Positive aspects of clear-cut logging? Ground bryophyte diversity along the age gradient of managed Pinus sylvestris stands

Bryophytes are important components of pine forests; however, the bryophyte layer is characterised by the dominance of a small number of taxa. Clear-cut logging changes microclimate conditions, while ploughing before planting young trees disrupts bryophyte patches. This promotes early successional species and can work in favour of species diversity provided that there are simultaneous regeneration of late successional species bryophytes. In the Tuchola Forest (north-western Poland), we investigated the occurrence and abundance of ground bryophytes using a chronosequence method. The study was carried out on plots that represented the following stand age classes: <= 10, 11-20, 21-40, 41-60, 61-80, > 80 years. Bryophyte richness was higher in the youngest stands than in the oldest ones. There are distinctive changes of species composition in the course of succession that range from colonists and stress-tolerant perennials to competitive perennials and from species growing in tufts to species growing in wefts. There are not true forest species even in the oldest stands. There is only a tendency for the exchange of species that prefer open habitats to species that prefer both forests and open habitats. However, clear cutting contributes to the increase of species richness of ground bryophytes and spatial diversity of plant patches in managed forests. The positive aspects of clear cutting can only be considered in relation to the species diversity in the oldest and managed stands but not with those in natural forests.