The creation of protected reserves may be pushing development to neighboring areas, confounding overall conservation efforts in regions where development pressures are high. Such “leakage” — as the displacement is called — makes it difficult to assess the effectiveness of protected areas strategies.
Reviewing the results of a study that found significant leakage near forest concessions in Peru, Robert M. Ewers of the Zoological Society of London and Ana S.L. Rodrigues of Cambridge University report on leakage concerns for conservation and methods for quantifying the effectiveness of nature reserves. The research is published in Trends in Ecology and Evolution.
Leakage in the Peruvian Amazon
The Peruvian study, published by P.J.C. Oliveira and colleagues in 2007 in the journal Science, found that the deforestation rate decreased inside a newly established restricted-use area but increased outside the areas surrounding the forest concessions, “indicating that human impacts had leaked from a restricted land-use area to a nearby, unrestricted area.”
 Forest clearing in Sarawak on the island of Borneo. Courtesy of Google Earth. |
Ewers and Rodrigues say the Peru study shows that “leakage can exaggerate the perceived effectiveness of reserves for reducing human impacts on biodiversity.”
“Leakage might lead to the impression that land-use restrictions are reducing impacts when in fact they might simply be displaced across space and/or time. Consequently, leakage might accelerate the rate at which reserves become isolated habitat remnants embedded in a highly impacted landscape,” the authors write.
“Leakage might affect our perception of the effectiveness of individual reserves, by magnifying differences in human impacts inside and outside their boundaries. For example, a direct comparison of deforestation rates inside versus outside a Peruvian forest concession in 2005 would show a large and significant difference, both because deforestation rates have diminished inside the concession and because they have increased outside the concession.”
“Naturally, reducing human impacts inside reserves is likely to be a good thing in its own right, but it is important to understand that this might be at the expense of reducing conservation options in the adjacent areas,” they continue. “A recent study of the response of land markets to conservation investments found that purchasing land for conservation in a given region might displace development towards biologically valuable areas in the same region, or even to accelerate the pace of development.”
 Forest clearing in Malaysia |
Still, irrespective of leakage, protected areas may have long-term conservation benefits by protecting fragments of natural habitat in landscapes that will otherwise completely converted for human use. Teasing out the effectiveness is tricky, say Ewers and Rodrigues.
“Assessing the positive effect of reserves and separating it from the negative effect of leakage requires a comparison of the levels of human impact — both inside reserves and in the surrounding area — with a baseline level,” they write. “However, establishing such a baseline is not straightforward.”
Ewers and Rodrigues propose using a combination remotely sensed data and on-the-ground observations to establish baselines of expected and observed human impacts inside and outside reserves. The method could help determine “whether the reserve has had the desired outcome of reducing human impacts in the landscape as a whole, or if those impacts have simply been spatially displaced.”
Nevertheless, the overall effectiveness of conservation will be judged by “whether biodiversity across the entire landscape, integrated across areas of restricted and unrestricted land-use, benefits from the creation of reserves,” write the authors.
Robert M. Ewers and Ana S.L. Rodrigues (2008). Estimates of reserve effectiveness are confounded by leakage. Trends in Ecology and Evolution Vol.23 No.3
