Reply to De Coster et al.: Exploring the complexity of ecosystem–human health relationships

We agree with De Coster et al. (1) that researchers should assess both positive and negative impacts of changes in the structure, composition, and function of natural systems on human health. In fact, one of the key points of our report (2) is that ecosystem changes can lead to either positive or negative health consequences, or even both at the same time along different dimensions of human health. For example, the loss of a wetland may diminish water-filtration or wave-attenuation services, increasing risk of water-borne disease or flooding, yet simultaneously reduce habitat for Anopheline mosquitoes and associated risk of malaria. In other cases, positive health impacts may be experienced by one population while negative impacts are experienced disproportionately by a different group or by future generations. This mix of positive and negative impacts is why our paper emphasizes that “a particular ecosystem alteration may provide health benefits for one segment of a population while incurring health costs for another” (2). Relationships of human health to ecosystem change are complex, reinforcing the importance of considering whose health is in question, as well as the multiple dimensions of health and the possible trade-offs between both positive and negative impacts.

With respect to De Coster et al.’s (1) examples of disease–ecology relationships, we believe it is important to distinguish between health impacts associated with the presence or absence of particular ecosystems and health impacts associated with alteration or degradation of those ecosystems. For example, De Coster et al. argue that spotted fever and leishmaniasis are common where people are in close contact with forests. However, this information tells us little about how exposure to the disease-causing agents or other dimensions of health would change as the structure, composition, or function of those forests changes. In addition, their statement that malaria in the Amazon basin increases with forest cover is contradicted by other studies that reveal the complex effects of land-use change on mosquitoes, humans, and human–mosquito contacts (3–5). This complexity is an invitation for nuanced research that identifies the conditions under which ecosystem changes lead to specific impacts on well-defined dimensions of the health of a particular population, exactly the research for which our article calls.

From a policy standpoint, we believe this is the most relevant question: How will changes in the state of a particular natural system lead to changes in different dimensions of human health? Answers to this question, enabling policy makers to anticipate and weigh the health consequences of particular decisions, would be of great practical value for both the public health and conservation fields.