S CIENCE’ S C OMPASS ● REVIEW REVIEW: ECOLOGY Economic Reasons for Conserving Wild Nature Andrew Balmford,1* Aaron Bruner,2 Philip Cooper,3 Robert Costanza,4† Stephen Farber,5 Rhys E. Green,1,6 Martin Jenkins,7 Paul Jefferiss,6 Valma Jessamy,3 Joah Madden,1 Kat Munro,1 Norman Myers,8 Shahid Naeem,9 Jouni Paavola,3 Matthew Rayment,6 Sergio Rosendo,3 Joan Roughgarden,10 Kate Trumper,1 R. Kerry Turner3 matched estimates of the marginal values of On the eve of the World Summit on Sustainable Development, it is timely to assess goods and services delivered by a biome progress over the 10 years since its predecessor in Rio de Janeiro. Loss and degradation when relatively intact, and when converted of remaining natural habitats has continued largely unabated. However, evidence has to typical forms of human use. To ensure been accumulating that such systems generate marked economic benefits, which the we did not neglect private benefits of con- available data suggest exceed those obtained from continued habitat conversion. We version, studies were only included if they estimate that the overall benefit:cost ratio of an effective global program for the covered the most important marketed conservation of remaining wild nature is at least 100:1. goods, as well as one or more nonmarketed services delivering local social or global benefits. We cross-validated figures for in- umans benefit from wild nature (1)in per hectare for each of 17 services across 16 dividual goods and services with other es- very many ways: aesthetically and cul- biomes and then extrapolating to the globe by timates from similar places. Finally, we Hturally; via the provision of ecological multiplying by each biome’s area, the Costanza checked that the comparisons across differ- services such as climate regulation, soil forma- team estimated the aggregated annual value of ent states of a biome used the same valua- tion, and nutrient cycling; and from the direct nature’s services (updated to 2000 US$) to lie tion techniques for particular goods and harvest of wild species for food, fuel, fibers, in the range of $18 trillion to $61 trillion (1012), services. Our survey uncovered only five and pharmaceuticals (2). In the face of increas- around a rough average of ϳ$38 trillion. These examples that met all these criteria. Here, ing human pressures on the environment, these figures are of similar size to global gross na- we summarize their findings, with all fig- benefits should act as powerful incentives to tional product (GNP), but have been criticized ures expressed as net present values (NPVs, conserve nature, yet evaluating them has by some in the economic community (5–9). in 2000 US$ haϪ1), and using the discount proved difficult because they are mostly not One problem is that such macroeconomic rates considered by the authors [see Fig. 1 captured by conventional, market-based eco- extrapolations are inconsistent with microeco- and supplemental online material (10) for nomic activity and analysis. nomic theory: extrapolation from the margin to further details]. In 1997, Costanza et al. published a synthe- a global total should incorporate knowledge Two studies quantified net marginal ben- sis (3) of more than 100 attempts to value about the shape of the demand curve (3, 5–8). In efits of different human uses of tropical forest ecosystem goods and services using a range of practice, it is very likely that per-unit demand areas. Kumari compared the values obtained techniques including hedonic pricing, contin- for nonsubstitutable services escalates rapidly as from timber plus a suite of nontimber forest gent valuation, and replacement cost methods supply diminishes, so that simple grossing-up of products (NTFPs), as well as the values of (4). Using case studies to derive average values marginal values (as is also done in calculating water supply and regulation, recreation, and GNP from prices) will probably underestimate the maintenance of carbon stocks and endan- true total values. On the other hand, high local gered species, for forests under a range of 1Conservation Biology Group, Department of Zoology, values of services such as tourism may not be management regimes in Selangor, Malaysia 2 University of Cambridge, Cambridge CB2 3EJ, UK. Cen- maintained if extrapolated worldwide. In addi- (11). Compared with two methods of re- ter for Applied Biodiversity Science at Conservation In- ternational, 1919 M Street, NW, Suite 600, Washington, tion, while some policy decisions are made us- duced-impact logging, high-intensity, unsus- DC 20036, USA. 3Centre for Social and Economic Re- ing macroeconomic indicators, many others are tainable logging was associated with greater search on the Global Environment (CSERGE), School of made at the margin, and so are more appropri- private benefits through timber harvesting (at Environmental Sciences, University of East Anglia, Nor- ately informed by marginal rather than total least at high discount rates and over one wich NR4 7TJ, UK. 4Center for Environmental Science, Biology Department and Institute for Ecological Eco- valuations (9). harvesting cycle), but reduced social and nomics, University of Maryland, Box 38, Solomons, MD Another problem with the original estimate global benefits (through loss of NTFPs, flood 20688, USA. 5Graduate School of Public and Internation- is that landscapes can yield substantial (albeit protection, carbon stocks, and endangered al Affairs, University of Pittsburgh, Pittsburgh, PA 15260, rather different) flows of goods and services species). Summed together, the total econom- USA. 6The Royal Society for the Protection of Birds, The Lodge, Sandy, Bedfordshire SG19 2DL, UK. 7UN Environ- after, as well as before, conversion by humans ic value (TEV) of forest was some 14% ment Programme–World Conservation Monitoring Cen- (which is of course why people convert them). greater when placed under more sustainable tre (UNEP-WCMC), 219 Huntingdon Road, Cambridge A clearer picture of the value of retaining habitat management (at ϳ$13,000 compared with CB3 ODL, UK. 8Green College, Woodstock Road, Oxford in relatively undisturbed condition might there- $11,200 haϪ1). OX2 6HG, UK; and Upper Meadow, Old Road, Heading- fore be obtained by estimating not the gross A study from Mount Cameroon, Cam- ton, Oxford OX3 8SZ, UK. 9Department of Zoology, University of Washington, 24 Kincaid Hall, Box 351800, values of the benefits provided by natural bi- eroon, comparing low-impact logging with Seattle, WA 98195–1800, USA.10Department of Biolog- omes, but rather the difference in benefit flows more extreme land-use change again found ical Sciences, Stanford University, Stanford, CA 94305, between relatively intact and converted versions that private benefits favor conversion, this USA. of those biomes. time to small-scale agriculture (12). Howev- *To whom correspondence should be addressed.E- er, a second alternative to retaining the forest, mail: [email protected] Net Marginal Benefits conversion to oil palm and rubber planta- †Address after Sept.2002: Gund Institute of Ecolog- ical Economics, The University of Vermont, Burling- To address these concerns, we reviewed tions, in fact yielded negative private benefits ton, VT 05405, USA. more than 300 case studies, searching for once the effect of market distortions was 950 9 AUGUST 2002 VOL 297 SCIENCE www.sciencemag.org S CIENCE’ S C OMPASS removed. Social benefits from NTFPs, sedi- did sustainable fishing (15). The social ben- vices outweighs the marketed marginal ben- mentation control, and flood prevention efits of sustainable exploitation, arising from efits of conversion, often by a considerable were highest under sustainable forestry, as coastal protection and tourism, were also lost amount. Across the four biomes studied, were global benefits from carbon storage upon dynamiting reefs. As a consequence, mean losses in TEV due to conversion run and a range of option, bequest, and exis- the TEV of retaining an essentially intact at roughly one-half of the TEV of relatively tence values. Overall, the TEV of sustain- reef was almost 75% higher than that of intact systems (mean ϭ 54.9%; SE ϭ able forestry was 18% greater than that of destructive fishing (at ϳ$3300 compared 13.4%; n ϭ 4). This is certainly not to say small-scale farming (ϳ$2570 compared with $870 haϪ1). that conversion has never been economical- with $2110 haϪ1), whereas plantations had One clear message from our survey is ly beneficial; in most instances, past clear- a negative TEV. the paucity of empirical data on the central ance of forests and wetlands for prime Three other biomes yielded single studies question of the changes in delivery of agricultural land and other forms of devel- meeting our criteria. Analysis of a mangrove goods and services arising from the conver- opment probably benefited society as a system in Thailand revealed that conversion sion of natural habitats for human use. For whole. But unless the present case studies for aquaculture made or the range of ser- sense in terms of vices and biomes short-term private examined in the lit- benefits, but not once erature are extreme- external costs were ly unrepresentative factored in (13). The (and we know of no global benefits of reason why this carbon sequestration should be the case), were considered to be our synthesis indi- similar in intact and cates that at present, degraded systems. conversion of re- However, the sub- maining habitat for stantial social bene- agriculture, aquac- fits associated with ulture, or forestry the original man- often does not make grove cover—from sense from the per- timber, charcoal, spective of global NTFPs, offshore sustainability. fisheries, and storm protection—fell to Continuing Losses almost zero follow- These results there- ing conversion. Sum- fore provide a clear ming all measured and compelling eco- goods and services, nomic case, alongside the TEV of intact sociocultural and mangroves exceeded moral arguments (16– that of shrimp farm- 18), for us to strength- ing by around 70% en attempts to con- (ϳ$60,400 com- serve what remains of pared with $16,700 natural ecosystems.