70 ECONOMICS OF FORESTRY. 



in the amount of rainfall, it would appear that the 

 forest area must be of considerable extent. 



Although some writers have, from existing meas- 

 urements, argued an influence on precipitation, 

 others have denied it. As stated above, we hold 

 that no reliable rainfall measurements are, as yet, 

 obtainable, and we must leave the question open. 



The more readily conceivable effect of a forest 

 growth on moisture conditions of the air is that 

 which it has in common, probably in increased 

 degree, with the so-called wind-break. By break- 

 ing the velocity of dry winds and possibly enriching 

 them somewhat with moisture, the rate of evapo- 

 ration over a neighboring field is considerably re- 

 duced, so that, in regions where winds are common, 

 the protection shows itself in increased crops on 

 protected fields. 



The same protection against cold winds may 

 make life more bearable, and enable the growing 

 of crops which could otherwise not succeed. Thus 

 it is believed that during the abnormal frosts 

 which a few years ago killed most of the orange 

 groves in Florida, many which had good forest 

 shelter survived. It is also reported that in France 

 the cultivation of the olive has become impossible 

 in the more northern departments, owing to de- 

 forestation. On the other hand, it may happen 

 that the opening toward warmer southern winds 

 may modify a severer climate favorably. This 

 consideration again points to the entirely local 



