Variation in stem mortality rates determines patterns of above-ground biomass in Amazonian forests: implications for dynamic global vegetation models

Michelle O. Johnson, David Galbraith, Manuel Gloor, Hannes De Deurwaerder, Matthieu Guimberteau, Anja Rammig, Kirsten Thonicke, Hans Verbeeck, Celso Von Randow, Abel Monteagudo, Oliver L. Phillips, Roel J.W. Brienen, Ted R. Feldpausch, Gabriela Lopez Gonzalez, Sophie Fauset, Carlos A. Quesada, Bradley Christoffersen, Philippe Ciais, Gilvan Sampaio, Bart KruijtPatrick Meir, Paul Moorcroft, Ke Zhang, Esteban Alvarez-Davila, Atila Alves De Oliveira, Ieda Amaral, Ana Andrade, Luiz E.O.C. Aragao, Alejandro Araujo-Murakami, Eric J.M.M. Arets, Luzmila Arroyo, Gerardo A. Aymard, Christopher Baraloto, Jocely Barroso, Damien Bonal, Rene Boot, Jose Camargo, Jerome Chave, Alvaro Cogollo, Fernando Cornejo Valverde, Antonio C. Lola Da Costa, Anthony Di Fiore, Leandro Ferreira, Niro Higuchi, Euridice N. Honorio, Tim J. Killeen, Susan G. Laurance, William F. Laurance, Juan Licona, Thomas Lovejoy, Yadvinder Malhi, Bia Marimon, Ben Hur Marimon, Darley C.L. Matos, Casimiro Mendoza, David A. Neill, Guido Pardo, Marielos Peña-Claros, Nigel C.A. Pitman, Lourens Poorter, Adriana Prieto, Hirma Ramirez-Angulo, Anand Roopsind, Agustin Rudas, Rafael P. Salomao, Marcos Silveira, Juliana Stropp, Hans Ter Steege, John Terborgh, Raquel Thomas, Marisol Toledo, Armando Torres-Lezama, Geertje M.F. van der Heijden, Rodolfo Vasquez, Ima Cèlia Guimarães Vieira, Emilio Vilanova, Vincent A. Vos, Timothy R. Baker

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Abstract

Understanding the processes that determine aboveground biomass (AGB) in Amazonian forests is important for predicting the sensitivity of these ecosystems to environmental change and for designing and evaluating dynamic global vegetation models (DGVMs). AGB is determined by inputs from woody productivity (woody NPP) and the rate at which carbon is lost through tree mortality. Here, we test whether two direct metrics of tree mortality (the absolute rate of woody biomass loss and the rate of stem mortality) and/or woody NPP, control variation in AGB among 167 plots in intact forest across Amazonia. We then compare these relationships and the observed variation in AGB and woody NPP with the predictions of four DGVMs. The observations show that stem mortality rates, rather than absolute rates of woody biomass loss, are the most important predictor of AGB, which is consistent with the importance of stand size-structure for determining spatial variation in AGB. The relationship between stem mortality rates and AGB varies among different regions of Amazonia, indicating that variation in wood density and height/diameter relationships also influence AGB. In contrast to previous findings, we find that woody NPP is not correlated with stem mortality rates, and is weakly positively correlated with AGB. Across the four models, basin-wide average AGB is similar to the mean of the observations. However, the models consistently overestimate woody NPP, and poorly represent the spatial patterns of both AGB and woody NPP estimated using plot data. In marked contrast to the observations, DGVMs typically show strong positive relationships between woody NPP and AGB. Resolving these differences will require incorporating forest size structure, mechanistic models of stem mortality and variation in functional composition in DGVMs
Original languageEnglish
Pages (from-to)3996-4013
JournalGlobal Change Biology
Volume22
Issue number12
DOIs
Publication statusPublished - 2016

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Johnson, M. O., Galbraith, D., Gloor, M., De Deurwaerder, H., Guimberteau, M., Rammig, A., ... Baker, T. R. (2016). Variation in stem mortality rates determines patterns of above-ground biomass in Amazonian forests: implications for dynamic global vegetation models. Global Change Biology, 22(12), 3996-4013. https://doi.org/10.1111/gcb.13315