Regional Mountain Conference

Climate change is reshaping Alpine forest ecosystems, as increasingly frequent drought events drive tree mortality and shift the distribution of both angiosperm and gymnosperm species. However, the physiological limits controlling drought resistance in these two major plant lineages remain poorly understood, restricting our ability to predict future changes in forest composition and function, and hindering efforts to develop effective management strategies under warming climates.

In this research, we assessed two central drought-related traits — xylem embolism vulnerability and bark insulation capacity — in juvenile branches of representative Alpine angiosperm (Acer pseudoplatanus, Alnus incana, Betula pendula, Betula pubescens, Fagus sylvatica, Populus tremula, Sorbus aucuparia) and gymnosperm species (Abies alba, Larix decidua, Picea abies, Pinus cembra, Pinus sylvestris).

Our results reveal clear functional contrasts between the two groups. Gymnosperms showed more uniform and generally greater resistance to xylem embolism than angiosperms (water potential causing 50% loss of xylem hydraulic conductivity: -3.55 ± 0.22 MPa vs. -2.86 MPa ± 1.12 MPa). However, gymnosperms also exhibited significantly higher bark water vapor conductance (5.37 ± 1.51 mmol m^-2 s^-1 vs. 2.90 ± 1.91 mmol m^-2 s^-1) and tended to have lower bark hygroscopicity and water storage capacity.

This trait combination suggests that gymnosperms may be more prone to bark‑mediated water loss during drought and less able to rehydrate from atmospheric moisture, despite their stronger xylem embolism resistance. Angiosperms, despite some of them being more vulnerable to embolism, may benefit from greater bark insulation and water retention, providing alternative drought‑mitigation strategies.

Taken together, our findings indicate that the higher bark water loss and limited rehydration capacity of Alpine gymnosperms may increase their need for frequent recovery following drought episodes, placing them at elevated risk of chronic drought stress. These insights improve our understanding of the physiological constraints shaping species performance in a warming climate and support more accurate forecasts of shifts in Alpine forest composition and resilience. However, additional research on complementary water-related traits (such as water uptake/loss through leaves and roots) is needed to achieve a more complete assessment of species’ adaptive potential under future climates.