Different drought responses of stem water relations and radial increments in Larix principis-rupprechtii and Picea meyeri in a montane mixed forest

Abstract

The heterogeneous responses of mixed forests to climate change are integral to the promotion of the resilience and resistance of forest ecosystems, yet the hydraulic and growth sensitivity of mixed tree species to environmental drivers remain largely unexplored. In this study, stem radial variations in larch (Larix principis-rupprechtii) and spruce (Picea meyeri) were monitored using high-resolution point dendrometers over six years (2014–2019) in a mixed coniferous stand in semi-humid China. The extracted hourly tree water deficit-induced stem shrinkage (TWD) and stem radial increment (SRI) were compared between tree species and among years, and the species-specific responses of the daily maximum TWD and cumulative SRI to environmental variables were fitted by linear mixed models. Averagely, larch had a lower TWD and greater SRI rate than spruce in all six growing seasons. The interspecific differences in the TWD (length, magnitude, and intensity) were significant in dry years, while significant differences in the SRI rates were in wet years. The SRI rate of larch showed a more rapid decrease than that of spruce with increasing intensity of TWD. Furthermore, the TWD of both species was mainly regulated by vapor pressure deficit (VPD) and soil water content (SWC). The TWD of larch had a stronger and earlier response to VPD, while TWD of spruce was more affected by SWC (10 cm depth). The daily SRI of larch was more significantly related to all the measured environmental variables, indicating a more sensitive response to environmental drivers than that of spruce. We identified a shift in competitive advantage from sensitive L. principis-rupprechtii to conservative P. meyeri under extreme drought conditions, providing deep insights into species‐specific water and carbon dynamics in mixed forests.