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.) understorey were evaluated for a trial in the boreal coniferous forest 56 years after establishment of the stand and 19 years after establishment of the trial. Wood density traits were measured by micro-densitometry for annual rings 21-30 extracted at breast height. In addition, ring width and mean density were measured for all annual rings. Growth rate was generally low with 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 moderate d fluctuations in ring width, but not in wood density. For annual rings 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 anti latewood percentage were higher in trees with the lowest growth rate compared to all other trees, while then were no significant effects due to shelterwood 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. Latewood percentage explained 84 % of the variation in wood density. (C) Inra/Elsevier, Paris.