Snag retention, wildlife usage, and surface fuel deposition following large, stand-replacing wildfires in dry coniferous forests

Background/Question/Methods Fire-killed trees provide critical habitat for wildlife species, but also add to surface fuel loads as they decay and fall. Recent debates over post-fire logging in dry coniferous forests have highlighted the need for a greater understanding of trade-offs between the ecological benefits of fire-killed trees as future wildlife habitat and the potential fire hazards of future surface fuels. The purpose of this study was to describe temporal patterns of snag decay and fall, surface fuel accumulations, and snag usage by cavity-nesting birds following stand-replacing wildfires in dry western coniferous forests. We sampled fire-killed trees and surface fuels on 126 plots within a chronosequence of 49 wildfires that burned dry coniferous forests of eastern Washington and Oregon during 1970-2007.

Results/Conclusions Surface accumulations of small diameter fuels (up to 7.6 cm) and larger diameter (> 7.6 cm) sound fuels increased to a maximum 10-20 years following fire and then declined, with large diameter fuels peaking later than small diameter fuels.  Rotten large diameter fuels increased monotonically with time since fire up to 37 years. Pre-fire stand basal area was positively correlated with amounts of large diameter fuels.  The probability of a standing snag containing a wildlife cavity increased over time, but probabilities varied among snag diameter size classes and species.  Snags with broken tops were more likely to have cavities than whole snags, and ponderosa pine snags were somewhat more likely to have cavities than Douglas-fir snags.  Habitat usage of medium diameter snags (30 to 60 cm diameter) increased at a faster rate than that of small or large diameter snags with time since fire up to 30 years.  Small diameter snags generally fell without being used by cavity-nesting species, while wildlife usage of large diameter snags was low for the first 20-30 years after wildfire.  Removing smaller trees after fire, especially in dense stands, may help reduce fuels with little impact on cavity nesters, but retaining some medium-sized snags along with large snags could help provide continuity in habitat availability for cavity-nesting wildlife species during the first few decades following wildfire.