WOOD PRODUCTION AND LATEWOOD PERCENTAGE OF DOUGLAS-FIR FROM DIFFERENT STANDS AND VITALITY CLASSES

Trunk wood production and amount of latewood of 171 Douglas-firs (Pseudotsuga menziesii (Mirb.) Franco) belonging to different vitality classes are analysed. The trees originated from 10 stands in the Netherlands varying in age from 25 to 70 years. Wood production is expressed as radial and volume increment over the last 15 years before sampling. The trees of 25-35 years old showed a better average vitality (less needle loss) than the older trees, and had a higher radial increment. Percentage of needle loss at the time of sampling was significantly and negatively correlated with radial and volume increment. The average latewood percentage over the last 15 years was the lowest in nonvital trees. In nonvital trees the wood-biomass production over the last 15 years was only approximately 30% of that in more vital trees. For the Netherlands as a whole the radial and volume increment in the last 15 years are estimated to be approximately 20% and approximately 4% lower, respectively, than they hypothetically would have been if all Douglas-firs belonged to the vitality classes 0 and 1. Total biomass production by Douglas-fir stands in the Netherlands is not greatly reduced by the small decrease in density in nonvital trees and is approximately 4% lower than if all trees were vital or slightly less vital.