Species mixing, competition and tree size jointly shape drought resilience and growth legacies on a Mediterranean pine forest

Increasing drought threatens Mediterranean forests. While structurally complex forests are proposed for climate adaptation, empirical evidence remains contradictory. We analysed drought resilience as a function of local competition in a mixed supramediterranean forest of Pinus nigra and Pinus sylvestris, evaluating the effects of species identity, competition intensity, neighbourhood composition, and tree diameter on secondary growth. Using tree-ring data and ARIMA models, we calculated classical resilience indices and cumulative impact metrics (including Growth Years Lost, GYL) for the 2005 and 2012 droughts. Responses differed between species and events; P. nigra was more resistant in 2005, whereas P. sylvestris performed better in the more severe 2012 drought. Species mixing acted as a species-specific buffer depending on the event. Local competition did not affect resistance but enhanced recovery, especially in P. sylvestris. Tree diameter strongly drove cumulative impacts: large trees suffered greater absolute growth losses, while small trees showed higher relative vulnerability (GYL). We show that traditional indices can mask key vulnerabilities, whereas cumulative metrics reveal hidden impacts across size classes. Overall, mixed-forest resilience is shaped by the interplay of species, size, and neighbourhood structure rather than stand composition alone. Our results challenge generalised density reduction as a universal adaptation strategy, suggesting that maintaining structural complexity while avoiding highly suppressed cohorts optimizes localised sheltering and ecosystem stability.