PARENT SESSION
Oral Session #10: Paleoecology. Presiding: S. Hotchkiss.
Monday, August 6, 2001. 8:00 AM to 12:00 PM. Hall of Ideas J.
Responses of fire and vegetation to Little-Ice-Age climatic change in boreal Alaska.
Tinner, Willy1,2, Hu, Feng Sheng1, 1 2
ABSTRACT- Paleoecologists have long hypothesized that fires exerted major controls over vegetation responses to Holocene climate variations, but this hypothesis has not been rigorously tested in the Alaskan boreal biome. To examine vegetation-fire-climate interactions during the past 1000 years, we analyzed a sediment core from Grizzly Lake (62° 43' N, 144°12' W) contiguously at 1 cm (= 19 ± 9 year) intervals for pollen, charcoal and sediment characteristics. Marked increases in charcoal abundance and magnetic susceptibility suggest increases in fire importance and soil erosion during the Little Ice Age (LIA) 1400 - 1900 A.D. Picea mariana, Salix, Populus, Alnus tenuifolia, Cyperaceae, Poaceae, and Sphagnum declined in response to LIA climate change and fire occurrence. Coincident with these changes, aquatic plants Nuphar, Potamogeton, Isoetes, and Pediastrum disappeared and A. crispa shrub thickets expanded. Increased fire importance as indicated by charcoal peaks was preceded by the expansion of plant taxa indicative of disturbance or cooling (Epilobium, Betula nana) at the expense of Betula papyrifera. LIA climatic cooling did not result in a decrease in fire frequency; instead it probably caused vegetation die-backs, leading to increases in fuel availability and fire occurrence. The relationships among climate, fire, and plant species during the past 1000 years appeared to differ greatly from those observed through modern ecological studies. These discrepancies highlight the complexity of climate-vegetation-fire interactions in boreal ecosystems and underscore the importance of using paleorecords to help predict boreal-forest response to future climatic change.
KEY WORDS: climate change, fire ecology, Little Ice Age, Alaska