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

Abstract:

The western Mediterranean basin is subject to ongoing climate change, exhibiting more pronounced drought periods during the growing season. Therein, the mountainous island of Corsica, France, was recently exposed to two extreme but strikingly different consecutive years: 2017 was especially dry and yielded a record minimum in annual precipitation whereas 2018 was particularly wet with summer precipitation more than doubling the long-term average. However, both years were equally warm, being the second and third warmest summers since 1900 for entire France. Within this setup, 42 pines were equipped with high-resolution band dendrometers spanning an E-W transect across the central mountain range. Circumference growth data were obtained at five study sites, located in three different elevation belts ranging from sea level up to 1600 m asl. We analyse the different reactions of Maritime pine (Pinus pinaster) in low regions and Corsican Black pine (Pinus nigra ssp. laricio) in high elevations, to the aforementioned climatic conditions. Results show distinctive differences in the length of the growing period in all elevation belts. During the summer drought of 2017, the two coastal sites showed stagnation or even shrinkage of tree circumferences, whereas the western part of the transect was more affected than the east. In contrast, all sites exhibited continuous growth over the summer months in 2018. Additionally, obtained microcore samples will help to pinpoint cambial activity and indicate the differences of earlywood and latewood formation in different elevations under inter-annually varying climatic conditions.

Abstract:

Located in the western Mediterranean basin, the island of Corsica (France) is expected to be strongly affected by climate change. With its diverse topography and altitudinal gradients from sea level to 2700m asl, it hosts two pine species, i.e. Pinus pinaster in lower areas and P. nigra ssp. laricio in higher regions up to the upper tree line. However, the growth performance of these two dominant forest tree species along different elevation belts is still unknown, so it is not clear how climate change will affect their distribution. The relationships between tree age, elevation, and growth performance were evaluated using growth trajectories derived from tree-ring analysis of pines in different age classes at 13 sites across the island, ranging from sea level to 1600m asl. Results show that the growth performance of both species under the same environmental conditions is very similar. For both species, we found that growth rates change over time, whereby trees younger than 50 years grew faster than older trees. We also found that P. pinaster is becoming common at higher elevation sites, indicating a migration upslope.