doi: 10.1289/ehp.120-a152.
Accounting for nature's benefits: the dollar value of ecosystem services
- PMID: 22469778
- PMCID: PMC3339477
- DOI: 10.1289/ehp.120-a152
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Accounting for nature's benefits: the dollar value of ecosystem services
Environ Health Perspect.
2012 Apr.
No abstract available
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Quantifying the Impact of Ecosystem Disturbances on Infectious Disease The idea that ecosystem services influence human health has been around for quite a while, says Rick Ostfeld, a disease ecologist at the Cary Institute of Ecosystem Studies in Millbrook, New York. Only more recently have researchers begun investigating the hypothesis that services provided by healthy ecosystems include moderating infectious disease. There is growing evidence—some experimental and some correlational—that a decline in biodiversity can boost disease transmission and that “preserving intact ecosystems and their endemic biodiversity should generally reduce the prevalence of infectious diseases,” Ostfelt and colleagues wrote in a recent review on the topic in Nature. When ecosystems are simplified or fragmented, as human development is wont to do, the changes often favor proliferation of more efficient vectors and wildlife reservoirs of infectious disease—chiefly arthropods and rodents, respectively—partly by reducing the population of predators that keep these creatures in check. The most efficient natural reservoirs of disease “tend to be the weedy, resilient species with a ‘live fast and die young’ life history,” says Ostfeld. “Those are the species left standing when we disturb or degrade the ecosystem.” He explains that predators that feed on the natural reservoirs tend to be more sensitive and disappear first when ecosystems are disturbed. There is direct evidence supporting an inverse relationship between biodiversity and infectious disease. In South America, for instance, converting forest to cereal production increases rodent populations, contributing to epidemics of viral hemorrhagic fever, says Samuel Myers, a research scientist in the Department of Environmental Health of the Harvard School of Public Health. Dams, irrigation systems, and deforestation have been linked to increases in malaria and schistosomiasis, diarrheal diseases are associated with road building, and dengue has been tied to urbanization. Nonetheless, “[t]here is a big gap between the research showing associations between changes in natural systems and health outcomes, and actually being able to quantify the specific health benefits or costs of incremental changes in the system,” Myers and colleague Jonathan Patz of the University of Wisconsin–Madison wrote in the 2009 edition of Annual Review of Environment and Resources. Illustration by Michael S. Klein
A Complex Undertaking The science that underlies ecosystem services is cumbersome. Taylor Ricketts, director of the Gund Institute for Ecological Economics at the University of Vermont, measured the productivity of bees as pollinators of coffee plantations in Costa Rica. The bees live in forests near the plantations. In a series of carefully controlled and lengthy experiments, he found that coffee plants within a kilometer of the forest were fully pollinated, whereas those beyond a kilometer received insufficient pollination, producing 20% fewer coffee beans. Using these results, Ricketts calculated that two forest patches were contributing $62,000 worth of pollination services annually to a single coffee farm. If those forests were destroyed, that farm would suffer a 7% drop in productivity, he estimated. Thus, the present value of the annual $62,000 would be the value of the service provided by those forest patches. However, pollination is just one of many ecosystem services performed by that forest, with others including carbon sequestration, support of biodiversity, and water purification, to name just a few, says Ricketts. At this early stage of the science of valuating ecosystem services, often it is impractical to determine the value of more than one or a few services. Part of the difficulty of determining the value of all the services within an ecosystem is that the methods for obtaining the necessary information are often so different for each service. In some cases, the studies required may be enormously time-consuming or otherwise difficult. For example, Ricketts’ pollination studies involved comparing coffee production among five similar trees at each of three different distances from the forest, after hand pollinating flowers on some branches at each location to simulate maximum pollination activity, allowing bees to do the job on other flowers, and covering some flowers to simulate no pollination. Measuring a forest’s capacity to purify water might involve determining the purity of a stream that runs through the forest after passing a pollution source by assaying pollutants at regular distances to determine how quickly they are declining. Assaying biodiversity involves taking a census of all plants, animals, and invertebrates on a plot of land. Ricketts says a thorough determination of ecosystem services from a single piece of land might involve 20 different studies for as many services. Illustration by Michael S. Klein
References
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- The MA represents the work of 1,360 experts from 95 countries. The reports focus on the connections between how changes in ecosystem services—usually involving deterioration—affect human well-being, and, based on these findings, call into question the ability of ecosystems to sustain future generations.
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