1. EFFECT OF HARVEST REMOVAL ON PRODUCTIVITY OF A 15-YEAR-OLD DOUGLAS-FIR PLANTATION. by Dale W. Cole and Jana E. Compton University of Washington and Harvard Forest ABSTRACT In 1979 a study was established in western Washington to examine the effect of harvest removal on second-rotation Douglas-fir productivity. Three levels of removal were included: bole only, whole-tree (above-ground), and whole-tree plus forest floor. The study was established in adjacent areas of low and medium site quality (24 vs. 34 m site index at 50 years for Douglas-fir). After 5 years, 224 kg urea N ha-1 was applied to one of the paired plots within each of the harvest removal treatments. Height growth records after 15 years indicate that for the low quality site, there is a consistent relationship between the amount of harvest removal and the reduction of height and diameter growth of the second-rotation plantations. Mean tree height on the complete- removal plot was 26% less than that on the bole-only plot with a similar reduction in mean diameters. However, this same growth reduction was not noted at the higher productivity site. Fertilization resulted in an increase in growth and largely restored the decrease in production caused by harvest removal. We conclude that the low quality site forest was N deficient and harvest removal further aggravated this deficiency

2. Table 1. Biomass and nitrogen contained within each ecosystem component prior to harvest, and the removal of biomass and nutrients through harvest. (from Compton and Cole 1990).

4. Table 2. Additional leaching of N, primarily as nitrate, past the 50-cm soil depth during the first year following harvesting (from Bigger and Cole, 1983). Net leaching losses were calculated by subtracting losses in the forested control from those in the treatment plots.

5. Table 3. Total loss of N by harvest removal and leaching following bole- only, whole-tree, and complete-removal.

6. Table 4. Average height (standard deviation) of seedlings on each plot, 15 years after harvest; significant differences are indicated with letters: “a” signifies the smallest average height (p<0.05; statistical comparisons were made between all treatment plots using Tukey’s HSD).