HOLOCENE PALYNOLOGY AND S E D I M E NT O LO G Y 



11 





I i I i L 



J L 



10 20 



30 



4 3 10 5 10 3 



Percent of total pollen 



I 



2 

 3 

 4 

 5 

 6 

 7 

 8 

 9 

 10 

 Scale 

 20 



30 



40 



50 



60 



70 



300 

 300 

 300 

 200 

 200 

 200 

 200 

 200 

 200 

 200 

 change 

 200 



200 



200 



200 



200 



200 



Core collected at 42°22.0' N. , 86° 11 .0' W. from 120.5 meters of water. 



also declines, but to a lesser extent. With the beginning of the ragweed increase, 

 Gramineae, Chenopodiineae, and Cyperaceae increase. Zone 4b, which extends 

 from 8 cm to the surface, exhibits a slight decrease and leveling off of ragweed 

 at about 30 to 35 percent and rather constant pine and oak percentages. Pollen 

 concentrations in zone 4b reach high values of 91,000 grains per gram. 



The pollen concentration diagram of the dominant taxa in core 100 0-3 C 

 (fig. 5) confirms the trends noted in the percentage diagram. The increase of 

 pine in zone 3 is very prominent. Oak and spruce also increase in concentration 

 in zone 3, indicating a general expansion of arboreal elements. The decline in 

 numbers of pine and oak grains with the introduction of land clearance and agri- 

 culture is abrupt. Pine declines from 29,000 grains per gram of sediment to 5,200 

 grains per gram and oak declines from 18,000 to 5,000 grains per gram between 

 20 cm and 14 cm. Forest clearance was apparently quite extensive in the pollen- 

 source areas of these sediments. 



The decline in arboreal pollen precedes the increase in ragweed pollen 

 (fig. 5). This sequence suggests that forest clearance and the resulting increase 

 in erosion preceded the buildup of ragweed populations . A similar time lag 



