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Aim: Tree crowns determine light interception, carbon and water exchange. Thus, understanding the factors causing tree crown allometry to vary at the tree and stand level matters greatly for the development of future vegetation modelling and for the calibration of remote sensing products. Nevertheless, we know little about large-scale variation and determinants in tropical tree crown allometry. In this study, we explored the continental variation in scaling exponents of site-specific crown allometry and assessed their relationships with environmental and stand-level variables in the tropics. Location: Global tropics. Time period: Early 21st century. Major taxa studied: Woody plants. Methods: Using a dataset of 87,737 trees distributed among 245 forest and savanna sites across the tropics, we fitted site-specific allometric relationships between crown dimensions (crown depth, diameter and volume) and stem diameter using power-law models. Stand-level and environmental drivers of crown allometric relationships were assessed at pantropical and continental scales. Results: The scaling exponents of allometric relationships between stem diameter and crown dimensions were higher in savannas than in forests. We identified that continental crown models were better than pantropical crown models and that continental differences in crown allometric relationships were driven by both stand-level (wood density) and environmental (precipitation, cation exchange capacity and soil texture) variables for both tropical biomes. For a given diameter, forest trees from Asia and savanna trees from Australia had smaller crown dimensions than trees in Africa and America, with crown volumes for some Asian forest trees being smaller than those of trees in African forests. Main conclusions: Our results provide new insight into geographical variability, with large continental differences in tropical tree crown allometry that were driven by stand-level and environmental variables. They have implications for the assessment of ecosystem function and for the monitoring of woody biomass by remote sensing techniques in the global tropics.
Bibliographical noteFunding Information:
This work is the product of a postdoctoral project (G.J.L.P.) funded by Wallonia‐Brussels‐International (WBI). We thank Dr Andrew Kerkhoff and two anonymous reviewers for their insightful comments on an earlier version of this manuscript. The major portion of the tree crown data was collected with the support of NERC, including Tropical Biomes in Transition (TROBIT; NE/D005590/1/), AMAZONICA (NE/F005806/1), and additional grants to the RAINFOR network from the Moore Foundation (#1656), support for the AfriTRON and T‐Forces networks from the European Research Council (Advanced Grant 291585) and a University of Leeds NERC PhD studentship to L.B. T.R.F. and O.L.P. were also supported by NERC grant NE/N011570/1. T.J. was supported by a U.K. NERC Independent Research Fellowship (grant number: NE/S01537X/1). A part of these data was acquired by the Sustainable Landscapes Brazil project supported by the Brazilian Agricultural Research Corporation (EMBRAPA), the U.S. Forest Service, and USAID, and the U.S. Department of State. We are grateful to Aurora Levesley and ForestPlots.net for archiving the major portion of the tree crown data compiled under this study and connecting the lead authors to data owners (ForestPlots Project #44). We thank colleagues and additional research projects with their respective funding agencies that have shared crown data (including SEOSAW with NE/P008755/1; DynAfFor and P3FAC projects with grant numbers CZZ1636.01D and CZZ1636.02D; International Foundation for Science with grant number D/5822‐1; National Natural Science Foundation of China with grant number 31700356; Gatsby Plants; CAPES and ABC‐CNPq grant 004/96, Brazil; Manchester Metropolitan University). We are grateful to Professor Jon Lloyd for helpful comments on earlier versions of the manuscript and for coordinating the TROBIT data collection. We gratefully acknowledge Dr Sandra Patiño (deceased) for the crown depth data she collected in numerous long‐term RAINFOR forest plots across Amazonia.
© 2020 The Authors. Global Ecology and Biogeography published by John Wiley & Sons Ltd
Copyright 2021 Elsevier B.V., All rights reserved.
- crown allometry
- stand-level variable
- tropical biomes
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