Climate change adaption of European beech forests: Silver fir admixtures drive understorey plant diversity

Abstract

Transformation of monodominant European beech forests into mixed forests by adding alternative tree species is a key strategy of silvicultural climate change adaption in Central Europe. Silver fir (Abies alba) is a promising candidate tree species in this context, as both European beech (Fagus sylvatica) and silver fir were shown to benefit from being cultivated in mixed stands. Sampling pure and mixed forests of the two tree species along a gradient of increasing canopy fractions of silver fir on both acidic and base-rich soils in two montane regions of Central Europe, we analysed the effects of silver fir admixture on the diversity and composition of the forest ground vegetation. Generalized mixed models showed that on both soil types, silver fir admixture significantly increased plant species richness. On acidic soils, plant community changes indicated the encroachment of mixed forests of beech and silver fir by highly acidophilous plant species typical of mixed mountainous conifer forests, with a corresponding shift in the relative abundance of plant strategy types towards more stress-tolerating species. Community change on base-rich soils was mostly driven by increasing abundances of typical forest herbs and light-demanding woody plants. These results show that enriching temperate beech forests with silver fir as a measure of climate change adaption can be considered ecologically acceptable, at least from the perspective of forest understorey vegetation.