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Late‐Wisconsinan Vegetational History at Wolf Creek, Central Minnesota
Author(s) -
Birks H. J. B.
Publication year - 1976
Publication title -
ecological monographs
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 4.254
H-Index - 156
eISSN - 1557-7015
pISSN - 0012-9615
DOI - 10.2307/1942564
Subject(s) - macrofossil , tundra , ecology , deciduous , vegetation (pathology) , pollen , woodland , plant community , ecotone , geology , geography , shrub , ecological succession , biology , ecosystem , medicine , pathology
The pollen and plant—macrofossil stratigraphy of Wolf Creek, an extensive marsh within one of the oldest drumlin fields in central Minnesota, is described for the period 20,500 to 9150 yr ago. The pollen stratigraphy is presented both as percentages and as "absolute" influx. Both the pollen and macrofossil data have been analyzed by numerical zonation procedures to reveal the major stratigraphic patterns with the two data sets. The vegetational reconstructions presented are based on the pollen percentage and influx data, on macrofossil assemblages, on comparisons of modern and fossil pollen spectra, and on the present ecology of the individual taxa concerned. From 20,500 to 14,700 yr ago, a mosaic of tundra—like vegetation prevailed, with wide—spread "tundra—barrens" of Dryas integrifolia, Arenaria rubella, Silene acaulis, and Vaccinium uliginosum var. alpinum. Between 14,700 and 13,600 yr ago, shrub vegetation with dwarf birch, Empetrum, willows, alder, and Shepherdia canadensis developed as a transitional phase prior to the establishment of spruce—dominated woodland 13,600 yr ago. Between this time and 10,000 yr ago, little change occurred in the upland vegetation, except for the expansion of some deciduous elements ° 12,250 yr ago. Local changes in wetland assemblages occurred, primarily in response to changes in lake level. At °10,000 yr ago, Pinus banksiana expanded at the expense of spruce to form a mixed coniferous—deciduous forest. Climatic interpretation of this vegetational development suggests a progressive increase in temperature since 14,700 yr ago. This unidirectional trend in climatic development contrasts with the glacial history of the state for the time period of interest, as the Lake Superior ice lobe advanced three times between 16,000 and 12,000 yr ago. The lack of correspondence between the pollen stratigraphy and the glacial history is discussed, and hypotheses are presented to explain this apparent anomaly.