PREVIEW 573 



many animals, provide millions of feet of lumber, and help to 

 protect and regulate the water supply of the country. No one 

 who has traveled over the great Southwest can fail to realize the 

 value of forest trees. Great areas of land lie devastated, sub- 

 ject to floods in winter and droughts in summer. Yet these 

 areas, if given water supply, would be capable of producing crops 

 in abundance. Irrigation has proved this in regard to similar 

 areas. Irrigation projects, which now provide homes and em- 

 ployment for thousands of people, besides producing annually 

 great quantities of food supplies, would be impossible were it not 

 for protected forest areas somewhere. Moreover, nearly 800 

 western communities, with a total population of nearly 3,000,000, 

 depend for their water supplies upon streams coming from areas 

 protected by national forests. When the earth's surface is covered 

 by trees, the roots prevent soil from being washed away and they 

 hold moisture in the ground. Devastation of immense areas in 

 China and considerable damage by floods in parts of Switzerland, 

 France, and the United States have resulted where the forest 

 covering has been removed. The annual spring " freshets " in 

 the East ; the floods in the Ohio and Mississippi valleys ; and 

 the damage done by sudden storms along stream beds in the 

 Southwest, are all examples of the great destruction that can be 

 wrought by water which is not controlled by forests at the river 

 sources. It has been estimated that the carrying power of water is 

 increased sixty-four times if its rate of flow is doubled ; that is, the 

 transporting power of water varies as the sixth power of its velocity. 

 This accounts for the tremendous destruction produced by a 

 mountain stream in a flood. 



Besides holding water in the ground in some localities forests 

 are used as windbreaks and to protect mountain towns against 

 avalanches. In winter they moderate the cold, and in summer 

 reduce the heat and lessen the danger from storms. The nesting 

 of birds in woods protects many valuable plants, which otherwise 

 might be destroyed by insects. 



The increasing population has meant the necessity of more 

 food, more and better water supplies, more power to light cities 

 and run machines, and more fuel. The balance of nature has 



