THE INTEGRATION OF TREE-RING AND ALLUVIAL FAN RECORDS OF FIRE HISTORY AT THE MISSIONARY RIDGE FIRE NEAR DURANGO, COLORADO

The Missionary Ridge Fire burned through more than 70,000 acres of forest near Durango, Colorado, in June of 2002. Several debris flow and flood events following the fire incised older alluvial fan and channel sediments throughout the burned area. This study focuses on a 1 km2 watershed where 3,000 years of fire-related depositional events have been exposed in the walls of the incised channel. We use the recently exposed sediment record to compare the frequency and type of fire-related geomorphic response with tree-ring records of fire history from the same drainage. Tree-ring records include fire-scarred cross-sections of ponderosa pine, age-structure data, and germination dates of Aspen patches. The tree-ring data at this mixed conifer site indicate that over the past 300 years, fire spread as low severity surface burns with patches of crown fire occurring at longer intervals. The depositional events preserved in the channel sediments are dominated by well-sorted and fine-grained sediments, which suggests a response to low or moderate severity fire regimes. The recent depositional events, which overlap with the tree-ring record, represent a portion of the overall fire events recorded in the tree-ring record, and likely occurred during years with a greater proportion of crown fire patches. The tree-ring data aids with the interpretation of the sediment record, and the integration of both records allows for a fuller understanding of the frequency, extent and severity of fires throughout the late Holocene. This research provides a new context for comparing the geomorphic response to the recent Missionary Ridge Fire with the response to fire behavior in the past.