Effects of natural forest dynamics on vascular plant, bryophyte, and lichen diversity in primeval Fagus sylvatica forests and comparison with production forests

Stand structure, mean tree age, deadwood amount and microclimate all change markedly in the course of natural forest dynamics. The last remaining primeval forests of the temperate forest biome are valuable study objects to investigate the effects of forest dynamics and management on forest structure and function as well as phytodiversity, which is not sufficiently understood. Three pairs of Fagus sylvatica primeval and production forests in eastern Slovakia were selected for studying the effects of natural forest development stages on vascular plant, bryophyte, and lichen species richness and composition. We further compared the diversity patterns in the initial, optimal and terminal stages of forest development with those of nearby production forests. The plot-level species richness of epiphytic bryophytes and lichens increased from the initial to the terminal stage, but only lichens exhibited a significantly higher cumulative species richness ( diversity) in the later (optimal and terminal) stages. No increase in species richness from the initial to the terminal stage was found for deadwood-inhabiting epiphytes and the ground-layer vascular plants. Canonical correspondence analyses identified characteristic bryophyte and lichen species for the different development stages, while the bulk of vascular ground layer species occurred across all stages with no stage preference. Stem diameter was an even more important driver of epiphyte diversity and species composition than the development stage. All stages of the primeval forests (including the initial) were more species-rich in epiphytes and, when investigating larger plot numbers, also in vascular plants than the production forests. Synthesis. In primeval forests of European beech, plant species richness did not differ significantly between the consecutive forest development stages, while species composition did. This is attributable to the small-scale mosaic structure of the forest, rapid gap closure by beech, and the continuity of deadwood across the stages, which reduces spatio-temporal differences in microhabitat availability in the forest. Bryophytes and lichens are species-richer, and vascular plants at least similarly rich, in the primeval as compared to the production forests, if the study area is sufficiently large.