Response of boreal forest vegetation to the fertility status of the organic layer along a climatic gradient

Relationships between boreal understorey vegetation and chemical composition of the organic layer, stand productivity and climatic factors were studied on 27 coniferous monitoring plots along a S-N gradient in Finland using ordination techniques (fitting environmental vectors and surfaces to the NMDS pattern). Total N, exchangeable Ca and Mg, BS, pH and organic layer thickness formed the subset of variables with maximum correlation with plant community composition. Of the stand parameters, site index (H 100 ), volume and basal area correlated best with the vegetation pattern. Our results support the hypothesis that site productivity can be predicted on the basis of the occurrence of understorey plants. This was especially true in herbaceous plants, where the number of species well depicted the site index on both pine and spruce plots. We present quantitative evidence that the response curves along an extensive nitrogen gradient varied between species representing dwarf shrubs, herbs, grasses, mosses and lichens.