10 



BULLETIN 863, U. S. DEPARTMENT OE AGRICULTURE 



erosion on unprotected hillsides and the use of trees as shelters in 

 pastures and about the farm buildings. 



Topics for study. — With an acquaintance formed with the different 

 species of trees, it will be worth while to learn their value both as in- 

 dividual trees and associated together in woodlands. 



Timber or wood products: Trees, grouped according to their value 

 for wood or timber. (This is expanded in Lesson IV.) 



How a forest cover conserves the water from rainfall or melting 



snow. 



Flow of streams from open and from forested land; seepage and 

 springs. Protecting watersheds of city reservoirs and headquarters 

 of large streams from erosion and floods. State and municipal 



Fig. 4.— The forest floor. Leaves and twig litter on the ground beneath the trees, spongy layer of de- 

 composed vegetable matter or humus, this and the lower layer of soil interlaced with tree roots and 

 rootlets, and the clay subsoil. Dense growth of seedling and sapling trees covering and protecting 

 the soil 



forests. The 150,000,000 acres of Government national forests held 

 for protection of watersheds and streams and for a permanent tim- 

 ber supply. Private owners hold four-fifths of the total standing 

 timber in the United States. 



How trees protect the soil against erosion and the formation of 

 gullies on steep slopes. Examples of local hillsides and regions of 

 the United States. 



Effect of woods as shelter against hot dry winds and cold winds 

 for growing grain and fruit crops, livestock, and the farm home. 

 The difference felt in temperature of the air in midsummer out in 

 the open road or field and in the shade of a single tree or of woods. 

 The same as experienced on a cold windy day in winter. 



