Bryophytes on Boulders Diversity, habitat preferences and conservation aspects

Weibull, H. 2000. Bryophytes on boulders diversity, habitat preferences and conservation aspects. Doctor’s dissertation. ISSN 1401-6230, ISBN 91-576-5893-5 The influence of different overstorey tree species on the floristic composition of bryophytes growing on boulders was studied in two deciduous forests. Covering tree species and amount of litter were the factors explaining most of the variation in bryophyte species composition. Boulders below base-rich deciduous tree species (ash, elm and maple) had a considerably different bryophyte species composition than boulders below Norway spruce, while the species composition was intermediate below oak and birch. Boulders below base-rich deciduous trees had approximately twice as many species as those below Norway spruce, while boulders below oak and birch were intermediate. Individual plots (1 Ox 10 cm) were on average not more species-rich on large boulders than on small ones, even though large boulders had more species. Transplanted patches of the moss Tortula ruralis were grown below the cover of five tree species. The growth was significantly lower below Norway spruce than below the deciduous tree species, which was related to lower amount of throughfall, lower pH in throughfall and lower relative light flux below Norway spruce. In laboratory experiments Tortula ruralis grew significantly less at pH 4.1 as compared to pH 4.5 or higher. At high RH Antitrichia curtipendula grew significantly more than at low RH. Antitrichia curtipendula grew significantly more and T. ruralis significantly less when watered often (every third day). The bryophyte flora was also studied in permanent plots on boulders in a deciduous forest between 1997 and 1999, in order to study the effects of three litter treatments (deciduous, coniferous or no litter). Species richness increased in plots with deciduous litter and decreased in plots with Norway spruce litter, while it was maintained in plots without litter. There was a considerable variation between years in cover of many species, which reduced the treatment-effects.