Strategies for Enhancing Western Gray Squirrels on Fort Lewis

Western gray squirrels (Sciurus griseus griseus) have become increasingly rare in Washington, and are listed as ‘threatened’ by the Washington Department of Fish and Wildlife. Western gray squirrels in Washington are at the northern extent of their range, where they are associated with Oregon white oak (Quercus garryana) woodland communities. Oak woodland communities are also in decline, and are considered ‘priority habitat’ by the Washington Department of Fish and Wildlife.

The purpose of this document is to provide information to guide the recovery of western gray squirrels on Fort Lewis by: a)describing their important habitat requirements, b) identifying potential threats to the population, and c) providing options for management actions that ameliorate those threats and enhance habitat quality. The development and implementation of these management options constitute the next logical steps in the conservation of wetsern gray squirrels on Fort Lewis, following on the initial success of actions to control dense stands of Scotch broom (Cytisus scoparius) and other woody invsives, remove invading conifers, and plant native oaks.

Oak woodland stands are distributed across the Fort Lewis landscape, but few stands appear to have been occupied by western gray squirrels int he recent past (Figure 1). Research describing the distribution and habitat of western gray squirrels on Fort Lewis revealed that oak-conifer stands used by squirrels were generally greater than 2 ha in size and less than 0.6 km from a water. High-use stands included a mix of conifers, oaks, and other hardwoods such as big leaf maple (Acer macrophyllum) and Oregon ash (Fraxinus latifolia) in the canopy. Large, healthy oaks and conifers (especially ponderosa pine [Pinus ponderosa]) are more likely to provide greater quantities of mast foods and more nest and den sites compared with smaller trees of the same species. Understory conditions in oak stands used by squirrels on Fort Lewis include patchy understory vegetation, consisting of native food-bearing shrubs or small trees such as Indian plum (Oemleria cerasiformis) and California hazelnut (Corylus cornuta), but devoid of Douglas-fir (Pseudotsuga menziesii) saplings, dense stands of snowberry (Symphoricarpos alba), and invasive species such as Scotch broom, blackberries (Rubus spp.), and non-native grasses.