Climate-growth relationships of Quercus gussonei (Borzì) Brullo in the Mediterranean region: adaptive traits and water use efficiency.

Abstract

Due to their marginal distribution, peripheral tree populations are highly vulnerable and are more likely to be influenced by extreme climate conditions. This occurrence is known to cause dieback in many species at their Mediterranean margins. Quercus gussonei (Borzì) Brullo is a deciduous oak endemic of Sicily. It is a thermophilous, peripheral form of Quercus cerris L. which is showing an incipient but ongoing decline. A deeper ecophysiological knowledge is urgently needed on this species in order to plan proper conservation actions and reduce the risk of its extinction. In the aim to understand at what extent changes in environmental conditions could be responsible for Q. gussonei decline, we carried out dendrochronological and water-use efficiency investigations. Annual ring widths, earlywood and latewood analyses were accomplished in order to assess the climatic factors influencing the growth of Q. gussonei. In addition, we determined the carbon isotope discrimination (Δ 13C) in tree rings, allowing to evaluate WUE variations and the expression of possible plant adaptive traits. Climate-growth relationship were analyzed using response functions. Our findings highlight significant relationships between tree-rings width and climate data. The dendrochronological analysis of Q. gussonei showed a rather good adaptation of this species to the typical Mediterranean climate and oak trees seem to retain a certain resilience to efficiently face 14 less favorable environmental conditions. Furthermore Δ 13C indicates a long-term adjustment in water-use efficiency and the increase of WUE could be interpreted as a fair adaptation of this species to drought-prone environments.