Functional mechanisms and drought responses in Mediterranean oaks: three decades of research and a categorical synthesis

Recurrent and intensifying droughts have emerged as a principal driver of decline in Mediterranean oak forests over the past three decades. This review synthesizes current understanding of the functional mechanisms shaping drought impacts in these ecosystems and complements existing work by combining a structured categorical overview with a multi- variate functional ordination of oak responses. We assembled a dataset of 240 records derived from 212 studies published between 1994 and 2024, spanning species with contrasting leaf habits (evergreen, deciduous, semi-persistent), diverse wood anatomies (diffuse-, ring-, and semi-ring-porous), and developmental stages ranging from seedlings to mature stands. The studies encompass a broad gradient of drought durations and intensities, enabling comparison of drought resistance and resil- ience across plant systems. Across the reviewed literature, key ecophysiological mechanisms include stomatal regulation, hydraulic and osmotic adjustment, morpho-anatomical plasticity, and phenological shifts. However, most studies investigate these mechanisms in isolation, and integrative, multi-trait analyses remain rare. Using coarse categorical metrics, we found no clear geographic structuring of resistance, resilience, or response mechanisms, likely reflecting uneven species represen- tation and heterogeneous experimental designs. Nonetheless, the dataset reveals functional patterns linked to plant diversity: deciduous, ring-porous species exhibit higher frequencies of low-resistance and low-resilience states, whereas evergreen, diffuse-porous species tend to display greater hydraulic safety and recovery capacity. Correspondence analysis further high- lights major axes of variation associated with leaf habit and wood anatomy, confirming divergent adaptive strategies among Mediterranean oak functional types. Collectively, these findings underscore the importance of functional diversity in shaping drought responses and provide a framework for future mechanistic research and climate-adapted forest managemen