A LATEGLACIAL PALEOFIRE RECORD FOR EAST-CENTRAL MICHIGAN

Fire frequency during changing climatic conditions yields insights into the ecological responses and adaptations of vegetation during times of stress. Yet few paleofire studies have been conducted in the Midwest in the temperate forests. This study presents a paleofire record spanning the interval from deglaciation to the very early Holocene including the Younger Dryas (12,900 – 11,600 Cal yr BP) for east-central Michigan. Four lakes south of Flint, Michigan were sampled within a 15 km radius range of each other. Two lakes (Big Fish and Lake Sixteen) lie atop hummocky drift near the limits of the outer Saginaw lobe moraines. Swift and Slack Lakes lie on topography proximal to the northwest of this moraine.

All four lakes contain high charcoal levels in sediments deposited since deglaciation. The elevated levels follow the rise in organic content, and peaks within the elevated levels follow changes in sediment type: high charcoal-high organic, lower charcoal-higher carbonate content.

The radiocarbon dates obtained for these lakes from oldest to youngest, are: Lake Sixteen 13,350 ± 55 years (15,840 Cal BP); Big Fish 12,850 ± 55 (15,160 Cal BP); Swift 12,200 ± 65 (14,050 Cal BP); Slack 12,050 ± 110 (13,900 Cal BP). The Lake Sixteen date coincides with an earlier charcoal peak not seen in the other three lakes and the date for Big Fish precedes the initial largest peak in this core. The dates on Swift and Slack both correspond with a charcoal high that appears to correlate across all four lakes.

Our preliminary estimate of duration of these charcoal intervals in such fluctuating ecological conditions is that they start around 14,050 Cal BP and continue for about 1,500 years until 12,550 BP. The date for Lake Sixteen also shows evidence of earlier fire in the Oldest Dryas. If so, contemporaneous fire occurrence began around the start of the Younger Dryas and continued until the middle of the Younger Dryas. We take these relationships to indicate that for these lakes the transition between climate states is a controlling factor.