180 PRODUCTIVE FARMING 



3. The drying out of soil is also prevented by the mulcb 

 of leaves and twigs which fall to the ground under the trees. 

 Trees and leaves check the flow of water over the land, thus 

 preventing the washing away of good soil. The soil is not so 

 badly beaten down by heavy rains. The water soaks into 

 the soil better and the flow-off is very gradual. 



4. By breaking the force of the wind trees will aid in 

 retaining moisture in the surface soil near the trees. The 

 evaporation decreases as the wind is checked. Water is also 

 held better in the soil shaded by the trees. A large amount 

 of water which the trees give off from their leaves is drawn 

 from the subsoil, without drawing on the water of the surface 

 soil. This moisture from the leaves increases the amount 

 in the surrounding air. Trees which have the roots near 

 the surface, as the elm and red maple, take up so much water 

 near the surface as to make it unwise to try to grow crops 

 near them. 



5. The destructive force of severe winds is often prevented 

 by trees. Tornadoes may be prevented or made of little 

 effect by large groups of trees. Certain crops may be grown 

 when protected by shelter-belts of trees that could not other- 

 wise be grown on the prairie. These shelters from high winds 

 prevent the blowing of soils. They lessen the severity of 

 cold winter winds both for stock and for people. 



How Trees Influence Water Supply. The proper dis- 

 tribution of water upon the land is the most important factor 

 in the growing of crops. In the natural course of the seasons 

 we have both floods and droughts. The proper holding of 

 the water from flood-time to drought is best accomplished 

 by the growth of trees and the protection of natural forests, 



Eain falling upon forested areas flows away slowly. 

 Springs and streams are kept constantly supplied from the 

 water of such areas. 



Instead of the waters of the rainy season producing heavy 

 floods and causing much destruction along the courses of 



