Drought-Induced Oak Decline—Factors Involved, Physiological Dysfunctions, and Potential Attenuation by Forestry Practices

Abstract

The increasing duration and intensity of droughtDrought is precipitating widespread episodes of forest declineDecline around the world, possibly in combination with other climatic (e.g. soilSoil water logging) and land-use (e.g. fire and coppicing suppression) changes that have been occurring through the last century. A meta-analysis of physiological data compiled from recent data bases indicates that, comparatively to other species, oaks are mostly tolerant to droughtDrought and anisohydricAnisohydric, although also relatively vulnerable to severe water stress. The succession of droughts in unmanaged overcrowdedOvercrowded stands is affecting many physiological processes associated with water transportXylem water transport and carbon metabolism and making trees more susceptible to further abioticAbiotic and bioticBiotic stresses. Although oaks maintain large reserves of nonstructural carbohydratesCarbohydrates (NSCNon structural carbohydrates (NSC)) in comparison with other tree species, water restrictions to net carbon gainCarbon gain in declining trees can reduce NSCNon structural carbohydrates (NSC) reserves and favor the sudden or more progressive death of trees. In view of correlative and process-based vegetation model simulations, oaks in the southern-most part of their range can undergo extinctions in the future due to increases in temperatureTemperature and droughtDrought. Hence, managing forests so as to increase acornAcorn production and seedlingSeedling recruitmentRecruitment is a necessary task to increase adaptability of oakOak forests to GlobalGlobal Change. Different silvicultural alternatives can improve the physiological status of residual trees and be employed to mitigate the sensitivity of oakOak forests to droughtDrought in the short and long run. However, more studies are needed to understand and mitigate oakOak declineDecline.