Linking patterns of forest dieback to triggering climatic and weather events: an overview on Mediterranean forests

Mediterranean forest ecosystems are highly vulnerable to climate extremes and anomalies induced by climate change, as evidenced by the increase in forest tree decline and death over the past few decades. Forest dieback may occur with different spatial patterns and in response to many climatic and weather events (i.e., drought spells, heat waves, compound events or hot drought, cold spells, and windstorms). This paper describes the physiological behaviour of Mediterranean tree species (namely evergreen sclerophyllous trees) under extreme climatic events, with a focus on embolism formation and carbon depletion. Additionally, we describe three widely recognised patterns of forest dieback: die-off, patchy dieback, and salt and pepper dieback. Overall, drought spells, heat waves, and compound events have been reported to induce all the mortality patterns described, revealing the great vulnerability of Mediterranean forests to rising air temperature and vapour pressure deficit trends. Many intrinsic factors of plant and structural and contingent factors of the forest can interact, favouring one mortality pattern over another. Patterns of dieback and mortality are the product of the interaction between the complexity of the landscape, the species assemblage, the kind and intensity of the disturbance, and biotic factors. Different patterns have different ecological consequences, and implications for monitoring and management. The combination of terrestrial and remote sensing (RS) is recommended.