The Effects of Climate Change on Zirben (Pinus cembra) Distribution in the Italian Alps

Abstract: Anthropogenic climate change has caused temperature increases all across the globe. Mountainous areas are among the most affected and are experiencing alarming rates of warming. Such rapid warming will have effects on alpine vegetation and their distribution throughout the alps. While there are many studies that have investigated shifting vegetation distribution around the world, none have found concrete evidence of an upwards shift of the tree line within the Alps to date. This study therefore investigates the potential size and timing of a tree line shift within the Martell Valley in the Italian Alps. Zirben (Pinus cembra) is a common tree species at the alpine tree line and is the focus of this investigation. Changes in average summer temperatures were the main factor investigated in this report as they were found to be the limiting factor for tree growth at the tree line. Average summer temperature differences were found between the current climate and for four different future climate scenarios: two for the near future and two for the far future. Differences in average summer temperatures between current (2011-2020) and future climates (RCP 4.5 & 8.5 2041-2060, RCP 4.5 & 8.5 2081-2100) ranged from 1°C to 7°C which corresponded to a potential upwards shift ranging between 194 and 794 meters. While these numbers indicate a potential shift, there are many factors that could delay a Zirben migration such as future climate uncertainties, alpine pasture usage, soil formation duration, seed dispersal and disturbance rate among other factors. In reality, the quantified shift values were concluded to be generalizations at best due to uncertainties in these factors. Future studies are recommended to physically study Zirben at the tree line for the next decades to a century to order to observe trends in tree line shift and Zirben migration.