Effects of summer sheep grazing on browse nutritive quality in autumn and winter

Prescribed livestock grazing in summer may improve the nutritive quality of autumn and winter browse for wild ungulates. We examined the effects of ea rly-summer versus late-summer sheep grazing on autumn ana winter browse qua lity in northern Idaho. Nutritive quality of 6 shrub species collected in S eptember (autumn) and November (winter) was measured following early-summer (May-June) sheep grazing, late-summer (August) sheep grazing, and no grazi ng in 1993 and 1994. Shrub samples were analyzed for crude protein (CP), av ailable protein, neutral detergent fiber (NDF), acid detergent fiber (ADF), and acid detergent lignin. Relative to the ungrazed control, early-summer sheep grazing improved both autumn and winter browse quality in redstem cea nothus (Ceanothus sanguineus), ninebark (Physocarpus malvaceus), rose (Rosa spp.), and snowberry (Symphoricarpus spp.). Early-summer sheep grazing imp roved browse quality of thimbleberry (Rubus parviflorus) in autumn but had no effect on its nutritive quality in winter. In contrast, late-summer shee p grazing reduced both autumn and winter browse quality in redstem ceanothu s and ninebark. Late-summer grazing reduced autumn browse quality in snowbe rry and rose but improved browse quality of rose in winter. Scouler willow (Salix scouleriana) was not readily selected by sheep in either grazing sea son, which explains why the nutritive quality of Scouler willow in autumn a nd winter was unaffected by the grazing treatments. For most browse species , fiber content in autumn and winter was higher in 1993 than 1994, due to w eather conditions. We conclude that prescribed sheep grazing can either imp rove or reduce autumn and winter browse nutritive quality for wild ungulate s, depending upon weather conditions and the intensity of sheep browsing. F or transitory ranges of the Inland Northwest, we suggest browse quality wil l likely improve if moderate sheep grazing (40-55% relative utilization) in summer ceases by mid- to late June. Autumn and winter browse quality shoul d be largely unaffected if moderate sheep grazing in summer ceases by mid-A ugust. Browse quality in autumn sill probably be lowered if sheep grazing o ccurs in late August, but moderate sheep grazing in late August will have r elatively minor effects on browse quality in winter.