82 H. A. GLEASON VEGETATIONAL HISTORY OF MIDDLE WEST 



are composed exclusively of mobile species and have been in existence 

 such a short time that they have not yet changed the nature of the 

 prairie soil 52 . 



Second Period of Forest Advance. — Settlement of the forested 

 regions of the Middle West began about the opening of the nineteenth 

 century, progressed steadily westward, and reached the Missouri Kiver 

 in fifty years. Actual settlement of the prairies was long avoided, vast 

 areas were still untouched at the time of the Civil War, and prairie 

 fires did not cease being a menace in parts of Illinois until 1860 and in 

 Iowa until somewhat later. As soon as fires ceased, the advance of the 

 forest was renewed, and at a rate probably more rapid than the original, 

 since considerable improvement of climate may have taken place since 

 the first advance was stopped by fires. 



Early literature contains many accounts of this spread of the forested 

 area, which was rapid enough to attract the attention of travellers. It 

 seems to have progressed in several different ways. The lateral advance 

 of the forest at right angles to the streams and the longitudinal advance 

 along the streams continued as before. Willows, cottonwoods, and some 

 hydrophytic shrubs moved rapidly up the rivers and creeks, and were 

 followed by elms, maples, and ashes. Thirty years after the first prairie 

 settlements were made in Macon and Moultrie counties, Illinois, these 

 fringing forests had extended one or two miles up the smaller streams. 

 Isolated colonies of mobile species, especially willow, Salix humilis, and 

 wild plum, Prunus americana, were established well out on the prairie, 

 grew into thickets, and frequently received further additions of forest 

 species, carried in by the birds which visited them or by wind. Large 

 areas of barrens were converted into forest as by magic, when the fires 

 that had maintained them were stopped and the oak sprouts became 

 trees. 



The total afforestation during this period was considerable and in some 

 cases almost unbelievable, and may best be indicated by a few examples. 

 Thus the driftless area of northwestern Illinois and southwestern 

 Wisconsin, which now gives the impression of having been heavily 

 forested, was 80-90% prairie a century ago, 53 and was described by 

 Keating 54 as presenting "the waved appearance of a somewhat ruffled 



62 Hopkins, C. G., J. G. Mosier, E. Van Alstine, & F. W. Garrett. Champaign 

 County soils. 111. Agr. Exp. Sta. Soil Report 18. 1918. 



ss Schoekel, Bernard H. History of development of Jo Daviess County. Illinois 

 State Geol. Surv. Bull. 26. 1916. 



s* Keating, William H. Narrative of an expedition to the source of St. Peter's 

 River . . . performed in the year 1823 . . . under the command of Stephen H. Long. 

 Philadelphia, 1824. 



