Wood density traits in Norway spruce understorey: effects of growth rate and birch shelterwood density

Effects of growth rate and birch shelterwood density (0, 300 and 600 trees ha(-1)) on wood density traits in Norway spruce (Picea abies (L.) Karst.) u nderstorey were evaluated for a trial in the boreal coniferous forest 56 ye ars after establishment of the stand and 19 years after establishment of th e trial. Wood density traits were measured by micro-densitometry for annual rings 21-30 extracted at breast height. In addition, ring width and mean d ensity were measured for all annual rings. Growth rate was generally low wi th a mean ring width of 1.3 mm. Radial variations in ring width and density depended more on calendar year than on cambial age. The shelterwoods had m oderate d fluctuations in ring width, but not in wood density. For annual r ings 21-30, the mean density was 12 % higher in trees of the lowest growth rate compared to trees of the highest growth rate. Also, minimum density an ti latewood percentage were higher in trees with the lowest growth rate com pared to all other trees, while then were no significant effects due to she lterwood treatment for any of the wood density baits tested. An increase in ring width from I to 2 mm resulted in an 18 % decrease in wood density. La tewood percentage explained 84 % of the variation in wood density. (C) Inra /Elsevier, Paris.