SOIL AS A LIMITING FACTOR OF FORESTS IN 

 LA SALLE COUNTY, ILLINOIS 



George D. Fuller^ The University of Chicago. 



La Salle County, Illinois, is situated in the north-central 

 part of the state within what is usually termed the "corn 

 belt" on account of the extensive culture of that crop on 

 the dark brown or black soils of the prairie. It is also 

 witliin the region of the early Wisconsin glaciation, the 

 Bloomington moraine skirting its northern boundary. The 

 surface is gently rolling, the highest altitude at the north- 

 west corner being 930 feet from which the plain slopes 

 gradually to about 630 feet at the edge of the Illinois River 

 valley. This valley, intersecting the county from east to 

 west, lies about 200 feet below the level of the adjacent 

 uplands. On account of the peculiar distribution of for- 

 ests in this prairie county it was selected in the autumn of 

 1918 as one of the areas to be included in a State Forestry 

 Survey. It seemed probable that it might present prob- 

 lems involving the factors which determine the relative 

 extent of grassland and woodland in the State of Illinois. 



This is not an opportune time to present the different 

 theories as to the causes of the development of a grassland 

 vegetation. These have been well summarized by Shimek^, 

 who has also given in the same report an excellent bibliog- 

 raphy of the earlier American literature upon the sub- 

 ject. Gleason- has stated some of the unsolved problems 

 of the prairies and Cowles^ has pointed out that the causes 

 which explain the prairie vegetation of Illinois must not 

 be applied, in all cases, to the great climatic prairies of the 

 farther west. 



1 Shimek. B. The prairies. Bull. Lab, Nat. Hist. State Univ. Iowa 6 : 169- 

 240. plates 13. map. 1911. 



* Gleason. H. A. Some unsolved problems of the prairies. Bull. Torr. Bot. 

 Club 36 : 265-271. 



* Cowles, H. C. The physiographic ecology of Chicago and vicinitv. Bot. 

 Gaz. 81 : 73-108, 145-182. figs. 35. 1901. 



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