Benefits Supplied to Human Societies by Natural Ecosystems

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Ecosystem Services: BenefitsSupplied to Human Societies

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Issues in Ecology Number 2 Spring 1997

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Ecosystem Services:Benefits Supplied to Human

Societies by Natural Ecosystems

SUMMARY

Human societies derive many essential goods from natural ecosystems, including seafood, game animals, fodder,fuelwood, timber, and pharmaceutical products. These goods represent important and familiar parts of the economy.What has been less appreciated until recently is that natural ecosystems also perform fundamental life-support serviceswithout which human civilizations would cease to thrive. These include the purification of air and water, detoxificationand decomposition of wastes, regulation of climate, regeneration of soil fertility, and production and maintenance ofbiodiversity, from which key ingredients of our agricultural, pharmaceutical, and industrial enterprises are derived. Thisarray of services is generated by a complex interplay of natural cycles powered by solar energy and operating across awide range of space and time scales. The process of waste disposal, for example, involves the life cycles of bacteria as wellas the planet-wide cycles of major chemical elements such as carbon and nitrogen. Such processes are worth manytrillions of dollars annually. Yet because most of these benefits are not traded in economic markets, they carry no pricetags that could alert society to changes in their supply or deterioration of underlying ecological systems that generatethem. Because threats to these systems are increasing, there is a critical need for identification and monitoring ofecosystem services both locally and globally, and for the incorporation of their value into decision-making processes.

Historically, the nature and value of Earth�s life support systems have largely been ignored until their disruption orloss highlighted their importance. For example, deforestation has belatedly revealed the critical role forests serve inregulating the water cycle -- in particular, in mitigating floods, droughts, the erosive forces of wind and rain, and siltingof dams and irrigation canals. Today, escalating impacts of human activities on forests, wetlands, and other naturalecosystems imperil the delivery of such services. The primary threats are land use changes that cause losses in biodiversityas well as disruption of carbon, nitrogen, and other biogeochemical cycles; human-caused invasions of exotic species;releases of toxic substances; possible rapid climate change; 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 technology.• 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 ecologicalservices 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 populations are required to sustain ecosystem services.• The functioning of many ecosystems could be restored if appropriate actions were taken in time.

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

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Ecosystem Services: Benefits Suppliedto Human Societies by Natural Ecosystems

byGretchen 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

Many societies today have technological capa-bilities undreamed of in centuries past. Their citizenshave such a global command of resources that even foodsflown in fresh from all over the planet are taken forgranted, and daily menus are decoupled from the limita-tions of regional growing seasons and soils. These de-velopments have focused so much attention uponhuman-engineered and exotic sources of fulfillment thatthey divert attention from the local biological underpin-nings that remain essential to economic prosperity andother aspects of our well-being.

These biological underpinnings are encompassedin the phrase ecosystem services, which refers to a widerange of conditions and processes through which natu-ral ecosystems, and the species that are part of them,help sustain and fulfill human life. These services main-tain biodiversity and the production of ecosystem goods,such as seafood, wild game, forage, timber, biomass fu-els, natural fibers, and many pharmaceuticals, industrialproducts, and their precursors. The harvest and trade ofthese goods represent important and familiar parts ofthe human economy. In addition to the production ofgoods, ecosystem services support life through (Holdrenand Ehrlich 1974; Ehrlich and Ehrlich 1981):

• purification of air and water.• mitigation of droughts and floods.• generation and preservation of soils and renewal of

their fertility.• detoxification and decomposition of wastes.• pollination of crops and natural vegetation.• dispersal of seeds.• cycling and movement of nutrients.• control of the vast majority of potential agricultural

pests.• maintenance of biodiversity.• protection of coastal shores from erosion by waves.• protection from the sun�s harmful ultraviolet rays.• partial stabilization of climate.• moderation of weather extremes and their impacts.• provision of aesthetic beauty and intellectual stimu-

lation that lift the human spirit.Although the distinction between �natural� and

�human-dominated� ecosystems is becoming increasinglyblurred, we emphasize the natural end of the spectrum,for three related reasons. First, the services flowing fromnatural ecosystems are greatly undervalued by society.For the most part, they are not traded in formal marketsand so do not send price signals that warn of changes intheir supply or condition. Furthermore, few people areconscious of the role natural ecosystem services play in

Figure 1-Aspen (Populus tremuloides)forest in Colorado, filtering and pu-rifying air and water.

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Figure 2-Woman carrying treetrunk for boat-making in a fishing village on Chiloe Island, Chile.Natural forests remain an important source ofwood for construction, fuel, and other uses.

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generating those ecosystem goods that are traded in themarketplace. As a result, this lack of awareness helpsdrive the conversion of natural ecosystems tohuman-dominated systems (e.g., wheatlands or oil palmfields), whose economic value can be expressed, at leastin part, in standard currency. The second reason to focuson natural ecosystems is that many human-initiated dis-ruptions of these systems -- such as introductions of ex-otic species, extinctions of native species, and alterationof the gaseous composition of the atmosphere throughfossil fuel burning -- are difficult or impossible to reverseon any time scale relevant to society. Third, if awarenessis not increased and current trends continue, humanitywill dramatically alter Earth�s remaining natural ecosys-tems within a few decades (Daily 1997a, b).

The lack of attention to the vital role of naturalecosystem services is easy to understand. Humanity cameinto being after most ecosystem services had been inoperation for hundreds of millions to billions of years.These services are so fundamental to life that they areeasy to take for granted, and so large in scale that it ishard to imagine that human activities could irreparablydisrupt them. Perhaps a thought experiment that re-moves these services from the familiar backdrop of theEarth is the best way to illustrate both the importanceand complexity of ecosystem services, as well as howill-equipped humans are to recreate them. Imagine, forexample, human beings trying to colonize the moon.Assume for the sake of argument that the moon hadalready miraculously acquired some of the basic condi-tions for supporting human life, such as an atmosphere,a climate, and a physical soil structure similar to thoseon Earth. The big question facing human colonists wouldthen be, which of Earth�s millions of species would needto be transported to the moon to make that sterile sur-face habitable?

One could tackle that question systematicallyby first choosing from among all the species exploited

directly for food, drink, spices, fiber, timber, pharmaceu-ticals, and industrial products such as waxes, rubber, andoils. Even if one were highly selective, the list could amountto hundreds or even thousands of species. And that wouldonly be a start, since one would then need to considerwhich species are crucial to supporting those used di-rectly: the bacteria, fungi, and invertebrates that helpmake soil fertile and break down wastes and organicmatter; the insects, bats, and birds that pollinate flow-ers; and the grasses, herbs, and trees that hold soil inplace, regulate the water cycle, and supply food for ani-mals. The clear message of this exercise is that no oneknows which combinations of species -- or even approxi-mately how many -- are required to sustain human life.

Rather than selecting species directly, one mighttry another approach: Listing the ecosystem servicesneeded by a lunar colony and then guessing at the typesand numbers of species required to perform each. Yetdetermining which species are critical to the functioningof a particular ecosystem service is no simple task. Letus take soil fertility as an example. Soil organisms arecrucial to the chemical conversion and physical transferof essential nutrients to higher plants. But the abun-dance of soil organisms is absolutely staggering. Undera square-yard of pasture in Denmark, for instance, thesoil is inhabited by roughly 50,000 small earthwormsand their relatives, 50,000 insects and mites, and nearly12 million roundworms. And that tally is only the begin-ning. The number of soil animals is tiny compared to thenumber of soil microorganisms: a pinch of fertile soil maycontain over 30,000 protozoa, 50,000 algae, 400,000fungi, and bill ions of individual bacteria(Overgaard-Nielsen 1955; Rouatt and Katznelson 1961;Chanway 1993). Which must colonists bring to the moonto assure lush and continuing plant growth, soil renewal,waste disposal, and so on? Most of these soil-dwellingspecies have never been subjected to even cursory in-spection: no human eye has ever blinked at them through

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Figure 3-Alpaca grazing on the Chilean alti-plano. Grassland ecosystems are an impor-tant source of animal products; they are alsothe original habitat of most domestic animalsand many crops, such as wheat, barley, andoats.

a microscope, no human hand has ever typed out a nameor description of them, and most human minds have neverspent a moment reflecting on them. Yet the soberingfact is, as E. O. Wilson put it: they don�t need us, but weneed them (Wilson 1987).

THE CHARACTER OF ECOSYSTEM SERVICES

Moving our attention from the moon back to Earth, letus look more closely at the services nature performs onthe only planet we know that is habitable. Ecosystemservices and the systems that supply them are so inter-connected that any classification of them is necessarilyrather arbitrary. Here we briefly explore a suite ofoverarching services that operate in ecosystems world-wide.

Production of Ecosystem GoodsHumanity obtains from natural ecosystems an

array of ecosystem goods� organisms and their partsand products that grow in the wild and that are useddirectly for human benefit. Many of these, such as fishesand animal products, are commonly traded in economicmarkets. The annual world fish catch, for example,amounts to about 100 million metric tons and is valuedat between $50 billion and $100 billion; it is the leadingsource of animal protein, with over 20% of the popula-tion in Africa and Asia dependent on fish as their pri-mary source of protein (UNFAO 1993). The commercialharvest of freshwater fish worldwide in 1990 totaledapproximately 14 million tons and was valued at about$8.2 billion (UNFAO 1994). Interestingly, the value ofthe freshwater sport fishery in the U.S. alone greatlyexceeds that of the global commercial harvest, with di-rect expenditures in 1991 totaling about $16 billion.When this is added to the value of the employment gen-

erated by sport fishing activities, it raises the total to$46 billion (Felder and Nickum 1992, cited in Postel andCarpenter 1997). The future of these fisheries is in ques-tion, however, because fish harvests have approached orexceeded sustainable levels virtually everywhere. Nineof the world�s major marine fishing areas are in declinedue to overfishing, pollution, and habitat destruction.(UNFAO 1993; Kaufman and Dayton 1997).

Turning our attention to the land, grasslands arean important source of marketable goods, including ani-mals used for labor (horses, mules, asses, camels, bul-locks, etc.) and those whose parts or products are con-sumed (as meat, milk, wool, and leather). Grasslandswere also important as the original source habitat formost domestic animals such as cattle, goats, sheep, andhorses, as well as many crops, such as wheat, barley,rye, oats, and other grasses (Sala and Paruelo 1997). Ina wide variety of terrestrial habitats, people hunt gameanimals such as waterfowl, deer, moose, elk, fox, boarand other wild pigs, rabbits, and even snakes and mon-keys. In many countries, game meat forms an importantpart of local diets and, in many places, hunting is aneconomically and culturally important sport.Natural ecosystems also produce vegetation used directlyby humans as food, timber, fuelwood, fiber, pharmaceu-ticals and industrial products. Fruits, nuts, mushrooms,honey, other foods, and spices are extracted from manyforest species. Wood and other plant materials are usedin the construction of homes and other buildings, as wellas for the manufacture of furniture, farming implements,paper, cloth, thatching, rope, and so on. About 15 per-cent of the world�s energy consumption is supplied byfuelwood and other plant material; in developing coun-tries, such �biomass� supplies nearly 40 percent of en-ergy consumption (Hall et al. 1993), although the por-tion of this derived from natural rather than

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As described in the previous section, biodiversityis a direct source of ecosystem goods. It also suppliesthe genetic and biochemical resources that underpin ourcurrent agricultural and pharmaceutical enterprises andmay allow us to adapt these vital enterprises to globalchange. Our ability to increase crop productivity in theface of new pests, diseases, and other stresses has de-pended heavily upon the transfer to our crops of genesfrom wild crop relatives that confer resistance to thesechallenges. Such extractions from biodiversity�s �geneticlibrary� account for annual increases in crop productiv-ity of about 1 percent, currently valued at $1 billion (NRC1992). Biotechnology now makes possible even greater

use of this natural storehouse of ge-netic diversity via the transfer to cropsof genes from any kind of organism�not simply crop relatives�and itpromises to play a major role in fu-ture yield increases. By the turn ofthe century, farm-level sales of theproducts of agricultural biotechnol-ogy, just now entering the market-place, are expected to reach at least$10 billion per year (World Bank1991, cited in Reid et al. 1996).In addition to sustaining the produc-tion of conventional crops, thebiodiversity in natural ecosystems mayinclude many potential new foods.Human beings have utilized around7,000 plant species for food over thecourse of history and another 70,000plants are known to have edible parts(Wilson 1989). Only about 150 foodplants have ever been cultivated on alarge scale, however. Currently, 82plant species contribute 90 percentof national per-capita supplies of foodplants (Prescott-Allen and

Prescott-Allen 1990), although a much smaller numberof these supply the bulk of the calories humans consume.Many other species, however, appear more nutritious orbetter suited to the growing conditions that prevail inimportant regions than the standard crops that domi-nate world food supply today. Because of increasingsalinization of irrigated croplands and the potential forrapid climate change, for instance, future food securitymay come to depend on drought- and salt-tolerant vari-eties that now play comparatively minor roles in agricul-ture.

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Figure 4-Harpoon-whaling in Flores, In-donesia. The oceans are a key sourceof animal protein for the human popu-lation.

human-dominated ecosystems is undocumented. In addi-tion, natural products extracted from many hundreds ofspecies contribute diverse inputs to industry: gums andexudates, essential oils and flavorings, resins and oleo-resins, dyes, tannins, vegetable fats and waxes, insecti-cides, and multitudes of other compounds (Myers 1983;Leung and Foster 1996). The availability of most ofthese natural products is in decline due to ongoing habi-tat conversion.

Generation and Maintenance of BiodiversityBiological diversity, or biodiversity for short, re-

fers to the variety of life forms at all levels of organiza-tion, from the molecular to the land-scape level. Biodiversity is generatedand maintained in natural ecosystems,where organisms encounter a widevariety of living conditions and chanceevents that shape their evolution inunique ways. Out of convenience ornecessity, biodiversity is usually quan-tified in terms of numbers of species,and this perspective has greatly influ-enced conservation goals. It is im-portant to remember, however, thatthe benefits that biodiversity suppliesto humanity are delivered throughpopulations of species residing in liv-ing communities within specific physi-cal settings� in other words, throughcomplex ecological systems, or eco-systems (Daily and Ehrlich 1995). Forhuman beings to realize most of theaesthetic, spiritual, and economic ben-efits of biodiversity, natural ecosys-tems must therefore be accessible. Thecontinued existence of coniferous treespecies somewhere in the world wouldnot help the inhabitants of a town in-undated by flooding because of the clearing of a pineforest upstream. Generally, the flow of ecosystem goodsand services in a region is determined by the type, spa-tial layout, extent, and proximity of the ecosystems sup-plying them. Because of this, the preservation of onlyone minimum viable population of each non-human spe-cies on Earth in zoos, botanical gardens, and the world�slegally protected areas would not sustain life as we knowit. Indeed, such a strategy, taken to extreme, would leadto collapse of the biosphere, along with its life supportservices.

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Figure 5-Trapping and releasing butterfliesin a mixed-agriculture landscape in CostaRica. Monitoring the impact of humanactivities on biodiversity and ecosystemservices is needed worldwide; butterfliesmay be useful indicators for monitoring.

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Turning to medicinal resources, a recent surveyshowed that of the top 150 prescription drugs used inthe United States, 118 are based on natural sources:74% on plants, 18% on fungi, 5% on bacteria, and 3%on one vertebrate (snake) species. Nine of the top tendrugs in this list are based on natural plant products(Grifo and Rosenthal, in press, as cited in Dobson 1995).The commercial value of pharmaceuticals in the devel-oped nations exceeds $40 billion per year (Principe 1989).Looking at the global picture, approximately 80% of thehuman population relies on traditional medical systems,and about 85% of traditional medicine involves the useof plant extracts (Farnsworth et al. 1985).

Saving only a single popula-tion of each species could have an-other cost. Different populations ofthe same species may produce differ-ent types or quantities of defensivechemicals that have potential use aspharmaceuticals or pesticides(McCormick et al. 1993); and theymay exhibit different tolerances toenvironmental stresses such asdrought or soil salinity. For example,the development of penicillin as atherapeutic antibiotic took a full 15years after Alexander Fleming�s fa-mous discovery of it in common breadmold. In part, this was because sci-entists had great difficulty producing,extracting, and purifying the sub-stance in needed quantities. One keyto obtaining such quantities was thediscovery, after a worldwide search,of a population of Fleming�s mold thatproduced more penicillin than theoriginal (Dowling 1977). Similarly,plant populations vary in their abilityto resist pests and disease, traits im-portant in agriculture. Many thousands of varieties ofrice from different locations were screened to find onewith resistance to grassy stunt virus, a disease that poseda serious threat to the world�s rice crop (Myers 1983).Despite numerous examples like these, many of the lo-calities that harbor wild relatives of crops remain unpro-tected and heavily threatened.

Climate and LifeEarth�s climate has fluctuated tremendously since

humanity came into being. At the peak of the last ice

age 20,000 years ago, for example, much of Europe andNorth America were covered by mile-thick ice sheets.While the global climate has been relatively stable sincethe invention of agriculture around 10,000 years ago,periodic shifts in climate have affected human activitiesand settlement patterns. Even relatively recently, from1550-1850, Europe was significantly cooler during aperiod known as the Little Ice Age. Many of these changesin climate are thought to be caused by alterations inEarth�s orbital rotation or in the energy output of thesun, or even by events on the Earth itself�sudden per-turbations such as violent volcanic eruptions and aster-oid impacts or more gradual tectonic events such as the

uplift of the Himalayas. Remarkably,climate has been buffered enoughthrough all these changes to sustainlife for at least 3.5 billion years(Schneider and Londer 1984). Andlife itself has played a role in this buff-ering.

Climate, of course, plays amajor role in the evolution and distri-bution of life over the planet. Yet mostscientists would agree that life itselfis a principal factor in the regulationof global climate, helping to offset theeffects of episodic climate oscillationsby responding in ways that alter thegreenhouse gas concentrations in theatmosphere. For instance, natural eco-systems may have helped to stabilizeclimate and prevent overheating of theEarth by removing more of the green-house gas carbon dioxide from theatmosphere as the sun grew brighterover millions of years (Alexander etal. 1997). Life may also exert a de-stabilizing or positive feedback thatreinforces climate change, particularly

during transitions between interglacial periods and iceages. One example: When climatic cooling leads to dropsin sea level, continental shelves are exposed to wind andrain, causing greater nutrient runoff to the oceans. Thesenutrients may fertilize the growth of phytoplankton, manyof which form calcium carbonate shells. Increasing theirpopulations would remove more carbon dioxide from theoceans and the atmosphere, a mechanism that shouldfurther cool the planet. Living things may also enhancewarming trends through such activities as speeding upmicrobial decomposition of dead organic matter, thus

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Figure 6-Bark of the Pacific yew tree (Taxus brevifolia),which is the source of the new anti-cancer drug, taxol,Willamette National Forest, Oregon.

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Figure 7-Herbal pharmacist in Dali, Yunnan Province,China. An estimated 80 percent of the world�s popu-lation relies on natural medicinal products.

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releasing carbon dioxide to the atmosphere (Schneiderand Boston 1991; Allegre and Schneider 1994). Therelative influence of life�s stabilizing and destabilizing feed-backs remains uncertain; what is clear is that climateand natural ecosystems are tightly coupled, and the sta-bility of that coupled system is an importantecosystemservice.

Besides their impact on the atmosphere, ecosys-tems also exert direct physical influences that help tomoderate regional and local weather. For instance, tran-spiration (release of water vapor from the leaves) of plantsin the morning causes thunderstorms in the afternoon,limiting both moisture loss from the region and the risein surface temperature. In the Amazon, for example,50% of the mean annual rainfall is recycled by the forestitself via evapotranspiration�that is, evaporation fromwet leaves and soil combined with transpiration (Salati1987). Amazon deforestation could so dramatically re-duce total precipitation that the forest might be unableto reestablish itself following complete destruction (Shuklaet al. 1990). Temperature extremes are also moderatedby forests, which provide shade and surface cooling andalso act as insulators, blocking searing winds and trap-ping warmth by acting as a local greenhouse agent.

Mitigation of Floods and DroughtsAn enormous amount of water, about 119,000

cubic kilometers, is rained annually onto the Earth�s landsurface�enough to cover the land to an average depthof 1 meter (Shiklomanov 1993). Much of this water is

soaked up by soils and gradually meted out to plant rootsor into aquifers and surface streams. Thus, the soil itselfslows the rush of water off the land in flash floods. Yetbare soil is vulnerable. Plants and plant litter shield thesoil from the full, destructive force of raindrops and holdit in place. When landscapes 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. Detachedsoil particles are splashed downslope and carried off byrunning water (Hillel 1991).

Erosion causes costs not only at the site wheresoil is lost but also in aquatic systems, natural andhuman-made, where the material accumulates. Localcosts of erosion include losses of production potential,diminished infiltration and water availability, and lossesof nutrients. Downstream costs may include disruptedor lower quality water supplies; siltation that impairs drain-age and maintenance of navigable river channels, har-bors, and irrigation systems; increased frequency andseverity of floods; and decreased potential for hydroelec-tric power as reservoirs fill with silt (Pimentel et al. 1995).Worldwide, the replacement cost of reservoir capacitylost to siltation is estimated at $6 billion per year.

In addition to protecting soil from erosion, livingvegetation�with its deep roots and above-ground evapo-rating surface�also serves as a giant pump, returningwater from the ground into the atmosphere. Clearing ofplant cover disrupts this link in the water cycle and leads

Services Supplied by SoilSoil represents an important component of a

nation�s assets, one that takes hundreds to hundreds ofthousands of years to build up and yet very few years tobe lost. Some civilizations have drawn great strengthfrom fertile soil; conversely, the loss of productivitythrough mismanagement is thought to have ushered manyonce flourishing societies to their ruin (Adams 1981).Today, soil degradation induced by human activities af-flicts nearly 20 percent of the Earth�s vegetated landsurface (Oldeman et al. 1990).In addition to moderating the water cycle, as describedabove, soil provides five other interrelated services (Dailyet al. 1997). First, soil shelters seeds and provides physi-cal support as they sprout and mature into adult plants.The cost of packaging and storing seeds and of anchor-ing plant roots would be enormous without soil.Human-engineered hydroponic systems can grow plantsin the absence of soil, and their cost provides a lowerbound to help assess the value of this service. The costsof physical support trays and stands used in such opera-tions total about US$55,000 per hectare (for the Nutri-ent Film Technique Systems; FAO 1990).

Second, soil retains and delivers nutrients toplants. Tiny soil particles (less than 2 microns in diam-eter), which are primarily bits of humus and clays, carrya surface electrical charge that is generally negative. Thisproperty holds positively charged nutrients�cations suchas calcium and magnesium�near the surface, in prox-imity to plant roots, allowing them to be taken up gradu-ally. Otherwise, these nutrients would quickly be leachedaway. Soil also acts as a buffer in the application offertilizers, holding onto the fertilizer ions until they are

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Figure 8-Early summer inthe Colorado Rockies.These subalpine forestsmitigate flood, drought,and temperature extremes;they soak up rain andsnowmelt and mete it outgradually to streams andto the atmosphere, creat-ing cooling afternoonthunderstorms.

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to potentially large increases in surface runoff, along withnutrient and soil loss. A classic example comes from theexperimental clearing of a New Hampshire forest, whereherbicide was applied to prevent regrowth for a 3-yearperiod after the clearing. The result was a 40 percentincrease in average stream flow. During one four-monthperiod of the experiment, runoff was more than 5 timesgreater than before the clearing (Bormann 1968). On amuch larger scale, extensive deforestation in the Hima-layan highlands appears to have exacerbated recent flood-ing in Bangladesh, although the relative roles of humanand natural forces remain debatable (Ives and Messerli1989). In addition, some regions of the world, such asparts of Africa, are experiencing an increased frequencyand severity of drought, possibly associated with exten-sive deforestation.

Wetlands are particularly well-known for their rolein flood control and can often reduce the need to con-struct flood control structures. Floodplain forests andhigh salt marshes, for example, slow the flow of floodwa-ters and allow sediments to be deposited within the flood-plain rather than washed into downstream bays or oceans.In addition, isolated wetlands such as prairie potholes inthe Midwest and cypress ponds in the Southeast, serveas detention areas during times of high rainfall, delayingsaturation of upland soils and overland flows into riversand thereby damping peak flows. Retaining the integrityof these wetlands by leaving vegetation, soils, and natu-ral water regimes intact can reduce the severity and du-ration of flooding along rivers (Ewel 1997). A relativelysmall area of retained wetland, for example, could havelargely prevented the severe flooding along the Missis-sippi River in 1993.

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Figure 9-Bacteria (Bradyrhizobium japonicum)in a soybean root nodule cell, magnified 3,550times. These bacteria fix atmospheric nitro-gen into a form that can be utilized by plants.

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required by plants. Hydroponic systems supply waterand nutrients to plants without need of soil, but the mar-gin for error is much smaller�even small excesses ofnutrients applied hydroponically can be lethal to plants.Indeed, it is a complex undertaking to regulate the nutri-ent concentrations, pH, and salinity of the nutrient solu-tion in hydroponic systems, as well as the air and solu-tion temperature, humidity, light, pests, and plant dis-eases. Worldwide, the area under hydroponic culture isonly a few thousand hectares and is unlikely to growsignificantly in the foreseeable future; by contrast, glo-bal cropped area is about 1.4 billion hectares (USDA1993).

Third, soil plays a centralrole in the decomposition of deadorganic matter and wastes, and thisdecomposition process also rendersharmless many potential humanpathogens. People generate a tre-mendous amount of waste, includ-ing household garbage, industrialwaste, crop and forestry residues,and sewage from their own popula-tions and their billions of domesti-cated animals. A rough approxima-tion of the amount of dead organicmatter and waste (mostly agricul-tural residues) processed each yearis 130 billion metric tons, about 30percent of which is associated withhuman activities (derived fromVitousek et al. 1986). Fortunately,there is a wide array of decompos-ing organisms�ranging from vul-tures to tiny bacteria�that extractenergy from the large, complex organic molecules foundin many types of waste. Like assembly-line workers, di-verse microbial species process the particular compoundswhose chemical bonds they can cleave and pass along toother species the end products of their specialized reac-tions. Many industrial wastes, including soaps, detergents,pesticides, oil, acids, and paper, are detoxified and de-composed by organisms in natural ecosystems if the con-centration of waste does not exceed the system�s capac-ity to transform it. Some modern wastes, however, arevirtually indestructible, such as some plastics and thebreakdown products of the pesticide DDT.

The simple inorganic chemicals that result fromnatural decomposition are eventually returned to plantsas nutrients. Thus, the decomposition of wastes and the

recycling of nutrients�the fourth service soils provide�are two aspects of the same process. The fertility ofsoils�that is, their ability to supply nutrients to plants�is largely the result of the activities of diverse species ofbacteria, fungi, algae, crustacea, mites, termites, spring-tails, millipedes, and worms, all of which, as groups, playimportant roles. Some bacteria are responsible for �fix-ing� nitrogen, a key element in proteins, by drawing itout of the atmosphere and converting it to forms usableby plants and, ultimately, human beings and other ani-mals. Certain types of fungi play extremely importantroles in supplying nutrients to many kinds of trees. Earth-

worms and ants act as �mechani-cal blenders,� breaking up and mix-ing plant and microbial material andother matter (Jenny 1980). Forexample, as much as 10 metrictonnes of material may passthrough the bodies of earthwormson a hectare of land each year, re-sulting in nutrient rich �casts� thatenhance soil stability, aeration, anddrainage (Lee 1985).

Finally, soils are a key fac-tor in regulating the Earth�s majorelement cycles�those of carbon,nitrogen, and sulfur. The amountof carbon and nitrogen stored insoils dwarfs that in vegetation, forexample. Carbon in soils is nearlydouble (1.8 times) that in plantmatter, and nitrogen in soils is about18 times greater (Schlesinger1991). Alterations in the carbonand nitrogen cycles may be costly

over the long term, and in many cases, irreversible on atime scale of interest to society. Increased fluxes of car-bon to the atmosphere, such as occur when land is con-verted to agriculture or when wetlands are drained, con-tribute to the buildup of key greenhouse gases, namelycarbon dioxide and methane, in the atmosphere(Schlesinger 1991). Changes in nitrogen fluxes causedby production and use of fertilizer, burning of wood andother biomass fuels, and clearing of tropical land lead toincreasing atmospheric concentrations of nitrous oxide,another potent greenhouse gas that is also involved inthe destruction of the stratospheric ozone shield. Theseand other changes in the nitrogen cycle also result inacid rain and excess nutrient inputs to freshwater sys-tems, estuaries, and coastal marine waters. This nutrient

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Figure 10-Sonoran bumble bee (Bombus sonorus) pollinat-ing a flower.

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Issues in Ecology Number 2 Spring 1997influx causes eutrophication of aquatic ecosystems andcontamination of drinking water sources�both surfaceand ground water� by high levels of nitrate-nitrogen(Vitousek et al. 1997).

PollinationAnimal pollination is required for the successful

reproduction of most flowering plants. About 220,000out of an estimated 240,000 species of plants for whichthe mode of pollination has been recorded require ananimal such as a bee or hummingbird to accomplish thisvital task. This includes both wild plants and about 70percent of the agricultural crop species that feed theworld. Over 100,000 different animal species�includ-ing bats, bees, beetles, birds, butterflies, and flies�areknown to provide these free pollination services that as-sure the perpetuation of plants in our croplands, back-yard gardens, rangelands,meadows and forests. Inturn, the continued availabil-ity of these pollinators de-pends on the existence of awide variety of habitat typesneeded for their feeding, suc-cessful breeding, andcompletion of their life cycles(Nabhan and Buchmann1997).

One third of humanfood is derived from plantspollinated by wild pollinators.Without natural pollinationservices, yields of important crops would decline precipi-tously and many wild plant species would become ex-tinct. In the United States alone, the agricultural valueof wild, native pollinators�those sustained by naturalhabitats adjacent to farmlands� is estimated in the bil-lions of dollars per year. Pollination by honey bees, origi-nally imported from Europe, is extremely important aswell, but these bees are presently in decline, enhancingthe importance of pollinators from natural ecosystems.Management of the honey bee in the New World is cur-rently threatened by the movement of, and hybridizationwith, an aggressive African strain of honey bee that wasaccidentally released in Brazil in 1956. Diseases of honeybee colonies are also causing a marked decline in thenumber of managed colonies. Meanwhile, the diversityof natural pollinators available to both wild and domesti-cated plants is diminishing: more than 60 genera of pol-linators include species now considered to be threatened,

endangered or extinct (Buchmann and Nabhan 1996).

Natural Pest Control ServicesHumanity�s competitors for food, timber, cotton,

and other fibers are called pests, and they include nu-merous herbivorous insects, rodents, fungi, snails, nema-todes, and viruses. These pests destroy an estimated 25to 50 percent of the world�s crops, either before or afterharvest (Pimentel et al. 1989). In addition, numerousweeds compete directly with crops for water, light, andsoil nutrients, further limiting yields.

Chemical pesticides, and the strategies by whichthey are applied to fight crop pests, can have harmfulunintended consequences. First, pests can develop resis-tance, which means that higher and higher doses of pes-ticides must be applied or new chemicals developed peri-odically to achieve the same level of control. Resistance

is now found in more than500 insect and mite pests,over 100 weeds, and inabout 150 plant pathogens(WRI 1994). Second, popu-lations of the natural en-emies of pests are decimatedby heavy pesticide use.Natural predators are oftenmore susceptible to syntheticpoisons than are the pestsbecause they have not hadthe same evolutionary expe-rience with overcoming plantchemicals that the pests

themselves have had. And natural predators also typi-cally have much smaller population sizes than those oftheir prey. Destruction of predator populations leads toexplosions in prey numbers, not only freeing target pestsfrom natural controls but often �promoting� othernon-pest species to pest status. In California in the1970s, for instance, 24 of the 25 most important agri-cultural pests had been elevated to that status by theoveruse of pesticides (NRC 1989). Third, exposure topesticides and herbicides may pose serious health risksto humans and many other types of organisms; the re-cently discovered declines in human sperm counts maybe attributable in part to such exposure (Colborn et al.1996).

Fortunately, an estimated 99 percent of poten-tial crop pests are controlled by natural enemies, includ-ing many birds, spiders, parasitic wasps and flies, ladybugs, fungi, viral diseases, and numerous other types of

activities such as gardeningand pet-keeping, nature pho-tography and film-making,bird feeding and watching,hiking and camping,ecotouring and mountaineer-ing, river-rafting and boat-ing, fishing and hunting, andin a wide range of other ac-tivities. For many, nature isan unparalleled source ofwonderment and inspiration,peace and beauty, fulfillment

and rejuvenation (e.g., Kellert and Wilson).

THREATS TO ECOSYSTEM SERVICES

Ecosystem services are being impaired and de-stroyed by a wide variety of human activities. Foremostamong the immediate threats are the continuing destruc-tion of natural habitats and the invasion of non-nativespecies that often accompanies such disruption; in ma-rine systems, overfishing is a major threat. The mostirreversible of human impacts on ecosystems is the lossof native biodiversity. A conservative estimate of therate of species loss is about one per hour, which unfortu-nately exceeds the rate of evolution of new species by afactor of 10,000 or more (Wilson 1989; Lawton andMay 1995). But complete extinction of species is onlythe final act in the process. The rate of loss of local popu-lations of species�the populations that generate eco-system services in specific localities and regions�is or-ders of magnitude higher (Daily and Ehrlich 1995; Hugheset al., in prep.). Destroying other life forms also disruptsthe web of interactions that could help us discover thepotential usefulness of specific plants and animals (Th-ompson 1994). Once a pollinator or a predacious insectis on the brink of extinction, for instance, it would bedifficult to discover its potential utility to farmers.

Other imminent threats include the alteration ofthe Earth�s carbon, nitrogen, and other biogeochemicalcycles through the burning of fossil fuels and heavy useof nitrogen fertilizer; degradation of farmland throughunsustainable agricultural practices; squandering of fresh-water resources; toxification of land and waterways; andoverharvesting of fisheries, managed forests, and othertheoretically renewable systems.

These threats to ecosystem services are drivenultimately by two broad underlying forces. One is rapid,unsustainable growth in the scale of the human enter-

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Figure 11-Ladybug larva (Cycloneda polita) eating an aphid.

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organisms (DeBach 1974).These natural biologicalcontrol agents save farmersbillions of dollars annuallyby protecting crops and re-ducing the need for chemi-cal control (Naylor andEhrlich 1997).

Seed DispersalOnce a seed germi-

nates, the resulting plant isusually rooted in place forthe rest of its life. For plants, then, movement to newsites beyond the shadow of the parent is usually achievedthrough seed dispersal. Many seeds, such as those ofthe dandelion, are dispersed by wind. Some are dispersedby water, the most famous being the seafaring coconut.Many other seeds have evolved ways of getting aroundby using animals as their dispersal agents. These seedsmay be packaged in sweet fruit to reward an animal forits dispersal services; some of these seeds even requirepassage through the gut of a bird or mammal beforethey can germinate. Others require burial�by, say, aforgetful jay or a squirrel which later leaves its cacheuneaten�for eventual germination. Still others areequipped with sticky or sharp, spiny surfaces designedto catch onto a passing animal and go for a long ridebefore dropping or being rubbed off. Without thousandsof animal species acting as seed dispersers, many plantswould fail to reproduce successfully. For instance, thewhitebark pine (Pinus albicaulis), a tree found in theRockies and Sierra Nevada - Cascade Mountains, cannotreproduce successfully without a bird called Clark�s Nut-cracker (Nucifraga columbiana), which chisels pine seedsout of the tightly closed cones and disperses and buriesthem; without this service, the cones do not open farenough to let the seeds fall out on their own. Animalseed dispersers play a central role in the structure andregeneration of many pine forests (Lanner 1996). Dis-ruption of these complex services may leave large areasof forest devoid of seedlings and younger age classes oftrees, and thus unable to recover swiftly from humanimpacts such as land clearing.

Aesthetic Beauty and Intellectual and Spiritual Stimu-lation

Many human beings have a deep appreciation ofnatural ecosystems. That is apparent in the art, reli-gions, and traditions of diverse cultures, as well as in

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Figure 12-The goods and services supplied by this badly deforested and eroded regionof Madagascar are all but gone and would be difficult to restore.

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prise: in population size, in per-capita consumption, andalso in the environmental impacts that technologies andinstitutions generate as they produce and supply thoseconsumables (Ehrlich et al. 1977). The other underlyingdriver is the frequent mismatch between short-term, in-dividual economic incentives and long-term, societalwell-being. Ecosystem services are generally greatly un-dervalued, for a number of reasons: many are not tradedor valued in the marketplace; many serve the public goodrather than provide direct benefits to individual landown-ers; private property owners often have no way to ben-efit financially from the ecosystem services supplied tosociety by their land; and, in fact, economic subsidiesoften encourage the conversion of such lands to other,market-valued activities. Thus, people whose activitiesdisrupt ecosystem services often do not pay directly forthe cost of those lost services. Moreover, society oftendoes not compensate landowners and others who do safe-guard ecosystem services for the economic benefits theylose by foregoing more lucrative but destructive land uses.There is a critical need for policy measures that addressthese driving forces and embed the value of ecosystemservices into decision making frameworks.

VALUATION OF ECOSYSTEM SERVICES

Human society would cease to exist in the ab-sence of ecosystem services. Thus, their immense valueto humanity is unquestionable. Yet quantifying the valueof ecosystem services in specific localities, and measur-ing their worth against that of competing land uses is nosimple task. When tradeoffs must be made in the alloca-tion of land and other resources to competing humanactivities, the resolution often requires a measure of what

is known as the marginal value. In the case of ecosystemservices, for example, the question that might be posedwould be: By how much would the flow of ecosystemservices be augmented (or diminished) with the preserva-tion (or destruction) of the next hectare of forest or wet-land? Estimation of marginal values is complex (e.g.,Bawa and Gadgil 1997; Daily 1997b). Often a qualita-tive comparison of relative values is sufficient� that is,which is greater, the economic benefits of a particulardevelopment project or the benefits supplied by the eco-system that would be destroyed, measured over a timeperiod of interest to people concerned about the well-beingof their grandchildren?

There are, and will remain, many cases in whichecosystem service values are highly uncertain. Yet thepace of destruction of natural ecosystems, and the irre-versibility of most such destruction on a time scale ofinterest to humanity, warrants substantial caution. Valu-ing a natural ecosystem, like valuing a human life, isfraught with difficulties. Just as societies have recog-nized fundamental human rights, however, it may be pru-dent to establish fundamental ecosystem protections eventhough uncertainty over economic values remains. Newinstitutions and agreements at the international andsubnational level will be needed to encourage fair partici-pation in such protections (see, e.g., Heal 1994).

The tremendous expense and difficulty of repli-cating lost ecosystem services is perhaps best illustratedby the results of the first Biosphere 2 �mission,� in whicheight people lived inside a 3.15-acre closed ecosystemfor two years. The system featured agricultural land andreplicas of several natural ecosystems such as forestsand even a miniature ocean. In spite of an investment ofmore than $200 million in the design, construction, and

13

Issues in Ecology Number 2 Spring 1997operation of this modelearth, it proved impossibleto supply the material andphysical needs of the eightBiospherians for the in-tended 2 years. Many un-pleasant and unexpectedproblems arose, including adrop in atmospheric oxygenconcentration to 14% (thelevel normally found at anelevation of 17,500 feet),high spikes in carbon diox-ide concentrations, nitrousoxide concentrations highenough to impair the brain,an extremely high level ofextinctions (including 19 of25 vertebrate species and allpollinators brought into theenclosure, which would haveensured the eventual extinc-tion of most of the plantspecies as well), overgrowthof aggressive vines and al-gal mats, and populationexplosions of crazy ants,cockroaches, and katydids.Even heroic personal effortson the part of the Biospherians did not suffice to makethe system viable and sustainable for either humans ormany nonhuman species (Cohen and Tilman 1996).

MAJOR UNCERTAINTIES

Society would clearly profit by further investigation intosome of the following broad research questions so thatwe might avoid on Biosphere 1, the earth, unpleasantsurprises like those that plagued the Biosphere 2 project(Holdren 1991; Cohen and Tilman 1996; Daily 1997b):

• What is the relative impact of various human activi-ties upon the supply of ecosystem services?

• What is the relationship between the condition of anecosystem�that is, relatively pristine or heavilymodified�and the quantity and quality of ecosys-tem services it supplies?

• To what extent do ecosystem services depend uponbiodiversity at all levels, from genes to species tolandscapes?

• To what extent have vari-ous ecosystem services al-ready been impaired? Andhow are impairment and riskof future impairment distrib-uted in various regions ofthe globe?• How interdependent aredifferent ecosystem ser-vices? How does exploitingor damaging one influencethe functioning of others?• To what extent, and overwhat time scale, are ecosys-tem services amenable torepair or restoration?• How effectively, and athow large a scale, can ex-isting or foreseeable humantechnologies substitute forecosystem services? Whatwould be the side effects ofsuch substitutions?• Given the current stateof technology and the scaleof the human enterprise,what proportion and spatialpattern of land must remainrelatively undisturbed, lo-

cally, regionally, and globally, to sustain the deliveryof essential ecosystem services?

CONCLUSIONS

The human economy depends upon the services performed�for free� by ecosystems. The ecosystem services sup-plied annually are worth many trillions of dollars. Eco-nomic development that destroys habitats and impairsservices can create costs to humanity over the long termthat may greatly exceed the short-term economic ben-efits of the development. These costs are generally hid-den from traditional economic accounting, but are none-theless real and are usually borne by society at large.Tragically, a short-term focus in land-use decisions oftensets in motion potentially great costs to be borne byfuture generations. This suggests a need for policiesthat achieve a balance between sustaining ecosystemservices and pursuing the worthy short-term goals ofeconomic development.

Figure 13-The production of this meal benefited from manyecosystem services, including natural pest control, pollina-tion, maintenance of soil fertility, purification of water, andmoderation of climate.

14


ACKNOWLEDGMENTS

We thank the Packard Foundation and the PewFoundation for financial support.

REFERENCES

Adams, R. McC. 1981. Heartland of Cities: Surveys of AncientSettlement and Land Use on the Central Floodplain of theEuphrates, Chicago: University of Chicago Press.

Alexander, S., S. Schneider, and K. Lagerquist. 1997. Ecosystemservices:Interaction of Climate and Life. Pages 71-92 in G.Daily, editor. Nature�s Services: Societal Dependence onNatural Ecosystems. Island Press, Washington, D.C.

Allegre, C. and S. Schneider. 1994. The evolution of the earth. Sci-entific American 271: 44-51.

Bawa, K. and M. Gadgil. 1997. Ecosystem services, subsistenceeconomies and conservation of biodiversity. Pages 295-310in G. Daily, editor. Nature�s Services: Societal Dependenceon Natural Ecosystems. Island Press, Washington, D.C.

Bormann, F., G. Likens, D. Fisher, and R. Pierce. 1968. Nutrient lossaccelerated by clear-cutting of a forest ecosystem. Science159: 882-884.

Buchmann, S.L. and G.P. Nabhan. 1996. The Forgotten Pollinators.Island Press, Washington, D.C.

Chanway, C. 1993. Biodiversity at risk: soil microflora. Pages229-238 in M. A. Fenger, E. H. Miller, J. A. Johnson, andE. J. R. Williams, editors. Our Living Legacy: Proceedingsof a Symposium on Biological Diversity. Royal British Columbia Museum, Victoria, Canada.

Cohen, J.E. and D. Tilman. 1996. Biosphere 2 and biodiversity: Thelessons so far. Science 274: 1150-1151.

Colborn, T., D. Dumanoski, and J. P. Myers. 1996. Our Stolen Fu-ture. Dutton, New York.

Daily, G.C. 1997a. Introduction: What are ecosystem services? Pages1-10 in G. Daily, editor. Nature�s Services: Societal De-pendence on Natural Ecosystems. Island Press, Washing-ton, D.C.

Daily, G.C. 1997b. Valuing and safeguarding Earth�s life supportsystems. Pages 365-374 in G. Daily, editor. Natures Ser-vices: Societal Dependence on Natural Ecosystems. IslandPress, Washington, D.C.

Daily, G.C., P.A. Matson, and P.M. Vitousek. 1997. Ecosystem ser-vices supplied by soil. Pages 113-132 in G. Daily, editor.Nature�s Services: Societal Dependence on Natural Eco-systems. Island Press, Washington, D.C.

Daily, G.C. and P.R. Ehrlich. 1995. Population diversity and thebiodiversity crisis. Pp. 41-51 in C. Perrings, K.G. Maler,C. Folke, C.S. Holling and B.O. Jansson (eds.), BiodiversityConservation: Problems and Policies, Dordrecht, KluwerAcademic Press.

DeBach, P. 1974. Biological Control by Natural Enemies. CambridgeUniversity Press, London.

Diamond, J. 1991. The Rise and Fall of the Third Chimpanzee. Ra-dius, London. Dobson, A. 1995. Biodiversity and humanhealth. Trends in Ecology and Evolution 10: 390-391.

Dowling, H.F. 1977. Fighting Infection. Harvard Univ. Press, Cam-bridge, MA.

Ehrlich, P.R. and A.H. Ehrlich. 1981. Extinction. Ballantine, NewYork.

Ehrlich, P.R., A.H. Ehrlich, and J.P. Holdren. 1977. Ecoscience: Popu-lation, Resources, Environment. Freeman and Co., San Fran-cisco.

Ewel, K. 1997. Water quality improvement: evaluation of an ecosys-tem service. Pages 329-344 in G. Daily, editor. Nature�sServices: Societal Dependence on Natural Ecosystems. Is-land Press, Washington, D.C.

Farnsworth, N.R., O. Akerele, A.S. Bingel, D.D. Soejarto, and Z.-G.Guo. 1985. Medicinal plants in therapy. Bulletin of theWorld Health Organization 63: 965-981.

Felder, A. J. and D. M. Nickum. 1992. The 1991 economic impactof sport fishing in the United States. American SportfishingAssociation, Alexandria, Virginia.

FAO (United Nations Food and Agriculture Organization). 1990.Soilless Culture for Horticultural Crop Production. Rome:FAO. Grifo, F. and J. Rosenthal, editors. 1997. Biodiversityand Human Health. Island Press, Washington, D.C.

Hall, D.O., F. Rosillo-Calle, R.H. Williams, and J. Woods. 1993. Bio-mass for energy: supply prospects. Pages 593-651 in T.Johansson, H. Kelly, A. Reddy, and R. Williams, editors.Renewable Energy: Sources for Fuels and Electricity. IslandPress, Washington, D.C.

Heal, G. 1994. Formation of international environmental agreements.Pages 301-332 in C. Carraro, editor, Trade, Innovation,Environment. Kluwer Academic Publishers, Dordrecht.

Hillel, D. 1991. Out of the Earth: Civilization and the Life of theSoil. The Free Press, New York.

Holdren, J. P. 1991. �Report of the planning meeting on ecologicaleffects of human activities.� National Research Council,11-12 October, Irvine, California, mimeo.

Holdren, J.P. and P.R. Ehrlich. 1974. Human population and the glo-bal environment. American Scientist 62: 282-292.

Hughes, J.B., G.C. Daily, and P.R. Ehrlich. In prep. The importance,extent, and extinction rate of global population diversity.

Ives, J. and B. Messerli. 1989. The Himalayan Dilemma: ReconcilingDevelopment and Conservation, London: Routledge.

Jenny, H. 1980. The Soil Resource. Springer-Verlag, New York.Kaufman, L. and P. Dayton. 1997. Impacts of marine resource ex

traction on ecosystem services and sustainability. Pages275-293 in G. Daily, editor. Nature�s Services: SocietalDependence on Natural Ecosystems. Island Press, Wash-ington, D.C.

Kellert, S.R. and E.O. Wilson, editors. 1993. The Biophilia Hypoth-esis. Island Press, Washington, D.C.

Lanner, R.M. 1996. Made for Eachother: A Symbiosis of Birds andPines. Oxford University Press, New York.

Lawton, J. and R. May, editors. 1995. Extinction Rates. OxfordUniversity Press, Oxford.

Lee, K. 1985. Earthworms: Their Ecology and Relationships withSoils and Land Use. Academic Press, New York.

Leung, A.Y. and S. Foster. 1996. Encyclopedia of Common NaturalIngredients Used in Food, Drugs, and Cosmetics. John Wiley& Sons, Inc., New York.

McCormick, K.D., M.A. Deyrup, E.S. Menges, S.R. Wallace, J.Meinwald, and T. Eisner. 1993. Relevance of chemistry toconservation of isolated populations: the case of volatileleaf components of Dicerandra mints. Proc. Nat. Acad.Sci. USA 90: 7701-7705.

15

Issues in Ecology Number 2 Spring 1997Myers, N. 1983. A Wealth of Wild Species. Westview Press, Boul-

der, CO. Myers, N. 1997. The worlds forests and theirecosystem services. Pages 215-235 in G. Daily, editor.Nature�s Services: Societal Dependence on Natural Eco-systems. Island Press, Washington, D.C.

Nabhan, G.P. and S.L. Buchmann. 1997. Pollination services:Biodiversity�s direct link to world food stability. Pages133-150 in G. Daily, editor. Nature�s Services: SocietalDependence on Natural Ecosystems. Island Press, Wash-ington, D.C.

National Research Council (NRC). 1989. Alternative Agriculture.National Academy Press, Washington, D.C.

National Research Council (NRC). 1992. Managing Global GeneticResources: The U.S. National Plant Germplasm System.National Academy Press, Washington, D.C.

Naylor, R. and P. Ehrlich. The value of natural pest control services inagriculture. Pages 151-174 in G. Daily, editor. Nature�sServices: Societal Dependence on Natural Ecosystems. Is-land Press, Washington, D.C.

Oldeman, L., V. van Engelen, and J. Pulles. 1990. �The extent ofhuman-induced soil degradation, Annex 5� of L. R.Oldeman, R. T. A. Hakkeling, and W. G. Sombroek, WorldMap of the Status of Human-Induced Soil Degradation: AnExplanatory Note, rev. 2d ed. Wageningen: InternationalSoil Reference and Information Centre.

Overgaard-Nielsen, C. 1955. Studies on enchytraeidae 2: Field stud-ies. Natura Jutlandica 4: 5-58.

Peterson, C.H. and J. Lubchenco. 1997. On the value of marineecosystem services to society. Pages 177-194 in G. Daily,editor. Nature�s Services: Societal Dependence on Natu-ral Ecosystems. Island Press, Washington, D.C.

Pimentel, D., C. Harvey, P. Resosudarmo, K. Sinclair, D. Kurz, M.McNair, S. Crist, L. Shpritz, L. Fitton, R. Saffouri, and R.Blair. 1995. �Environmental and economic costs of soilerosion and conservation benefits.� Science 267:1117-1123.

Pimentel, D., L. McLaughlin, A. Zepp, B. Lakitan, T. Kraus, P.Kleinman, F. Vancini, W. Roach, E. Graap, W. Keeton, andG. Selig. 1989. Environmental and economic impacts ofreducing U.S. agricultural pesticide use. Handbook of PestManagement in Agriculture 4: 223-278.

Postel, S. and S. Carpenter. 1997. Freshwater ecosystem services.Pages 195-214 in G. Daily, editor. Nature�s Services:Societal Dependence on Natural Ecosystems. Island Press,Washington, D.C. Prescott-Allen, R. and C. Prescott-Allen.1990. How many plants feed the world? Conservation Bi-ology 4: 365-374.

Principe, P.P. 1989. The economic significance of plants and theirconstituents as drugs. Pages 1-17 in H. Wagner, H. Hikino,and N.R. Farnsworth, editors. Economic and MedicinalPlant Research, Vol. 3, Academic Press, London.

Reid, W.V., S.A. Laird, C.A. Meyer, R. Gamez, A. Sittenfeld, D. Janzen,M. Gollin, and C. Juma. 1996. Biodiversity prospecting.Pages 142-173 in M. Balick, E. Elisabetsky, and S. Laird,editors. Medicinal Resources of the Tropical Forest:Biodiversity and Its Importance to Human Health. Colum-bia Univ. Press, New York.

Rouatt, J. and H. Katznelson.1961. A study of bacteria on the rootsurface and in the rhizosphere soil of crop plants. J. Ap-plied Bacteriology 24: 164-171.

Sala, O.E. and J.M. Paruelo. 1997. Ecosystem services in grass-lands. Pages 237-252 in G. Daily, editor. Nature�s Ser-vices: Societal Dependence on Natural Ecosystems. IslandPress, Washington, D.C.

Salati, E. 1987. The forest and the hydrological cycle. Pages 273-294in R. Dickinson, editor. The Geophysiology of Amazonia.John Wiley and Sons, New York.

Schlesinger, W. 1991. Biogeochemistry: An Analysis of GlobalChange. Academic Press, San Diego.

Schneider, S. and P. Boston, editors. 1991. Scientists on Gaia. MITPress, Boston.

Schneider, S. and R. Londer. 1984. The Coevolution of Climate andLife. Sierra Club Books, San Francisco.

Shiklomanov, I.A. 1993. World fresh water resources. Pp. 13-24 inP. Gleick, editor. Water in Crisis: A Guide to the World�sFresh Water Resources. Oxford University Press, New York.

Shukla, J., C. Nobre, and P. Sellers. 1990. Amazon deforestationand climate change. Science. 247: 1322-1325.

Tilman, D. 1997. Biodiversity and ecosystem functioning. Pages93-112 in G. Daily, editor. Nature�s Services: SocietalDependence on Natural Ecosystems. Island Press, Wash-ington, D.C.

Thompson, J.N. 1994. The Coevolutionary Process. Chicago Univ.Press, Chicago. United Nations Food and Agriculture Or-ganization (UNFAO). 1993. Marine Fisheries and the Lawof the Sea: A Decade of Change. Fisheries Circular No.853, Rome.

United Nations Food and Agriculture Organization (UNFAO). 1994.FAO Yearbook of Fishery Statistics. Volume 17.

United States Department of Agriculture (USDA). 1993. World Ag-riculture: Trends and Indicators, 1970-91. Washington,DC: USDA.

Vitousek, P., P. Ehrlich, A. Ehrlich, and P. Matson. 1986. Humanappropriation of the products of photosynthesis. BioScience36: 368-373.

Vitousek, P., J. Aber, R. Howarth, G. Likens, P. Matson, D. Schindler,W. Schlesinger, and D. Tilman. 1997. Human alteration ofthe global nitrogen cycle: causes and consequences. [COMPLETE]

Wilson, E.O. 1987. The little things that run the world: The impor-tance and conservation of invertebrates. Conservation Bi-ology 1: 344-346. Wilson, E.O. 1989. Threats tobiodiversity. Scientific American Sept: 108-116.

World Bank. 1991. Agricultural Biotechnology: The Next GreenRevolution? World Bank Technical Paper no. 133. Wash-ington, D.C.

World Resources Institute (WRI). 1994. World Resources: A Guideto the Global Environment. Oxford University Press, Ox-ford.

FOR MORE INFORMATION

About the Panel of ScientistsThis report presents the consensus reached by a

panel of 11 scientists chosen to include a broad array ofexpertise in this area. This report underwent peer reviewand was approved by the Board of Editors of Issues inEcology. The affiliations of the members of the panel ofscientists are:

environment. All reports undergo peer review and mustbe approved by the editorial board before publication.

Editorial Board of Issues in EcologyDr. David Tilman, Editor-in-Chief, Department of Ecol-ogy, Evolution and Behavior, University of Minnesota,St. Paul, MN 55108-6097. E-mail: [email protected]

Board membersDr. Stephen Carpenter, Center for Limnology, University

of Wisconsin, Madison, WI 53706Dr. Deborah Jensen, The Nature Conservancy, 1815

North Lynn Street, Arlington, VA 22209Dr. Simon Levin, Department of Ecology & Evolutionary

Biology, Princeton University, Princeton, NJ08544-1003

Dr. Jane Lubchenco, Department of Zoology, OregonState University, Corvallis, OR 97331-2914

Dr. Judy L. Meyer, Institute of Ecology, The University ofGeorgia, Athens, GA 30602-2202

Dr. Gordon Orians, Department of Zoology, Universityof Washington, Seattle, WA 98195

Dr. Lou Pitelka, Appalachian Environmental Laboratory,Gunter Hall, Frostburg, MD 21532

Dr. William Schlesinger, Departments of Botany andGeology, Duke University, Durham, NC 27708-0340

Additional CopiesTo receive additional copies of this report or pre-

vious Issues in Ecology, please contact:

Public Affairs OfficeEcological Society of America

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Special thanks to the U.S. Environmental Protec-tion Agency Office of Sustainable Ecosystems and Com-munities for supporting printing and distribution of thisdocument.

Cover photo credits, clockwise from top left:Nadine Cavender, Nadine Cavender, Nadine Cavender,Claude Cavender, Jr., Nadine Cavender, unknown, ClaudeCavender, Jr., and unknown.


16

Dr. Gretchen C. Daily, Panel Chair, Department of Bio-logical Sciences, Stanford University, Stanford, CA 94305

Dr. Susan Alexander, Earth Systems Science and Policy,California State University, Monterey Bay, 100 CampusCenter, Seaside, CA 93955

Dr. Paul R. Ehrlich, Department of Biological Sciences,Stanford University, Stanford, CA 94305

Dr. Larry Goulder, Department of Economics, StanfordUniversity, Stanford, CA 94305

Dr. Jane Lubchenco, Department of Zoology, OregonState University, Corvallis, OR 97331

Dr. Pamela A. Matson, Environmental Science Policy andManagement, University of California, Berkeley, CA94720

Dr. Harold A. Mooney, Department of Biological Sciences,Stanford University, Stanford, CA 94305

Dr. Sandra Postel, Global Water Policy Project, 107 Lark-spur Drive, Amherst, MA 01002

Dr. Stephen H. Schneider, Department of Biological Sci-ences, Stanford University, Stanford, CA 94305

Dr. David Tilman, Department of Ecology, Evolution andBehavior, University of Minnesota, St. Paul, MN 55108-609

Dr. George M. Woodwell, Woods Hole Research Center,P.O. Box 296, Woods Hole, MA 02543

Much of the information in this report was de-rived from G. Daily, editor. 1997. Nature�s Services:Societal Dependence onNatural Ecosystems. IslandPress, Washington, D.C.

About the Science WriterYvonne Baskin, a science writer, edited the re-

port of the panel of scientists to allow it to more effec-tively communicate its findings with non-scientists.

About Issues in EcologyIssues in Ecology is designed to report, in lan-

guage understandable by non-scientists, the consensusof a panel of scientific experts on issues relevant to the

lAbout Issues in Ecology

Issues in Ecology is designed to report, in language understandable by non-scientists, theconsensus of a panel of scientific experts on issues relevant to the environment. Issues inEcology is supported by the Pew Scholars in Conservation Biology program and by the Eco-logical Society of America. It is published at irregular intervals, as reports are completed. Allreports undergo peer review and must be approved by the Editorial Board before publication.

Issues in Ecology is an official publication of the Ecological Society of America, the nation�sleading professional society of ecologists. Founded in 1915, ESA seeks to promote theresponsible application of ecological principles to the solution of environmental problems.For more information, contact the Ecological Society of America, 2010 Massachusetts Av-enue, NW, Suite 400, Washington, DC, 20036. ISSN 1092-8987

Benefits Supplied to Human Societies by Natural Ecosystems

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