Thinning and Prescribed Fire Effects on Snag Abundance and Spatial Pattern in an Eastern Cascade Range Dry Forest, Washington, USA

Mechanical thinning and prescribed burning practices are commonly used to address tree stocking, spacing, composition, and canopy and surface fuel conditions in western US mixed conifer forests. We examined the effects of these fuel treatments alone and combined on snag abundance and spatial pattern across 12 10-ha treatment units in central Washington State. A snag census was conducted before and immediately after treatments on each unit where all snags were measured and classified as either "new" (<1 year as a snag) or "old" (>1 year as a snag) mortality, and bark beetle species were censused on the bottom 3-m of the bole. Before treatment, snags were found in all units and more than two-thirds of the snags were ponderosa pine. Burning (bum-only and thin + burn combined) treatments led to increases in total snag abundance in all but the largest diameter class. Snag abundance in the large snag class (>60 cm dbh) decreased in most treatment units indicating that units with high abundance before treatment had the potential to lose more snags with treatment or time. Treatments also affected the spatial distribution of snags. The thin-only treatment reduced clumpiness, leading to a more random snag distribution, whereas the burn-only and thin + burn treatments generally retained or enhanced a clumped snag distribution. Bark beetles attacked >75% of snags across all units before and after treatments, and red turpentine beetle (Dendroctonus valens LeConte) occurrence tended to increase after prescribed burning. Managers can use this information to tune silvicultural prescriptions to meet stocking, spacing, and fuel reduction objectives while retaining or recruiting snags, thereby increasing the utility of conditions for certain wildlife species. FOR. SCI. 56(1):74-87.