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. These climate conditions can become crucial for the vitality of pine trees on the island. The interdisciplinary bundle project CorsicArchive integrates dendroecological, climatological, and hydrological studies on 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 of pine trees and in the hydrological cycle. We analyzed stable oxygen isotope data in intra-annual resolution from tree-ring cellulose, needle water, precipitation and underground water at five different locations along an altitudinal gradient ranging from sea level to 1600 m asl. With this approach we were able to disentangle which water sources are used by the trees growing under different climate conditions. Altitudinal differences in absolute isotope ratios were obvious in all materials except tree-ring cellulose. The isotope values of tree-ring cellulose and their intra-annual distribution pattern depend on the water sources used by the trees. We could clearly distinguish different intra-annual oxygen isotope patterns for trees with access to groundwater from trees which depend on precipitation during the growing season as their main water source.