Microclimate and forest density drive plant population dynamics under climate change

Macroclimatic changes are impacting ecosystems worldwide. However, a large portion of terrestrial species live under conditions where impacts of macroclimate change are buffered, such as in the shade of trees, and how this buffering impacts future below-canopy biodiversity redistributions at the continental scale is unknown. Here we show that shady forest floors due to dense tree canopies mitigate severe warming impacts on forest biodiversity, while canopy opening amplifies macroclimate change impacts. A cross-continental transplant experiment in five contrasting biogeographical areas combined with experimental heating and irradiation treatments was used to parametize 25-m resolution mechanistic demographic distribution models and project the current and future distributions of 12 common understorey plant species, considering the effects of forest microclimate and forest cover density. These results highlight microclimates and forest density as powerful tools for forest managers and policymakers to shelter forest biodiversity from climate change.