The 2002 Biscuit Fire burned through more than 200,000 ha of mixed-conifer/evergreen hardwood
forests in southwestern Oregon and northwestern California. The size of the fire and the diversity of
conditions through which it burned provided an opportunity to analyze relationships between crown
damage and vegetation type, recent fire history, geology, topography, and regional weather conditions
on the day of burning. We measured pre- and post-fire vegetation cover and crown damage on 761
digital aerial photo-plots (6.25 ha) within the unmanaged portion of the burn and used random forest
and regression tree models to relate patterns of damage to a suite of 20 predictor variables. Ninety-eight
percent of plots experienced some level of crown damage, but only 10% experienced complete crown
damage. The median level of total crown damage was 74%; median damage to conifer crowns was 52%.
The most important predictors of total crown damage were the percentage of pre-fire shrub-stratum
vegetation cover and average daily temperature. The most important predictors of conifer damage were
average daily temperature and ‘‘burn period,’’ an index of fire weather and fire suppression effort. The
median level of damage was 32% within large conifer cover and 62% within small conifer cover. Open tree
canopies with high levels of shrub-stratum cover were associated with the highest levels of tree crown
damage, while closed canopy forests with high levels of large conifer cover were associated with the
lowest levels of tree crown damage. Patterns of damage were similar within the area that burned
previously in the 1987 Silver Fire and edaphically similar areas without a recent history of fire. Lowproductivity
sites on ultramafic soils had 92% median crown damage compared to 59% on non-ultramafic
sites; the proportion of conifer cover damaged was also higher on ultramafic sites. We conclude that
weather and vegetation conditions — not topography — were the primary determinants of Biscuit Fire
crown damage.

Keywords: Biscuit Fire, Fire severity, Random forest analysis, Mixed-conifer and evergreen hardwood, forest, Ultramafic, Reburn