12 ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 496 



LAKE MICHIGAN CORE I000-3C 



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total pollen 



Fig. 4 - Diagram of percentages of pollen for Lake Michigan core 1000-3C. 

 The radiocarbon dates were obtained from residual organic carbon 



between logging and the weed increase has been noted in sediment cores from 

 southern Ontario (J. H. McAndrews, personal correspondence, 1974). It is not 

 until zone 4b that the pollen concentration approaches its presettlement value 

 and pine and oak regain a prominent place in the pollen record. In zone 4b, oak 

 increases to its former prominence and pine increases to about half of its previous 

 value. Oak has been more important than pine in the second-growth forests of the 

 Lake Michigan area, and the pollen data reflect this man-made shift in dominance. 



Interestingly, the number of ragweed grains per gram has continued to in- 

 crease since settlement even though the numbers of oak and pine have recovered 

 significantly. This increase possibly reflects changing land-use patterns in the 

 last 130 years. After initial forest clearance, much of it for the timber, agricul- 

 turally unprofitable areas were allowed to return to forest, thereby increasing the 



