Forage Availability in Relation to Browsing of Douglas-Fir Seedlings by Black-Tailed Deer

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Abstract
Relationships between forage availability and browsing of planted Douglas fir (Pseudotsuga menziesii) by black-tailed deer (Odocoileus hemionus columbianus) were studied between June, 1961, and Feb., 1964, in a 340-acre enclosure occupied by known numbers of deer. The study area, in the Tillamook Burn of northwest Oregon, was burned by 3 wildfires between 1933 and 1945 which destroyed virtually all conifers. Since 1945, much of the enclosure has been highly disturbed by salvage logging and subsequent erosion, and vegetation consists mainly of seral species of 6 plant communities. Overstory plant cover averaged 12 [degree]/o and understory cover 77 [degree]/o in the summer of 1963. Green weights of summer forage averaged about 2600 lb/acre and forage available for the following winter about 640 lb/acre at the end of the growing season. By midwinter, weathering losses and deer utilization had greatly reduced this amount. Winter growth of herbaceous forage produced about 90 lb/acre of green feed in March, and by May, forage was again abundant. Leaves of trailing blackberry (Rubus ursinus) were highly preferred forage during winter. Salal (Gaultheria shallon) ranked high but was limited in distribution and abundance. Red huckleberry (Vaccinium parvifolium) and cascara (Rhamnus purshiana) were preferred among common woody plants, but red alder (Alnus rubra), hazel (Corylus cornuta), and wine maple (Acer circinatum) were browsed only when green herbage was unavailable. Green herbage was highly important in winter and early spring. Leaves of forbs and woody plants supplied most summer forage and were utilized in all seasons when available. Planted Douglas fir seedlings ranked higher in preference than most common woody species. Browsing on Douglas fir began with the first snowfall and continued through the winter. It is evident that browsing of Douglas fir will continue until seedlings grow out of reach of deer, because this species is an important food source during winter when preferred green forage is least available.

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