PARENT SESSION
Oral Session #10: Paleoecology. Presiding: S. Hotchkiss.
Monday, August 6, 2001. 8:00 AM to 12:00 PM. Hall of Ideas J.

Early Holocene vegetation in the western Great Lakes region: two distinct no-analog types.

Calcote, Randy¹, Davis, Margaret¹, Douglas, Christine¹, ¹

ABSTRACT- Early Holocene pollen assemblages that are unlike modern assemblages have baffled paleoecologists for decades. They are difficult to interpret because there is no modern equivalent. They are generally lumped together as a group. Rather than depend on modern pollen samples to classify fossil samples, we classified all fossil and modern pollen assemblages together. We identified 22 pollen assemblage types, including two distinct non-analog types, using cluster analysis of 1,781 modern and fossil pollen samples from the western Great Lakes region. Shifts in the abundance and distribution of assemblage groups occurred throughout the Holocene, with several groups having two peaks of abundance. Spruce and sedge pollen were abundant 14,000-12,000 years ago with an increasing frequency of a no-analog type containing ash, poplar, ironwood and spruce. This type was abundant near the retreating ice 12,000 years ago near spruce woodlands. By 10,000 years ago it was most common near pine sites between Lake Agassiz and the Superior ice lobe. A second and distinct no-analog vegetation type containing elm and oak occurred 10,000 years ago in southern Minnesota and Iowa. This second group contracted toward the east with the prairie-forest border, disappearing 6000 years ago. This method of classifying pollen assemblages allows recognition of distinct vegetation types within no-analog assemblages. Differentiating no-analog groups and comparing their histories with regional climate models may provide a more mechanistic understanding of their causes.

KEY WORDS: pollen analysis, no analog pollen assemblages, Holocene, vegetation classification