Global change effects on Mediterranean pine forests: hotspots of dieback

The effects of climate extremes on the vulnerability to forest dieback of widely distributed Mediterranean pine species are poorly understood but important for forecasting their responses to climate change. As air temperature increases, evaporative demand will also rise, exceeding the drought tolerance of tree species to pervasive droughts. Using a spatially comprehensive network of six pine species with > 800 tree-ring chronologies, > 500 plots from the the ICP-forest network (defoliation, moratlity, etc) and drought-induced mortality database combined with NDVI (Normalized Difference Vegetation Index) encompassing the wide ecological and climatic gradients across Mediterranean Basin. We show that an increase of climate water deficit produced legacy post-drought effects on growth with strong variation in growth across its distributional range, but common patterns were found within each provenance. Vulnerability to legacy effects of extreme droughts were most prevalent in dry provenances and western, in contrast to limited legacy effects after drought observed in wet provenances and high-elevation sites. Post‐drought legacies decreased with latitude and wetter conditions but decreased with spring precipitation in western mediterranean. Trees from dry, rear-edges sites in the Mediterranean Basin were more vulnerable to recurrent droughts than trees from wet. The increase in summer temperature and evapotranspiration favour hotter droughts that can increase defoliation, decrease tree growth and productity casusing drought-induced forest dieback in drier regions over the next decades.