Developing a mitigation hierarchy framework to conserve wetland biodiversity under pressure from development

Abstract

Wetlands are severely affected by human development. About 50 % of their original global extent has been lost, their populations of plants and animals have declined faster than for any other ecosystem, and 25 % of wetland-dependent species are threatened. As the main reason for these declines is habitat loss, often caused by infrastructure development, it is critical to develop conservation strategies targeting this particular pressure. The mitigation hierarchy (MH) provides for a promising solution, outlining how no net loss (NNL) of biodiversity can be achieved through the four steps avoid, minimize, restore, and offset impact losses. Although increasingly applied worldwide, the MH suffers from poor implementation and a lack of standardized methods, impeding practical application and successful conservation. In this study, I develop a landscape-scale MH methodology from scientific best-practices and demonstrate how it can be used to improve impact mitigation efforts in wetlands. By planning on a landscape scale, managers can consider how, and to what degree, many small development impacts together exert a cumulative pressure on natural environments. In the outlined approach, I calculate area-specific wetland conservation values from easily available data on species distributions, species threat level and ecosystem condition, and show how simple spatial analysis can be used to map areas of special importance for avoidance and offsetting. I also show how the same values can be used to determine offset sizes large enough to compensate for residual biodiversity losses. The landscape-scale mitigation planning approach presented here can provide for 1) a rapid assessment of wetland conservation value, 2) early anticipation of potential biodiversity impacts, 3) avoidance of valuable wetlands; reducing offset costs, 4) identification of potentially degraded wetlands for restoration offsets, and 5) a visualization of how NNL of biodiversity can be achieved.