Reforestation Systems Compared on Coastal Clearcuts: 10-Year Results.

摘要

In a large factorial study replicated in six locations, responses of five Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) and two western hemlock (Tsuga heterophylla (Raf.) Sarg.) stock types, tubed and untubed, were observed when planted after each of four site preparation treatments with and without later release. In 10 years, more Douglas-fir seedlings survived than did western hemlock seedlings, 69.6 vs. 57.7 percent, averaged much taller, 543.7 vs. 416.6 cm, and larger in diameter, 8.2 vs. 5.2 cm. Survival of tubed seedlings averaged 82.2 percent, untubed 50.5 percent. Seedling survival, height, and diameter averaged highest in areas prepared by preburn spraying followed by broadcast burning and later release. Large Douglas-fir stock (2+1 and large 2+0) outgrew medium or small stock. Stems clipped near ground line in the first 3 years, largely by mountain beavers (Aplodontia rufa), comprised two-thirds of all mortality. In repeated examinations, vegetative cover was measured along linear transects, stem density and height on milacre plots, and live biomass by destructive sampling. Live vegetative cover averaged 52 percent before site preparation. Rapid establishment of pioneering herbaceous species after site preparation soon erased temporary reductions in total cover. The woody shrub component of total cover was reduced from 23.7 to 9.8 percent by broadcast burning and from 28.0 to 2.5 percent by preburn spraying and broadcast burning. By the third examination, woody shrub cover was double as much in control areas as in the spray-and-burn treatments, 42.0 vs. 20.4 percent. Spraying herbicide for release caused only a minor reduction in woody shrub cover. By the 10th year, woody shrub cover averaged 47.9 percent in the control but only 32.1 percent in the spray-and-burn treatment. More tree cover after spray-and-burn than for other site preparation treatments appears attributable to lower competition of woody shrubs throughout the decade. Red alder (Alnus rubra Bong.) and salmonberry (Rubus spectabilis Pursh) were the most abundant competitors.