Manual Release in an "old" Douglas-fir Plantation Increases Diameter Growth

Philip M. McDonald

01/1989 · U.S. Department of Agriculture, Forest Service, Pacific Southwest Forest and Range Experiment Station

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Twelve-year-old Douglas-fir saplings on the Mad River Ranger District, Six Rivers National Forest, Califomia were released by cutting competing vegetation in a 9-foot radius to test the timing and efficacy of this method in plantations older than 1 those in which such work traditionally is done--the I first 5 years. Nine years after release, the average stem diameter (3.60 inches or 9.14 cm) of released Douglas-fir saplings, taken at 12 inches (30 cm) above mean groundline, differed significantly from that of mntrol saplings (2.98 inches or 7.57 cm)(p 0.05), although the average height did nor differ (p 0.05). In spite of this finding, the stem diameter of released saplings was 40 percent less than that needed to comply with regional Forest Service growth objectives. Cost of release averaged $428 per acre or $1058/ha in 1978 dollars.