Vegetation, soil- and air temperature studies within alpine treeline ecotones of southern Norway

Abstract

The alpine treeline ecotone (ATE) is the transition zone between closed forest and the treeless alpine zone. The main objective of this study is to investigate air and soil temperatures within the ATE from seven different areas which have previously been described to be climatically limited. The study areas include a gradient in oceanity, wherein forest limits have been mapped to vary from below 800 m to higher than 1,100 m. In the ATE, soil temperatures were measured using data loggers at a depth of 10 cm in the top soil layer and gridded air temperatures (2 m above ground) were obtained from the Norwegian Meteorological Institute. The Kruskal-Wallis test showed statistically significant differences between the study areas, with higher summer temperature values in the oceanic influenced areas. Seven vegetation communities were categorized by TWINSPAN analysis and gradients in vegetation were explained using the soil- and air- temperature frost sum, growing season soil temperature and growing season length (calculated using soil temperature). The current ATE position could be explained by growing season length (air and soil temperature), temperature frost sum, and duration of the frozen soil period. The results suggest that temperatures may not be critical for current ATE altitudinal positions in oceanic areas.