Tropical forests in the Americas are changing too slowly to track climate change.

Understanding the capacity of forests to adapt to climate change is of pivotal importance for conservation science, yet this is still widely unknown. This knowledge gap is particularly acute in high-biodiversity tropical forests. Here, we examined how tropical forests of the Americas have shifted community trait composition in recent decades as a response to changes in climate. Based on historical trait-climate relationships, we found that, overall, the studied functional traits show shifts of less than 8% of what would be expected given the observed changes in climate. However, the recruit assemblage shows shifts of 21% relative to climate change expectation. The most diverse forests on Earth are changing in functional trait composition but at a rate that is fundamentally insufficient to track climate change. Species are expected to shift their ranges as the climate changes, but shifts may not occur fast enough, especially for immobile species such as plants. Two papers in this issue assess the degree to which plant species are tracking climate change in the American tropics, where data availability has constrained inference. Ramírez-Barahona . show that in Mesoamerican cloud forests, climate change and deforestation together have led to a mean upward shift in species ranges since 1979, mainly due to contracting lower range edges. In tropical forests across the Americas, Aguirre-Gutiérrez . found that tree traits are not shifting fast enough to track climate change based on trait-climate relationships, with smaller shifts in montane forests. —Bianca Lopez