Aspect-dependent drought constraints on Pinus canariensis growth along an elevation gradient

Topographic heterogeneity strongly shapes tree growth in oceanic island forests by modulating local microclimatic conditions and buffering climatic stress. However, climate warming threatens this buffering capacity by increasing atmospheric evaporative demand and intensifying drought constraints. We combined tree-ring chronologies, high-resolution dendrometer measurements, stable carbon isotope (δ¹³C) analyses, and Vaganov–Shashkin (VS) model simulations to investigate Pinus canariensis growth dynamics across a topoclimatic gradient spanning contrasting slope aspects and elevations. North-facing stands maintained comparatively stable growth under more favourable hydrological conditions and exhibited higher drought resistance and resilience than south-facing stands. In contrast, south-facing stands showed stronger moisture limitation and long-term growth declines, greater drought sensitivity, higher interannual growth variability, increasingly negative growth trends, and sustained years-long stem water deficits lasting nearly two years. VS simulations indicated that temperature primarily controls growth onset, whereas soil moisture increasingly regulates growth duration and continuity, particularly on south-facing slopes, where water availability is lower and evaporative stress is greater. Intrinsic water-use efficiency (iWUE) increased over time across all stands, with a steeper increase on south-facing slopes, where it was also associated with declining growth. Our results demonstrate that fine-scale topoclimatic heterogeneity shapes drought limitation in P. canariensis forests, with slope aspect emerging as a major driver of differences in growth and drought resilience. By combining long-term growth records with physiological indicators and process-based simulations, this study provides a multi-proxy assessment of drought vulnerability that can help identify exposed stands for targeted monitoring and support adaptive conservation and forest management in these endemic island ecosystems.