Fire Scarring Patterns in Sierra Nevada Wilderness Areas Burned by Multiple Wildland Fire Use Fires

Uncertainty associated with fire-scar reconstructions of historical fire occurrence has led to questioning both estimates of frequency derived from these methods and the inferences on fire regimes drawn from these estimates. Using information from multiple, naturally-occurring fires (referred to as wildland fire use (WFU) fires) in two Sierra Nevada wilderness areas, we identified forest structural, topographic, and fire characteristics influencing fire scarring in trees and conducted direct comparisons of fire-scar reconstructed fire extent and frequency to fire atlas-based estimates of fire extent and frequency. The most important factor influencing the probability of sampled Pinus jeffreyi trees scarring from WFU fires was the length of time since previous fire. When intervals between successive fires are short, probabilities of scarring were low. Tree basal area and aspect were also significant factors explaining observed pattern of tree scarring. In all WFU fires but one, the reconstructed extent of fires was substantially smaller than the fire atlas extent. As a result, fire-scar reconstructed estimates of fire rotation were much longer than fire atlas fire rotation. This information can provide some necessary insight in interpreting and accounting for uncertainty in fire-scar reconstructions for drier low- to mid-elevation forest types throughout the western United States.