30 



These fign-ires serve to show that returns are dependent upon the 

 form of product, and the period required to produce a wood crop, as 

 well as on the amount of wood which can be grown annually. The an- 

 nual increment of the twenty-year plot, 1.195 cords per acre, gives a net 

 return of 0.83 per acre annually as pulpwood. The higher annual incre- 

 ment of the 45-year old plot, 1.291 cords per acre, gives a net return of 

 but $0.37 per acre annually as pulpwood ; but harvested as veneering it 

 gives a net return of $2.67 per acre annually. 



The Rock River System 



The upper stretches of the Rock River flow through a region of 

 numerous lakes. The soils over the entire drainage basin are light, 

 gravels and sands predominating. Consequently, this river is not sub- 

 ject to extreme flood conditions, nor does it have extensive bottoms where 

 water stands for several weeks. The forests in many respects resemble 

 those described under the mixed hardwoods of bottoms of secondary 

 streams. Approximately 92 per cent of the bottomland is cleared. The 

 remaining bottomland forests, totaling 12,700 acres, are on the islands or 

 as strips along the river margin. About 41 per cent of this area is in 

 timber of good sawlog size, chiefly elm, ash, cottonwood. soft maple, 

 bur oak, and basswood. Samples totaling 2.5 acres show the following 

 representation of species by per cents : elm, 35 ; basswood, 20 ; ash, 16 ; 

 soft maple, 11 ; black walnut, 11 ; hackberry, 5 ; and bur oak, 2. 



Very little of the Rock River region is in organized drainage dis- 

 tricts, and probably the present forested area will be retained. The Rock- 

 ford furniture factories offer a market for high-grade logs for furniture, 

 or low grade for crating ; but in general the bottomland forests have sup- 

 plied very little material. 



A sample acre of virgin bottomland shows the association, sizes, and 

 yield of such stands. 



(3) MIXED HARDWOODS OF BOTTOMS OF SECONDARY STREAMS 



The bottoms of the minor streams of the state have accumulated the 

 wash from adjacent slopes and the deposits from occasional floods. These 

 soils are generally mixed loams, rich, deep, well drained, and highly valued 

 for crop land. Originally forested, they are now cleared wherever in 



