Human Domination of Earth's Ecosystems Peter M
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: . - : :: : . .. :: .. .. .. .. .. .. ... .. .. ...... ........ .. .... ..... ...... .. ... ... .... ... ..:. : .: :. : :::. ..:. :. .. ...5 .::.X'jC:' jj : 00 ,: ;; ;dA SV D ) 0 Sa C::: dS:: : :'; .SS;d. ;id)fV A .:Q ....;: ..:: ....; .: .: ..0 .....:: Human Domination of Earth's Ecosystems Peter M. Vitousek, HaroldA. Mooney, Jane Lubchenco, Jerry M. Melillo Humanalteration of Earthis substantialand growing. Between one-thirdand one-half interactwith the atmosphere,with aquatic of the land surface has been transformedby human action; the carbon dioxide con- systems,and with surroundingland. More- centrationin the atmosphere has increased by nearly30 percent since the beginningof over, land transformationinteracts strongly the IndustrialRevolution; more atmospheric nitrogen is fixed by humanitythan by all with most other componentsof global en- naturalterrestrial sources combined;more than halfof all accessible surface fresh water vironmentalchange. is put to use by humanity;and about one-quarterof the birdspecies on Earthhave been The measurementof land transforma- drivento extinction. By these and other standards, it is clear that we live on a human- tion on a globalscale is challenging;chang- dominated planet. es can be measuredmore or less straightfor- wardly at a given site, but it is difficult to aggregatethese changesregionally and glo- bally. In contrastto analysesof human al- Aii organismsmodify their environment, reasonablywell quantified;all are ongoing. teration of the global carbon cycle, we and humans are no exception. As the hu- These relativelywell-documented changes cannot install instrumentson a tropical man populationhas grownand the powerof in turn entrain further alterationsto the mountainto collect evidence of land trans- technology has expanded, the scope and functioningof the Earthsystem, most no- formation. Remote sensing is a most useful nature of this modification has changed tably by drivingglobal climatic change (1) technique,but only recentlyhas there been drastically.Until recently, the term "hu- and causingirreversible losses of biological a seriousscientific effortto use high-resolu- man-dominated ecosystems" would have diversity(2). tion civilian satellite imagery to evaluate elicited images of agricultural fields, pas- even the more visible forms of land trans- tures, or uLrbanlandscapes; now it applies Land Transformation formation, such as deforestation, on conti- with greater or lesser force to all of Earth. nental to global scales (3). Many ecosystems are dominated directly by The use of land to yield goods and services Land transformation encompasses a humanity, and no ecosystem on Earth's sur- representsthe most substantialhuman al- wide variety of activities that vary sub- face is free of pervasive human influence. terationof the Earthsystem. Human use of stantially in their intensity and conse- This article provides an overview of hu- land alters the structure and functioning of quences. At one extreme, 10 to 15% of man effects on Earth's ecosystems. It is not ecosystems,and it alters how ecosystems Earth's land surface is occupied by row- intended as a litany of environmental disas- ters, though some disastrous situations are described; nor is it intended either to down- Fig. 1. A conceptual play or to celebrate environmental success- model illustrating hu- Human population manity's direct and indi- Size Resource use es, of which there have been many. Rather, rect effects on the Earth we explore how large humanity looms as a system [modified from presence on the globe-how, even on the (56)]. Human enterprises grandest scale, most aspects of the structure and functioning of Earth's ecosystems can- Agriculture Industry Recreation Internationalcommerce not be understood without accounting for the strong, often dominant influence of humanity. Land Biotic additions We view human alterations to the Earth transformationc andlosses system as operating through the interacting Landclearing Ib Invasion processes summarized in Fig. 1. The growth Forestry En Hunting Grazing Global Fishing of the human population, and growth in the Intensification K biogeochemistry p a resource base used by humanity, is main- Carbon tained by a suite of human enterprises such Nitrogen as agriculture, industry, fishing, and inter- Water Synthetic chemicals national commerce. These enterprises Other elements transform the land surface (through crop- ping, forestry, and urbanization), alter the major biogeochemical cycles, and add or remove species and genetically distinct pop- ulations in most of Earth's ecosystems. Many of these changes are substantial and IT ,' IFll Climate change Loss of biological diversity P. M. Vitousek and H. A. Mooney are in the Department Enhanced of Biological Sciences, Stanford University,Stanford, CA PI Extinctionof species 94305, USA. J. Lubchenco is in the Department of Zool- greenhouse populations ogy, Oregon State University, Corvallis, OR 97331, Aerosols ~~~~~~and USA. J. M. Melillois at the U.S. Office of Science and of ecosystems Technology Policy, Old Executive Office Building, Room Land cover ~~~~~Loss 443, Washington, DC 20502, USA. 494 SCIENCE * VOL. 277 * 25 JULY 1997 * www.sciencemag.org m HUMAN-DOMINATED ECOSYSTEMS: ARTICLES crop agricultureor by urban-industrialar- the reactive chemistryof the troposphere, tion growsto morethan 25%for upwelling eas, and another 6 to 8% has been con- bringing elevated carbon monoxide con- areasand to 35% for temperatecontinen- verted to pastureland (4); these systems centrations and episodes of urban-like tal shelf systems (13). are wholly changed by human activity. At photochemical air pollution to remote Many of the fisheries that capturema- the other extreme,every terrestrialecosys- tropical areas of Africa and South Amer- rine productivityare focused on top pred- tem is affected by increased atmospheric ica; and it causes runoff of sediment and ators,whose removalcan alter marineeco- carbon dioxide (CO2), and most ecosys- nutrientsthat drive substantialchanges in systems out of proportionto their abun- tems have a history of hunting and other stream,lake, estuarine,and coral reef eco- dance. Moreover, many such fisheries low-intensity resource extraction. Be- systems (7-10). have proved to be unsustainable,at least tween these extremes lie grassland and The central importanceof land trans- at our present level of knowledge and semiaridecosystems that are grazed (and formation is well recognized within the control. As of 1995, 22% of recognized sometimesdegraded) by domestic animals, communityof researchersconcerned with marine fisheries were overexploitedor al- and forests and woodlands from which global environmentalchange. Several re- ready depleted, and 44% more were at wood products have been harvested; to- search programsare focused on aspects of their limit of exploitation (14) (Figs. 2 gether, these represent the majority of it (9, 11); recent and substantialprogress and 3). The consequencesof fisheries are Earth'svegetated surface. toward understandingthese aspects has not restricted to their target organisms; The variety of human effects on land been made (3), and much more progress commercial marine fisheries around the makesany attemptto summarizeland trans- can be anticipated. Understanding land worlddiscard 27 million tons of nontarget formationsglobally a matterof semanticsas transformationis a difficult challenge; it animals annually, a quantity nearly one- well as substantialuncertainty. Estimates of requiresintegrating the social, economic, third as largeas total landings(15). More- the fractionof land transformedor degraded and culturalcauses of land transformation over, the dredgesand trawlsused in some by humanity(or its corollary,the fractionof with evaluations of its biophysicalnature fisheries damage habitats substantiallyas the land'sbiological production that is used and consequences. This interdisciplinary they are draggedalong the sea floor. or dominated)fall in the rangeof 39 to 50% approach is essential to predicting the A recent increase in the frequency, (5) (Fig. 2). These numbershave largeun- course, and to any hope of affecting the extent, and duration of harmful algal certainties,but the fact that they arelarge is consequences, of human-caused land blooms in coastal areas (16) suggeststhat not at all uncertain.Moreover, if anything transformation. human activity has affected the base as these estimates understatethe global im- well as the top of marine food chains. pact of land transformation,in that land Oceans Harmfulalgal blooms are sudden increases that has not been transformedoften has in the abundanceof marine phytoplank- been divided into fragmentsby human al- Human alterations of marine ecosystems ton that produce harmful structures or terationof the surroundingareas. This frag- are moredifficult to quantifythan those of chemicals. Some but not all of these phy- mentation affects the species composition terrestrialecosystems, but several kinds of toplankton are stronglypigmented (red or and functioningof otherwiselittle modified informationsuggest that they are substan- brown tides). Algal blooms usually are ecosystems(6). tial. The human populationis concentrat- correlated with changes in temperature, Overall, land transformationrepresents ed near coasts-about 60% within 100 nutrients, or salinity; nutrients in coastal the primarydriving force in the loss of km-and the oceans' productive coastal waters,in particular,are much modifiedby biological diversity worldwide.Moreover, margins