Regional Mountain Conference

Increasing drought frequency and intensity under climate change threaten forest functioning, particularly at the dry margins of species’ distributions. Norway spruce (Picea abies (L.) Karst.), a key Alpine conifer, is considered highly vulnerable to water stress, yet the roles of stand composition and elevation in shaping drought resilience remain poorly understood.

This study uses a multi-proxy dendroecological approach to investigate the long- and short-term responses to drought events in pure and mixed stands of Norway spruce along altitudinal gradients (1100–1600 m a.s.l.) in the Venosta Valley, one of the driest regions in the Alps. The integration of dendroanatomy and carbon stable isotopes (δ¹³C), together with estimates of intrinsic water-use efficiency (iWUE), allowed quantification of drought resistance, recovery, resilience, and long-term structural and physiological trends.

Results showed that drought events (2003 and 2018) caused a strong and persistent reduction in growth and hydraulic efficiency with varying recovery times among different anatomical traits. Mixed stands exhibited slightly higher growth resistance and resilience than pure stands, although not consistent across elevations. Elevation strongly influenced drought responses, with higher sites showing greater resistance but slower recovery. Intrinsic water-use efficiency increased significantly, especially after the 2003 drought at most sites, particularly in pure stands at mid and high elevations, indicating enhanced stomatal regulation under water stress. Long-term analyses revealed a sustained increase in iWUE over the past 30 years, consistent with increasing temperature and drought pressure in the study-area.

Overall, these results highlight how stand structure and elevation jointly influence drought structural and physiological resilience, underscoring the value of multi-proxy approaches for assessing forest responses to ongoing and forecasted climate change. With continued warming, the strong dependence on water availability and the multi-year legacies of extreme droughts raise concerns about the future competitiveness of Norway spruce in Alpine environments, particularly at lower elevations.