A biome-dependent distribution gradient of tree species range edges is strongly dictated by climate spatial heterogeneity

Understanding the causes of the arrest of species distributions has been a fundamental question in ecology and evolution. These questions are of particular interest for trees owing to their long lifespan and sessile nature. A surge in data availability evokes a macro-ecological analysis to determine the underlying forces limiting distributions. Here we analyse the spatial distribution of >3,600 major tree species to determine geographical areas of range-edge hotspots and find drivers for their arrest. We confirmed biome edges to be strong delineators of distributions. Importantly, we identified a stronger contribution of temperate than tropical biomes to range edges, adding strength to the notion that tropical areas are centres of radiation. We subsequently identified a strong association of range-edge hotspots with steep spatial climatic gradients. We linked spatial and temporal homogeneity and high potential evapotranspiration in the tropics as the strongest predictors of this phenomenon. We propose that the poleward migration of species in light of climate change might be hindered because of steep climatic gradients.