Human health risks of forest conservation

In PNAS, Myers et al. (1) present a paper in which they discuss adverse effects of ecosystem degradation on human health. We sincerely think that this is one of the more comprehensive papers in this field, but would like to draw attention to a number of findings from studies on Brazilian forest ecosystems that the authors seem to have overlooked.

Conservationists customarily highlight benefits—in terms of goods and services—that result from the protection of natural ecosystems, but they often fail to mention that the latter may also adversely affect human welfare. In their report, Myers et al. indeed convincingly demonstrate that anthropogenic land-use changes can increase the prevalence of several diseases (1), but they overlook the fact that natural forest may also act as wild reservoirs that propitiate disease outbreaks. For example, infections with Rickettsia rickettsii, a major tick-borne zoonotic disease in Brazil that causes spotted fever, mainly occur where humans and dogs live in close contact to forests (2). Additionaly, various vectors of cutaneous and visceral leishmaniasis (sand flies Lutzomyia spp.) are present in an Atlantic Forest region in the state of Rio de Janeiro that is popular with ecotourists (3). Finally, it has been recently shown that malaria incidence tends to increase with forest cover in the Brazilian Amazon (4). Concealing such patterns may hamper a better understanding of relationships between natural ecosystems and human health risks. Indeed, there are many open questions on relationships between landscape structure and disease dynamics (5). For example, what is the functional role of forest fragments in the maintenance of zoonoses? How does the connectivity of forest fragments influence the dispersal of disease vectors? Neglecting these questions may hamper scenarios to minimize human health risks during, for example, forest conservation and restoration (4).

In summary, the purpose of this letter is to urge conservationists to cover the full range of consequences of ecosystem alteration and protection, which may or may not be as anticipated and may or may not contribute to human welfare. In addition to being more ethically correct, we sincerely believe that this impartiality will eventually benefit both man and nature.