Auswirkungen der Wertastung auf das Douglasien-Wachstum: Ergebnisse aus Nordwestdeutschland

Effects of pruning on the growth of Douglas-fir: findings from northwestern Germany Owing to Douglas-firs' insufficient self-pruning ability, for the production of high-grade wood, manual pruning is mandatory. Pruning of live branches increases the branch-free tree volume considerably. Branchiness is important for grading wood quality, but with pruning this detrimental characteristic loses its significance for the value of the Douglas-fir asset. In 1980, trials were conducted in the forest district of Ahlhorn (Lower Saxony, Germany) with three-year-old Douglas- firs to test the effects of live pruning on tree growth. The sample material consists of 93 trees which were periodically pruned beginning from a height of 6 to 8 m up to 20, 40 and 60% of tree height, as well as of 9 Douglas-firs of the unpruned control group. However, only specimens with a pruning height of 60% had live branches removed at each pruning. By means of a multivariate linear regression model the effects of pruning on the dependent variates diameter at breast height (dbh), tree height, stem taper of the butt log and maximum branch diameter approximately at a whorl's height of 5 m were studied up to the age of 39 years. Pruning of live branches had a significant effect on periodic radial growth as well as on bottom log allocation, though not on tree height or branch diameter. Live prune led to moderate reduction of radial increment and had a positive effect on stem taper. The results of the study largely agree with earlier studies on the effects of pruning on Douglas-fir growth.