80 II. A. GLEASON VEGETATIONAL HISTORY OF MIDDLE WEST 



The extent of migration up the streams beyond the present limit of 

 forest can be considered with less accuracy. The original land surveys 

 frequently show small areas of forest isolated from the main body along 

 the head waters of a stream. Also, the upstream end of the forest belts 

 is regularly wide and blunt. Modern observation shows that in the 

 same area establishment of new forest is rapid as far upstream as there 

 is a differentiation of upland, bluff, and floodplain. If the interruped 

 belts were made continuous and were extended upstream according to 

 the topography, there appears to be room in Champaign County for at 

 least 28 more miles of forest belt, comprising probably 14 square miles. 

 There is also evidence that the moraines were forested wholly or in part 

 in prehistoric time. Fragments of the forests still persist in sheltered 

 places in Champaign County, and well developed morainal forests 

 occupy considerable areas of McLean County. In Champaign County, 

 about 50 square miles of land is morainal and may have been forested. 



The land survey maps indicate 44,846 acres of forest in Champaign 

 County, and this figure is apparently somewhat too small, since the 

 surveyors frequently referred to trees up to two feet in diameter stand- 

 ing on land designated on the map as prairie. Increasing this amount 

 by 64 square miles makes a possible total of nearly 86,000 acres of 

 prehistoric forests, almost twice the present extent, and increases the 

 proportion of forest, from 7.1% to 13.5% of the total area. While the 

 accuracy of this estimate can not be proved, we may safely conclude 

 that the forested area was at one time greatly larger than its present 

 extent through Illinois and Iowa, and doubtless also through the prairie 

 region of Wisconsin and Indiana. 



Second Period of Prairie Dominance. The advance of the forest 

 would in time have given a continuous forest covering to the Middle 

 West, except on those limited habitats where tree growth is impossible 

 for edaphic reasons. The forest would have extended west to the 

 climatic limit of tree growth and tongues would have projected beyond 

 the principal area along the habitats where special environmental con- 

 ditions compensated for the unfavorable climate. This advance came to 

 a sudden conclusion with the arrival of the American Indian and the 

 consequent introduction of prairie fires. This stage in the history of 

 the Middle West has been discussed in an earlier paper 50 and needs 

 only brief recapitulation here. 



Prairie fires were set annually by the Indians in the autumn months 

 to drive game from the open prairies into the forest, where it was more 

 easily stalked. Sweeping eastward before the prevailingly westerly 

 winds of that season, the fires destroyed seedling trees at the west margin 

 of the forest, preventing further advance in that direction. It is doubt- 



