Community-level responses to climate change in forests of the eastern United States

Aim Climate change has impacted forest ecosystems, leading to species-level tree migration. However, the impacts of climate change on forest communities are mostly unknown. Here, we assess changes to forest communities at three scales: within-community changes in species composition, individual community spatial shifts and changes across all communities. Location Eastern USA. Major taxa studied Forest tree species. Methods Using a region-wide forest inventory dataset from the United States Department of Agriculture Forest Service's Forest Inventory and Analysis Program with > 70,000 plots, we identified forest communities using the latent Dirichlet allocation method. We analysed changes in species composition within communities and assessed community-level spatial shifts over the last three decades to quantify the responses of individual communities to climate change. We used the distribution of forest communities across climate conditions to predict where communities could migrate to during the study period and compared climate-predicted shifts with observed community shifts. Changes across all communities were modelled as a function of climatic and non-climatic variables using generalized linear mixed-effects models. Results We identified 12 regional forest communities of the eastern USA, which varied in their stability of species composition over the study period. All communities experienced relatively short yet significant shifts in their spatial distribution (median = 8.0 km/decade). Historical climate and changes in seasonal temperature variability were the best predictors of change across all communities. However, the distance and direction of individual community migration were poorly predicted by climate change, and the observed direction was often the opposite of the predicted direction. Main conclusions Forest communities shifted their distributions over the last three decades, but climate change outpaced the rate of community migration. Continued lags between climate change and forest community responses and the lack of migration in the direction predicted by climate change might lead to the inability of forests to keep up with changing climate.