VEGETATIONAL AND CLIMATIC INFLUENCES ON FIRE REGIMES IN THE SOUTHERN BROOKS RANGE, ALASKA

HIGUERA, P.¹, BRUBAKER, L.¹, ANDERSON, P.¹, HU, F.S.², CLEGG, B.², BROWN, T.³, RUPP, S.⁴

¹ University of Washington, Seattle WA, ² University of Illinois, Urbana IL, ³ Lawrence Livermore National Laboratory, Livermore CA, ⁴ University of Alaska, Fairbanks, AK

We document vegetation, climate, and fire history over the past 13 k years with pollen, chirionomid/isotope, and macroscopic charcoal data from multiple lakes in the southern Brooks Range. All records indicate that fires occurred when birch-dominated shrub tundra covered the region and climate was cooler and drier than present, > ca. 10 k ybp. Fire occurrence decreased when vegetation communities changed to deciduous forests dominated by Populus, despite evidence suggesting a Holocene thermal maximum. Coincident with a decrease in Populus and the addition of white spruce to the shrub tundra during the early Holocene, charcoal records at most sites suggest an increase in fire occurrence. Climate records indicate a gradual cooling throughout the Holocene, with moistening around 6-7 k ybp. Despite this pattern, the most pronounced change in fire regimes occurs with the addition of black spruce during the mid-Holocene, when both charcoal abundance and charcoal peak frequencies increased to maximum levels. Our records provide (1) examples of counter-intuitive climate-fire relationships, given that fire frequency increased under cooler and/or moister climatic conditions and decreased during a period of presumably maximum Holocene warmth, and (2) strong evidence that vegetation was the dominant variable controlling fire regimes at millennial time scales.