BAER soil burn severity maps do not measure fire effects to vegetation: A comment on Odion and Hanson (2006)

We comment on a recent Ecosystem paper by Odion and Hanson (Ecosystems 9:1177-1189, 2006), in which the authors claim that high severity fire is rare in the Sierra Nevada under current conditions. Odion and Hanson's results are predicated on BAER soil burn severity maps, which are based primarily on fire effects to soil, not vegetation. Odion and Hanson, and we fear others as well, are misinformed as to the nature of the BAER severity mapping process, and proper applications of BAER soil burn severity maps. By comparing the BAER soil burn severity maps to a true vegetation burn severity measure (RdNBR) calibrated by field data, we show that the area in the high soil burn severity class for the three fires analyzed by Odion and Hanson is substantially less than the area of stand-replacing fire, and that BAER maps-especially hand-derived maps such as those from two of the three fires-also greatly underestimate the heterogeneity in vegetation burn severity on burned landscapes. We also show that, contrary to Odion and Hanson's claims, Fire Return Interval Departure (FRID) is strongly correlated with fire severity in conifer stands within the perimeter of the McNally Fire.