Assessing Amazon forest vulnerability and resilience to dry periods across soil moisture and microenvironmental gradients

Climate-change-related droughts in the Amazon rainforest can cause widespread tree mortality, resulting in large carbon emissions, with potential feedbacks to regional and global climate (Phillips et al. 2009; Brienen et al. 2015). However, much of our knowledge of tropical forest drought responses comes from deep water table depth (WT) forests. Shallow WT forests are severely under-researched, despite occupying ~50% of the Amazon basin, and being expected to respond differently to drought (Costa, Schietti, Stark, Smith 2022). Recent results indicate that shallow WT areas benefit from moderate drying, which reduces anoxia and extends the growing season (Esteban et al. 2021, Sousa et al. 2022). As such, shallow WT forests may be more resilient to drought, potentially capable of offsetting large carbon losses anticipated from deep WT forests. To accurately project the future of this globally important ecosystem and set conservation priorities, we need to understand the contribution of shallow WT forests to Amazon forest carbon balance and how soil water availability influences tropical forest vulnerability or resilience to drought.

We will investigate how soil water availability (using WT as a proxy) influences Amazon forest responses to seasonal dry periods (and if observed, droughts). Specifically, we will quantify seasonal patterns of key components of forest carbon-vertical leaf area distributions (from ground-based lidar) and tree woody growth (from dendrometers) -and test potential drivers, including soil moisture, microenvironmental conditions, and tree hydraulic strategy.