timber as the remaining three-quarters of upland. Approximately 12. 37 

 per cent of the present timbered area of the state is in good sawlog sizes, 

 6.72 being upland and 5.55 bottomland. For the entire state an area equal 

 to 19.74 per cent of the original forested area is still forested, while but 

 18.4 per cent of the upland area originally forested is timbered. Based 

 upon good sawlog timber we have 5.79 per cent of the bottomland area 

 originally forested still in such timber, and 1.64 per cent of the original 

 upland area, or an average for the entire state of 2.42 per cent. 



In actual quantity, including not only stands yielding enough to in- 

 sure efficient logging, but including all merchantable timber of the state 

 regardless of the expense of harvesting it, there is 4.00 per cent of sawlog 

 timber left from the original forests of the bottomlands ; and 6.24 per cent 

 of the upland timber — 5,36 per cent for the entire state. The acreage 

 and estimated yield of bottomland forests by rivers is shown in the tabu- 

 lation p. 17. Data taken in the best upland stand and the best bottom- 

 land stand show the following comparison. 



No. of 



trees Maximum Maximum Average 



per acre diameter height diameter 



Upland 73 38 ' 95 13.8 



Bottomland ... 53 40 130 16.8 



FOREST TYPES 



The bottomland forests have been subdivided into three types: (1) 

 cypress and mixed hardwood, (2) mixed hardwoods of the main streams, 

 (3) mixed hardwoods of the secondary streams. The cypress and mixed 

 hardwood type is the association common to the bayous of the lower 

 Mississippi region but is limited by climatic factors to southern Illinois. 

 The difiference between (2) the mixed hardwoods of the main streams, 

 and (3) those of the secondary streams, is largely due to flood conditions. 



The upland forests have also been subdivided into three types, based 

 largely upon soil conditions: (1) post oak (2) scrub oak (3) upland 

 hardwoods. The so-called post oak type is foimd on the heavy, acidulous 

 soils usually having a clay subsoil. Post oak, scrub oak, hickory, and 

 black oak are the usual associates, post oak being the commonest tree. 

 The so-called scrub oak type is found on the sands. Scrub oak may be 

 entirely absent here, in which case a stunted form of black oak. Hill's 

 oak, or bur oak, with hickory, forms the association. The heavy soils, 

 largely south of the Sangamon River, support both post and scrub oak ; 

 while the sands, generally north of the Sangamon, support scrub or black 

 oak, but post oak is uncommon. Both the post oak and the scrub oak 

 tj'pes are on soils of high acidity, low in organic elements, and subject to 

 excessive drying. The growth rates are very slow, and the species native to 

 such sites are few. The area of forested upland in the post oak and the 

 scrub oak types aggregates but 21 per cent of the total forested upland. 

 The third upland type, the mixed hardwoods, constitutes the remaining 

 79 per cent of upland forests, and is found on all upland soils between 

 the extremes of open sands and tight loams over clay. 



