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- 
cesstully 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 modily- 
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 
