Abstract
Alpine treeline ecotones north of the Alps in Central Europe occur in 11 mountain ranges, including the Harz Mountains (Germany), mountain chains of the High Sudetes (Czech Republic and Poland) and the Western Carpathians (Czech Republic, Poland and Slovakia). These mountains are characterized by pronounced maritime-continental gradients, large differences in the mass elevation effect, and varying distance between the treeline and summits.
We evaluated how these factors influence treeline temperatures and thus treeline elevation. We compared various treeline temperature metrics for all mountain ranges in the study region both among the mountain ranges and with treeline temperatures in the Alps.
Our results show that treelines along the 50th parallel increase their elevation by approximately 94 m per 100 km towards the east, a reflection of a rise in elevation of isotherms of growing season temperatures along the maritime-continental gradient and with increasing mass elevation effect. Among the majority of evaluated mountain ranges, growing season treeline temperatures did not differ significantly, suggesting identical thermal limitation of tree growth in these ranges.
However, we identified 4 regions (the Harz, Králický Sněžník, Hrubý Jeseník and Velká Fatra Mountains) where the uppermost tree stands are situated below the common treeline isotherm, an indication that trees are limited by other factors (e.g. biomass loss). Based on a comparison of various treeline temperature metrics, we suggest that to reliably describe treeline climates in regions with pronounced maritime-continental gradients, it is necessary to use metrics capturing the entire growing season.
Such metrics show that treeline temperatures in the study region are similar to those in the Alps.