94 



D. B. H., that the height of the dominant trees is decidedly less than for 

 the other two upland types, and that the yields for corresponding decades 

 are the lowest. Reference to the tabulation of the D. B. H. of the aver- 

 age tree brings out the point that these stands do not enter the sawlog 

 class — minimum D. B. H. 10 inches — within the first hundred years. The 

 product is suitable for posts, mine timbers, and cordwood at about 60 

 years. 



Scrub Oak Type 



The scrub oak plots selected were on the sands in central and north- 

 ern Illinois. The representation of species on the plots measured, shows 

 black oak 62 per cent, scrub oak 39, hickory 8, and white oak 1 per cent. 

 A marked variation in the individual plots as to growth indicates that 

 probably in Illinois the sandy sites within this type should be classified; 

 but insufficient data compelled a general grouping of all plots on sand. 

 The tabulation, on page 96, brings out the fact that the diameter growth 

 on sand in these plots averages even greater than for corresponding dec- 

 ades on the more fertile soils of the upland hardwoods type. This fact 

 was also borne out in the individual tree study (see table on pp. 81-89). 

 The height growth is less at similar periods for trees of the scrub oak 

 type than for those of the upland hardwood type and the number of trees 

 per acre beyond the 60-year period on sand is the least for the upland 

 types. These stands enter the sawlog class at about 65 years. The yields 

 given are for a fully stocked acre on which all trees are sound and free 

 from crooks. The stands of the scrub oak type are very defective and 

 the trees both limby and crooked, hence the use of the factor 4.4 into the 

 cubic yield, giving a result only for sound straight trees, gives too high 

 yields for characteristic scrub oak stands. 



Upland Hardivood Type 



The plots on the upland hardwood type were taken on those upland 

 soils between sands and loams over clay. The commonest soil types 

 are the yellow and yellow-gray silt loams, and in general the upland soils 

 are heavier than upland soils in Connecticut and Massachusetts. The 

 point brought out in the individual tree study that growth on the upland 

 sandy loams is better than on the heavier loams is also apparent in the. 

 plots, as those selected on sandy loams have an average yield above the 

 average for the general upland type. The representation of species by 

 per cents on these plots is as follows : white oaks, 52, black oaks, 26, 

 hickory, 11, elm, 5, hard maple and cherry totaling 4, the remaining 2 per 

 cent being made up of nine other species. Since white oak is one of our 

 slowest growing hardwoods and constitutes more than half of the stands 

 on these plots, it is very evident that in managed forests of this kind yields 

 can be increased by the substitution of such trees as tulip, red oak, and 

 ash. Reference to the tabulation of the D. B. H. of the average tree 

 (Table 6, p. 96) shows that these stands enter the sawlog class at about 

 63 years. 



