The Partial Influence of Norway Spruce Stands on Understorey Vegetation in Montane Forests of the Bavarian Alps

Natural mixed forests of European beech (Fagus sylvatica), Norway spruce (Picea abies), and silver fir (Abies alba) were widely replaced by spruce-dominated stands in the montane belt of the northern Calcareous Alps in historical times. This accounts for changing forest structure, diversity, and hemeroby. Observations in other parts of Europe suggest that this development should have led to a replacement of the native understorey vegetation by species typical of coniferous forests and to an increase in plants that are indicators for acidity and nitrogen. The statistical relationships between understorey vegetation structure and species richness, Ellenberg indicator values, and the proportion of Norway spruce in the tree layer were studied in 84 stands selected in a stratified random design in the Bavarian Alps, while controlling for the influence of the natural environment. The results show that the richness of coniferous forest species and the occurrence of acid indicators have been significantly favored by Norway spruce canopies, while understorey species characteristic of deciduous forests and nitrogen indicators have not been affected. While bryophytes and some shallow-rooted vascular plants respond positively to a coniferous canopy, most vascular plants are resilient to changes in the canopy. This can be attributed to the high buffering capacity of the soils under the mountain forests studied.