254 BULLETIN UNIVKRSITV OF M(3NTANA 



proximately twenty inches bears a luxuriant forest growth. In the 

 former situations, the winds are excessive. In the latter, they are neither 

 so frequent nor so strong. 



From the above it will be seen that the main cause for the absence of 

 trees in a greater part of the state of Montana is the lack of sufficient 

 moisture. In some places, however, where there is sufficient moisture, 

 winds, fires, and grazing animals may prevent the growth of trees and 

 thus favor the prairie. 



