Leininger and Sharrow evaluated sheep browsing of Douglas-fir (Pseudotsuga menziesii) seedlings in 1981 and 1982, on the Coast Range of Oregon. Most sheep browsing of Douglas-fir seedlings was confined to spring when new, succulent growth was present. Sheep removed some lateral foliage from 75 to 100% of all study trees in both May-grazed plantations each year. The number of trees that received lateral browsing from sheep was lower during July and August than during May. Consumption of Douglas-fir current annual growth (CAG) by sheep was highest both years of the study in Y-My where it averaged 40%. In contrast, sheep only consumed 1% of the CAG of the study trees in the 2-year-old plantation grazed in July (Y-Jy) and the two older plantations grazed in July and August. Although 96% of the seedlings 50 cm or less in height had terminal leaders browsed by sheep, only 15% in the 111- to 120-cm height class had terminals browsed. Mechanical impacts of sheep on Douglas-fir seedlings were very low during all seasons regardless of plantation age. In neither year did sheep mechanically impact more than 3% of the trees in any plantation. Sheep primarily impact planted regeneration by browsing their foliage rather than by trampling. Data suggest that Douglas-fir forests can be grazed by sheep with little to no damage to conifer regeneration, except in younger plantations in spring.
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