The interacting effects of climate and land-cover change on bird communities in the United States

Human activities exert numerous, simultaneous pressures on biodiversity. In particular, land cover and climate change are major contributors to biodiversity change, and these pressures can vary spatiotemporally and interact in complex ways. Adding to this complexity is the necessity to evaluate a suite of biodiversity metrics in concert, given that single-metric assessments have proven insufficient for a comprehensive understanding of community dynamics. We examined the effects of interactions between climate and land-cover change on bird communities across the continental United States over nearly three decades. We analyzed temperature and precipitation data alongside data on tree canopy, cropland, urban, and surface-water cover to understand how climate/land-cover change interactions influence observed richness, rarefied richness, and community abundance. Temporal trends in species richness and abundance were both associated with temporal trends in climate and land cover; however, richness responses were variable, while abundances tended to decline across the entire range of climate and land-cover change predictors. These concurrent biodiversity responses suggest that communities lost individuals from more common species, and consequently increased in evenness. Critically, we found that these community changes were jointly shaped by climate and land-cover change in 18 out of 24 biodiversity/climate/land-cover combinations, while climate-change impacts were dominant relative to land-cover change in the remaining six combinations. These results highlight the potential for both positive and negative synergies between climate change and land-cover change.