From pattern to process : Studies on limestone grassland, with emphasis on the bryophyte-lichen layer and its effects on vascular plants

Abstract: Patterns in space and time at different scales in the bryophyte-lichen layer, aud multi-species spatial patterns of bryophytes, lichens and vascular plants were studied in Avenetum limestone grassland on the Great Alvar of the Baltic Island of Öland, south-eastem Sweden.Spatiotemporal patterns of bryophytes and Iichens in grazed and ungrazed alvar grassland demonstrated that dominant species forming large patches were relatively stable in time, whereas less frequent species forming small patches were more mobile. Many species showed a high cumulative frequency at both sites, which supported the Carousel model concerning within-community species dynamics. In the grazed grassland none of the species showed a clear decline over time. Bryophytes characteristic of grazed grassland yet occurring in theungrazed site, had greater losses than gains at both small (16 cm2) and larger (1024 cm2) scales. This, together with an increase in the number of negative bryophyte associations over two years, suggests that competition between bryophyte species might occur in ungrazed grasslands.Multi-species patterns of bryophytes and lichens, vascular plants, and of all species together, based on 100 cm2 plots, were detected by Detrended Correspondence Analysis followed by pattern analysis with the program PASFRAN. Cryptogams and phanerogams together formed multi-species patterns that differed from those of the two vegetation layers when analysed separately. This suggests that interactions between cryptogams and phanerogams may occor.Greenhouse experiments with artificial bryophyte communities at different densities showed that alvar bryophytes are organised in a competitive hierarchy. There were significant effects of interactions at the community level; hence interactions between species may affect bryophyte community composition.Additional greenhouse experiments showed that both mosses and lichens might negatively affect seedling emergence of certain vascular plant species. Removal experiments conducted in the field also showed that mosses and lichens were able to hinder the recruitment and growth of both short-lived and long-lived phanerogams, and to reduce species richness. However, only lichens and not bryophytes affected phanerogam biomass negatively.In conclusion, it is suggested that interactions between species and vegetation layers might be one of the factors structuring both the bryophyte-lichen and the vascular plant layers in the studied limestone grassland community.