In order to investigate the question of whether global climate change is causing a shift in tree boundaries, the Bayreuth researchers chose the Mediterranean island of Crete because the conditions for such a study were unusually favourable there. "It is a rare stroke of luck for research that aerial photographs of a mountainous region exist in relatively high resolution, which cover a period of 70 years and allow us to see with sufficient accuracy whether tree populations have changed. Using climate data and new geoinformatics methods, we were able to document decades of climate change and at the same time prove that the trees native to the mountains of Crete have not moved to higher elevations," says first author Mirela Beloiu, who earned her doctorate at the University of Bayreuth and is now a postdoctoral researcher at ETH Zurich. The research in Crete was carried out in close collaboration with the Remote Sensing Laboratory at the Institute of Applied and Computational Mathematics of the Foundation for Research and Technology Hellas (FORTH). The institute also provided the historical and recent aerial images.
In their study, the researchers identify several climatic and topographic factors that may be contributing to the persistence of Crete's mountain forests in their decades-old locations. During the study period, the mean annual temperature at the tree line increased by 0.81 degrees Celsius, while the average rainfall decreased by 170 millimetres. Increasing drought is apparently a stress factor that inhibits plant dispersal. In addition, regions above the tree line are exposed to very strong winds. As a result, young trees do not find the protection they need to establish themselves at higher elevations. "If ecosystems, such as the high mountain forests of Crete, are unable to respond to climatic changes and protect themselves adequately as a result of topographical conditions, possibilities should be explored as to how humans can strengthen their adaptation through creative nature management," says Beierkuhnlein.
Publication:
Mirela Beloiu et al.: No treeline shift despite climate change over the last 70 years. Forest Ecosystems (2022), DOI: https://doi.org/10.1016/j.fecs.2022.100002