Thursday, September 1, 2011

New paper finds fire activity was highest when CO2 levels were "safe"

A paper published today in Geophysical Research Letters reconstructs the annual area burned in the Northern Rockies from 1626 to 2008 and finds the periods of greatest fire activity were in the early 1600's and during the period 1929-1945, both of which had "safe" levels of CO2 below 350 ppm.

Key Points
  • Fire suppression and forest harvest masked a likely major fire period.
  • High-elevation conifers can serve as proxy for area burned
  • High-elevation conifer chronologies are a cost-effective source to analyze fires
Paul A. Knapp
Peter T. Soule'
We used a tree-ring chronology as a proxy for annual area burned (AAB) in the Northern Rockies, USA during AD 1626-2008. We correlated annual ring widths of alpine larch trees (Larex lyallii) sampled at a single high-elevation site in western Montana with AAB for the United States Forest Region 1. Radial growth was significantly associated with AAB (R2=0.35, p<0.001), demonstrating the potential to use high-elevation conifers as markers of interannual variations in fire activity. The results suggest that the period 1929-1945 would have been the most active since the early 1600s had not extensive fire suppression and harvest activities altered the fire regime. Comparisons of the predicted values of area burned to a century-long fire atlas were significant for both the entire record (rs=0.333, p < 0.01) and reconstruction period (rs =0.645 p < 0.001). Similarly, predicted AAB was significantly correlated (r = 0.230) to fire-scar data during 1650-1900. These results suggest the feasibility of using tree-ring chronologies as an additional measure of fire activity, particularly as they allow an assessment and comparison of fire activity during centuries with and without fire suppression and harvest activities.

Related: Global warming causes increased and decreased wildfires

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