DO FIRE SCAR SAMPLING METHODS AFFECT ESTIMATES OF FIRE FREQUENCY?

VAN HORNE, M.L. AND FULÉ, P.Z.

Ecological Restoration Institute, School of Forestry, P.O. Box 15018, Northern Arizona University, Flagstaff, AZ 86011.

Fire scars have been used extensively to understand the historical role of fire in ponderosa pine (Pinus ponderosa) ecosystems. However, the sampling methods and interpretation of fire scar data have been criticized as statistically invalid, biased, and leading to exaggerated fire frequency estimates (e.g., Johnson and Gutsell [1994], Baker and Ehle [2001]). We tested alternative sampling schemes by comparing “targeted” sampling, random sampling, and grid-based sampling to a comprehensive measurement and mapping of all fire-scarred trees in the study site. We also compared temporal and spatial patterns of fire frequency using subsets of the comprehensive data. We collected 1,479 fire-scarred partial cross-sections from 1-km2 of Northern Arizona University’s Centennial Forest in 2002. Quantification of the differences in sampling approaches will not resolve all the limitations of fire-scar methods, since scarred trees are inherently point-sources of data. But measurement of sampling uncertainty will reduce the scope of “uncertainty” in interpretation of fire regime statistics.