Local hydrological conditions influence tree diversity and composition across the Amazon basin
Authors: Marca‐Zevallos Manuel J. , Moulatlet Gabriel M. , Sousa Thaiane R. , Schietti Juliana , Coelho Luiz de Souza , Ramos José Ferreira , Lima Filho Diogenes de Andrade , Amaral Iêda Leão , de Almeida Matos Francisca Dionízia , Rincón Lorena M. , Cardenas Revilla Juan David , Pansonato Marcelo Petratti , Gribel Rogério , Barbosa Edelcilio Marques , Miranda Ires Paula de Andrade , Bonates Luiz Carlos de Matos , Guevara Juan Ernesto , Salomão Rafael P. , Ferreira Leandro Valle , Dantas do Amaral Dário , Pitman Nigel C. A. , Vriesendorp Corine , Baker Tim R. , Brienen Roel , Carim Marcelo de Jesus Veiga , Guimarães José Renan da Silva , Núñez Vargas Percy , Huamantupa‐Chuquimaco Isau , Laurance William F. , Laurance Susan G. W. , Andrade Ana , Camargo José Luís , Monteagudo Mendoza Abel , Vasquez Rodolfo , Valenzuela Gamarra Luis , Mogollón Hugo F. , Marimon‐Junior Ben Hur , Marimon Beatriz S. , Killeen Timothy J. , Farias Emanuelle de Sousa , Neill David , de Medeiros Marcelo Brilhante , Simon Marcelo Fragomeni , Terborgh John , Carlos Montero Juan , Licona Juan Carlos , Mostacedo Bonifacio , García‐Villacorta Roosevelt , Araujo‐Murakami Alejandro , Arroyo Luzmila , Villarroel Daniel , Dávila Nállarett , Coelho de Souza Fernanda , Carvalho Fernanda Antunes , Comiskey James A. , Alonso Alfonso , Dallmeier Francisco , Oliveira Alexandre A. , Castilho Carolina V. , Lloyd Jon , Feldpausch Ted R. , Ríos Paredes Marcos , Castaño Arboleda Nicolás , Cárdenas López Dairon , Aymard Corredor Gerardo A. , Di Fiore Anthony , Rudas Agustín , Prieto Adriana , Barbosa Flávia Rodrigues , Noronha Janaína Costa , Rodrigues Domingos de Jesus , Carpanedo Rainiellen de Sá , Honorio Coronado Eurídice N. , Peres Carlos A. , Milliken William , Fuentes Alfredo , Tello J. Sebastián , Cerón Carlos , Klitgaard Bente , Tirado Milton , Sierra Rodrigo , Young Kenneth R. , Rivas‐Torres Gonzalo Francisco , Stevenson Pablo R. , Cano Angela , Wang Ophelia , Baider Cláudia , Barlow Jos , Ferreira Joice , Berenguer Erika , Stropp Juliana , Balslev Henrik , Ahuite Reategui Manuel Augusto , Mesones Italo , Valderrama Sandoval Elvis H. , Gonzales Therany , Pansini Susamar , Reis Neidiane Farias Costa , Sampaio Adeilza Felipe , Vos Vincent Antoine , Palacios Cuenca Walter , Manzatto Angelo Gilberto , Farfan‐Rios William , Silman Miles R. , Garcia‐Cabrera Karina , von Hildebrand Patricio , Guedes Marcelino Carneiro , Costa Janaina Barbosa Pedrosa , Phillips Juan Fernando , Vela César I. A. , de Toledo José Julio , Pauletto Daniela , Valverde Fernando Cornejo , Umaña Maria Natalia , Phillips Oliver L. , Magnusson William E. , ter Steege Hans , Costa Flávia R. C. 
Published: September 2022

Tree diversity and composition in Amazonia are known to be strongly determined by the water supplied by precipitation. Nevertheless, within the same climatic regime, water availability is modulated by local topography and soil characteristics (hereafter referred to as local hydrological conditions), varying from saturated and poorly drained to well‐drained and potentially dry areas. While these conditions may be expected to influence species distribution, the impacts of local hydrological conditions on tree diversity and composition remain poorly understood at the whole Amazon basin scale. Using a dataset of 443 1‐ha non‐flooded forest plots distributed across the basin, we investigate how local hydrological conditions influence 1) tree alpha diversity, 2) the community‐weighted wood density mean (CWM‐wd) – a proxy for hydraulic resistance and 3) tree species composition. We find that the effect of local hydrological conditions on tree diversity depends on climate, being more evident in wetter forests, where diversity increases towards locations with well‐drained soils. CWM‐wd increased towards better drained soils in Southern and Western Amazonia. Tree species composition changed along local soil hydrological gradients in Central‐Eastern, Western and Southern Amazonia, and those changes were correlated with changes in the mean wood density of plots. Our results suggest that local hydrological gradients filter species, influencing the diversity and composition of Amazonian forests. Overall, this study shows that the effect of local hydrological conditions is pervasive, extending over wide Amazonian regions, and reinforces the importance of accounting for local topography and hydrology to better understand the likely response and resilience of forests to increased frequency of extreme climate events and rising temperatures.