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The impact of winter deer (Odocoileus virginianus) browsing on apple production was studied in three commercial orchards in southwestern Wisconsin. Estimates of the proportion of apple buds available to deer, the percentage of available buds browsed, and the apple production were obtained for about 500 sample trees in 1975 and 1976. The accuracy and precision of estimation procedures were evaluated, and the relationship between browsing and production was analyzed. The availability of apple buds to browsing deer was primarily a function of the size and shape of the apple trees. Visual and photographic appraisal indicated that ellipsoids best described the shapes of apple tree crowns, so the proportion of buds available was calculated from equations for ellipsoid volumes for each tree. Good estimates of proportions of available buds browsed were obtained from bud and nip counts on a 2.5 percent sample of the trees, and subjective estimates of the proportion of available buds browsed were correlated with proportions calculated from the actual counts. Multiple regression analyses suggested that the degree of browsing was related to the cultivar, size, and location of the apple trees. In the orchards studied, 34 and 10 percent of the growing points were removed by deer in 1975 and 1976, respectively. Analyses indicated that deer browsing decreased apple production on size-controlled (dwarf and semidwarf) trees, but not on standard sized trees. Two methods of evaluating deer damage are proposed. The first method uses realized production figures and estimates of the percentage of the orchard browsed, whereas the second method requires only an estimate of buds browsed in the damaged areas to predict production loss.
vertebrate pest control, deer damage, deer browsing, damage assessment, evaluation of deer damage, deer damage to orchards, orchards, apple trees, appraisal methods
wildlife manager, Wisconsin Department of Natural Resources, Plymouth, Wis
Leader, University of Wisconsin, Madison, Wis