The global biogeography of tree leaf form and habit
Haozhi Ma, Thomas W. Crowther, Lidong Mo, Daniel S. Maynard, Susanne S. Renner, Johan van den Hoogen, Yibiao Zou, Jingjing Liang, Sergio de‐Miguel, G.J. Nabuurs, Peter B. Reich, Ülo Niinemets, Meinrad Abegg, Yves C. Adou Yao, Giorgio Alberti, Angélica M. Almeyda Zambrano, Braulio Vílchez Alvarado, Esteban Álvarez‐Dávila, Patricia Álvarez-Loayza, Luciana F. Alves, Christian Ammer, Clara Antón‐Fernández, Alejandro Araujo‐Murakami, Luzmila Arroyo, Valerio Avitabile, Gerardo A. Aymard C., Timothy R. Baker, Radomir Bałazy, Olaf Bánki, Jorcely Barroso, Meredith L. Bastian, Jean‐François Bastin, Luca Birigazzi, Philippe Birnbaum, Robert Bitariho, Pascal Boeckx, Frans Bongers, Olivier Bouriaud, Pedro H. S. Brancalion, Susanne Brandl, Francis Q. Brearley, Roel Brienen, Eben N. Broadbent, Helge Bruelheide, Filippo Bussotti, Roberto Cazzolla Gatti, Ricardo G. César, Goran Češljar, Robin L. Chazdon, Han Y. H. Chen, Chelsea Chisholm, Hyunkook Cho, Emil Cienciala, Connie J. Clark, David B. Clark, Gabriel Dalla Colletta, David A. Coomes, Fernando Cornejo Valverde, José Javier Corral‐Rivas, Philip M. Crim, Jonathan Cumming, Selvadurai Dayanandan, André Luís de Gasper, Mathieu Decuyper, Géraldine Derroire, Ben DeVries, Ilija Djordjević, Jiří Doležal, Aurélie Dourdain, Nestor Laurier Engone Obiang, Brian J. Enquist, Teresa J. Eyre, Adandé Belarmain Fandohan, Tom M. Fayle, Ted R. Feldpausch, Leandro Valle Ferreira, Leena Finér, Markus Fischer, Christine Fletcher, Jonas Fridman, Lorenzo Frizzera, Javier G. P. Gamarra, Damiano Gianelle, Henry B. Glick, David J. Harris, Andy Hector, Andreas Hemp, Geerten Hengeveld, Bruno Hérault, John Herbohn, Martin Herold, Annika Hillers, Eurídice N. Honorio Coronado, Cang Hui, Thomas Ibanez, Iêda Leão do Amaral, Nobuo Imai, Andrzej M. Jagodziński, Bogdan Jaroszewicz, Vivian Kvist Johannsen
Abstract
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.