Snag dynamics in a chronosequence of 26 wildfires on the east slope of the Cascade Range in Washington State, USA

Snag numbers and decay class were measured on a chronosequence of 26 wildfires (ages 1-81 years) on the east slope of the Cascade Range in Washington. Snag longevity and resultant snag densities varied spatially across burns in relation to micro-topographic position. Longevity of snags < 41 cm dbh was greater for thin-barked Engelmann spruce (Picea engelmannii), subalpine fir (Abies lasiocarpa) and lodgepole pine (Pinus contorta) than thick-barked Douglas-fir (Pseudotsuga menziesii) and ponderosa pine (Pinus ponderosa). With larger diameter snags, however, Douglas-fir persisted longer than Engelmann spruce. The time period required for recruitment of soft snags > 23 cm dbh was estimated to exceed snag longevity for ponderosa pine, Engelmann spruce, lodgepole pine, and subalpine fir, causing an "on-site gap" in soft snags for these species. Snags of Douglas-fir greater than or equal to 41 cm dbh stood for a sufficient time (40% standing after 80 years) to potentially overlap the recruitment of soft snags greater than or equal to 23 cm dbh from the replacement stand. Providing continuity in soft snags following stand-replacement events would require a landscape-scale perspective, incorporating adjacent stands of different ages or disturbance histories. Results suggest that standards and guidelines for snags on public forest lands need to be sufficiently flexible to accommodate both disturbance and stand development phases and differences in snag longevity among species and topographic positions.