Heterogeneity in semi-natural grasslands: the importance of the elevational gradient

Heterogeneity patterns in semi-natural grasslands were studied within 20 sites at 4 different elevational levels ranging from 530 m a.s.1. at level 1 (southern boreal region) to 1230 m a.s.1. at level 4 (low alpine region) in Vang, southern Norway. Vegetational heterogeneity decreased with elevation for vascular plants. Cryptogam species increased in heterogeneity at mid-elevational levels (750 and 915 m a.s.1.), but heterogeneity decreased again at level 4. Mean values of soil nutrients and other soil variables (e.g. loss on ignition), and their heterogeneity increased with elevation, while pH showed a decrease for both parameters. The general increase in environmental heterogeneity in the soil was not reflected in vascular plant heterogeneity because soil variables explained 40 % variation at both level 1 and 4. However, the relative differences among levels suggest that vascular plant species patterns were more sensitive to soil heterogeneity at lower elevational levels. Soil variables were also relatively more important in structuring cryptogam species at higher elevations (level 3 and 4) compared to vascular plant species. The discrepancy between vascular plants and cryptogams are also shown in the relationship between heterogeneity and diversity. Gamma diversity decreased with decreasing heterogeneity of vascular plants, while the highest value of large scale cryptogam diversity corresponded with the lowest heterogeneity value at level 4. Alfa-diversity peaked at an intermediate level of heterogeneity for vascular plants while alfa-diversity of cryptogams decreased with increasing values of heterogeneity.