The mid-Holocene (ca. 8000-4000 cal yr BP) was a time of marked aridity throughout much of Minnesota, and the changes due to mid-Holocene aridity are seen as an analog for future responses to global warming. In this study, we compare the transition into (ca. 9000-7000 yr ago) and out of (ca. 5000-2500 yr ago) the mid-Holocene (MH) period at Kimble Pond and Sharkey Lake, located along the prairie forest ecotone in south-central Minnesota, using high resolution (∼ 5-36 yr) sampling of pollen, charcoal, sediment magnetic and loss-on-ignition properties. Changes in vegetation were asymmetrical with increasing aridity being marked by a pronounced shift from woodland/forest-dominated landscape to a more open mix of grassland and woodland/savanna. In contrast, at the end of the MH, grassland remained an important component of the landscape despite increasing effective moisture, and high charcoal influxes (median 2.7-4.0 vs. 0.6-1.7 mm2 cm- 2 yr- 1 at start of MH) suggest the role of fire in limiting woodland expansion. Asymmetric vegetation responses, variation among and within proxies, and the near-absence of fire today suggest caution in using changes associated with mid-Holocene aridity at the prairie forest boundary as an analog for future responses to global warming.
Bibliographical noteFunding Information:
This work was supported by National Science Foundation EB grant 0092704, NSF/ATM grant 9909523, grants to St Olaf College and Carleton College from the Howard Hughes Medical Institute, a grant to St Olaf from Merck/AAAS, as well as Bush Class of ’49, and FDE Fellowships from Carleton College. Sediment magnetic analyses were conducted at the Institute for Rock Magnetism, University of Minnesota. Special thanks go to M. Sharkey and B. Reichel for access to the lakes. We thank T. Brown at the Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory, for assisting with the AMS 14 C dating, and J. Kenning, J. Limmer, N. Nowinski, L. Dvorak, and K. Walkup and R. Van Wieren for laboratory assistance. The following people were instrumental in assisting with field work: T. Jeffers, A. Matney, M. Swift, B. Welch, and J. Lavine. Thanks to Mike Swift, Derek Booth, and two anonymous reviewers for many helpful comments on the manuscript.
Copyright 2011 Elsevier B.V., All rights reserved.
- Big Woods
- Mid-Holocene aridity
- Prairie forest border
Continental Scientific Drilling Facility tags