Negative resilience trends to more frequent extreme droughts in Mediterranean oak species

Recent changes in climate have triggered widespread mortality events in oak forests worldwide. Despite the ecological importance of these ecosystems, limited information exists on the long-term resilience of oak forests in response to extreme climate events. Quercus canariensis, a semi-deciduous oak sensitive to summer drought characteristic of the Mediterranean climate, is currently showing defoliation and mortality episodes in the drier areas of its natural range. Here, we investigated the long-term impacts of climate on the radial growth of Q. canariensis and assessed changes in resilience to extreme droughts across eight populations in S Spain following an environmental gradient. We observed a clear latitudinal gradient in growth performance, as reflected by resilience indices across populations. Since 1970, Q. canariensis has shown a marked decline in resilience to extreme drought events at the wettest region, resulting in a diminished capacity to recover pre-drought growth levels. This trend has preceded growth declines in certain populations, suggesting increased vulnerability to the increasing frequency of extreme climatic events. Through growth analyses, we identified early-warning signals of forest decline in this Mediterranean oak species, highlighting the most sensitive populations and its high susceptibility to extreme droughts impacts.