HOW CLIMATE AND VEGETATION INFLUENCED BOREAL FIRE REGIMES DURING THE HOLOCENE: THE ALASKAN PERSPECTIVE

HU, F.S. (1), BRUBAKER, L.B. (2), GAVIN, D.G. (1), HIGUERA, P.E. (2), LYNCH, J.A. (3), RUPP, T.S. (4) AND TINNER, W. (5).

(1) Departments of Plant Biology and Geology, and Program in Ecology and Evolutionary Biology, University of Illinois, Urbana, IL 6180, (2)College of Forest Resources, University of Washington, Seattle, WA 98915, (3)Department of Biology, North Central College, Naperville, IL 60540, (4)Department of Forest Sciences, University of Alaska, Fairbanks, AK 99775, (5) Institut für Pflanzenwissenschaften, Universität Bern, Altenbergrain 21, CH 3013 Bern.

We synthesize our recent results from lake-sediment studies of Holocene fire-climate-vegetation interactions in Alaskan boreal ecosystems. The most robust pattern is the dramatic increase in fire frequency accompanying the establishment of Picea mariana forests 7500-5500 BP (from >500 yrs to as low as ~80 yrs). The establishment of P. mariana forests was associated with a regional climatic shift toward cooler/wetter conditions. Because cooler/wetter climate should not favor fire occurrence, the fire-frequency increase most likely reflects the influence of highly flammable fuels in P. mariana forests. Increased lightning associated with altered atmospheric circulation may have also played a role in certain areas where fire frequency increased around 4000 cal BP without an apparent vegetational change. When viewed together, the paleo-fire records reveal that fire histories differed among sites in the same modern fire regime and that the fire regime and plant community similar to those of today became established at different times. Thus the spatial array of regional fire regimes was non-static through the Holocene. Advancing our understanding of climate-fire-vegetation interactions will require a network of charcoal records across various ecoregions, quantitative paleoclimate reconstructions, ecosystem modeling, and improved knowledge of how sedimentary charcoal records fire events.