Understanding what controls global leaf type variation in trees is crucial for comprehending their role in terrestrial ecosystems, including carbon, water and nutrient dynamics. Yet our understanding of the factors influencing forest leaf types remains incomplete, leaving us uncertain about the global proportions of needle-leaved, broadleaved, evergreen and deciduous trees. To address these gaps, we conducted a global, ground-sourced assessment of forest leaf-type variation by integrating forest inventory data with comprehensive leaf form (broadleaf vs needle-leaf) and habit(evergreen vs deciduous) records. We found that global variation in leaf habit is primarily driven by isothermality and soil characteristics, while leaf form is predominantly driven by temperature. Given these relationships, we estimate that 38% of global tree individuals are needle-leaved evergreen, 29% are broadleaved evergreen, 27% are broadleaved deciduous and 5% are needle-leaved deciduous. The aboveground biomass distribution among these tree types is approximately 21% (126.4 Gt), 54% (335.7 Gt), 22% (136.2 Gt) and 3% (18.7 Gt), respectively. We further project that, depending on future emissions pathways, 17–34% of forested areas will experience climate conditions by the end of the century that currently support a different forest type, highlighting the intensification of climatic stress on existing forests. By quantifying the distribution of tree leaf types and their corresponding biomass, and identifying regions where climate change will exert greatest pressure on current leaf types, our results can help improve predictions of future terrestrial ecosystem functioning and carbon cycling.

Fil: Peri, Pablo Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro de Investigaciones y Transferencia de Santa Cruz. Universidad Tecnológica Nacional. Facultad Regional Santa Cruz. Centro de Investigaciones y Transferencia de Santa Cruz. Universidad Nacional de la Patagonia Austral. Centro de Investigaciones y Transferencia de Santa Cruz; Argentina

Fil: Reich, Peter B.. University of Minnesota; Estados Unidos. University of Western Sydney; Australia. University of Michigan; Estados Unidos

Fil: de Miguel, Sergio Ruben. Universidad de Lleida; España. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

Fil: Maynard, Daniel S.. University College London; Estados Unidos. Swiss Federal Institute of Technology Zurich; Suiza

Fil: Alberti, Giorgio. Università di Udine; Italia. National Biodiversity Future Center; Italia

Fil: Abegg, Meinrad. Swiss Federal Institute for Forest, Snow and Landscape Research; Suiza

Fil: Araujo Murakami, Alejandro. Museo de Historia natural Noel kempff Mercado; Bolivia

Fil: Antón Fernández, Clara. Norwegian Institute of Bioeconomy Research; Noruega

Fil: van den Hoogen, Johan. Swiss Federal Institute of Technology Zurich; Suiza