15,000 years ago to present
As the glaciers retreated different plant zones followed the retreating ice. Pollen grains recovered from core retrieved from lakes sediments document these changes in the plant communities. First, at about 15,000 years ago there were forest dominated by spruce trees and then a mixed conifer deciduous forest dominated by ash and spruce spread across the region. Later a rapid decline in spruce and ash pollen and an increase in Elm and Oak pollen occurs at 11,000 years ago the at 9,000 years ago the environment becomes drier and elm trees decline while grass and other prairie species and oak trees dominate the communities. At 5,000 years ago Oak savannahs begin to dominant the landscape pollen grains are dominated by prairie plants with oak pollen declining but sill a significant contributor.