Tropical rainforests—adapted to a thermally stable climate—are suggested to be particularly vulnerable to global warming, but this hypothesis remains poorly evaluated due to data scarcity. This project uses a unique elevation gradient experiment in Rwanda to explore if projected global warming will lead to exceedance of biochemical thermal tolerance limits in different tropical tree species. The experiment includes 5400 trees of 20 species with contrasting ecological strategies, grown at three sites with large differences in climate (18-24 °C mean daytime temperature; 1050-2100 mm precipitation) and water supply treatments (irrigation, rainfall exclusion). Our past research on photosynthesis and leaf thermal regulation have demonstrated large heat stress and associated mortality in some species. Here we propose new measurements and modelling to explore heat stress impacts for a broader range of species and at larger spatial scale. Results have important implications for tree community composition and, thus, carbon storage and biodiversity, of tropical forests in a warmer world. The project brings together different departments and disciplines (ecophysiology, remote sensing, modelling) and is highly relevant for BECC’s research strategy. Close involvement and interactions with key stakeholders facilitates efficient use of the research results in society.