Net Precipitation under a Douglas-Fir Forest
Abstract:Under dense stands of old-growth Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) and associated species typical of Douglas-fir forests of western Oregon and Washington, throughfall averaged 76 percent of gross summer precipitation. Throughfall varied with storm size from near 0 percent in storms under 0.05 inch to about 82 percent in storms over 3 inches. Density of old-growth stands, which ranged from 75 percent to 92 percent, had some influence on interception. However, since estimates of density are not generally available, a relationship based on storm size was determined to be more useful. A linear relation, which fits the data best, explained 96 percent of the variation in throughfall in summer months. Throughfall in winter months increased to an average of about 86.3 percent. A precise relationship with storm size was not determined, but in storms producing 8 inches or more gross precipitation, throughfall was estimated to approach 96 percent. Stemflow was relatively unimportant for nearly all species. Weighted average stemflow measured in the 1959-60 water year was only slightly more than 0.27 percent of the total precipitation.
Document Type: Journal Article
Affiliations: Project leader, watershed management research, Pacific Northwest Forest and Rge. Expt. Sta., Forest Service, U.S. Dept. Agric.
Publication date: December 1, 1963
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