Vegetation change in boreonemoral forest during succession - trends in species composition, richness and differentiation diversity

We compared the diversity and composition of understorey vegetation of four successional stages (recently clearcut, young, middle-aged and old stands) in an Estonian boreonemoral coniferous forest under homogeneous soil conditions. The ordination analysis (NMDS) showed that successional age was the main driver of understorey species composition with soil pH and P content responsible for some variation as well. Species composition in old-growth stands was more similar to the vegetation of young and clear-cut stands than to the composition of mid-aged stands. Species richness in 1-m(2) plots was higher in recently disturbed and young stands due to the higher abundance of disturbance-related species. The differentiation diversity, characterising species turnover among plots within a stand, was higher in recently disturbed and young stands than in mid-aged and old stands. The results indicate that earlier successional stages are characterised by spatially heterogeneous and diverse vegetation, whereas older stands develop more homogeneous vegetation composition.