HR: 16:15h
AN: PP54A-02    [Abstracts]
TI: Divergence Effect at Alaska's Treelines a Result of Sub-Population Behavior?
AU: * Wilmking, M
EM: wilmking@uni-greifswald.de
AF: Ecosystem Dynamics University Greifswald, Institut fuer Botanik und Landschaftsökologie Grimmer Strasse 88, Greifswald, MV 17487, Germany
AU: Singh, J
EM: jayendra1673@yahoo.co.uk
AB: The "divergence effect" (off-set between tree-ring based temperature reconstruction and measured temperatures) in northern forest poses a serious question to tree-ring based climate reconstructions, since it seems to violate the uniformitarian principle of dendroclimatology. Several possible reasons emerge, among them false assumptions about 1) climate data (e.g. which climate parameter can be modeled most effectively), 2) tree-ring data (e.g. shift in climate sensitivity of tree growth) or 3) a truly new and unprecedented phenomenon (e.g. rapid climate warming exceeding the adaptive capacity of trees). Here we test, if undetected emergent sub-population behavior at Alaska's treelines might result in a divergence effect. We reanalyzed seven data sets spanning the entire northern treeline in the Brooks Range, Alaska, which showed populations of trees responding positively, non-significant and negatively to recent warming. There is no effect of standardization (i.e. conventional versus RCS) technique on the grouping and we thus used RCS for the following analysis. Without grouping into sub- populations, a clear divergence between tree-ring based temperature reconstruction and actual climate data emerged. However, if only those trees were used for the climate reconstruction, which showed a consistent positive response to the target temperatures (June/July), tree growth modeled climate data extremely well following the rise in temperature during the last decades (actual climate data 0.53°/decade versus tree-ring based reconstruction 0.44°/decade over 1970-2000 period). This result hints at the possibility that some of the reported divergence might be eliminated (at least at Alaska's treelines) through careful test of sub-population behavior.
DE: 1620 Climate dynamics (0429, 3309)
DE: 1630 Impacts of global change (1225)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting