Vegetation Control for Douglas-Fir Regeneration on the Siuslaw National Forest: A Decision Analysis

Author： Knapp Walter H. Turpin Thomas C. Beuter John H.

Publisher： Society of American Foresters

ISSN： 0022-1201

Source： Journal of Forestry, Vol.82, Iss.3, 1984-03, pp. : 168-173

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Abstract

Records from 324 plantations on the Siuslaw National Forest of western Oregon were used to develop stocking outcomes from various methods of controlling competing vegetation before and after trees were placated. A decision-tree analysis indicated that if no site preparation or release were practiced, the forest as a whole would develop 63 percent of the mean annual increment and 35 percent of the present net worth expected if all means for chemical and manual vegetation control were available and used. With only manual means of vegetation control available (no chemicals), the expected values would be 78 and 57 percent, respectively. Where all means except phenoxy herbicides were available, the expected MAI and PNW were reduced only slightly. These values varied with the type of prelogging vegetation and aspect: declines were least on southwest aspects with predominantly conifers before logging and greatest on northeast aspects that had supported hardwoods. In all strata, however, a restriction against phenoxy herbicides had mirror effect. The results of this case study may or may not apply elsewhere, but the method of analysis should be useful.