Factors determining bryophyte species richness and community composition on insular siliceous erratic boulders in calcareous landscapes

Aim Pleistocene erratic boulders are rocks that were relocated by glaciers during the Ice Ages. When their geology differs from of landscape surrounds them, form habitat islands for regionally rare, edaphically specialised, rock-dwelling cryptogams (bryophytes, ferns and lichens). Such constitute terrestrial model systems exploring island biogeographic predictions effect environmental variables on species diversity community composition, which we studied in order to provide basic knowledge ecology, with relevance conservation, these unusual systems. Location Siliceous calcareous Swiss Plateau Jura Mountains. Methods For 160 recorded all bryophyte a diverse set variables. specialist (acidophile rock-dwellers) separately, analysed species–area relationships nestedness, explored between variables, composition. Results We found 138 species, 19 specialists boulders. A steeper curve boulder than total richness underlined properties species. Large more likely harbour numerous communities small nested within present large However, at level contributed few same surface area. Erratic near settlements less specialists. Boulders open land harboured different forests. Conclusions undisturbed rare number Conservation should thus prioritise this type Furthermore, conserving is logistically easier, they may function as flagships also contribute biodiversity landscapes.