Fertilization effects and vegetation-environment relationships in a boreal pine forest in Åmli, S Norway

Species composition in 144 sample plots, each 1 m², in 35-year old pine forest in Åmli municipality in Aust-Agder, S Norway, was recorded. The plots were systematically placed within the 12 blocks in a factorial fertilization experiment [addition of nitrogen (2 levels), magnesium and phosphorus], initiated six years before our analysis was carried out. At each sample plot, 28 explanatory variables were recorded. Results obtained by parallel use of three ordination methods demonstrated existence of one main coenocline from lichen-rich sites to sites rich in mosses and ericaceous species. The coenocline was interpreted by analysis of correlations between plot positions and explanatory variables, and by analysis of spatial structure using geostatistical methods, as a fine-scale moisture complex-gradient. Important correlated variables were: humus depth, tree density and canopy closure, and microtopography.

Small, but significant effects of fertilization by nitrogen and phosphorus on the vegetation was demonstrated and discussed.