Tree diversity is changing across tropical Andean and Amazonian forests in respone to global change

Climate and atmospheric changes are impacting forest function and structure worldwide, but their effects on tropical forest diversity are unclear. Nowhere is the scientific challenge greater than in the Andes and the Amazon, which together include the world’s most diverse forests. Here, using permanent plots spanning four decades of intact lowland and montane forest dynamics, we test for long-term change in species richness and assess the influence of climate and other variables. We show that at a continental scale, species richness appears stable, but this masks significant regional variation. Species richness increased in Northern Andean and Western Amazon plots, yet declined in the Central Andes, Guyana Shield, and Central-Eastern Amazon. Overall, warmer, drier, and more seasonal forests lost species, while those at higher elevations, in less-fragmented areas, and with faster rates of tree turnover, experienced increases. Region specific drivers, particularly precipitation seasonality and demographic factors, modulated these trends. The results highlight the variety of ways in which Amazon-Andes forests are changing, and the critical need to preserve large-scale ecosystem integrity to conserve local tree diversity. If we can do this, Northern Andean forests in particular can provide a critical refuge for species increasingly displaced by climate change.