Altitudinal Gradients and Forest Response:
Climate, Hydrology and Isotope Variability
of a Mediterranean Ecosystem

Abstract:

The mountainous island of Corsica in the western Mediterranean basin hosts Mediterranean as well as alpine ecosystems. It is highly affected by current climate change which manifests in an increasing number of heat waves and drought periods. The interdisciplinary bundle project CorsicArchive integrates dendroecological, climatological, and hydrological studies on the island of Corsica. The superordinate aim of the project is to better understand the forcing factors and fractionation processes responsible for spatial and temporal oxygen isotope variability in tree rings and in the hydrological cycle. Here, we present results from the dendroecological part of the project. We established a 30-year long intra-annual oxygen isotope chronology from tree-ring cellulose of Corsican Black pine (Pinus nigra ssp. laricio) growing at an upper tree line site in order to identify typical intra-annual patterns and the climate parameters responsible for the oxygen isotope variability. The isotope ratios in the early part of the early wood are strongly influenced by the amount of snow during winter, while patterns in the remaining part of the tree ring are mainly determined by summer precipitation conditions. In total, three different intra-annual patterns could be observed which can be attributed to different climate conditions during the vegetation period. The stable isotope pattern reflecting dry-warm conditions during summer occurs with higher frequency after 2007, thus confirming a trend towards pronounced drought stress during summer, which might become critical for Black pine growing at dry sites if becoming more extreme in the future.