SMALL-SCALE DYNAMICS AND SPECIES RICHNESS IN SUCCESSIONAL ALVAR PLANT-COMMUNITIES

Species richness and small-scale spatial dynamics (turnover) were compared in four sites during 1990-1993: 1) former alvar grassland, now young Pinus sylvestris forest, 2) clear-cut in 1990, 3) clear-cut and grazed by sheep, 4) nearby grassland. It was hypothesized that in communities which show large-scale dynamics, small-scale dynamics is also more rapid to support succession. Area-based species richness and shoot density increased in the cut and grazed site. No significant dynamics was found in shoot-based species richness. Therefore the forest was considered to be stable and the cut and grazed site large-scale dynamical (successional). Almost equally high small-scale turnover values were found in all sites, which supports the carousel model for successional communities, but means we had to reject the initial hypothesis. The successional and intrinsic small-scale dynamics of the communities studied were two separate processes which acted at different scales, but the scale could not be only spatially determined, it depended also on the shoot density. The overgrowing of this former alvar grassland has resulted in the decrease of shoot density and thus the decrease of species richness per unit area, but the total number of species has not changed much. Consequently the possibility to restore grassland communities remains.