sign in sign up
<<
Home , Biosphere, Ecosystem service, Island Press, Value of Earth

Published by the Ecological of America Number 2, Spring 1997 Services: Benefits Ecosystem Services: Supplied toHumanSocieties

Issues in Ecologyby NaturalEcosystems Issues in Number 2 Spring 1997

Ecosystem Services: Benefits Supplied to by Natural

SUMMARY

Human societies derive many essential goods from natural ecosystems, including , , fodder, fuelwood, timber, and pharmaceutical products. These goods represent important and familiar parts of the . What has been less appreciated until recently is that natural ecosystems also perform fundamental -support services without which human civilizations would cease to thrive. These include the purification of air and , detoxification and of wastes, regulation of , regeneration of fertility, and production and maintenance of , from which key ingredients of our agricultural, pharmaceutical, and industrial enterprises are derived. This array of services is generated by a complex interplay of natural cycles powered by solar and operating across a wide range of and scales. The process of waste disposal, for example, involves the life cycles of as well as the planet-wide cycles of major chemical elements such as and . Such processes are worth many trillions of dollars annually. Yet because most of these benefits are not traded in economic markets, they carry no price tags that could alert society to changes in their supply or deterioration of underlying ecological systems that generate them. Because threats to these systems are increasing, there is a critical need for identification and monitoring of ecosystem services both locally and globally, and for the incorporation of their value into decision-making processes.

Historically, the and value of ’s life support systems have largely been ignored until their disruption or loss highlighted their importance. For example, has belatedly revealed the critical role serve in regulating the water cycle -- in particular, in mitigating , droughts, the erosive forces of and , and silting of dams and canals. Today, escalating impacts of human activities on forests, , and other natural ecosystems imperil the delivery of such services. The primary threats are use changes that cause losses in biodiversity as well as disruption of carbon, nitrogen, and other biogeochemical cycles; human-caused invasions of exotic ; releases of toxic substances; possible rapid ; and depletion of stratospheric ozone.

Based on available scientific evidence, we are certain that: • Ecosystem services are essential to civilization. • Ecosystem services operate on such a grand scale and in such intricate and little-explored ways that most could not be replaced by . • Human activities are already impairing the flow of ecosystem services on a large scale. • If current trends continue, humanity will dramatically alter virtually all of Earth’s remaining natural ecosystems within a few decades.

In addition, based on current scientific evidence, we are confident that: • Many of the human activities that modify or destroy natural ecosystems may cause deterioration of ecological services whose value, in the long term, dwarfs the short-term economic benefits society gains from those activities. • Considered globally, very large numbers of species and are required to sustain ecosystem services. • The functioning of many ecosystems could be restored if appropriate actions were taken in time.

We believe that and development policies should strive to achieve a balance between sustaining vital ecosystem services and pursuing the worthy short-term goals of economic development.

1 Issues in Ecology Number 2 Spring 1997 Ecosystem Services: Benefits Supplied to Human Societies by Natural Ecosystems

by Gretchen C. Daily, Susan Alexander, Paul R. Ehrlich, Larry Goulder, Jane Lubchenco, Pamela A. Matson, Harold A. Mooney, Sandra Postel, Stephen H. Schneider, David Tilman, George M. Woodwell • INTRODUCTION purification of air and water. • mitigation of droughts and floods. • Many societies today have technological capa- generation and preservation of and renewal of bilities undreamed of in centuries past. Their citizens their fertility. • have such a global command of that even detoxification and decomposition of wastes. • flown in fresh from all over the planet are taken for of and natural vegetation. • granted, and daily menus are decoupled from the limita- dispersal of seeds. • tions of regional growing seasons and soils. These de- cycling and movement of nutrients. • velopments have focused so much attention upon control of the vast majority of potential agricultural human-engineered and exotic sources of fulfillment that pests. • they divert attention from the local biological underpin- maintenance of biodiversity. • nings that remain essential to economic prosperity and protection of coastal shores from by waves. • other aspects of our well-being. protection from the sun’s harmful ultraviolet rays. • These biological underpinnings are encompassed partial stabilization of climate. • in the phrase ecosystem services, which refers to a wide moderation of extremes and their impacts. • range of conditions and processes through which natu- provision of aesthetic beauty and intellectual stimu- ral ecosystems, and the species that are part of them, lation that lift the human spirit. help sustain and fulfill human life. These services main- Although the distinction between “natural” and tain biodiversity and the production of ecosystem goods, “human-dominated” ecosystems is becoming increasingly such as seafood, wild game, forage, timber, fu- blurred, we emphasize the natural end of the spectrum, els, natural fibers, and many pharmaceuticals, industrial for three related reasons. First, the services flowing from products, and their precursors. The harvest and trade of natural ecosystems are greatly undervalued by society. these goods represent important and familiar parts of For the most part, they are not traded in formal markets the human economy. In addition to the production of and so do not send price signals that warn of changes in goods, ecosystem services support life through (Holdren their supply or condition. Furthermore, few people are and Ehrlich 1974; Ehrlich and Ehrlich 1981): conscious of the role natural ecosystem services play in

Figure 1-Aspen (Populus tremuloides) in Colorado, filtering and pu- rifying air and water. Photo by J. Robert Stottlemeyer/Biological Service 21 Issues in Ecology Number 2 Spring 1997

Figure 2-Woman carrying treetrunk for boat- making in a fishing village on Chiloe Island, Chile. Natural forests remain an important source of for construction, fuel, and other uses. Photo by Taylor Ricketts Photo by Taylor generating those ecosystem goods that are traded in the directly for , drink, , fiber, timber, pharmaceu- marketplace. As a result, this lack of awareness helps ticals, and industrial products such as waxes, rubber, and drive the conversion of natural ecosystems to oils. Even if one were highly selective, the list could amount human-dominated systems (e.g., wheatlands or oil palm to hundreds or even thousands of species. And that would fields), whose economic value can be expressed, at least only be a start, since one would then need to consider in part, in standard currency. The second reason to focus which species are crucial to supporting those used di- on natural ecosystems is that many human-initiated dis- rectly: the bacteria, fungi, and invertebrates that help ruptions of these systems -- such as introductions of ex- make soil fertile and break down wastes and organic otic species, extinctions of native species, and alteration ; the insects, bats, and birds that pollinate flow- of the gaseous composition of the atmosphere through ers; and the grasses, herbs, and that hold soil in fuel burning -- are difficult or impossible to reverse place, regulate the water cycle, and supply food for ani- on any time scale relevant to society. Third, if awareness mals. The clear message of this exercise is that no one is not increased and current trends continue, humanity knows which combinations of species -- or even approxi- will dramatically alter Earth’s remaining natural ecosys- mately how many -- are required to sustain human life. tems within a few decades (Daily 1997a, b). Rather than selecting species directly, one might The lack of attention to the vital role of natural try another approach: Listing the ecosystem services ecosystem services is easy to understand. Humanity came needed by a lunar colony and then guessing at the types into being after most ecosystem services had been in and numbers of species required to perform each. Yet operation for hundreds of millions to billions of years. determining which species are critical to the functioning These services are so fundamental to life that they are of a particular is no simple task. Let easy to take for granted, and so large in scale that it is us take as an example. Soil are hard to imagine that human activities could irreparably crucial to the chemical conversion and physical transfer disrupt them. Perhaps a thought experiment that re- of essential nutrients to higher . But the abun- moves these services from the familiar backdrop of the dance of soil organisms is absolutely staggering. Under Earth is the best way to illustrate both the importance a square-yard of pasture in Denmark, for instance, the and complexity of ecosystem services, as well as how soil is inhabited by roughly 50,000 small ill-equipped are to recreate them. Imagine, for and their relatives, 50,000 insects and mites, and nearly example, human beings trying to colonize the . 12 million roundworms. And that tally is only the begin- Assume for the sake of argument that the moon had ning. The number of soil animals is tiny compared to the already miraculously acquired some of the basic condi- number of soil : a pinch of fertile soil may tions for supporting human life, such as an atmosphere, contain over 30,000 protozoa, 50,000 algae, 400,000 a climate, and a physical soil structure similar to those fungi, and billions of individual bacteria on Earth. The big question facing human colonists would (Overgaard-Nielsen 1955; Rouatt and Katznelson 1961; then be, which of Earth’s millions of species would need Chanway 1993). Which must colonists bring to the moon to be transported to the moon to make that sterile sur- to assure lush and continuing growth, soil renewal, face habitable? waste disposal, and so on? Most of these soil-dwelling One could tackle that question systematically species have never been subjected to even cursory in- by first choosing from among all the species exploited spection: no human eye has ever blinked at them through 3 Issues in Ecology Number 2 Spring 1997 a microscope, no human hand has ever typed out a name erated by sport fishing activities, it raises the total to or description of them, and most human minds have never $46 billion (Felder and Nickum 1992, cited in Postel and spent a moment reflecting on them. Yet the sobering Carpenter 1997). The future of these is in ques- fact is, as E. O. Wilson put it: they don’t need us, but we tion, however, because fish harvests have approached or need them (Wilson 1987). exceeded sustainable levels virtually everywhere. Nine of the ’s major marine fishing areas are in decline THE CHARACTER OF ECOSYSTEM SERVICES due to , , and destruction. (UNFAO 1993; Kaufman and Dayton 1997). Moving our attention from the moon back to Earth, let Turning our attention to the land, are us look more closely at the services nature performs on an important source of marketable goods, including ani- the only planet we know that is habitable. Ecosystem mals used for labor (horses, mules, asses, camels, bul- services and the systems that supply them are so inter- locks, etc.) and those whose parts or products are con- connected that any classification of them is necessarily sumed (as meat, milk, wool, and leather). Grasslands rather arbitrary. Here we briefly explore a suite of were also important as the original source habitat for overarching services that operate in ecosystems world- most domestic animals such as cattle, goats, sheep, and wide. horses, as well as many crops, such as wheat, barley, rye, oats, and other grasses (Sala and Paruelo 1997). In Production of Ecosystem Goods a wide variety of terrestrial , people hunt game Humanity obtains from natural ecosystems an animals such as waterfowl, deer, moose, elk, fox, boar array of ecosystem goods— organisms and their parts and other wild pigs, rabbits, and even snakes and mon- and products that grow in the wild and that are used keys. In many countries, game meat forms an important directly for human benefit. Many of these, such as fishes part of local diets and, in many places, hunting is an and products, are commonly traded in economic economically and culturally important sport. markets. The annual world fish catch, for example, Natural ecosystems also produce vegetation used directly amounts to about 100 million metric tons and is valued by humans as food, timber, fuelwood, fiber, pharmaceu- at between $50 billion and $100 billion; it is the leading ticals and industrial products. Fruits, nuts, mushrooms, source of animal protein, with over 20% of the popula- honey, other foods, and spices are extracted from many tion in and Asia dependent on fish as their pri- forest species. Wood and other plant materials are used mary source of protein (UNFAO 1993). The commercial in the construction of homes and other buildings, as well harvest of freshwater fish worldwide in 1990 totaled as for the manufacture of furniture, farming implements, approximately 14 million tons and was valued at about paper, cloth, thatching, rope, and so on. About 15 per- $8.2 billion (UNFAO 1994). Interestingly, the value of cent of the world’s energy is supplied by the freshwater sport in the U.S. alone greatly fuelwood and other plant material; in developing coun- exceeds that of the global commercial harvest, with di- tries, such “biomass” supplies nearly 40 percent of en- rect expenditures in 1991 totaling about $16 billion. ergy consumption (Hall et al. 1993), although the por- When this is added to the value of the employment gen- tion of this derived from natural rather than

Figure 3-Alpaca on the Chilean alti- plano. ecosystems are an impor- tant source of animal products; they are also the original habitat of most domestic animals and many crops, such as wheat, barley, and oats. Photo by Taylor Ricketts Photo by Taylor 4 Issues in Ecology Number 2 Spring 1997 human-dominated ecosystems is undocumented. In addi- As described in the previous section, biodiversity tion, natural products extracted from many hundreds of is a direct source of ecosystem goods. It also supplies species contribute diverse inputs to industry: gums and the genetic and biochemical resources that underpin our exudates, essential oils and flavorings, resins and oleo- current agricultural and pharmaceutical enterprises and resins, dyes, tannins, vegetable fats and waxes, insecti- may allow us to adapt these vital enterprises to global cides, and multitudes of other compounds (Myers 1983; change. Our ability to increase productivity in the Leung and Foster 1996). The availability of most of face of new pests, diseases, and other stresses has de- these natural products is in decline due to ongoing habi- pended heavily upon the transfer to our crops of genes tat conversion. from wild crop relatives that confer resistance to these challenges. Such extractions from biodiversity’s “genetic Generation and Maintenance of Biodiversity library” account for annual increases in crop productiv- Biological diversity, or biodiversity for short, re- ity of about 1 percent, currently valued at $1 billion (NRC fers to the variety of life forms at all levels of organiza- 1992). Biotechnology now makes possible even greater tion, from the molecular to the land- use of this natural storehouse of ge- scape level. Biodiversity is generated netic diversity via the transfer to crops and maintained in natural ecosystems, of genes from any kind of — where organisms encounter a wide not simply crop relatives—and it variety of living conditions and chance promises to play a major role in fu- events that shape their in ture yield increases. By the turn of unique ways. Out of convenience or the century, -level sales of the necessity, biodiversity is usually quan- products of agricultural biotechnol- tified in terms of numbers of species, ogy, just now entering the market- and this perspective has greatly influ- place, are expected to reach at least enced conservation goals. It is im- $10 billion per year (World Bank portant to remember, however, that 1991, cited in Reid et al. 1996). the benefits that biodiversity supplies In addition to sustaining the produc- to humanity are delivered through tion of conventional crops, the populations of species residing in liv- biodiversity in natural ecosystems may ing communities within specific physi- include many potential new foods. cal settings— in other words, through Human beings have utilized around complex ecological systems, or eco- 7,000 plant species for food over the systems (Daily and Ehrlich 1995). For course of history and another 70,000 human beings to realize most of the plants are known to have edible parts Photo by Taylor Ricketts Photo by Taylor aesthetic, spiritual, and economic ben- (Wilson 1989). Only about 150 food efits of biodiversity, natural ecosys- Figure 4-Harpoon-whaling in Flores, In- plants have ever been cultivated on a tems must therefore be accessible. The donesia. The are a key source large scale, however. Currently, 82 continued existence of coniferous of animal protein for the human popu- plant species contribute 90 percent species somewhere in the world would lation. of national per-capita supplies of food not help the inhabitants of a town in- plants (Prescott-Allen and undated by flooding because of the clearing of a pine Prescott-Allen 1990), although a much smaller number forest upstream. Generally, the flow of ecosystem goods of these supply the bulk of the calories humans consume. and services in a region is determined by the type, spa- Many other species, however, appear more nutritious or tial layout, extent, and proximity of the ecosystems sup- better suited to the growing conditions that prevail in plying them. Because of this, the preservation of only important regions than the standard crops that domi- one minimum viable of each non-human spe- nate world food supply today. Because of increasing cies on Earth in zoos, botanical gardens, and the world’s salinization of irrigated croplands and the potential for legally protected areas would not sustain life as we know rapid climate change, for instance, future it. Indeed, such a strategy, taken to extreme, would lead may come to depend on drought- and salt-tolerant vari- to collapse of the , along with its life support eties that now play comparatively minor roles in agricul- services. ture. 5 Issues in Ecology Number 2 Spring 1997 Turning to medicinal resources, a recent survey age 20,000 years ago, for example, much of Europe and showed that of the top 150 prescription drugs used in North America were covered by mile-thick sheets. the United States, 118 are based on natural sources: While the global climate has been relatively stable since 74% on plants, 18% on fungi, 5% on bacteria, and 3% the invention of agriculture around 10,000 years ago, on one vertebrate (snake) species. Nine of the top ten periodic shifts in climate have affected human activities drugs in this list are based on natural plant products and settlement patterns. Even relatively recently, from (Grifo and Rosenthal, in press, as cited in Dobson 1995). 1550-1850, Europe was significantly cooler during a The commercial value of pharmaceuticals in the devel- period known as the Little Ice Age. Many of these changes oped nations exceeds $40 billion per year (Principe 1989). in climate are thought to be caused by alterations in Looking at the global picture, approximately 80% of the Earth’s orbital rotation or in the energy output of the human population relies on traditional medical systems, sun, or even by events on the Earth itself—sudden per- and about 85% of traditional medicine involves the use turbations such as violent volcanic eruptions and aster- of plant extracts (Farnsworth et al. 1985). oid impacts or more gradual tectonic events such as the Saving only a single popula- uplift of the Himalayas. Remarkably, tion of each species could have an- climate has been buffered enough other cost. Different populations of through all these changes to sustain the same species may produce differ- life for at least 3.5 billion years ent types or quantities of defensive (Schneider and Londer 1984). And chemicals that have potential use as life itself has played a role in this buff- pharmaceuticals or pesticides ering. (McCormick et al. 1993); and they Climate, of course, plays a may exhibit different tolerances to major role in the evolution and distri- environmental stresses such as bution of life over the planet. Yet most drought or soil salinity. For example, scientists would agree that life itself the development of penicillin as a is a principal factor in the regulation therapeutic antibiotic took a full 15 of global climate, helping to offset the years after Alexander Fleming’s fa- effects of episodic climate oscillations mous discovery of it in common bread by responding in ways that alter the mold. In part, this was because sci- greenhouse gas concentrations in the entists had great difficulty producing, atmosphere. For instance, natural eco- extracting, and purifying the sub- systems may have helped to stabilize stance in needed quantities. One key R. Ehrlich Photo by Paul climate and prevent overheating of the to obtaining such quantities was the Figure 5-Trapping and releasing butterflies Earth by removing more of the green- discovery, after a worldwide search, in a mixed-agriculture in Costa house gas carbon dioxide from the of a population of Fleming’s mold that Rica. Monitoring the impact of human atmosphere as the sun grew brighter produced more penicillin than the activities on biodiversity and ecosystem over millions of years (Alexander et original (Dowling 1977). Similarly, services is needed worldwide; butterflies al. 1997). Life may also exert a de- plant populations vary in their ability may be useful indicators for monitoring. stabilizing or positive that to resist pests and disease, traits im- reinforces climate change, particularly portant in agriculture. Many thousands of varieties of during transitions between interglacial periods and ice rice from different locations were screened to find one ages. One example: When climatic cooling leads to drops with resistance to grassy stunt , a disease that posed in sea level, continental shelves are exposed to wind and a serious threat to the world’s rice crop (Myers 1983). rain, causing greater nutrient runoff to the oceans. These Despite numerous examples like these, many of the lo- nutrients may fertilize the growth of phytoplankton, many calities that harbor wild relatives of crops remain unpro- of which form calcium carbonate shells. Increasing their tected and heavily threatened. populations would remove more carbon dioxide from the oceans and the atmosphere, a mechanism that should Climate and Life further cool the planet. Living things may also enhance Earth’s climate has fluctuated tremendously since warming trends through such activities as speeding up humanity came into being. At the peak of the last ice microbial decomposition of dead organic matter, thus 6 Issues in Ecology Number 2 Spring 1997 soaked up by soils and gradually meted out to plant roots or into and surface streams. Thus, the soil itself slows the rush of water off the land in flash floods. Yet bare soil is vulnerable. Plants and plant litter shield the soil from the full, destructive force of raindrops and hold it in place. When are denuded, rain com- pacts the surface and rapidly turns soil to mud (espe- cially if it has been loosened by tillage); mud clogs sur- face cavities in the soil, reduces infiltration of water, in- creases runoff, and further enhances clogging. Detached soil are splashed downslope and carried off by running water (Hillel 1991). Erosion causes costs not only at the site where soil is lost but also in aquatic systems, natural and human-made, where the material accumulates. Local costs of erosion include losses of production potential, Photo by Michael Graybill & Jan Hodder/ Biological Service diminished infiltration and water availability, and losses Figure 6-Bark of the Pacific yew tree (Taxus brevifolia), of nutrients. Downstream costs may include disrupted which is the source of the new anti-cancer drug, taxol, or lower quality water supplies; siltation that impairs drain- Willamette National Forest, Oregon. age and maintenance of navigable river channels, har- releasing carbon dioxide to the atmosphere (Schneider bors, and irrigation systems; increased frequency and and Boston 1991; Allegre and Schneider 1994). The severity of floods; and decreased potential for hydroelec- relative influence of life’s stabilizing and destabilizing feed- tric power as reservoirs fill with silt (Pimentel et al. 1995). backs remains uncertain; what is clear is that climate Worldwide, the replacement cost of reservoir capacity and natural ecosystems are tightly coupled, and the sta- lost to siltation is estimated at $6 billion per year. bility of that coupled system is an important In addition to protecting soil from erosion, living ecosystemservice. vegetation—with its deep roots and above-ground evapo- Besides their impact on the atmosphere, ecosys- rating surface—also serves as a giant pump, returning tems also exert direct physical influences that help to water from the ground into the atmosphere. Clearing of moderate regional and local weather. For instance, tran- plant cover disrupts this link in the water cycle and leads spiration (release of water vapor from the leaves) of plants in the morning causes thunderstorms in the afternoon, limiting both moisture loss from the region and the rise in surface temperature. In the Amazon, for example, 50% of the mean annual rainfall is recycled by the forest itself via evapotranspiration—that is, evaporation from wet leaves and soil combined with transpiration (Salati 1987). Amazon deforestation could so dramatically re- duce total precipitation that the forest might be unable to reestablish itself following complete destruction (Shukla et al. 1990). Temperature extremes are also moderated by forests, which provide and surface cooling and also act as insulators, blocking searing and trap- ping warmth by acting as a local greenhouse agent.

Mitigation of Floods and Droughts Photo by Catherine M. Pringle/Biological Service An enormous amount of water, about 119,000 cubic kilometers, is rained annually onto the Earth’s land Figure 7-Herbal pharmacist in Dali, Yunnan Province, surface—enough to cover the land to an average depth China. An estimated 80 percent of the world’s popu- of 1 meter (Shiklomanov 1993). Much of this water is lation relies on natural medicinal products. 7 Issues in Ecology Number 2 Spring 1997

Figure 8-Early summer in the Colorado Rockies. These subalpine forests mitigate , drought, and temperature extremes; they soak up rain and snowmelt and mete it out gradually to streams and to the atmosphere, creat- ing cooling afternoon thunderstorms. Photo by Gretchen C. Daily to potentially large increases in surface runoff, along with Services Supplied by Soil nutrient and soil loss. A classic example comes from the Soil represents an important component of a experimental clearing of a New Hampshire forest, where nation’s assets, one that takes hundreds to hundreds of herbicide was applied to prevent regrowth for a 3-year thousands of years to build up and yet very few years to period after the clearing. The result was a 40 percent be lost. Some civilizations have drawn great strength increase in average stream flow. During one four-month from fertile soil; conversely, the loss of productivity period of the experiment, runoff was more than 5 through mismanagement is thought to have ushered many greater than before the clearing (Bormann 1968). On a once flourishing societies to their ruin (Adams 1981). much larger scale, extensive deforestation in the Hima- Today, soil degradation induced by human activities af- layan highlands appears to have exacerbated recent flood- flicts nearly 20 percent of the Earth’s vegetated land ing in Bangladesh, although the relative roles of human surface (Oldeman et al. 1990). and natural forces remain debatable (Ives and Messerli In addition to moderating the water cycle, as described 1989). In addition, some regions of the world, such as above, soil provides five other interrelated services (Daily parts of Africa, are experiencing an increased frequency et al. 1997). First, soil shelters seeds and provides physi- and severity of drought, possibly associated with exten- cal support as they sprout and mature into adult plants. sive deforestation. The cost of packaging and storing seeds and of anchor- Wetlands are particularly well-known for their role ing plant roots would be enormous without soil. in flood control and can often reduce the need to con- Human-engineered hydroponic systems can grow plants struct flood control structures. Floodplain forests and in the absence of soil, and their cost provides a lower high salt marshes, for example, slow the flow of floodwa- bound to help assess the value of this service. The costs ters and allow sediments to be deposited within the flood- of physical support trays and stands used in such opera- plain rather than washed into downstream bays or oceans. tions total about US$55,000 per hectare (for the Nutri- In addition, isolated wetlands such as prairie potholes in ent Film Technique Systems; FAO 1990). the Midwest and cypress ponds in the Southeast, serve Second, soil retains and delivers nutrients to as detention areas during times of high rainfall, delaying plants. Tiny soil particles (less than 2 microns in diam- saturation of upland soils and overland flows into rivers eter), which are primarily bits of humus and clays, carry and thereby damping peak flows. Retaining the integrity a surface electrical charge that is generally negative. This of these wetlands by leaving vegetation, soils, and natu- property holds positively charged nutrients—cations such ral water regimes intact can reduce the severity and du- as calcium and magnesium—near the surface, in prox- ration of flooding along rivers (Ewel 1997). A relatively imity to plant roots, allowing them to be taken up gradu- small area of retained , for example, could have ally. Otherwise, these nutrients would quickly be leached largely prevented the severe flooding along the Missis- away. Soil also acts as a buffer in the application of sippi River in 1993. fertilizers, holding onto the fertilizer ions until they are 8 Issues in Ecology Number 2 Spring 1997 required by plants. Hydroponic systems supply water of nutrients—the fourth service soils provide— and nutrients to plants without need of soil, but the mar- are two aspects of the same process. The fertility of gin for error is much smaller—even small excesses of soils—that is, their ability to supply nutrients to plants— nutrients applied hydroponically can be lethal to plants. is largely the result of the activities of diverse species of Indeed, it is a complex undertaking to regulate the nutri- bacteria, fungi, algae, crustacea, mites, termites, spring- ent concentrations, pH, and salinity of the nutrient solu- tails, millipedes, and worms, all of which, as groups, play tion in hydroponic systems, as well as the air and solu- important roles. Some bacteria are responsible for “fix- tion temperature, humidity, light, pests, and plant dis- ing” nitrogen, a key element in proteins, by drawing it eases. Worldwide, the area under hydroponic culture is out of the atmosphere and converting it to forms usable only a few thousand hectares and is unlikely to grow by plants and, ultimately, human beings and other ani- significantly in the foreseeable future; by contrast, glo- mals. Certain types of fungi play extremely important bal cropped area is about 1.4 billion hectares (USDA roles in supplying nutrients to many kinds of trees. Earth- 1993). worms and ants act as “mechani- Third, soil plays a central cal blenders,” breaking up and mix- role in the decomposition of dead ing plant and microbial material and organic matter and wastes, and this other matter (Jenny 1980). For decomposition process also renders example, as much as 10 metric harmless many potential human tonnes of material may pass pathogens. People generate a tre- through the bodies of earthworms mendous amount of waste, includ- on a hectare of land each year, re- ing household garbage, industrial sulting in nutrient rich “casts” that waste, crop and residues, enhance soil stability, aeration, and and from their own popula- drainage (Lee 1985). tions and their billions of domesti- Finally, soils are a key fac- cated animals. A rough approxima- tor in regulating the Earth’s major tion of the amount of dead organic element cycles—those of carbon, matter and waste (mostly agricul- nitrogen, and sulfur. The amount tural residues) processed each year of carbon and nitrogen stored in is 130 billion metric tons, about 30 soils dwarfs that in vegetation, for percent of which is associated with example. Carbon in soils is nearly human activities (derived from Photo by L. Evans Roth/Biological Service double (1.8 times) that in plant Vitousek et al. 1986). Fortunately, Figure 9-Bacteria (Bradyrhizobium japonicum) matter, and nitrogen in soils is about there is a wide array of decompos- in a soybean root nodule , magnified 3,550 18 times greater (Schlesinger ing organisms—ranging from vul- times. These bacteria fix atmospheric nitro- 1991). Alterations in the carbon tures to tiny bacteria—that extract gen into a form that can be utilized by plants. and nitrogen cycles may be costly energy from the large, complex organic molecules found over the long term, and in many cases, irreversible on a in many types of waste. Like assembly-line workers, di- time scale of interest to society. Increased fluxes of car- verse microbial species process the particular compounds bon to the atmosphere, such as occur when land is con- whose chemical bonds they can cleave and pass along to verted to agriculture or when wetlands are drained, con- other species the end products of their specialized reac- tribute to the buildup of key greenhouse gases, namely tions. Many industrial wastes, including soaps, detergents, carbon dioxide and methane, in the atmosphere pesticides, oil, acids, and paper, are detoxified and de- (Schlesinger 1991). Changes in nitrogen fluxes caused composed by organisms in natural ecosystems if the con- by production and use of fertilizer, burning of wood and centration of waste does not exceed the system’s capac- other biomass fuels, and clearing of tropical land lead to ity to transform it. Some modern wastes, however, are increasing atmospheric concentrations of nitrous oxide, virtually indestructible, such as some plastics and the another potent greenhouse gas that is also involved in breakdown products of the pesticide DDT. the destruction of the stratospheric ozone shield. These The simple inorganic chemicals that result from and other changes in the also result in natural decomposition are eventually returned to plants acid rain and excess nutrient inputs to freshwater sys- as nutrients. Thus, the decomposition of wastes and the tems, , and coastal marine . This nutrient 9 Issues in Ecology Number 2 Spring 1997 influx causes eutrophication of aquatic ecosystems and endangered or extinct (Buchmann and Nabhan 1996). contamination of sources—both surface and ground water— by high levels of nitrate-nitrogen Natural Control Services (Vitousek et al. 1997). Humanity’s competitors for food, timber, cotton, and other fibers are called pests, and they include nu- Pollination merous herbivorous insects, rodents, fungi, snails, nema- Animal pollination is required for the successful todes, and . These pests destroy an estimated 25 of most flowering plants. About 220,000 to 50 percent of the world’s crops, either before or after out of an estimated 240,000 species of plants for which harvest (Pimentel et al. 1989). In addition, numerous the mode of pollination has been recorded require an weeds compete directly with crops for water, light, and animal such as a bee or hummingbird to accomplish this soil nutrients, further limiting yields. vital task. This includes both wild plants and about 70 Chemical pesticides, and the strategies by which percent of the agricultural crop species that feed the they are applied to fight crop pests, can have harmful world. Over 100,000 different animal species—includ- unintended consequences. First, pests can develop resis- ing bats, bees, beetles, birds, butterflies, and flies—are tance, which means that higher and higher doses of pes- known to provide these free pollination services that as- ticides must be applied or new chemicals developed peri- sure the perpetuation of plants in our croplands, back- odically to achieve the same level of control. Resistance yard gardens, , is now found in more than meadows and forests. In 500 insect and mite pests, turn, the continued availabil- over 100 weeds, and in ity of these de- about 150 plant pathogens pends on the existence of a (WRI 1994). Second, popu- wide variety of habitat types lations of the natural en- needed for their feeding, suc- emies of pests are decimated cessful breeding, and by heavy pesticide use. completion of their life cycles Natural predators are often (Nabhan and Buchmann more susceptible to synthetic 1997). poisons than are the pests One third of human because they have not had food is derived from plants J. Bryant/Biological Photo Service Photo by Peter the same evolutionary expe- pollinated by wild pollinators. Figure 10-Sonoran bumble bee (Bombus sonorus) pollinat- rience with overcoming plant Without natural pollination ing a flower. chemicals that the pests services, yields of important crops would decline precipi- themselves have had. And natural predators also typi- tously and many wild plant species would become ex- cally have much smaller population sizes than those of tinct. In the United States alone, the agricultural value their prey. Destruction of predator populations leads to of wild, native pollinators—those sustained by natural explosions in prey numbers, not only freeing target pests habitats adjacent to farmlands— is estimated in the bil- from natural controls but often “promoting” other lions of dollars per year. Pollination by honey bees, origi- non-pest species to pest status. In in the nally imported from Europe, is extremely important as 1970s, for instance, 24 of the 25 most important agri- well, but these bees are presently in decline, enhancing cultural pests had been elevated to that status by the the importance of pollinators from natural ecosystems. overuse of pesticides (NRC 1989). Third, exposure to Management of the honey bee in the New World is cur- pesticides and herbicides may pose serious health risks rently threatened by the movement of, and hybridization to humans and many other types of organisms; the re- with, an aggressive African strain of honey bee that was cently discovered declines in human sperm counts may accidentally released in Brazil in 1956. Diseases of honey be attributable in part to such exposure (Colborn et al. bee colonies are also causing a marked decline in the 1996). number of managed colonies. Meanwhile, the diversity Fortunately, an estimated 99 percent of poten- of natural pollinators available to both wild and domesti- tial crop pests are controlled by natural enemies, includ- cated plants is diminishing: more than 60 genera of pol- ing many birds, spiders, parasitic wasps and flies, lady linators include species now considered to be threatened, bugs, fungi, viral diseases, and numerous other types of 10 Issues in Ecology Number 2 Spring 1997 organisms (DeBach 1974). activities such as gardening These natural biological and pet-keeping, nature pho- control agents save farmers tography and film-making, billions of dollars annually bird feeding and watching, by protecting crops and re- hiking and camping, ducing the need for chemi- ecotouring and mountaineer- cal control (Naylor and ing, river-rafting and boat- Ehrlich 1997). ing, fishing and hunting, and in a wide range of other ac- Seed Dispersal tivities. For many, nature is Once a seed germi- an unparalleled source of nates, the resulting plant is J. Bryant/Biological Photo Service Photo by Peter wonderment and inspiration, usually rooted in place for Figure 11-Ladybug larva (Cycloneda polita) eating an aphid. peace and beauty, fulfillment the rest of its life. For plants, then, movement to new and rejuvenation (e.g., Kellert and Wilson). sites beyond the shadow of the parent is usually achieved through seed dispersal. Many seeds, such as those of THREATS TO ECOSYSTEM SERVICES the dandelion, are dispersed by wind. Some are dispersed by water, the most famous being the seafaring coconut. Ecosystem services are being impaired and de- Many other seeds have evolved ways of getting around stroyed by a wide variety of human activities. Foremost by using animals as their dispersal agents. These seeds among the immediate threats are the continuing destruc- may be packaged in sweet fruit to reward an animal for tion of natural habitats and the invasion of non-native its dispersal services; some of these seeds even require species that often accompanies such disruption; in ma- passage through the gut of a bird or mammal before rine systems, overfishing is a major threat. The most they can germinate. Others require burial—by, say, a irreversible of human impacts on ecosystems is the loss forgetful jay or a squirrel which later leaves its cache of native biodiversity. A conservative estimate of the uneaten—for eventual germination. Still others are rate of species loss is about one per hour, which unfortu- equipped with sticky or sharp, spiny surfaces designed nately exceeds the rate of evolution of new species by a to catch onto a passing animal and go for a long ride factor of 10,000 or more (Wilson 1989; Lawton and before dropping or being rubbed off. Without thousands May 1995). But complete extinction of species is only of animal species acting as seed dispersers, many plants the final act in the process. The rate of loss of local popu- would fail to reproduce successfully. For instance, the lations of species—the populations that generate eco- whitebark pine (Pinus albicaulis), a tree found in the system services in specific localities and regions—is or- Rockies and Sierra Nevada - Cascade Mountains, cannot ders of magnitude higher (Daily and Ehrlich 1995; Hughes reproduce successfully without a bird called Clark’s Nut- et al., in prep.). Destroying other life forms also disrupts cracker (Nucifraga columbiana), which chisels pine seeds the web of interactions that could help us discover the out of the tightly closed cones and disperses and buries potential usefulness of specific plants and animals (Th- them; without this service, the cones do not open far ompson 1994). Once a or a predacious insect enough to let the seeds fall out on their own. Animal is on the brink of extinction, for instance, it would be seed dispersers play a central role in the structure and difficult to discover its potential utility to farmers. regeneration of many pine forests (Lanner 1996). Dis- Other imminent threats include the alteration of ruption of these complex services may leave large areas the Earth’s carbon, nitrogen, and other biogeochemical of forest devoid of seedlings and younger age classes of cycles through the burning of fossil fuels and heavy use trees, and thus unable to recover swiftly from human of nitrogen fertilizer; degradation of farmland through impacts such as land clearing. unsustainable agricultural practices; squandering of fresh- ; toxification of land and waterways; and Aesthetic Beauty and Intellectual and Spiritual Stimu- overharvesting of fisheries, managed forests, and other lation theoretically renewable systems. Many human beings have a deep appreciation of These threats to ecosystem services are driven natural ecosystems. That is apparent in the art, reli- ultimately by two broad underlying forces. One is rapid, gions, and traditions of diverse cultures, as well as in unsustainable growth in the scale of the human enter- 11 Issues in Ecology Number 2 Spring 1997 prise: in population size, in per-capita consumption, and is known as the marginal value. In the case of ecosystem also in the environmental impacts that and services, for example, the question that might be posed institutions generate as they produce and supply those would be: By how much would the flow of ecosystem consumables (Ehrlich et al. 1977). The other underlying services be augmented (or diminished) with the preserva- driver is the frequent mismatch between short-term, in- tion (or destruction) of the next hectare of forest or wet- dividual economic incentives and long-term, societal land? Estimation of marginal values is complex (e.g., well-being. Ecosystem services are generally greatly un- Bawa and Gadgil 1997; Daily 1997b). Often a qualita- dervalued, for a number of reasons: many are not traded tive comparison of relative values is sufficient— that is, or valued in the marketplace; many serve the public good which is greater, the economic benefits of a particular rather than provide direct benefits to individual landown- development project or the benefits supplied by the eco- ers; private property owners often have no way to ben- system that would be destroyed, measured over a time efit financially from the ecosystem services supplied to period of interest to people concerned about the well-being society by their land; and, in fact, economic subsidies of their grandchildren? often encourage the conversion of such to other, There are, and will remain, many cases in which market-valued activities. Thus, people whose activities ecosystem service values are highly uncertain. Yet the disrupt ecosystem services often do not pay directly for pace of destruction of natural ecosystems, and the irre- the cost of those lost services. Moreover, society often versibility of most such destruction on a time scale of does not compensate landowners and others who do safe- interest to humanity, warrants substantial caution. Valu- guard ecosystem services for the economic benefits they ing a natural ecosystem, like valuing a human life, is lose by foregoing more lucrative but destructive land uses. fraught with difficulties. Just as societies have recog- There is a critical need for policy measures that address nized fundamental human rights, however, it may be pru- these driving forces and embed the value of ecosystem dent to establish fundamental ecosystem protections even services into decision making frameworks. though uncertainty over economic values remains. New institutions and agreements at the international and VALUATION OF ECOSYSTEM SERVICES subnational level will be needed to encourage fair partici- pation in such protections (see, e.g., Heal 1994). Human society would cease to exist in the ab- The tremendous expense and difficulty of repli- sence of ecosystem services. Thus, their immense value cating lost ecosystem services is perhaps best illustrated to humanity is unquestionable. Yet quantifying the value by the results of the first “mission,” in which of ecosystem services in specific localities, and measur- eight people lived inside a 3.15-acre closed ecosystem ing their worth against that of competing land uses is no for two years. The system featured agricultural land and simple task. When tradeoffs must be made in the alloca- replicas of several natural ecosystems such as forests tion of land and other resources to competing human and even a miniature . In spite of an investment of activities, the resolution often requires a measure of what more than $200 million in the design, construction, and Photo by Gretchen C. Daily Figure 12-The goods and services supplied by this badly deforested and eroded region of Madagascar are all but gone and would be difficult to restore. 12 Issues in Ecology Number 2 Spring 1997 • operation of this model To what extent have vari- earth, it proved impossible ous ecosystem services al- to supply the material and ready been impaired? And physical needs of the eight how are impairment and risk Biospherians for the in- of future impairment distrib- tended 2 years. Many un- uted in various regions of pleasant and unexpected the globe? • problems arose, including a How interdependent are drop in atmospheric different ecosystem ser- concentration to 14% (the vices? How does exploiting level normally found at an or damaging one influence elevation of 17,500 feet), the functioning of others? • high spikes in carbon diox- To what extent, and over ide concentrations, nitrous what time scale, are ecosys- oxide concentrations high tem services amenable to enough to impair the brain, repair or restoration? • an extremely high level of How effectively, and at extinctions (including 19 of how large a scale, can ex- 25 vertebrate species and all isting or foreseeable human pollinators brought into the technologies substitute for , which would have ecosystem services? What ensured the eventual extinc- would be the side effects of tion of most of the plant such substitutions? • species as well), overgrowth Given the current state of aggressive vines and al- Figure 13-The production of this meal benefited from many of technology and the scale gal mats, and population ecosystem services, including natural pest control, pollina- of the human enterprise, explosions of crazy ants, tion, maintenance of soil fertility, purification of water, and what proportion and spatial cockroaches, and katydids. moderation of climate. pattern of land must remain Even heroic personal efforts relatively undisturbed, lo- on the part of the Biospherians did not suffice to make cally, regionally, and globally, to sustain the delivery the system viable and sustainable for either humans or of essential ecosystem services? many nonhuman species (Cohen and Tilman 1996). CONCLUSIONS MAJOR UNCERTAINTIES The human economy depends upon the services performed Society would clearly profit by further investigation into “for free” by ecosystems. The ecosystem services sup- some of the following broad research questions so that plied annually are worth many trillions of dollars. Eco- we might avoid on Biosphere 1, the earth, unpleasant nomic development that destroys habitats and impairs surprises like those that plagued the Biosphere 2 project services can create costs to humanity over the long term (Holdren 1991; Cohen and Tilman 1996; Daily 1997b): that may greatly exceed the short-term economic ben- efits of the development. These costs are generally hid- • What is the relative impact of various human activi- den from traditional economic accounting, but are none- ties upon the supply of ecosystem services? theless real and are usually borne by society at large. • What is the relationship between the condition of an Tragically, a short-term focus in land-use decisions often ecosystem—that is, relatively pristine or heavily sets in motion potentially great costs to be borne by modified—and the quantity and quality of ecosys- future generations. This suggests a need for policies tem services it supplies? that achieve a balance between sustaining ecosystem • To what extent do ecosystem services depend upon services and pursuing the worthy short-term goals of biodiversity at all levels, from genes to species to economic development. landscapes? 13 Issues in Ecology Number 2 Spring 1997 Ehrlich, P.R. and A.H. Ehrlich. 1981. Extinction. Ballantine, New ACKNOWLEDGMENTS York. Ehrlich, P.R., A.H. Ehrlich, and J.P. Holdren. 1977. Ecoscience: Popu- We thank the Packard Foundation and the Pew lation, Resources, Environment. Freeman and Co., San Fran- Foundation for financial support. cisco. Ewel, K. 1997. improvement: evaluation of an ecosys- tem service. Pages 329-344 in G. Daily, editor. Nature’s REFERENCES Services: Societal Dependence on Natural Ecosystems. Is- land Press, Washington, D.C. Adams, R. McC. 1981. Heartland of Cities: Surveys of Ancient Farnsworth, N.R., O. Akerele, A.S. Bingel, D.D. Soejarto, and Z.-G. Settlement and Land Use on the Central Floodplain of the Guo. 1985. Medicinal plants in therapy. Bulletin of the Euphrates, Chicago: University of Chicago Press. World Health Organization 63: 965-981. Alexander, S., S. Schneider, and K. Lagerquist. 1997. Ecosystem Felder, A. J. and D. M. Nickum. 1992. The 1991 economic impact services:Interaction of Climate and Life. Pages 71-92 in G. of sport fishing in the United States. American Sportfishing Daily, editor. Nature’s Services: Societal Dependence on Association, Alexandria, Virginia. Natural Ecosystems. , Washington, D.C. FAO (United Nations Food and Agriculture Organization). 1990. Allegre, C. and S. Schneider. 1994. The evolution of the earth. Sci- Soilless Culture for Horticultural Crop Production. Rome: entific American 271: 44-51. FAO. Grifo, F. and J. Rosenthal, editors. 1997. Biodiversity Bawa, K. and M. Gadgil. 1997. Ecosystem services, subsistence and Human Health. Island Press, Washington, D.C. and conservation of biodiversity. Pages 295-310 Hall, D.O., F. Rosillo-Calle, R.H. Williams, and J. . 1993. Bio- in G. Daily, editor. Nature’s Services: Societal Dependence mass for energy: supply prospects. Pages 593-651 in T. on Natural Ecosystems. Island Press, Washington, D.C. Johansson, H. Kelly, A. Reddy, and R. Williams, editors. Bormann, F., G. Likens, D. Fisher, and R. Pierce. 1968. Nutrient loss : Sources for Fuels and Electricity. Island accelerated by clear-cutting of a forest ecosystem. Science Press, Washington, D.C. 159: 882-884. Heal, G. 1994. Formation of international environmental agreements. Buchmann, S.L. and G.P. Nabhan. 1996. The Forgotten Pollinators. Pages 301-332 in C. Carraro, editor, Trade, Innovation, Island Press, Washington, D.C. Environment. Kluwer Academic Publishers, Dordrecht. Chanway, C. 1993. Biodiversity at risk: soil microflora. Pages Hillel, D. 1991. Out of the Earth: Civilization and the Life of the 229-238 in M. A. Fenger, E. H. Miller, J. A. Johnson, and Soil. The Free Press, New York. E. J. R. Williams, editors. Our Living Legacy: Proceedings Holdren, J. P. 1991. “Report of the planning meeting on ecological of a Symposium on Biological Diversity. Royal British Co effects of human activities.” National Research Council, lumbia Museum, Victoria, Canada. 11-12 October, Irvine, California, mimeo. Cohen, J.E. and D. Tilman. 1996. Biosphere 2 and biodiversity: The Holdren, J.P. and P.R. Ehrlich. 1974. Human population and the glo- lessons so far. Science 274: 1150-1151. bal environment. American Scientist 62: 282-292. Colborn, T., D. Dumanoski, and J. P. Myers. 1996. Our Stolen Fu- Hughes, J.B., G.C. Daily, and P.R. Ehrlich. In prep. The importance, ture. Dutton, New York. extent, and extinction rate of global population diversity. Daily, G.C. 1997a. Introduction: What are ecosystem services? Pages Ives, J. and B. Messerli. 1989. The Himalayan Dilemma: Reconciling 1-10 in G. Daily, editor. Nature’s Services: Societal De- Development and Conservation, London: Routledge. pendence on Natural Ecosystems. Island Press, Washing- Jenny, H. 1980. The Soil . Springer-Verlag, New York. ton, D.C. Kaufman, L. and P. Dayton. 1997. Impacts of marine resource ex Daily, G.C. 1997b. Valuing and safeguarding Earth’s life support traction on ecosystem services and . Pages systems. Pages 365-374 in G. Daily, editor. Ser- 275-293 in G. Daily, editor. Nature’s Services: Societal vices: Societal Dependence on Natural Ecosystems. Island Dependence on Natural Ecosystems. Island Press, Wash- Press, Washington, D.C. ington, D.C. Daily, G.C., P.A. Matson, and P.M. Vitousek. 1997. Ecosystem ser- Kellert, S.R. and E.O. Wilson, editors. 1993. The Biophilia Hypoth- vices supplied by soil. Pages 113-132 in G. Daily, editor. esis. Island Press, Washington, D.C. Nature’s Services: Societal Dependence on Natural Eco- Lanner, R.M. 1996. Made for Eachother: A Symbiosis of Birds and systems. Island Press, Washington, D.C. Pines. Oxford University Press, New York. Daily, G.C. and P.R. Ehrlich. 1995. Population diversity and the Lawton, J. and R. May, editors. 1995. Extinction Rates. Oxford biodiversity crisis. Pp. 41-51 in C. Perrings, K.G. Maler, University Press, Oxford. C. Folke, C.S. Holling and B.O. Jansson (eds.), Biodiversity Lee, K. 1985. Earthworms: Their Ecology and Relationships with Conservation: Problems and Policies, Dordrecht, Kluwer Soils and Land Use. Academic Press, New York. Academic Press. Leung, A.Y. and S. Foster. 1996. Encyclopedia of Common Natural DeBach, P. 1974. Biological Control by Natural Enemies. Cambridge Ingredients Used in Food, Drugs, and Cosmetics. John Wiley University Press, London. & Sons, Inc., New York. Diamond, J. 1991. The Rise and Fall of the Third Chimpanzee. Ra- McCormick, K.D., M.A. Deyrup, E.S. Menges, S.R. Wallace, J. dius, London. Dobson, A. 1995. Biodiversity and human Meinwald, and T. Eisner. 1993. Relevance of to health. Trends in Ecology and Evolution 10: 390-391. conservation of isolated populations: the case of volatile Dowling, H.F. 1977. Fighting Infection. Harvard Univ. Press, Cam- leaf components of Dicerandra mints. Proc. Nat. Acad. bridge, MA. Sci. USA 90: 7701-7705. 14 Issues in Ecology Number 2 Spring 1997 Myers, N. 1983. A Wealth of Wild Species. Westview Press, Boul- Sala, O.E. and J.M. Paruelo. 1997. Ecosystem services in grass- der, CO. Myers, N. 1997. The forests and their lands. Pages 237-252 in G. Daily, editor. Nature’s Ser- ecosystem services. Pages 215-235 in G. Daily, editor. vices: Societal Dependence on Natural Ecosystems. Island Nature’s Services: Societal Dependence on Natural Eco- Press, Washington, D.C. systems. Island Press, Washington, D.C. Salati, E. 1987. The forest and the hydrological cycle. Pages 273-294 Nabhan, G.P. and S.L. Buchmann. 1997. Pollination services: in R. Dickinson, editor. The Geophysiology of Amazonia. Biodiversity’s direct link to world food stability. Pages John Wiley and Sons, New York. 133-150 in G. Daily, editor. Nature’s Services: Societal Schlesinger, W. 1991. : An Analysis of Global Dependence on Natural Ecosystems. Island Press, Wash- Change. Academic Press, San Diego. ington, D.C. Schneider, S. and P. Boston, editors. 1991. Scientists on Gaia. MIT National Research Council (NRC). 1989. Alternative Agriculture. Press, Boston. National Academy Press, Washington, D.C. Schneider, S. and R. Londer. 1984. The Coevolution of Climate and National Research Council (NRC). 1992. Managing Global Genetic Life. Sierra Club Books, San Francisco. Resources: The U.S. National Plant Germplasm System. Shiklomanov, I.A. 1993. World resources. Pp. 13-24 in National Academy Press, Washington, D.C. P. Gleick, editor. Water in Crisis: A Guide to the World’s Naylor, R. and P. Ehrlich. The value of natural pest control services in Fresh Water Resources. Oxford University Press, New York. agriculture. Pages 151-174 in G. Daily, editor. Nature’s Shukla, J., C. Nobre, and P. Sellers. 1990. Amazon deforestation Services: Societal Dependence on Natural Ecosystems. Is- and climate change. Science. 247: 1322-1325. land Press, Washington, D.C. Tilman, D. 1997. Biodiversity and ecosystem functioning. Pages Oldeman, L., V. van Engelen, and J. Pulles. 1990. “The extent of 93-112 in G. Daily, editor. Nature’s Services: Societal human-induced soil degradation, Annex 5” of L. R. Dependence on Natural Ecosystems. Island Press, Wash- Oldeman, R. T. A. Hakkeling, and W. G. Sombroek, World ington, D.C. Map of the Status of Human-Induced Soil Degradation: An Thompson, J.N. 1994. The Coevolutionary Process. Chicago Univ. Explanatory Note, rev. 2d ed. Wageningen: International Press, Chicago. United Nations Food and Agriculture Or- Soil Reference and Information Centre. ganization (UNFAO). 1993. Marine Fisheries and the Law Overgaard-Nielsen, C. 1955. Studies on enchytraeidae 2: stud- of the Sea: A Decade of Change. Fisheries Circular No. ies. Natura Jutlandica 4: 5-58. 853, Rome. Peterson, C.H. and J. Lubchenco. 1997. On the value of marine United Nations Food and Agriculture Organization (UNFAO). 1994. ecosystem services to society. Pages 177-194 in G. Daily, FAO Yearbook of Fishery Statistics. Volume 17. editor. Nature’s Services: Societal Dependence on Natu- United States Department of Agriculture (USDA). 1993. World Ag- ral Ecosystems. Island Press, Washington, D.C. riculture: Trends and Indicators, 1970-91. Washington, Pimentel, D., C. Harvey, P. Resosudarmo, K. Sinclair, D. Kurz, M. DC: USDA. McNair, S. Crist, L. Shpritz, L. Fitton, R. Saffouri, and R. Vitousek, P., P. Ehrlich, A. Ehrlich, and P. Matson. 1986. Human Blair. 1995. “Environmental and economic costs of soil appropriation of the products of photosynthesis. BioScience erosion and conservation benefits.” Science 267: 36: 368-373. 1117-1123. Vitousek, P., J. Aber, R. Howarth, G. Likens, P. Matson, D. Schindler, Pimentel, D., L. McLaughlin, A. Zepp, B. Lakitan, T. Kraus, P. W. Schlesinger, and D. Tilman. 1997. Human alteration of Kleinman, F. Vancini, W. Roach, E. Graap, W. Keeton, and the global nitrogen cycle: causes and consequences. [COM G. Selig. 1989. Environmental and economic impacts of PLETE] reducing U.S. agricultural pesticide use. Handbook of Pest Wilson, E.O. 1987. The little things that run the world: The impor- Management in Agriculture 4: 223-278. tance and conservation of invertebrates. Conservation Bi- Postel, S. and S. Carpenter. 1997. Freshwater ecosystem services. ology 1: 344-346. Wilson, E.O. 1989. Threats to Pages 195-214 in G. Daily, editor. Nature’s Services: biodiversity. Scientific American Sept: 108-116. Societal Dependence on Natural Ecosystems. Island Press, World Bank. 1991. Agricultural Biotechnology: The Next Green Washington, D.C. Prescott-Allen, R. and C. Prescott-Allen. Revolution? World Bank Technical Paper no. 133. Wash- 1990. How many plants feed the world? Conservation Bi- ington, D.C. ology 4: 365-374. World Resources Institute (WRI). 1994. World Resources: A Guide Principe, P.P. 1989. The economic significance of plants and their to the Global Environment. Oxford University Press, Ox- constituents as drugs. Pages 1-17 in H. Wagner, H. Hikino, ford. and N.R. Farnsworth, editors. Economic and Medicinal Plant Research, Vol. 3, Academic Press, London. FOR MORE INFORMATION Reid, W.V., S.A. Laird, C.A. Meyer, R. Gamez, A. Sittenfeld, D. Janzen, M. Gollin, and C. Juma. 1996. Biodiversity prospecting. About the Panel of Scientists Pages 142-173 in M. Balick, E. Elisabetsky, and S. Laird, This report presents the consensus reached by a editors. Medicinal Resources of the : panel of 11 scientists chosen to include a broad array of Biodiversity and Its Importance to Human Health. Colum- bia Univ. Press, New York. expertise in this area. This report underwent peer review Rouatt, J. and H. Katznelson.1961. A study of bacteria on the root and was approved by the Board of Editors of Issues in surface and in the rhizosphere soil of crop plants. J. Ap- Ecology. The affiliations of the members of the panel of plied Bacteriology 24: 164-171. scientists are: 15 Issues in Ecology Number 2 Spring 1997 Dr. Gretchen C. Daily, Panel Chair, Department of Bio- environment. All reports undergo peer review and must logical Sciences, , Stanford, CA 94305 be approved by the editorial board before publication.

Dr. Susan Alexander, Earth Systems Science and Policy, Editorial Board of Issues in Ecology California State University, Monterey Bay, 100 Campus Dr. David Tilman, Editor-in-Chief, Department of Ecol- Center, Seaside, CA 93955 ogy, Evolution and Behavior, University of Minnesota, St. Paul, MN 55108-6097. E-mail: [email protected] Dr. Paul R. Ehrlich, Department of Biological Sciences, Stanford University, Stanford, CA 94305 Board members Dr. Stephen Carpenter, Center for , University Dr. Larry Goulder, Department of , Stanford of Wisconsin, Madison, WI 53706 University, Stanford, CA 94305 Dr. Deborah Jensen, The Nature Conservancy, 1815 North Lynn Street, Arlington, VA 22209 Dr. Jane Lubchenco, Department of , Oregon Dr. Simon Levin, Department of Ecology & Evolutionary State University, Corvallis, OR 97331 , Princeton University, Princeton, NJ 08544-1003 Dr. Pamela A. Matson, Policy and Dr. Jane Lubchenco, Department of Zoology, Oregon Management, University of California, Berkeley, CA State University, Corvallis, OR 97331-2914 94720 Dr. Judy L. Meyer, Institute of Ecology, The University of Georgia, Athens, GA 30602-2202 Dr. Harold A. Mooney, Department of Biological Sciences, Dr. Gordon Orians, Department of Zoology, University Stanford University, Stanford, CA 94305 of Washington, Seattle, WA 98195 Dr. Lou Pitelka, Appalachian Environmental Laboratory, Dr. Sandra Postel, Global Water Policy Project, 107 Lark- Gunter Hall, Frostburg, MD 21532 spur Drive, Amherst, MA 01002 Dr. William Schlesinger, Departments of and , Duke University, Durham, NC 27708- Dr. Stephen H. Schneider, Department of Biological Sci- 0340 ences, Stanford University, Stanford, CA 94305 Additional Copies Dr. David Tilman, Department of Ecology, Evolution and To receive additional copies of this report or pre- Behavior, University of Minnesota, St. Paul, MN 55108- vious Issues in Ecology, please contact: 609 Public Affairs Office Dr. George M. Woodwell, Woods Hole Research Center, Ecological Society of America P.O. Box 296, Woods Hole, MA 02543 2010 Massachusetts Avenue, NW Suite 400 Much of the information in this report was de- Washington, DC 20036 rived from G. Daily, editor. 1997. Nature’s Services: [email protected] Societal Dependence onNatural Ecosystems. Island (202) 833-8773 Press, Washington, D.C.

About the Science Writer Special thanks to the U.S. Environmental Protec- Yvonne Baskin, a science writer, edited the re- tion Agency Office of Sustainable Ecosystems and Com- port of the panel of scientists to allow it to more effec- munities for supporting printing and distribution of this tively communicate its findings with non-scientists. document.

About Issues in Ecology Cover photo credits, clockwise from top left: Issues in Ecology is designed to report, in lan- Nadine Cavender, Nadine Cavender, Nadine Cavender, guage understandable by non-scientists, the consensus Claude Cavender, Jr., Nadine Cavender, unknown, Claude of a panel of scientific experts on issues relevant to the Cavender, Jr., and unknown. 16 enue, NW, Suite400, Washington, DC,20036. ISSN 1092-8987 For moreinformation, contacttheEcologicalSocietyofAmerica,2010 Massachusetts Av- responsible applicationofecologicalprinciplestothe solutionofenvironmentalproblems. leading professionalsocietyofecologists.Founded in1915,ESAseekstopromotethe Issues inEcology reports undergo peerreviewandmustbeapprovedbytheEditorialBoardbeforepublication. asreportsarecompleted. logical SocietyofAmerica. It ispublishedatirregularintervals, All Ecology consensus ofapanelscientificexpertsonissues relevanttotheenvironment. Issues inEcology is supportedbythePew BiologyprogramandbytheEco- ScholarsinConservation isanofficialpublicationoftheEcologicalSociety America,thenation’s isdesignedtoreport,inlanguageunderstandable bynon-scientists,the About IssuesinEcology Issues in

l