22 ELEMENTARY FORESTRY. 



which prevents the drying- out of the soil. They check the 

 flow of water over the land, thus preventing- the washing- away 

 or compacting- of the soil by heavy rains and giving- the water 

 a better chance to soak into the ground. 



( 5. ) A tree protects from the destructive force of severe 

 winds. A single tree or group of trees may seem to have 

 little effect on tornadoes, bub larg-e groups of trees may possi- 

 bly prevent their formation or greatly lessen their violence. 

 Protection from severe winds may greatly affect the growing 

 of plants, since on accountof the winds many plants that may 

 be successfully grown when protected by shelter belts cannot 

 be grown on the open prairie. This protection when present 

 serves to lessen the fuel necessary to warm dwelling houses 

 and also lessens the food eaten by animals. It also keeps the 

 surface soil in fields from being blown away. 



In these five principal ways a single tree affects the con- 

 ditions of climate and soil in its immediate vicinity. To be 

 sure some of them are not so very evident where a single tree 

 grows in an open field, but where trees are growing in groups 

 or on large tracts of land all of these factors are important 

 in modifying climate and soil conditions and will be referred 

 to at greater length. 



INFLUENCE OF FORESTS ON WATER SUPPLIES. 



It is very evident that the proper disposition of water up- 

 on the land is the most important factor in the growing of 

 crops and it is equally evident that nature's changeful and 

 wasteful ways of supplying water to crops are not the best 

 ways of so doing, for we know that not only in the arid regions 

 but in general wherever irrigation is used, crops are produced 

 in greatest abundance and certainty. This once recognized 

 then the proper distribution of the available water supplies 

 becomes a question of immediate interest. Human effort can, 

 to a limited extent, direct the laws of nature that influence 

 climate and soil conditions and it becomes necessary that we 

 have a clear understanding of the forces that are at work in 

 nature in order that we may know where we may or may not 

 expect to be successful in directing them. In order that we 

 may better understand this subject, I quote the following ex- 

 tract on forest influences from the report of the Forestry 



