Ice Breakage in Partially Cut and Uncut Second Growth Douglas-Fir Stands

Abstract Douglas-fir second growth stands in the Pacific Northwest are usually very uniform in character. Although there may be considerable range in diameters, heights are often approximately equal, and the long slender boles will support a more or less even, unbroken canopy. When such a stand is partially cut, particularly a stand so young as to be of marginal merchantability, the breaking of this uniform canopy results in abnormal exposure of the residual trees. Losses will result because of physiological inability to adapt to changed site conditions, because of insects and pathogens, and because of climatic damage. Normally these losses are not appreciated because the trees die off intermittently and the extent of the mortality is not evident at any one time. The thinned stands have but a narrow margin of safety against the various inimical factors affecting this species, and their increased vulnerability over the uncut stands is demonstrated whenever such inimical factors attain epidemic proportions. A recent ice storm in western Oregon is a case in point, emphasizing a silvical problem in managing these stands, the maintenance of the optimum number of stems per acre without incurring either stagnation or loss by exposure.