| Abstract: | "Forage quality and quantity are nutritional attributes that influence ungulate populations through bottom-up processes. In northern Idaho, harsh winters occasionally cause substantial mortality of elk (Cervus canadensis) and deer (Odocoileus hemionus) populations; however, recent studies in the Western United States show that nutritional deficiencies on summer range also affect populations by reducing reproduction and survival. In fact, in many settings, nutritional deficiencies in summer may have a more limiting effect on elk populations than deficiencies in winter. Large tracts of mid- and late-succession forests, a product of fire suppression and declines in timber harvest in many areas of the West, often support forage resources of relatively low quantity and quality. Natural disturbance events and forest management can greatly increase forage quantity and quality to improve forage resources across landscapes. We sampled plant communities in northern Idaho during the summers of 2016 and 2017 to describe patterns of forage quantity and quality among seral stages and potential vegetation communities from late spring through early autumn. In this report, we summarized these patterns and provided insights for managing forests to improve forage for elk. For all potential vegetation (PV) series ranging from Douglas-fir to subalpine fir, early-seral communities (<25 years old) provided greater forage abundance and often forage of higher quality. But forage response to disturbance varied among PV series. Forage quality was higher in PV series at higher elevations (e.g., the spruce-fir, western redcedar, and western hemlock series), particularly in late summer. Early-seral communities created by stand-replacing disturbance produced the best forage (high quantity and high quality) for elk in the western redcedar, western hemlock, and wetter extents of the grand fir and spruce-fir series, providing the greatest benefit to elk relative to the cost of increasing forage through forest management. In PV series where climate is especially conducive to conifer growth (e.g., western redcedar, western hemlock, and wetter extents of the grand fir series), forest overstory development after disturbance was rapid, and duration of abundant, nutritious forage in the early-seral communities was short. Successional development of the overstory in drier PV series at lower elevations (Douglas-fir series) and at the highest elevations (spruce-fir series) was slower, and forage readily consumed by elk persisted into older stands to a greater degree than in series where climate supports rapid conifer development. Dense mid- and late-seral forests greatly dominated across central and eastern portions of our study area, suggesting that restoring early-seral communities, well-distributed across the region, will benefit elk and other wildlife that depend on these productive, diverse community types". |
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