Effects of management and altitude on bryophyte species diversity and composition in montane calcareous fens

We examined patterns of bryophyte species richness and communities in 36 montane calcareous fens in Switzerland. Sites differed in management regime (grazing vs, mowing) and altitude. In addition, several environmental variables were measured. Bryophyte diversity was determined as species density (mean of 5 plots per site), as species richness (number of all species of a site) and as beta -diversity. Species richness was 20% higher at grazed than at mown sites. We interpret this as the result of higher environmental heterogeneity at grazed sites. This could also be the cause for the significantly higher beta -diversity at grazed sites. However, there was a significant management x altitude interaction caused by species-poor sites at low altitudes under grazing. This interaction might be caused by more intensive grazing at low altitude. Grazed sites contained the higher overall species richness (117 vs. 79), more exclusive species (47 vs. 9), and more Red List-species (12 vs. 6). Altitude had only an effect on the number of exclusive species, which was highest at high-altitude sites. No differences could be found for species densities both between management regimes and between altitude classes. This result indicates no differences in habitat heterogeneity at the within-plot scale. For analysis of effects of environmental variables on bryophyte communities, we used a direct ordination technique (CCA). The variables pH, amount of total carbon in the soil and management turned out to be the most important in explaining variation in the species data. However, variation explained by total carbon could also be explained in terms of total nitrogen or moisture. For preserving bryophyte diversity in montane wet meadows, extensive grazing by cattle is crucial. Due to slightly different bryophyte communities under the different management regimes, however, bryophyte diversity at the landscape level will be highest when both types of management are maintained.