REGIONAL DIFFERENCES IN FLORISTIC CHANGE IN SOUTH SWEDISH OAK FORESTSAS RELATED TO SOIL CHEMISTRY AND LAND-USE

Changes of the ground-layer vegetation between 1983 and 1993 were stud ied on permanent oak forest plots in Skane and eastern Smaland, two re gions of South Sweden rich in oak but with different climatic conditio ns. 79 of the 123 more common species differed considerably in frequen cy between Skane and Smaland. The oak forests in Skane contained more typical forest species, whereas the number of light-demanding grasslan d species was higher in Smaland. Almost half of the more common specie s showed significant changes in frequency between 1983 and 1993. Sever al species of clearings and some light-demanding grassland species inc reased their frequency in Skane. They were probably favoured by canopy thinning which occurred in 65 out of 95 permanent plots. Only two spe cies 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 estab lishment of new species at intense management. A small general increas e in species numbers was recorded in Smaland. Species richness was mor e closely related to soil pH in Skane than in Smaland. The floristic v ariability between the oak forest plots was closely related to soil pH in both Skane and Smaland. We suggest that changes of light condition s as a result of changes in forest management are important for curren t secondary succession in South Swedish oak forests, whereas the gener al floristic pattern is to a large extent controlled by soil acidity.