Response of trees to regional climate – a sensitivity study in Jämtland

Global warming is a key topic of present-day research, with the effects projected to be enlarged in Sweden. The county of Jämtland lies in the central Scandinavian mountains and is highly affected by changes in temperature and precipitation. Vegetation and ecotones depend on the climate and this connection creates the possibility of studying past vegetation growth in relation to climatic variables. Because of the location of Jämtland, it is affected by two different airmasses, the maritime from the west and the continental from the east, making it a suitable locality for studying differences in trees and their responses to climate. Not only will this gain an increased knowledge of the relationship between them but will also add validation to future projections. Tree rings are useful proxies in climate studies, and the aim of this study is to analyze and correlate tree ring width (TRW) against the climatic variables of temperature and precipitation. The chronologies span 207 years for Storlien, 1814-2020, respectively 402 years for Snasahögarna, 1619-2020, although this study focus on the past 101 years. During this period, each study site shows a similar pattern in TRW. Both chronologies are statistically significant against temperature, but not precipitation. This study implicates that regional climate is the main driving factor of radial growth in trees, which improves the possibilities to analyze climatic changes and expected growth responses. Our conclusions: ❖ Our results reveal that the trees, chosen for this study,show a large sensitivity to climate, specifically regional temperature. This relationship has mostly been sustained during the last 101 years. ❖ The maritime climate influences the growth of trees in this region, but indications suggest that the trees at Snasahögarna are more influenced by the continental airmasses than the trees at Storlien. Although the two sites display an overall agreement during the studied time period, small differences were detected, especially during the 1970s. ❖ A tree line movement to higher altitude has occurred between 1957 and 2020, most likely due to a changing climate. At some locations, the tree line movement are limited by steep slopes