Vegetation Changes in Old Stands of Pinus sylvestris L. in Southern Finland

Vegetation changes taking place over a period of approximately 30 years in old Scots pine stands growing on dry and subdry heaths (Calluna site type and Vaccinium site type) in southern Finland were examined on 16 permanent sample plots. The coverage of Dicranum polysetum increased on the average from 11% to 22%, and the frequency from 81% to 97%. The coverage of Pleurozium schreberi decreased from 53% to 41%, and that of Hylocomium splendens from 15% to 8%. The coverage of lichens, mainly Cladonia species, decreased on the Calluna site types on the average from 30% to 22%, and the frequency from 91% to 78%. The coverage of Vaccinium vitis-idaea decreased on the average from 33% to 20%. The changes in Vaccinium myrtillus and Calluna vulgaris were less, and more variable on the different types of site, than those of Vaccinium vitis-idaea. No marked changes were found in the occurrence of grasses or herbs. The material does not give any definite answers to the question of which factors have brought about the vegetation changes. In addition to natural succession and annual variation of some species, the effect of air pollution has also been given consideration.