Did the 2002 Hayman Fire, Colorado, USA, Burn with Uncharacteristic Severity?

摘要

There is considerable interest in evaluating whether recent wildfires in dry conifer forests of western North America are burning with uncharacteristic severity—that is, with a severity outside the historical range of variability. In 2002, the Hayman Fire burned an unlogged 3400 ha dry conifer forest landscape in the Colorado Front Range, USA, that had been the subject of previous fire history and forest age structure research. We opportunistically leveraged pre-existing data from this research, in combination with post-fire aerial imagery, to provide insight into whether the Hayman Fire’s patterns of high-severity, stand-replacing fire effects were uncharacteristic. Living old overstory trees were well distributed and abundant in the landscape before the Hayman Fire, despite the fact that some stand-replacing burning had been a component of the landscape’s historical mixed-severity fire regime. Of 106 randomly selected stand polygons that were sampled for the age of the oldest living overstory tree prior to the fire, 30% contained only trees ≤200 yr, while 70% contained at least one tree 200 yr and 29% contained at least one tree 400 yr. Following the Hayman Fire, only 5% of the polygons contained any living trees; these polygons were all immediately adjacent to the reservoir in the center of the landscape. At most, 4% of the polygons contained one or more trees 200 yr post fire, and 3% contained one or more trees 400 yr. The nearly complete loss of old trees, most of which were located in areas with evidence of past non-stand-replacing burning, leads us to conclude that the amount and extent of stand-replacing burning within the Hayman Fire were uncharacteristic for this landscape over at least the last two to four centuries.