Fire-history implications of fire scarring

Fire scars are widely used to reconstruct fire history, yet patterns of scarring are poorly understood, hampering effective sampling and analysis. Factors that influence the probability a tree will receive a scar (SP) and the fraction of trees that scar (SF) are little studied. We analyzed scarring in 16 fires in ponderosa pine (Pinus ponderosa Douglas ex P. Lawson & C. Lawson) forests in northern Arizona. SP was significantly related to char height, presence of a preceding scar, tree diameter, and years since a preceding fire. Mean SF was 0.375, but varied from 0.121 to 0.728, with SF significantly higher with higher mean char height, larger scar dimensions, higher fire severity, larger tree diameter, and where no preceding fire had burned within 30 years. The expected healing times exceeded 55 years for 33% of scars and 100 years for 11% of scars. Scars with a preceding scar were 38% larger than new scars, with expected healing about 20-25 years longer. Scars were clustered, particularly at scales from > 20 to > 40 m. Scar directions generally aligned with fire-spread directions, which were complex. Variability in SF complicates fire-history methods that use fire counts rather then area burned. Methods that account for spatial and temporal variability in the abundance of evidence are needed.