Assistant Professor University of Pittsburgh Pittsburgh, Pennsylvania, United States
Habitat heterogeneity is crucial to preserving biodiversity in many ecosystems. One approach to reverse biodiversity declines in heterogeneous landscapes relies on a suite of multiple focal species with differing habitat requirements and sensitivities to threats to guide management decisions. Despite the popularity of this multi-focal species approach, its effectiveness at promoting richness of non-target species has largely been restricted to theoretical tests, not evaluations of implemented programs. Here, we evaluate how a real-world implementation of a multi-focal species conservation program for two imperiled forest bird species, Golden-winged Warbler (GWWA, Vermivora chrysoptera) and Cerulean Warbler (CERW, Setophaga cerulea), influences richness of other forest bird species in forests of the eastern United States. Using data from n=1,875 point count surveys across three central Appalachian states, we fit occupancy models to identify the conditions that promote the highest occupancy of the focal species, predict species richness at sites in each of these conditions, and assess habitat preferences in a community of 65 species of forest birds.
Our model found that species richness at managed sites (26-27 species) was higher than at unmanaged sites (18-22 species). We identified the optimal tree basal area and year since management for GWWA and CERW, as well as predicted species richness in these conditions (GWWA: 10 ft2/acre basal area, 7 years, 26 species; CERW: 50 ft2/acre, 2 years, 27 species). Maximum modeled richness (31 species) was achieved at sites optimally managed for GWWA (10 ft2/acre basal area) but 0-2 years post management. Comparing the 65 species’ occupancy probabilities in these three conditions and unmanaged conditions, we found 20 species were most likely to occupy sites that were in optimal conditions for GWWA, 11 species were most likely to occupy sites in optimal conditions for CERW, 18 species were most likely to occupy sites in conditions associated with maximum richness, and 16 species were most likely to occupy unmanaged sites. Thus, a heterogeneous mixture of sites managed for the two focal species within a matrix of unmanaged habitat is associated with greater landscape-level diversity. Our results show that multi-focal species conservation programs can benefit non-target species when management creates varying forest successional stages, highlighting the importance of heterogeneity in promoting biodiversity.