HR: 16:45h
AN: PP54A-04    [Abstracts]
TI: Temperature Meets Tree Physiology: Potential Influence of Different Characteristics of Recorded Temperature Increases in Alaska on the Diverging Growth Responses of White Spruce.
AU: * Juday, G P
EM: g.juday@uaf.edu
AF: School of Natural Resources, P.O. Box 757200, Fairbanks, AK 99709,
AB: To be useful for temperature reconstructions, tree growth must respond to the same climate parameters today in the same way it has in the past. Recent studies which show tree ring widths from the northern high latitudes are diverging from previous sensitivity to temperature parameters may be partly influenced by new patterns of warm temperature anomalies as well as the limits of possible physiological response by trees. Both factors may be influencing white spruce growth in Alaska. In the 104-year record at UES/Fairbanks, daily maximum temperatures (May:August) have increased only slightly (~0.5 C), while daily minima have increased over 3 C per century, and frost-free growing season length has increased 50% to about 120 days (ca. 150 days at lower temperature thresholds suitable for native species). Total yearly days above freezing have increased by about 20 days. Spring snow and ice dissipation is earlier by about 5 to 6 days. Winters mean temperatures are 2 to 3 C greater and include fewer days below –20, -30, and –40 C. At stations across central Alaska with a shorter 60 to 90-year record (McGrath, Bettles, Talkeetna) trends are similar. In Alaska chronologies, high summer temperatures "kill" growth the following year on many sites. Years with high numbers of days with daily maxima above 70 F (21.1 C) are followed by significant "pointer" years (e.g. 1924, 1940-41, 1958-59, 1974-75, 2005) with small tree rings. White spruce is a determinate growth species, meaning current year growth is disproportionately influenced by reserves accumulated in the previous growing season. In a given year, when maximum moisture stress encountered by a particular tree first exceeds a critical threshold, cell production switches from earlywood (large diameter, thin-walled) to latewood (small diameter, thick-walled) type, which limits further width expansion. These climate trends and tree chronology patterns are consistent with (1) a shorter snow accumulation season and longer evapotranspiration season reducing potential spring melt input, which (2) exhausts early season soil moisture earlier and on previously non-sensitive sites, thus (3) inducing cell type switch earlier in the year and on previously non-sensitive sites, resulting in smaller ring formation and negative sensitivity to previous (and secondarily current) summer-season temperature. The next stage in the warming process would be temperature and moisture combinations near lethal conditions which could injure white spruce so severely that their actual realized growth would underperform previous climatic predictions for a 1 to 3 year period. In addition, outbreaks of insects that reduce tree growth would be released from previous climatic limits and become a more significant factor in determining annual net growth, and thus size of ring formed. Finally, empirical relations of growth versus temperature predictors in existing, negative-responding Alaska white spruce populations suggest that temperature increases of 2.5 to 4 C would result in tree death at low elevations represented by climate stations. Environments suitable for white spruce survival might be found in mountain environments.
DE: 4920 Dendrochronology
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting