Cavities in snags along a wildfire chronosequence in eastern Washington

We sampled occurrence of bird-excavated cavities in snags in a chronosequcnce of 26 wildfire burns (ages 1-81 years) on the east slope of the Washington Cascade Range, USA. Cavities occurred in 5.5% of the 1,867 recorded snags; most (69%) were in burns <20 years old. Cavities occurred at higher rates in ponderosa pine (Pinus ponderosa, 28%) and Douglas-fir (Pseudotsuga menziesii, 8.4%) snags than in snags of other tree species (less than or equal to5%). Few or no cavities were found in large samples (n > 250) of subalpine fir (Abies lasiocarpa; 0.2%) and lodgepole pine (Pinus contorta; 0.0%) snags. Cavities occurred in about 4% of the small samples (n < 100) of Engelmarm spruce (Picea engelmannii; n = 48) and western larch (Larix occidentalis; n = 74) snags. Large diameter, burn age :20 years, soft-decay condition (Class 3+ :), broken-top condition, and moderate height were important predictors of cavities in ponderosa pine and Douglas-fir snags. Cavity-bearing ponderosa pine snags were best characterized as largediameter (>34 cm diameter at breast height [dbh]) snags >2 m tall and located in middle-age to older burns (>19 years old). Cross-validated accuracy of the classification tree model was 97% for cavity snags and 82% for snags without cavities. Cavity-bearing Douglas-fir snags were best characterized as large-diameter snags (>33 cm dbh), or as smaller soft snags (Class 4, 5) at elevations <1,200 m. Accuracy of the classification tree model was 88% and 73% for snags with and without cavities, respectively. In burns <20 years old, Douglas-fir snags with broken tops had higher cavity excavation rates (6%) than snags with whole tops (0.25%). Aspect, slope, slope position, and elevation had negligible or no value for classification. To ensure good post-fire snag habitat, manage pre-fire green stands for tree species, large size, defect (e.g., broken tops), and spatial pattern that will provide cavity snags in short and long terms. When salvaging burns, retain snags with defects incurred prior to fire, especially broken tops, and large-diameter snags of species known to be most suitable for cavity excavation in that area.