TIMBER: FORESTRY 



407 



the White Mountains, the Adirondacks, the central and south- 

 ern Appalachians, and western mountain ranges which are 

 used as sources of water for irrigation should be forested. 1 



375. Forest growth prevents erosion. Along with the value 

 of the forest in regulating the flow of streams, account must be 

 taken of its importance 

 in preventing the wash- 

 ing away or erosion 

 of the earth's surface. 

 Not only mountain and 

 hillsides but cultivated 

 slopes everywhere are 

 subject to great losses by 

 washing during thaws 

 after snows and during 

 rainstorms. How much 

 earth is thus annually 

 carried to the Gulf by 

 the Mississippi alone 

 has already been stated 

 (Sect. 29). Fig. 345 

 represents a newly 

 cleared slope under 

 cultivation, and Fig. 

 346 an early stage in 

 the formation of gul- 

 lies on a steeper slope 

 after clearing. The 

 land in the latter case 



is already past the stage in which it can be cultivated in the 

 ordinary way. Left to itself the tendency is for the washing 

 to continue until the hillside becomes a series of miniature 

 ravines, strewn with bowlders and separated by bare ridges. 

 Thousands of acres in the southern United States and hundreds 



1 See Fernow, "Forest Influences," Bulletin 7, Division of Forestry, U. S. 

 Dept. Agr. 



FIG. 328. How the forest holds the soil 



The river in the foreground often overflows its 

 banks, but little erosion occurs 



