequestration, which help regulate global climate regimes regardless of where they are located; or, in these days of global trade in goods, areas of food or fiber production. There may be only one location in the world providing this global benefit (as is the case with a valuable endemic species), or several locations may be required (as is the case with food provisioning or carbon sequestration)—nonetheless, the localized ecological systems provide a global service.
Scale thus comes into play in many ways in assessing and managing ecosystem services. Over what scale is the ecosystem service actually delivered? Over what scale do people benefit from this service? Over what scale do the ecological processes underpinning this service operate? Over what scale is the ecosystem service in question managed? Rarely do these scales coincide for a particular ecosystem service, much less across the full suite of ecosystem services. Residents in a particular location hoping to benefit from a bundle of ecosystem services must rely on management institutions that operate across many scales, sometimes in very distant locations. Managers at a particular location devoted to delivering a broader public good should be cognizant of the implications of their decisions on those outside the immediate constituency. These issues of scale and the management implications are covered in many of the chapters in this section but are the particular focus of chapters VI.1 by Scholes and VI.11 by Perrings.
Whenever humans choose to pursue some goal that erodes ecosystem services, they are making a judgment about the relative value of those services. When we convert habitat to schools, libraries, or hospitals; when we accept at least some impact on waterways and airways in exchange for mobility; when we acquire exotic goods or materials from distant places in spite of the risk this brings of invasion, we are accepting that sometimes human wellbeing is enhanced by degradation of ecosystem services. In the words of economists, we are substituting some other service or benefit for ecosystem services in our pursuit of happiness or utility.
There are, of course, limits to the degree to which we can substitute other types of benefits for ecosystem services. We must eat, and therefore some baseline capacity for provisioning services must be maintained. Human quality of life is greatly eroded in the face of grave uncertainties about the future; if we want to maintain dynamic ecological processes within certain bounds—avoid the crossing of thresholds with attendant catastrophic shifts in ecosystem functioning, for instance—we should focus on regulating services. But it is simply not true that society must maintain all ecosystem services at extant levels or restore them to earlier levels. Decisions should be made, whenever possible, with a full awareness of the consequences, but sometimes human well-being can be enhanced by trading off ecosystem services for some other gain.
The sheer magnitude of technological innovation that characterized the last century makes the future of these trade-offs even more intriguing. Some ecosystem services may ultimately be able to be replaced with human-made substitutes. We have already reduced the demand for natural fibers from what it might have been through the invention of synthetic materials (many of which are better providers of the services of warmth, protection, or glamour than their natural counterparts). The advent of air-conditioning has reduced the demand for, and value placed on, localized climate regulation in many parts of the world. I have long wondered if the virtual reality machines of the future will alter the flow of cultural services humans receive from ecological systems. If my mind believes I have touched, tasted, smelled, seen, and heard the Amazon rainforest while ensconced in a virtual-reality suit, is that fundamentally different from actually being there? It may be for those in my generation, or earlier generations, with our uneasy relationships to technology, but will it be true for those who, from the earliest age, interact with technological gadgets that operate almost as extensions of the individual? And even if the technological experience differs from the “real” one, does it differ enough to justify the CO2 emissions required to get there or the impact on the forest from tourists wanting to be there? Technology is likely to fundamentally alter the flow of services we receive from the Earth’s ecosystems; it will certainly alter the strategies we employ in managing them. Goklany covers the technological aspects of ecosystem services more fully (see chapter VI.12).
For well over a decade now, there has been an emerging dialogue concerning the need to connect conservation activities to human well-being. For some, this connection is a normative one—people have a moral obligation both toward their fellow humans and toward the other species with whom we share the planet. Conservationists must therefore recognize and balance the trade-offs between human and nonhuman well-being where such trade-offs exist. For others, the connection is a practical one. The primary motivation is still saving species (or other aspects of the biosphere), but it is recognized that the extent and efficacy of the conservation endeavor will require support from people who may not place as much value on nonhuman species as do conservationists. Alternative motivations for conservation must be provided.
There are many challenges to integrating conservation and human well-being. It may well be, for instance, that the primary benefits of conservation do not derive to people alive now and living close to conservation areas but to more geographically distant, or even future, people. Although conservation can deliver some benefits to local people—ecotourism opportunities or provisioning of fresh water, for instance—the costs of conservation, including the opportunity costs of foreclosed, nonconservation options, may be enormous, particularly for marginalized or poverty-stricken people. When conservation activities are highly valued by people living far away, the mechanisms and institutions that allow them to secure conservation—paying local stewards so conservation is beneficial to them as well, for instance—are often lacking. The problem of scale rears its head once again.
The ecosystem services framework developed by the MA seems to be a reasonable platform on which to build a conservation agenda that joins ecological integrity with human well-being. But if conservationists were to seriously embrace an ecosystem services perspective, conservation priorities would almost certainly change. A recent article by Chan et al. (2006), for instance, examined conservation strategies under different end goals—some focused on traditional conservation goals of saving species, and others focused on ecosystem services such as forage production, recreation, and pollination, among others. There was only a partial overlap to the conservation strategies that emerged under different goals—saving species was not always the best way to enhance delivery of ecosystem services. Nonetheless, many conservation organizations are embracing the concept of ecosystem services. But it remains to be seen whether such a concept does turn out to be a constructive framework for conducting a complicated social dialogue over options, trade-offs, and priorities. This subject is the focus of Rodríguez’s chapter (chapter VI.13).
A focus on ecosystem services necessitates a multidisciplinary perspective. In spite of this being a guide to ecology, we need to understand that the ecological contributions to understanding ecosystem services are, of necessity, limited. What we should conserve and how we should conserve it must inevitably depend on what people value and whether there are other ways to get what they value. Scientists have their own values in this—often emphasizing, for instance, native species richness above all else, in spite of evidence that it is not always high native species richness that most effectively delivers the full suite of ecosystem services society cares about. To provide the right answer for society, ecologists must partner with economists, other social scientists, and technologists. Scientists must also try to remove their own values from scientific assessments— articulating as scientists, for instance, what the various possibilities are for the future of ecosystem services without injecting their own bias as to which of these is necessarily better. As citizens, they can hold and articulate those views, but as scientists, they must continually question the extent to which their own values influence their conclusions. Ecosystem services are the province of all of humanity, after all. If nothing else, a multidisciplinary conversation can help reveal those biases and values.
Chan, K.M.A., M. R. Shaw, D. R. Cameron, E. C. Underwood, and G. C. Daily. 2006. Conservation planning for ecosystem services. PLoS Biology 4: 2138–2152.
Daily, G. C., ed. 1997. Nature’s Services: Societal Dependence on Natural Ecosystems. Washington, DC: Island Press.
Ehrlich, P. R., and H. A. Mooney. 1983. Extinction, substitution, and the ecosystem services. BioScience 33: 248–254.
Heywood, V., ed. 1995. Global Biodiversity Assessment. Cambridge, UK: Cambridge University Press.
Levin, S. A. 1999. Fragile Dominions: Complexity and the Commons. New York: Basic Books.
The Millennium Ecosystem Assessment (MA). 2005. Ecosystems and Human Well-Being: Multivolume Set. Washington, DC: Island Press. Also available on line at http://www.millenniumassessment.org/en/index.aspx.
Mooney, H. A., and P. R. Ehrlich. 1997. Ecosystem services: A fragmentary history. In G. Daily, ed. Nature’s Services. Washington, DC: Island Press, 11–19.