Water table depth modulates productivity and biomass across Amazonian forests

Funding: This work was part of the PhD thesis of the first author, developed at the Graduate Program in Ecology of the National Institute of Amazonian Research (INPA), with a fellowship funded by Coordenação de Aperfeiçoamento de Pessoal de Nível Superior – Brasil (CAPES), Finance Code 001, (88887.141433/2017-00). The authors are also grateful for the financial and research support of the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), Amazonas State Research Foundation (FAPEAM), the Newton Fund via the Natural Environment Research Council (NE/M022021/1 to O.L.P. and F.R.C.C.), PPBio Manaus, Centro de Estudos Integrados da Biodiversidade Amazônica and RAINFOR. We also thank Karina Melgaço, Aurora Levesley and Gabriela Lopez-Gonzalez for curating and managing ForestPlots.net. This was ForestPlots.net Project 26 led by Thaiane Sousa. This is publication number 832 of the Technical Series of the Biological Dynamics of Forest Fragments Project (BDFFP, INPA/STRI). Aim : Water availability is the major driver of tropical forest structure and dynamics. Most research has focused on the impacts of climatic water availability, whereas remarkably little is known about the influence of water table depth and excess soil water on forest processes. Nevertheless, given that plants take up water from the soil, the impacts of climatic water supply on plants are likely to be modulated by soil water conditions. Location : Lowland Amazonian forests. Time period : 1971–2019. Methods : We used 344 long-term inventory plots distributed across Amazonia to analyse the effects of long-term climatic and edaphic water supply on forest functioning. We modelled forest structure and dynamics as a function of climatic, soil-water and edaphic properties. Results : Water supplied by both precipitation and groundwater affects forest structure and dynamics, but in different ways. Forests with a shallow water table (depth