416 A NATIONAL PLAN FOR AMERICAN FORESTRY 



to each class of forest is based largely on the location of the forest with 

 respect to regions where conditions are particularly conducive to 

 excessive surface run-off and erosion. The forests of each protection 

 class are shown in figure 6. 



The forests having a moderate and heavy influence are in the silt 

 loam uplands, Crowley's Ridge, and the hill lands of southeastern 

 Missouri. However, only 25 percent or less of the total area of these 

 erosive uplands is now forested. Therefore, if the protective influence 

 of forest is to be more fully realized there should be marked extension 

 of the present forest area and the restoration of forest cover to large 

 areas of now idle land. Such upland forests as remain afford some- 

 what less than the maximum possible protection, but they unquestion- 

 ably exert a considerable and beneficial influence on erosion and on 

 stream flow. In the Yazoo River flood period of 1931-32, the Southern 

 Forest Experiment Station found that of the 27 inches of rain that 

 fell, 62 percent ran off cultivated fields immediately and carried soil 

 with it at the rate of 34 tons per acre. In barren abandoned fields 

 the run-off was 54 percent of the total rainfall. During the heaviest 

 rains from 75 to 95 percent of the rain falling on these classes of land 

 became surface run-off. On the other hand, of the 27 inches of rain 

 falling on an undisturbed oak forest, less than 0.5 percent ran off the 

 surface, taking only about 75 pounds of soil per acre. The run-off 

 from a plot located in a scrub-oak forest, and with a litter cover, was 

 2 percent of the rainfall. 



For the period of observation, the surface or flood run-off from land 

 in cultivation was 127 tunes greater than from forest land, and the 

 eroded soil over 900 times greater. 



WATERSHED AREA IN NEED OF SPECIAL ATTENTION 



As the upland area of the lower Mississippi Basin has such an inti- 

 mate bearing upon floods and upon the amount of eroded material 

 which reaches the Mississippi River, it is one of the outstanding 

 critical areas of the country, one in which every effort should be made 

 to bring about more favorable conditions. 



Of these uplands, the situation in the Yazoo River drainage probably 

 is in most need of early attention. From this unit of roughly 3 ,487 ,000 

 acres gross, surface run-off is quickly concentrated hi drainage chan- 

 nels and the flood waters are almost immediately debouched into the 

 low-lying, poorly drained Delta where extensive areas of true agricul- 

 tural land are subject to destructive inundation as the result of unwise 

 land use in the adjacent uplands. Residents of the Yazoo Delta, 

 one of the most productive of all agricultural regions, with half of its 

 nearly 6 million acres in fertile farm lands, have made numerous 

 demands for the construction of a complete system of levees, which 

 would protect them not only from the Mississippi floods but also 

 from those of the Yazoo as well. Engineers estimate, however, that 

 adequate levee protection from floods would cost many millions of 

 dollars. In this whole situation lies strong evidence of a need rather 

 to control run-off at its source through changes in land utilization in 

 adjacent uplands. 



Something like 35 percent, or 1,214,000 acres, of the Yazoo uplands 

 are in cultivated crops. This large area appears to be a serious ob- 

 stacle to any program aimed at complete control through forest cover. 



