A Double-Edged Sword: Crown Illumination Amplifies the Drought Vulnerability of Large Trees in a Tropical Forest

Tan, Zheng-Hong

JOURNAL OF GEOPHYSICAL RESEARCH-BIOGEOSCIENCES

2026

131

5

Hu, YH; Lin, LX

Tropical droughts are becoming more frequent and intense, which has raised concerns about their impact on tropical forests. However, the specific impacts of drought on these forests and the underlying response mechanisms remain poorly understood. Understanding these dynamics is critical, as tropical forests are vital for maintaining high biodiversity, storing large amounts of biomass, and sustaining high rates of carbon assimilation. To investigate the response of a tropical rainforest to severe drought, we analyzed a comprehensive 12-year data set of continuous dendrometer recordings from over 2,700 trees. Data showed that biomass increment was significantly inhibited during the drought period. Interestingly, multidimensional analyses based on 10 key functional traits revealed limited explanatory power for both drought and recovery effects, suggesting that intrinsic functional signals might be largely masked by high environmental heterogeneity. Furthermore, the linear mixed model identified that crown illumination, tree size and season-specifically their three-way interaction-as the dominant drivers of the drought effect (conditional R 2 = 0.674). Conversely, competition index and habitat type showed relatively limited effects. Our results indicate that the widely observed vulnerability of large trees is not a simple function of tree size but an interactive response mediated by crown illumination and seasonal dynamics. We propose that the photosynthetic benefits of high light acquisition in large trees are likely counterbalanced by the amplified atmospheric stress and hydraulic risk during drought. These findings emphasize the importance of incorporating individual-level microclimate data to gain a comprehensive understanding of tropical forest resilience in a heterogeneous environment.