Release of Douglas-fir seedlings: growth and treatment costs

Should a plantation be released?And if released, what would be the tradeoffs between stem caliper growth of Douglas-fir seedlings and treatment costs?Such questions often are asked by foresters and plantation managers.A 3-year-old plantation on the Klamath National Forest in northern California was released from deerbrush by several manual and chemical techniques: grubbing shrub and herbaceous seedlings in a 2-, 4-, and 6-foot(0.6-,1.2-, and 1.8-m) radius around Douglas-fir seedlings; and applying 2,4-0 as a direct spray in a 3-foot (0.9-m) radius around seedlings and throughout an entire one-seventh acre (0.06 hal area.Treatments were applied twice at a 2-year interval.Four years after the first treatment, Douglas-fir stem caliper at 12 inches (30 em) above mean ground line differed significantly (0.69 ± .30inch or 1.75 ± .76 em) between the entire area (one-seventh acre) directly sprayed with 2,4-0 and the untreated control.Additional analyses, which compared various combinations of treatment means indicated by the data, showed significant differences in Douglas-fir seedling survival (46.5 ± 19.5 percent) and stem caliper (0.58 ±.32 inch or 1.47 ± .81em).In addition, biological data such as density, cover, height, and internal moisture stress of deerbrush, and annual stem caliper increment, annual height increment, and internal moisture stress of Douglas-fir, suggest that Douglas-fir will show additional response to the treatments in the near future.Costs for two applications of each treatment ranged from $46 to $617 per acre ($114 to $1525/ha), with grubbing a 6-foot (1.8-m) radius being the most expensive and spraying the entire area with 2,4-0 the least expensive.Grubbing small radii (less than 5.0 feet or 1.5 m) around Douglas-fir seedlings did not appear to be effective because roots of "edge" plants rapidly extended into the cleared area.Douglas-fir seedlings competing with many shrubs had smaller stem caliper increments than did seedlings with at least some growing space.Seedlings in the contrOl, for example, had to sacrifice stem caliper and live crown development for height extensionaverage stem caliper growth during the study increased an average of 35 percent; average height, by 168 percent.Information collected on growth dynamics and internal moisture stress relationships of deerbrush add to our knowledge on the ecology ofthis widespread and highly competitive shrub.