Tropical forest responses to climate extremes: an analysis using an individual-based demographic vegetation model

Abstract. Tropical forests play a crucial role in the global carbon and water cycles, yet their response to the climate extremes remains uncertain. Here, an individual-based demographic vegetation model is used to investigate the effects of warming and drought on ecosystem dynamics across three neotropical sites that span a precipitation gradient. By explicitly resolving plant hydraulic constraints and demographic processes, the study provides a mechanistic understanding of forest responses to climate stressors. The results reveal that warming had the strongest impact on carbon assimilation in the wettest sites (Paracou and Barro Colorado Island). This reduction was primarily driven by a rising vapor pressure deficit, which induced hydraulic failure even in the absence of soil moisture depletion. In contrast, the driest site (Tapajos National Forest) exhibited the highest sensitivity to drought, driven by severe soil moisture depletion. The analysis also shows that the timescale of imposed stress matters: short daily hot-dry events led to weaker impacts due to partial recovery between pulses, whereas yearly-scale warming and drought produced much stronger, persistent reductions in productivity. These findings highlight the site-specific vulnerabilities of tropical forests to climate extremes, where VPD-induced hydraulic stress limits carbon assimilation under warming in moist sites, while soil moisture constraints dominate in drier ecosystems.