CLIMATE CHANGE & THE DEVELOPMENT OF BOREAL FOREST & FIRE REGIMES ON THE KENAI LOWLANDS, ALASKA

ANDERSON, R.S. (1), JASS, R.B. (2), BERG, E. (3), TONEY, J.L. (4), HALLETT, D.J. (1), de FONTAINE, C.S. (5), AND DeVOLDER, A. (6)

(1) Center for Environmental Sciences & Education, & Quaternary Sciences Program, Box 5694, Northern Arizona University, Flagstaff, AZ 86011; (2)  4014A Lewis Lane, Austin, TX, 78756; (3) Kenai National Wildlife Refuge, U.S. Fish & Wildlife Service, Box 2139, Soldotna, AK 99669; (4) Quaternary Sciences Program, Box 5644, Northern Arizona University, Flagstaff, AZ 86011; (5)  Department of Geology, Box 4099, Northern Arizona University, Flagstaff, AZ 86011; (6) US Fish & Wildlife Service, 2800 Cottage Way, Sacramento, CA 95825.

Several authors have noted a relationship between vegetation type and fire frequency, yet despite the importance of ecosystem processes, such as fire, the long-term relationships between disturbance, climate and vegetation type are incompletely understood.  We analyzed pollen, plant macrofossils and sedimentary charcoal stratigraphies from three lakes within the Kenai lowlands of southwest Alaska to determine post-glacial relationships between disturbance, climate and vegetation for the boreal forest there.  A herb tundra was established in the lowlands following deglaciation by 13,000 cal BP.   Betula papyrifera, Salix and Alnus immigrated to the area after 10,700 cal BP, followed by Picea glauca by 8,500 cal BP.  P. mariana became established by 4,600 cal BP.  The early Holocene was probably the driest time during the post-glacial, as determined by aquatic plant macrofossils.  Lake levels reached near-modern conditions by at least 8,000 cal BP.  Mean Fire Intervals (MFI) were highest during the shrub - herb tundra phase (130 ± 66 yrs), declined after immigration of B. papyrifera, Salix, and Populus (81 ± 41 yrs) and Picea glauca (77 ± 49 yrs), and increased again with the arrival of P. mariana (138 ± 65 yrs).  Unlike previous studies, our data demonstrate more frequent fire during the early Holocene, with less frequent fire during the late Holocene.  Early Holocene forests of P. glauca and B. papyrifera existed in summers that were longer and drier than today, while the increasingly wetter and cooler climates of the late Holocene most certainly hindered the spread and perhaps the size of fires at that time.