Vegetation development after the exclusion of grazing cattle in a meadow area in the south of Sweden

Abstract

A study of 24 years of secondary succession was based on data from semi-permanent quadrats from investigations in 1952, 1955, 1968 and 1976, involving two exclosures, the first in a meadow grazed for hundreds of years but now abandoned, the second in a meadow mowed for hundreds of years and grazed for the last 50 years. A first order classification of quadrats produced units, which formed distinct spatial patterns indicating similar gradients, but also differences in response to the ceased grazing, in the two exclosures. A second order classification of units into groups revealed a rather simple structure of spatial and temporal relations. Eleven groups of species with similar behaviour could be recognized within a system of spatial and temporal species distributions. The vegetation in both exclosures developed towards an increased differentiation and heterogeneity or patchiness. The border between two soil types was clearly reflected in the spatial pattern of units. Rates of change were greatest in the beginning and were shown to closely follow logarithmic functions of time. The average number of species per m² decreased in all plots, in some cases as much as 50%. It was concluded that the diversity had decreased as a consequence of decreased species richness, decreased evenness and decreased pattern diversity. Many individual species distributions showed a pattern of nuclei surrounded with marginal belts. Differences in rate of change and persistence of spatial patterns between the plots, could be attributed to the differences in management history. These differences have disappeared as the succession has proceeded. The two exclosures have instead both conformed to the same floristic gradient, in turn based on a similar pattern of environmental gradients, primarily moisture. In the observed changes the emphasis was on the shifting importance of competing species populations, as some gained in importance at the expense of others. Competition has so far been a more important process in the vegetation development than immigration/extinction rates.