Grazing and Douglas-Fir Growth in the Oregon White-Oak Type
Douglas-fir seedlings planted in an Oregon White Oak foothill area grew faster in plots subjected to carefully-controlled short-term spring sheep grazing time in ungrazed plots. In 1952 and 1953, 2-0 Douglas-fir seedlings were planted in three situations: (1) clearcut, (2) thinned white oak, and (3) fully-stocked white oak. From 1955 to 1960, inclusive, yearling ewes were grazed three or four weeks each spring on one-half of each of the three original plots. Animal weights and weight gains were recorded. Animals were brought in each spring when there was adequate herbaceous forage; they were removed when they ceased to gain. Soil moisture at three depths was measured throughont the growing season on all grazed and ungrazed plots. Gravimetrically-calibrated Coleman fiberglass moisture units were used. After three years of spring grazing, Douglas-fir tree-height growth became significantly greater on the grazed plots than in the ungrazed plots, and continued so during four more years of grazing and until the third year after grazing was terminated, when the growth differential had disappeared. More abundant soil moisture at the 5-inch and 12-inch depths each summer on the grazed plots correlated well with removal of much palatable herbage by the sheep. Seedling growth was most rapid on the clearcut plot, fair on the thinned plot, and slowest on the plot with the full oak company. Ten years after grazing started, Douglas-fir tree heights averaged 25 inches greater (27 percent greater) on the grazed than on the ungrazed plots.
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Document Type: Journal Article
Affiliations: Professor of Forest Management Oregon State University, Corvallis
Publication date: 01 November 1966