TRENDS OF TREE GROWTH IN SWEDISH FORESTS 1953-1992 - AN ANALYSIS BASED ON SAMPLE TREES FROM THE NATIONAL FOREST INVENTORY

Average tree height and basal area growth for Scots pine (Pinus sylves tris L.) and Norway spruce (Picea abies (L.) Karst.) in Sweden were st udied as functions of species, age, stand density, location and year o f inventory in the period 1953-1992, on the basis of sample tree data from the National Forest Inventory. A highly significant annual increa se of both height and basal area growth was found, of the magnitude 0. 5-0.8%, during the 40 yr period. Possible reasons for the trend are di scussed. The altered way of cutting in the early 1950s, from selective cutting to clear felling and thinning from below, has had a large imp act. Also, improved regeneration methods, nitrogen fertilization and d itching have increased growth. The increasing atmospheric deposition o f nitrogen is another possible factor.