The effects of fertilization and thinning on wood quality of a 24-year-old Douglas-fir stand

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Abstract
This report describes the growth and wood density response of a coastal Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) stand on a poor site to thinning and nitrogen fertilization. The treatment plots were established in 1971 and 1972 at about 24 year of age. The effects of fertilization and thinning were evaluated 12 and 13 years after the initial treatments of the 1972 and 1971 plots, respectively, and 3 years after refertilization of the 1972 plots in 1981. Ring-width and ring-density data were obtained from pith to bark for all trees and were derived from computerized X-ray densitometry. Fertilization reduced ring density at breast height and 25% stem height by an average of 16% for a 3- to 4-year period after treatment, but not thereafter. Reductions in ring density resulted from decreases in the density of earlywood and latewood, as well as from decreases in the percent of latewood. Effects were only pronounced in the lower half of the stem. Thinning resulted in a slight ring-density gain in the lower bole and a reduction in the top. The combined treatments had an intermediate effect on ring density. Ring density showed an increasing trend from pith to bark at all heights, except at the 75% height, and a decrease with increasing height in the bole. Fertilization and thinning both increased diameter growth, and their beneficial effects were still evident 13 years after treatments.