FOREST INFLUENCES. 29 



(4.) The leaves that fall to the ground form a mulch which pre- 

 vents 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, but large groups of trees may possibly prevent 

 their formation or greatly lessen their violence. Protection 

 from severe winds may greatly affect the growing of plants, 

 since on account of the winds many plants that may be suc- 

 cessfully 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 condi- 

 tions 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 modify- 

 ing 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 upon 

 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 gen- 

 eral 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 condi- 

 tions, and it becomes necessary that we have a clear understand- 

 ing 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 



