Abstracts
SEARCH Open Science Meeting
October 27, 2003
Seattle, Washington, USA
The Response of the Alaskan Boreal Forest to a Warming Climate
Valerie A. Barber1, Glenn P. Juday2, Martin Wilmking3
1Forest Sciences, University of Alaska Fairbanks, P.O. Box 7200, Faibanks, AK, 99775-7200, USA, Phone 907-474-6794, Fax 907-474-6184, ffvab@uaf.edu
2Forest Sciences, University of Alaska Fairbanks, P.O. Box 7200, Fairbanks, AK, 99775-7200, USA, Phone 907-474-6717, Fax 907-474-7439, g.juday@uaf.edu
3Forest Sciences, University of Alaska Fairbanks, P.O. Box 7200, Fairbanks, AK, 99775-7200, USA, Phone 907-474-7471, ftmw@uaf.edu
The Alaska boreal forest is one of the largest forest regions in the U.S., is largely free of human disturbance, and has experienced a major climate warming since the 1970s. In Alaska, black spruce dominated stands are the dominant forest cover type, making up about 55% of the boreal forest, followed by white spruce at about 25% and birch-dominated stands at 14%. Tree disks and cores from black and white spruce and birch were collected throughout interior Alaska to determine climate sensitivity and potential for carbon credits and storage. We also include information from white spruce cores collected in the Brooks and Alaska Ranges.
Interior Alaskan low elevation upland white spruce show a consistent negative radial growth response to summer temperature, but black spruce and birch show varied responses. Growth of different populations of black spruce is correlated with several different climate factors, and the relationships are statistically strong enough that excellent predictive relationships can be developed. Growth of slope and ridgetop black spruce is negatively related to early and late summer temperatures at Fairbanks; the trees grow best in cool summers and least in warm summers. Growth of valley bottom black spruce on permafrost is either positive to winter temperature or negative to early spring (April) temperature. Growth of black spruce on Tanana Valley surfaces near Fairbanks responds positively to midwinter temperatures. Radial growth of birch on south-facing slopes near Fairbanks is highly negatively correlated with summer temperature. Growth of older birch on an east-facing slope in Bonanza Creek LTER is positively correlated with individual summer months over a 3-year period.
Future growth of boreal tree species, derived from these empirical relationships with past temperature, have been developed for 5 GCM scenarios including the Canadian Climate Center and Hadley Center models. Model results for monthly variables for the Fairbanks grid cell for 2001-2099 were calibrated from the 1990-2000 period of overlap. Although all models produced increasing warmth, some failed to reproduce variability consistent with recorded data, and some produced systematic divergence in seasonal temperatures not present in the recorded data. The models produce climates indicating that some populations of at least 2 of the tree species would not survive, because rates of growth would approach zero within 70-100 years.
Abstract Categories: Changes on Land
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