LONG-TERM VEGETATION CHANGES IN STANDS OF PINUS-SYLVESTRIS IN SOUTHERN FINLAND

Understorey vegetation dynamics in Pinus sylvestris L. stands were examined over 30 yr in southern Finland. Data were collected from 112 permanent sample plots twice, first in 1950-1956 and again in 1983-1986. Between the two surveys 52 stands were clear-felled and in the 60 remaining old stands thinnings of various magnitude were conducted. In the mature, thinned stands species presence remained virtually unchanged. With the exception of a few species, including Vaccinium vitis-idaea, Hylocomium splendens, and Dicranum polysetum, the changes in species cover were also slight. In the clear-felled plots the changes in species presence were minor but the cover of many species changed strongly. The average cover of Vaccinium myrtillus and Hylocomium splendens dropped to near zero and that of Vaccinium vitisidaea and Pleurozium schreberi decreased 2 - 4 times on all sites. The cover of Calluna vulgaris approximately doubled, and Cladina rangiferina and Cladina arbuscula also increased after canopy removal. In addition to intrinsic successional change, a special interest in this study was to investigate vegetation dynamics in relation to forest land classification methods in which understorey vegetation is used as part of the classification criteria. The results support the Cajanderian site classification approach, in the case of boreal Scots pine stands, that sites can be classified on the basis of understorey vegetation at different successional phases. However, because of the strong successional and site-to-site variation in species cover, it is suggested that site classification be based primarily on species presence.