109 



The Forests of Illinois, Original and Present 



THE original FORESTS 



The pioneers who were to settle in this region, viewing for the first 

 time extensive natural prairies, were so impressed that they named Illi- 

 nois the prairie state. Yet it appears that over 40 per cent of the state 

 was originally wooded. 



Estimates made by early explorers, and later tentatively confirmed 

 by the State Soil Survey, indicated that this forest area was about one 

 third of the state. A map prepared from the reports of the Soil Survey 

 reveals the original distribution of this timber. The southern counties 

 were all heavily timbered. These timber areas extended northward along 

 all the streams, diminishing in quantity and area as the land became 

 more level and true prairie more abundant. An extensive belt of woods 

 followed the Mississippi and the Illinois rivers, and in the northwestern 

 counties woodland again increased in area. 



By carefully checking existing records it has been concluded that 

 the original area of woodland in the state was larger than these previous 

 estimates have indicated, being approximately 1.5,588,965 acres, or 4ilAG 

 per cent of the total of 35,867,520 acres of land in Illinois. 



The manner in which these forest areas have thus been reconstructed 

 brings out points of considerable interest. In conducting the intensive 

 work of soil-mapping, the Illinois Soil Survey found that a very sharp 

 distinction existed between prairie soils and forest soils in the amount 

 of humus content. The soils which had been continuously in prairie, 

 under a heavy sod of grasses, contained about twice the per cent of 

 humus that was found in soils of similar origin and structure, but which 

 had continuously borne forest-cover. This difTerence was caused by the 

 effects of the grass roots, which filled the upper layers of the soil with 

 vegetable matter and excluded air, favoring the accumulation of humus, 

 while, by contrast, tree roots in decaying admitted air and were oxidized, 

 while most of the tree litter was burned, or oxidized, on the surface. 



The balance between forest and prairie seems to have remained fairly 

 constant over a considerable period and to have been determined by two 

 factors, topography and soil being one, and fire the other. Wherever 

 the surface was broken or hilly, as along streams, tree vegetation became 

 established, aided by soils which contained coarser materials, while on 

 the flat, poorly drained prairie the soil was a black loam, of a fine texture 

 which is less favorable for tree growth even in planted groves than for 

 farm crops. Trees might and probably would have invaded the prairies 



