Evenness mediates the global relationship between forest productivity and richness
Iris Hordijk, Daniel S. Maynard, Simon P. Hart, Lidong Mo, Hans ter Steege, Jingjing Liang, Sergio de‐Miguel, G.J. Nabuurs, Peter B. Reich, Meinrad Abegg, Constant Yves Adou Yao, Giorgio Alberti, Angélica M. Almeyda Zambrano, Braulio Vílchez Alvarado, Álvarez-Dávila Esteban, 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, 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, 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, Amaral Iêda, Aurélie Dourdain, Engone Obiang Nestor Laurier, Brian J. Enquist, Teresa J. Eyre, Adandé Belarmain Fandohan, Tom M. Fayle, Leandro Valle Ferreira, Ted R. Feldpausch, Leena Finér, Markus Fischer, Christine Fletcher, Lorenzo Frizzera, Javier G. P. Gamarra, Damiano Gianelle, Henry B. Glick, David J. Harris, Andy Hector, Andreas Hemp, Geerten Hengeveld, Bruno Hérault, John Herbohn, Annika Hillers, Eurídice N. Honorio Coronado, Cang Hui, Hyunkook Cho, Thomas Ibanez, Il Bin Jung, Nobuo Imai, Andrzej M. Jagodziński, Bogdan Jaroszewicz, Vivian Johanssen, Carlos Alfredo Joly, Tommaso Jucker, Viktor Karminov, Kuswata Kartawinata, Elizabeth Kearsley, David Kenfack
Abstract
Abstract 1. Biodiversity is an important component of natural ecosystems, with higher species richness often correlating with an increase in ecosystem productivity. Yet, this relationship varies substantially across environments, typically becoming less pronounced at high levels of species richness. However, species richness alone cannot reflect all important properties of a community, including community evenness, which may mediate the relationship between biodiversity and productivity. If the evenness of a community correlates negatively with richness across forests globally, then a greater number of species may not always increase overall diversity and productivity of the system. Theoretical work and local empirical studies have shown that the effect of evenness on ecosystem functioning may be especially strong at high richness levels, yet the consistency of this remains untested at a global scale. 2. Here, we used a dataset of forests from across the globe, which includes composition, biomass accumulation and net primary productivity, to explore whether productivity correlates with community evenness and richness in a way that evenness appears to buffer the effect of richness. Specifically, we evaluated whether low levels of evenness in speciose communities correlate with the attenuation of the richness–productivity relationship. 3. We found that tree species richness and evenness are negatively correlated across forests globally, with highly speciose forests typically comprising a few dominant and many rare species. Furthermore, we found that the correlation between diversity and productivity changes with evenness: at low richness, uneven communities are more productive, while at high richness, even communities are more productive. 4. Synthesis . Collectively, these results demonstrate that evenness is an integral component of the relationship between biodiversity and productivity, and that the attenuating effect of richness on forest productivity might be partly explained by low evenness in speciose communities. Productivity generally increases with species richness, until reduced evenness limits the overall increases in community diversity. Our research suggests that evenness is a fundamental component of biodiversity–ecosystem function relationships, and is of critical importance for guiding conservation and sustainable ecosystem management decisions.