Impacts of economic degradation on avian functional diversity

Abstract Past harvesting has led to forests with reduced economic potential across portions of the northeastern United States. Tree species composition and structure vary with the reduction of this economic potential (i.e. forest economic degradation). These changes may lead to unknown consequences for the ecosystem functions provided by wildlife. We investigated the functional diversity of avian communities and its relationship to forest economic degradation. We specifically examined the ecosystem functions of seed dispersal, nutrient cycling, and insect pest control. We found that the most economically degraded forests had the lowest functional diversity across all ecosystem functions. However, the least economically degraded forests did not have the highest functional diversity. Instead, the highest functional diversity was present in stands with moderate economic degradation levels. Stands with moderate economic degradation supported increased tree species diversity and canopy structure, likely driving an increase in functional diversity. Additionally, we found important relationships between forest structure and specific avian traits that influence ecosystem functions. For example, birds that have larger hand-wing index (and thus greater dispersal ability) were positively associated with stands that showed larger tree diameter. Stands with larger tree diameters were also positively associated with birds which exhibited caching behavior. We provide specific silvicultural recommendations to enhance avian functional diversity and its associated ecosystem functions.