Climate Change and the Emergence of No‐Analog Forest Assemblages in North America

Future climate change is expected to result in tree species shifting their geographic distributions in ways that could reorganize species into assemblages with no contemporary analog. These projected no-analog forests raise concern as their ecological function could similarly shift, which may challenge established conservation and management efforts. Here, we implement a community-level modelling approach to identify the key climatic and topographic drivers of forest composition in North America, and then use these models to predict the distribution of "disappearing" and "novel" forest assemblages in future climate. We applied this modelling technique to both the taxonomic and phylogenetic composition of forest trees, to identify where species turnover may be greatest, and whether species are likely to be replaced with close relatives. Our work shows that approximately 11.9% of contemporary North American forests have low predicted similarity to future forests, and 26.2% of future forests could be compositionally novel compared with contemporary forests, but there was substantial geographic variability in the magnitude of these metrics across the continent. High-elevation regions in the west tend to be nearest to their closest compositional analog, suggesting these regions may be most likely to realize the future predicted composition. This work provides a new approach to understanding how forest composition may shift in future climates in a way that avoids the need for individual species predictions and extends climate-matching approaches with meaningful biological data.