INFLUENCES OF REGIONAL CLIMATE VARIABILITY ON FIRE OCCURRENCE ACROSS THE PONDEROSA PINE ZONE OF THE NORTHERN COLORADO FRONT RANGE

SHERRIFF, R. L.(1) AND VEBLEN, T.T. (2)

(1) University of Hawaii at Hilo, (2) University of Colorado, Boulder

Fire in the montane forests of the Colorado Front Range is strongly linked to inter-annual variability in moisture availability that in turn is linked to El Niño-Southern Oscillation (ENSO).  Recent studies suggest that conditions in the north Pacific and north Atlantic Oceans are influential on regional climate conditions in the Western U.S. and may also affect variability in fire regimes.  The present study relates multiple broad-scale climate influences to historic (pre-1915) fire occurrence throughout the ponderosa pine (montane) zone of the northern Colorado Front Range.  Fifty-four fire history sites were sampled for tree-ring evidence of fire frequency and severity across the full elevational range of ponderosa pine.  In the lower montane zone (below c. 2000m), the historic fire regime consisted of relatively frequent fires in which preceding wet conditions favored fuel accumulation prior to dry fire years.  However, in the mid to upper montane zone (above c. 2000m) moderate (mean fire interval; MFI > 30 years) to low frequency (MFI > 40 years) fires of mixed to high severity were the dominant fire regime in which preceding moisture conditions prior to fire years were less important.  Across the montane zone, fires tend to occur during years of below-average moisture associated with ENSO, Pacific Decadal Oscillation (PDO) and Atlantic Multidecadal Oscillation (AMO).  Regionally widespread fire years strongly coincide during years with combinations of negative ENSO, negative PDO and positive AMO conditions.