Compositional response of Amazon forests to climate change.

Adriane Esquivel‐Muelbert,Adriano José Nogueira Lima,Luisa Fernanda Duque,Frans Bongers,Eliana Jimenez‐Rojas,Raquel Thomas,James Singh,Agustín Rudas,Ted R Feldpausch,Marielos Peña‐Claros,Edmar Almeida De Oliveira,Fernando Cornejo Valverde,Adriana Prieto,Timothy R Baker,Lourens Poorter,Pieter A Zuidema,David Neill,Simon L Lewis,Wendeson Castro,Marisol Toledo,Christopher Baraloto,Hans Ter Steege,Julie Peacock,Ima Célia Guimarães Vieira,Luis Valenzuela Gamarra,Hirma Ramírez‐Angulo,Anthony Di Fiore,Juliana Stropp,Ricardo Keichi Umetsu,Alejandro Araujo‐Murakami,Abel Monteagudo‐Mendoza,Ana Andrade,Omar Aurelio Melo Cruz,Simone Aparecida Vieira,Armando Torres‐Lezama,Lan Qie,Oliver L Phillips,Natalino Silva,Damien Bonal,Anand Roopsind,Peter J Van De Meer,Fernando Elias,David Galbraith,Julien Engel,Zorayda Restrepo Correa,John Terborgh,Yadvinder Malhi,José Luís Camargo,Wannes Hubau,Maxime Réjou‐Méchain,Paulo S Morandi,Gerardo Flores Llampazo,Martin J P Sullivan,Marcos Silveira,Percy Núñez Vargas,Kyle G Dexter,Emanuel Gloor,Gerardo A Aymard C,Javier Silva Espejo,Esteban Álvarez-Dávila,Alexander Parada Gutierrez,Guido Pardo,Luzmila Arroyo,Bruno Hérault,Jos Barlow,Rafael Herrera Fernández,Sophie Fauset,J A Comiskey ,Susan G Laurance ,Antonio Costa ,Roel Brienen ,Everton Cristo De Almeida ,René Boot ,Rafael P Salomão ,César I A Vela ,Níro Higuchi ,Vincent Vos ,Gabriela López-González ,Jorcely Barroso ,Geertje M F Van Der Heijden ,Jérôme Chave ,William F Laurance ,Thomas Ε Lovejoy ,Luiz E O C Aragão ,Rodolfo Vásquez Martínez ,María Cristina Peñuela‐Mora ,Ben Hur Marimon‐Junior ,Nigel C A Pitman ,Nadir Pallqui Camacho ,Georgia Pickavance ,Jhon Del Aguila‐Pasquel ,Eurídice N Honorio Coronado ,Terry L Erwin ,Carlos Alberto Quesada ,Emilio Vilanova Torre ,Nallaret Dávila Cardozo ,P Van Der Hout ,Beatriz Schwantes Marimon ,E.j.m.m Arets ,Clément Stahl ,Pascal Pétronelli ,Víctor Chama Moscoso ,J Lloyd ,Plínio Barbosa De Camargo

doi:10.1111/gcb.14413

Abstract

Most of the planet's diversity is concentrated in the tropics, which includes many regions undergoing rapid climate change. Yet, while climate‐induced biodiversity changes are widely documented elsewhere, few studies have addressed this issue for lowland tropical ecosystems. Here we investigate whether the floristic and functional composition of intact lowland Amazonian forests have been changing by evaluating records from 106 long‐term inventory plots spanning 30 years. We analyse three traits that have been hypothesized to respond to different environmental drivers (increase in moisture stress and atmospheric CO 2 concentrations): maximum tree size, biogeographic water‐deficit affiliation and wood density. Tree communities have become increasingly dominated by large‐statured taxa, but to date there has been no detectable change in mean wood density or water deficit affiliation at the community level, despite most forest plots having experienced an intensification of the dry season. However, among newly recruited trees, dry‐affiliated genera have become more abundant, while the mortality of wet‐affiliated genera has increased in those plots where the dry season has intensified most. Thus, a slow shift to a more dry‐affiliated Amazonia is underway, with changes in compositional dynamics (recruits and mortality) consistent with climate‐change drivers, but yet to significantly impact whole‐community composition. The Amazon observational record suggests that the increase in atmospheric CO 2 is driving a shift within tree communities to large‐statured species and that climate changes to date will impact forest composition, but long generation times of tropical trees mean that biodiversity change is lagging behind climate change.

Highlights

Tropical forests represent the world's most biodiverse ecosystems, as well as providing its largest stores of living carbon and contributing more to biomass productivity than any other biome on the planet
Tree communities have become increasingly dominated by large‐statured taxa, but to date there has been no detectable change in mean wood density or water deficit affiliation at the community level, despite most forest plots having experienced an intensification of the dry season
There has been a significant increase in the potential size (PS) of tree communities: the community weighted mean (CWM) of PS when weighted by basal area increased by 0.03 cm/year or 0.06% per year with basal gains increasing in PS by 0.06 cm/year meaning that plots have been progressively occupied by larger statured genera (Table 2)

Summary

| INTRODUCTION

Tropical forests represent the world's most biodiverse ecosystems, as well as providing its largest stores of living carbon and contributing more to biomass productivity than any other biome on the planet. 1994; Qie et al, 2017), while in Amazonia increases in mortality have caused a recent weakening of the biomass carbon sink (Brienen et al, 2015) It remains unclear whether these structural and dynamic changes are associated with concerted changes in the species richness and composition of Amazonian forests. The forest has clearly responded to these recent fluctuations in climate—for example, tree mortality rates increased markedly during and after drought events causing at least temporary losses of standing biomass (Brienen et al, 2015; Feldpausch et al, 2016; Phillips et al, 2009; Zuleta, Duque, Cardenas, Muller‐Landau, & Davies, 2017). Based on predictions from plant physiology supported by experimental studies, we expect increases in dry season duration or intensity to shift floristic composition towards dry‐affiliated and smaller‐statured genera with high wood density (McDowell & Allen, 2015; Rowland et al, 2015). We examine trends in abundance for individual genera, which allows us to understand which taxa dominate the changes in functional composition

| MATERIALS AND METHODS

| RESULTS

| DISCUSSION

Findings

Graphical Abstract