Vegetation databases provide a close-up on altitudinal tree species distribution in the Bavarian Alps

Abstract

Thermal limits of tree species are of paramount interest in monitoring and projecting effects of climate warming. Based on the large phytosociological database BERGWALD, a database of forest inventory plots, and phytosociological tables of vegetation above treeline, tree species occurrence along a regional elevation gradient was assessed separately for tree and regeneration layer individuals. Upper limits in the database were compared to altitudinal limits given in Oberdorfer’s regional flora and to northern latitudinal limits given in worldwide distribution maps. For 26 of 32 tree species, the known distribution limits had to be raised based on plot data, demonstrating the high potential of vegetation databases to deliver ecological information. In most species, regeneration layer occurrences markedly exceeded the altitudinal limit of trees, indicating a potential for rather rapid advances of treelines under climate warming. Regional altitudinal and global latitudinal limits were quite closely related in the majority of tree species. However, several tree species climb to much higher elevation in the Alps than their latitudinal limits suggest. The boreal-subalpine mismatch in cold limits is only partly explained by vicariism and endemism. Sorbus aria, Acer pseudoplatanus, Fagus sylvatica and Taxus baccata are important elements of temperate mountain forests, which do not reach thermally equivalent northern latitudes for unknown reasons.