Relationships between tree stand density and burn severity as measured by the Composite Burn Index following a ponderosa pine forest wildfire in the American Southwest

•Tested a rapid visual classification of stand density for use by land managers.•Density classes were highly correlated with CBI scores.•BAER severity classes were highly correlated with CBI scores.•Reducing density of southwest ponderosa may significantly lower burn severity.

The Trigo fire burned 5548 ha of the Manzano Mountains in central New Mexico in 2008. The fire burned with mixed severity through ponderosa pine (Pinus ponderosa) stands on the Cibola National Forest and private lands. The burned area exhibited a range of stand densities enabling this research to quantify the relationship between variation in tree density and burn severity using the Composite Burn Index (CBI) severity classification. Across 90 CBI plots, high tree density was strongly associated with high burn severity. The CBI method allowed classification of burn severity to a range of forest vertical fuels strata. Tree mortality and duff consumption are two attributes that recorded higher severity in plots with higher tree densities. The CBI approach is designed for rapid on-the-ground assessments; to compliment this procedure a rapid visual classification of stand density was tested to determine its accuracy for land managers. This visual assessment correlated well with quantitative measurements of tree density. Since density classes were also highly correlated with CBI scores they may therefore be a good predictor of burn severity in a stand. This is a more rapid way for land managers to categorize stand density than traditional density measurements. These findings demonstrate that reducing tree density in southwestern ponderosa pine stands may significantly lower burn severity resulting from wildfire.