Regional differences in floristic change in South Swedish oak forests as related to soil chemistry and land use

Changes of the ground-layer vegetation between 1983 and 1993 were studied on permanent oak forest plots in Skane and eastern Smaland, two regions of South Sweden rich in oak but with different climatic conditions. 79 of the 123 more common species differed considerably in frequency between Skane and Smaland. The oak forests in Skane contained more typical forest species, whereas the number of light-demanding grassland species was higher in Smaland. Almost half of the more common species showed significant changes in frequency between 1983 and 1993. Several species of clearings and some light-demanding grassland species increased their frequency in Skane. They were probably favoured by canopy thinning which occurred in 65 out of 95 permanent plots. Only two species decreased in frequency in Skane, but 14 species showed a decrease in Smaland. All were typical grassland species and their decline may be regarded as a long-term response to ceased grazing and tree canopy closure as almost no tree cutting occurred during the study period in Smaland. Total species richness increased with management intensity in Skane. This was due to decreasing species losses and increasing establishment of new species at intense management. A small general increase in species numbers was recorded in Smaland. Species richness was more closely related to soil pH in Skane than in Smaland. The floristic variability between the oak forest plots was closely related to soil pH in both Skane and Smaland. We suggest that changes of light conditions as a result of changes in forest management are important for current secondary succession in South Swedish oak forests, whereas the general floristic pattern is to a large extent controlled by soil acidity.