Ecosystem Services:Benefits Supplied to Human Societies by Natural Ecosystems
Published by the Ecological Society of America Number 2, Spring 1997 Ecosystem Services: Benefits Supplied to Human Societies by Natural Ecosystems Issues in Eco logy
Issues in Ecology Number 2 Spring 1997 Ecosystem Services: Benefits Supplied to Human Societies by Natural Ecosystems SUMMARY Human societies derive many sential goods from natural esy fuelwood.timber. ang pharm al produ These represent important an sof the econ without which human civilizations would cease to thrive.These include the purification of air and water,detoxification and decomposition of wastes,regulation of climate,regeneration of soil fertility.and production and maintenance of biodiversity,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 energy and operating across a rocess of waste disposal,for ple,involves the life cycles of bacte ria as we ide cycles of major chemic eleme as carbon an are worth many ars annually.Yet because most of these benefits are not traded in economic markets,they carry no pric 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 nature and value of Earth's life tems have largely been their disruption oss highlighted their importance m o defores has h elatedly reve led e regulating the water cycle- in particular,in mitigating floods,droughts,the erosive forces of wind and rain.and siting of dams and irrigation canals.Today,escalating impacts of human activities on forests,wetlands,and other natural ecosystems imperil the delivery of such services.The primary threats are land use changes that cause losses in biodiversity as 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 depletionof stratospheric oe. 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,hum alter virtually all of Earth' emaining 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 very large mbers of species and populations arere quired to sustain ecosvstem 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 vital ecosystem services and pursuing the worthy short-term goals of economic development
Issues in Ecology Number 2 Spring 1997 1 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 services without which human civilizations would cease to thrive. These include the purification of air and water, detoxification and decomposition of wastes, regulation of climate, regeneration of soil fertility, and production and maintenance of biodiversity, 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 energy and operating across a wide range of space and time scales. The process of waste disposal, for example, involves the life cycles of bacteria as well as the planet-wide cycles of major chemical elements such as carbon and nitrogen. 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 nature and value of Earths life support systems have largely been ignored until their disruption or loss highlighted their importance. For example, deforestation has belatedly revealed the critical role forests serve in regulating the water cycle -- in particular, in mitigating floods, droughts, the erosive forces of wind and rain, and silting of dams and irrigation canals. Today, escalating impacts of human activities on forests, wetlands, and other natural ecosystems imperil the delivery of such services. The primary threats are land use changes that cause losses in biodiversity as 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 Earths 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 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 vital ecosystem services and pursuing the worthy short-term goals of economic development
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 fhrlich enco.Pamela A.Matson.Harold A.Moon INTRODUCTION purification of air and water mitigation of droughts and floods Many societies today have technological capa- generation and preservation of soils and renewal of bilities undreamed of in centuries past.Their citizens their fertility. have such a global command of resources that even foods detoxification and decomposition of wastes flown in fresh from all over the planet are taken for pollination of crops and natural vegetation. pled from the limita dispersal of seeds. nd soils.These de 。and moy sed so much attention upor men t of nutrients e vast majority of potential agricultura 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 erosion by waves other aspects of our well-being. protection from the sun's harmful ultraviolet rays These biological underpinnings ar enc mpassed artial stabilization of climate. in the system s services. ather extremes and thei acts d proce through whic 0 ral ecosystems,and the species that are part of them 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,biomass fu- blurred,we emphasize the natural end of the spectrum els,natural fibers,and many phar naceuticals.industrial for three related reasons.First,the services flowing from oducts and thei The ha cosystems are grea ndervalued by P tant partsof For the most part. they are not tra ded in forr market: the human economy.In addition to the production of and so do not send price signals that wam 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 forest in Colorado,filtering and pu- rifying air and water
12 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 Many societies today have technological capabilities undreamed of in centuries past. Their citizens have such a global command of resources that even foods flown in fresh from all over the planet are taken for granted, and daily menus are decoupled from the limitations of regional growing seasons and soils. These developments have focused so much attention upon human-engineered and exotic sources of fulfillment that they divert attention from the local biological underpinnings that remain essential to economic prosperity and other aspects of our well-being. These biological underpinnings are encompassed in the phrase ecosystem services, which refers to a wide range of conditions and processes through which natural ecosystems, and the species that are part of them, help sustain and fulfill human life. These services maintain biodiversity and the production of ecosystem goods, such as seafood, wild game, forage, timber, biomass fuels, natural fibers, and many pharmaceuticals, industrial products, and their precursors. The harvest and trade of these goods represent important and familiar parts of the human economy. In addition to the production of goods, ecosystem services support life through (Holdren and 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 suns harmful ultraviolet rays. • partial stabilization of climate. • moderation of weather extremes and their impacts. • provision of aesthetic beauty and intellectual stimulation that lift the human spirit. Although the distinction between natural and human-dominated ecosystems is becoming increasingly blurred, we emphasize the natural end of the spectrum, for three related reasons. First, the services flowing from natural ecosystems are greatly undervalued by society. For the most part, they are not traded in formal markets and so do not send price signals that warn of changes in their supply or condition. Furthermore, few people are conscious of the role natural ecosystem services play in Figure 1-Aspen (Populus tremuloides) forest in Colorado, filtering and purifying air and water. Photo by J. Robert Stottlemeyer/Biological Photo Service
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 wood for construction,fuel,and other uses generating those ecosystem goods that are traded in the directly for food,drink.spices,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 only be a start.since one would then need to consider inpart,in standard which those usedi Dacterla. ngi,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 matter:the insects,bats.and birds that pollinate flow of the gaseous composition of the atmosphere through ers:and the grasses,herbs.and trees that hold soil in fossil fuel burning are difficult or impossible to reverse a hird if av The clea of this is that no nd ntinue, kno tions species ven appr will dra tically alter Earth' remain ing 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 for hundreds of millions to billion deter re critical to the functionin are so funda I to life that mining which species of a parti osystem easy to take service for gran nted,and s large in s us lake oil fertility as an example hard to imagine that human activities could irreparably crucial to the chemical conversion and physical transter disrupt them. Perhaps a thought experiment that re of essential nutrients to higher plants. 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 earthworms are to em. their relatives.50.OO nd L ngs trying to n rou And t tally is only the begi 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 microorganisms: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 bacteri on Earth.The big question facing hum an colonists wo (Overgaard-Nielsen955:Rouatt and then be.which of Earth's millic on would Cha y 1993).Which must colonists bri ng to the to be rted to the moon to make sterile sur to assure lus and plant growth.soil renewa face habitable? waste disposal,and so on?Most of these soil-dwelling One could tackle that question systematicall 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 Figure 2-Woman carrying treetrunk for boatmaking in a fishing village on Chiloe Island, Chile. Natural forests remain an important source of wood for construction, fuel, and other uses. Photo by Taylor Ricketts generating those ecosystem goods that are traded in the marketplace. As a result, this lack of awareness helps drive the conversion of natural ecosystems to human-dominated systems (e.g., wheatlands or oil palm fields), whose economic value can be expressed, at least in part, in standard currency. The second reason to focus on natural ecosystems is that many human-initiated disruptions of these systems -- such as introductions of exotic species, extinctions of native species, and alteration of the gaseous composition of the atmosphere through fossil fuel burning -- are difficult or impossible to reverse on any time scale relevant to society. Third, if awareness is not increased and current trends continue, humanity will dramatically alter Earths remaining natural ecosystems within a few decades (Daily 1997a, b). The lack of attention to the vital role of natural ecosystem services is easy to understand. Humanity came into being after most ecosystem services had been in operation for hundreds of millions to billions of years. These services are so fundamental to life that they are easy to take for granted, and so large in scale that it is hard to imagine that human activities could irreparably disrupt them. Perhaps a thought experiment that removes these services from the familiar backdrop of the Earth is the best way to illustrate both the importance and complexity of ecosystem services, as well as how ill-equipped humans are to recreate them. Imagine, for example, human beings trying to colonize the moon. Assume for the sake of argument that the moon had already miraculously acquired some of the basic conditions for supporting human life, such as an atmosphere, a climate, and a physical soil structure similar to those on Earth. The big question facing human colonists would then be, which of Earths millions of species would need to be transported to the moon to make that sterile surface habitable? One could tackle that question systematically by first choosing from among all the species exploited directly for food, drink, spices, fiber, timber, pharmaceuticals, and industrial products such as waxes, rubber, and oils. Even if one were highly selective, the list could amount to hundreds or even thousands of species. And that would only be a start, since one would then need to consider which species are crucial to supporting those used directly: the bacteria, fungi, and invertebrates that help make soil fertile and break down wastes and organic matter; the insects, bats, and birds that pollinate flowers; and the grasses, herbs, and trees that hold soil in place, regulate the water cycle, and supply food for animals. The clear message of this exercise is that no one knows which combinations of species -- or even approximately how many -- are required to sustain human life. Rather than selecting species directly, one might try another approach: Listing the ecosystem services needed by a lunar colony and then guessing at the types and numbers of species required to perform each. Yet determining which species are critical to the functioning of a particular ecosystem service is no simple task. Let us take soil fertility as an example. Soil organisms are crucial to the chemical conversion and physical transfer of essential nutrients to higher plants. But the abundance of soil organisms is absolutely staggering. Under a square-yard of pasture in Denmark, for instance, the soil is inhabited by roughly 50,000 small earthworms and their relatives, 50,000 insects and mites, and nearly 12 million roundworms. And that tally is only the beginning. The number of soil animals is tiny compared to the number of soil microorganisms: a pinch of fertile soil may contain over 30,000 protozoa, 50,000 algae, 400,000 fungi, and billions of individual bacteria (Overgaard-Nielsen 1955; Rouatt and Katznelson 1961; Chanway 1993). Which must colonists bring to the moon to assure lush and continuing plant growth, soil renewal, waste disposal, and so on? Most of these soil-dwelling species have never been subjected to even cursory inspection: no human eye has ever blinked at them through
Issues in Ecology Number Spring 1997 hand hasever typed out aname erated by sport fishing activities.it raises the total to or description of the m,and most man inds hav citedin Postel and spent a mo treflecting on them Yet the sobering Carpenter).The future of these fisheries isinq fact is.as E..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 world's major marine fishing areas are in decline THE CHARACTER OF ECOSYSTEM SERVICES due to overfishing,pollution.and habitat destruction (UNFAO 1993:Kaufman and Dayton 1997). ottmt the moto Eth,e attentior he land, more closely at the service an impo rce of marketable goods 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 poats.sheep.and wide. horses. as well as many crops such rley rye,oats,and other grass 1997八. Production of Ecosystem Goods a wide variety of terrestrial habitats,people hunt game Humanity obtains from natural ecosystems an animals such as watertowl.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 fishe and s nly tra aded in Part ets and.many paces.is n econom mportant sport. markets. catch, example n used directly amounts to about 100 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 mgiAeamh2e7 honey.other foods,and spices are extracted from many 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 fre ter fish worldwide in 1990 totaled as for the re of furniture far nd was d at al (UNFA).Interestingly the vue of paper,cloth,thatch out cent of the world's energy consumption is supplied by the freshwater sport fishery 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 grazing on the Chilean alti- plano Grassland ecos they re the of most domesticanima and many crops.such as wheat,barley,and oats
4 Issues in Ecology Number 2 Spring 1997 Figure 3-Alpaca grazing on the Chilean altiplano. Grassland ecosystems are an important source of animal products; they are also the original habitat of most domestic animals and many crops, such as wheat, barley, and oats. a microscope, no human hand has ever typed out a name or description of them, and most human minds have never spent a moment reflecting on them. Yet the sobering fact is, as E. O. Wilson put it: they dont need us, but we need them (Wilson 1987). THE CHARACTER OF ECOSYSTEM SERVICES Moving our attention from the moon back to Earth, let us look more closely at the services nature performs on the only planet we know that is habitable. Ecosystem services and the systems that supply them are so interconnected that any classification of them is necessarily rather arbitrary. Here we briefly explore a suite of overarching services that operate in ecosystems worldwide. Production of Ecosystem Goods Humanity obtains from natural ecosystems an array of ecosystem goods organisms and their parts and products that grow in the wild and that are used directly for human benefit. Many of these, such as fishes and animal products, are commonly traded in economic markets. The annual world fish catch, for example, amounts to about 100 million metric tons and is valued at between $50 billion and $100 billion; it is the leading source of animal protein, with over 20% of the population in Africa and Asia dependent on fish as their primary source of protein (UNFAO 1993). The commercial harvest of freshwater fish worldwide in 1990 totaled approximately 14 million tons and was valued at about $8.2 billion (UNFAO 1994). Interestingly, the value of the freshwater sport fishery in the U.S. alone greatly exceeds that of the global commercial harvest, with direct expenditures in 1991 totaling about $16 billion. When this is added to the value of the employment generated by sport fishing activities, it raises the total to $46 billion (Felder and Nickum 1992, cited in Postel and Carpenter 1997). The future of these fisheries is in question, however, because fish harvests have approached or exceeded sustainable levels virtually everywhere. Nine of the worlds major marine fishing areas are in decline due to overfishing, pollution, and habitat destruction. (UNFAO 1993; Kaufman and Dayton 1997). Turning our attention to the land, grasslands are an important source of marketable goods, including animals used for labor (horses, mules, asses, camels, bullocks, etc.) and those whose parts or products are consumed (as meat, milk, wool, and leather). Grasslands were also important as the original source habitat for most domestic animals such as cattle, goats, sheep, and horses, as well as many crops, such as wheat, barley, rye, oats, and other grasses (Sala and Paruelo 1997). In a wide variety of terrestrial habitats, people hunt game animals such as waterfowl, deer, moose, elk, fox, boar and other wild pigs, rabbits, and even snakes and monkeys. In many countries, game meat forms an important part of local diets and, in many places, hunting is an economically and culturally important sport. Natural ecosystems also produce vegetation used directly by humans as food, timber, fuelwood, fiber, pharmaceuticals and industrial products. Fruits, nuts, mushrooms, honey, other foods, and spices are extracted from many forest species. Wood and other plant materials are used in the construction of homes and other buildings, as well as for the manufacture of furniture, farming implements, paper, cloth, thatching, rope, and so on. About 15 percent of the worlds energy consumption is supplied by fuelwood and other plant material; in developing countries, such biomass supplies nearly 40 percent of energy consumption (Hall et al. 1993), although the portion of this derived from natural rather than Photo by Taylor Ricketts