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HOLOCENE VEGETATION, FIRE, AND CLIMATE HISTORY FROM THE SOUTHERN BROOKS RANGE, ALASKA.

HIGUERA, PHILIP E.  University of Washington, Seattle.
Brubaker, Linda B.  University of Washington, Seattle.
Anderson, Patricia M.  University of Washington, Seattle.
Hu, Feng Sheng  University of Illinois, Urbana.
Clegg, Ben  University of Illinois, Urbana.
Brown, Tom  Lawrence Livermore National Laboratory, CAMS.
Rupp, Scott  University of Alaska, Fairbanks.

Interactions between climate, vegetation, and fire regimes are poorly understood but will likely play key roles in determining boreal forest response to future climatic change. With paleo records from lakes across the southern Brooks Range we are documenting how vegetation and fire regimes have interacted, and how each has responded to climatic changes over the past 10,000 years. Centennial-scale changes in temperature and vegetation are documented with fossil chironomid assemblages and pollen/stomate records, respectively. Continuous records of macroscopic charcoal document landscape burning at decadal time scales. Charcoal analysis is aided by the use of a statistical model based on fire regime parameters observed in modern Alaskan boreal forests. This model creates hypothetical sediment-charcoal records that help us understand the accuracy of our records and explore the potential mechanisms causing variations in fossil charcoal stratigraphy.

Our records show evidence of fire regimes changing both between and within dominant vegetation types. Infrequent but distinct charcoal peaks during the early Holocene offer some of the first evidence of fires in the shrub tundra during this period. The replacement of shrub tundra with forest ca. 5000 years ago is accompanied by increases in both charcoal accumulation and the frequency of charcoal peaks. The absence of a step change in our climate proxies at this time suggests that vegetation, rather than climate, explains this increase in burning on the landscape. During the late Holocene, vegetation assemblages remained stable, but changes in charcoal accumulation suggest that fire frequency varied during this period. The details of these variations are still being resolved, but shifts in fire regimes in the absence of vegetation change would imply that fire regimes can be sensitive to climatic changes that do not affect vegetation assemblages. While climate ultimately controls both vegetation and fire, our records suggest that vegetation can play an important intermediary role between climate and fire.


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