Early leaf senescence under heat and drought: Linking experimental physiology and landscape-scale forest responses

Pia Labenski, Ph.D. – Karlsruhe Institute of Technology

Early leaf senescence under heat and drought: Linking experimental physiology and landscape-scale forest responses Heat and drought increasingly disrupt the seasonal dynamics of temperate forests, leading to premature leaf discoloration and shedding. However, the functional role of this response remains debated. Early leaf senescence may reduce transpirational demand and help maintain hydraulic safety, but it can also reflect hydraulic failure or thermal damage at the leaf level.This talk combines experimental physiology, field observations, and satellite-based analyses to explore the mechanisms and consequences of drought-induced leaf senescence. Experimental work demonstrates how drought-induced leaf shedding can reduce canopy water demand and delay critical losses of hydraulic conductance, while combined heat and drought constrain transpirational cooling, increase leaf temperatures, and promote thermal damage to leaf tissues. Field observations further reveal close links between drought-induced defoliation, xylem embolism formation and subsequent canopy dieback. These processes are reflected in emerging large-scale patterns of early senescence detected across temperate forests during recent hot drought events. Together, these observations shed light on the role of early leaf senescence in forest resilience under intensifying climate extremes.