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The role of Late Holocene climate variability in the expansion of yellow birch in the western Great Lakes region

Authors

  • Stephen T. Jackson,

    Corresponding author
    1.  Department of Botany, University of Wyoming, Laramie, Wy 82071, U.S.A.
      Corresponding author: E-mail: jackson@uwyo.edu
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    • 1

       All ages reported in this paper are in calendar years Before Present (yr bp) using the 1950 AD datum, based on the CALIB 4.1 program (Stuiver & Reimer, 1993).

  • Robert K. Booth

    1.  Department of Botany, University of Wyoming, Laramie, Wy 82071, U.S.A.
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  • *

    Stephen T. Jackson.

  • 2

    We note that a recently published record from Nelson Lake (eastern Upper Michigan) shows first appearance of yellow birch macrofossils at 4411 yr bp (Delcourt et al., 2002).

Corresponding author: E-mail: jackson@uwyo.edu

Abstract

Abstract. Pollen records from the western Great Lakes region of North America show substantial increases in birch pollen percentages during the late Holocene. The vegetational and population dynamics underlying the birch increase have received little attention, in part because of the inability to discriminate among species of birch based on pollen morphology. We used analyses of pollen and plant macrofossils from four lakes in the Upper Peninsula of Michigan to document that the birch pollen increase represents a regional expansion of yellow birch (Betula alleghaniensis) populations, which was initiated c. 4500 years ago. Whether yellow birch invaded the region at this time or simply expanded from small, previously established populations is not clear, although it probably did not grow near our study sites before the expansion. The initial expansion occurred during an independently documented period of high moisture and high water levels in Lake Michigan. A subsequent expansion in yellow birch abundance and distribution occurred c. 3000 years ago, coinciding with a second period of increased moisture and high lake-levels. The yellow birch expansion may have been modulated by millennial-scale climate variability, with most rapid expansion occurring during relatively wet periods.

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Ancillary