2026 Articles

Tropical forests are facing increasing risks of exposure to critical temperature thresholds

van Tiel, Nina; Lenczner, Gaston; Rao, Mukund Palat; Grossiord, Charlotte; Tuia, Devis

Understanding how close tropical tree species are to critical temperature thresholds that might impede photosynthetic activity is vital in a world where heat waves have become more severe and frequent. Using remotely sensed surface temperature and species distribution maps, we studied the spatiotemporal variation in the thermal safety margins (TSM, i.e., the difference between , the critical photosynthetic temperature, and the maximum canopy temperature) of tropical tree species in South America, Southeast Asia, and Central Africa during the period 2001–2020. Despite overall high-temperature tolerance with an average of C, we observed a consistent decline in the TSM of tropical forests across the globe. The average pantropical TSM decline was C per decade, with the strongest decline in South America (C per decade). Over the -y period, areas that experienced canopy temperatures surpassing the average across reported species increased from Mha to Mha in the tropics, representing of the studied area. This number increases to when computing areas where temperatures have surpassed the of the most vulnerable reported species. When considering future trends, as predicted by Earth System Models under medium-to-high emission scenarios, average may be exceeded in an area of Mha by and Mha by (over of the studied area), suggesting major feedback to the global carbon cycle and the world’s biodiversity.

Keywords: Tropical Forests, Heat Wave, Tipping Point, Critical Temperature, Climate Change