Plant Industries and Climatic Plant Formations 367 



U . S. Forest Service 



Fig. 232. Fighting a forest fire. During a recent 5-year period, fire destroyed 56 million 

 acres of forest in the United States. 



Fire patrol. Most of the Western forest reserves and of the 

 smaller state forests are regularly patrolled during the summer 

 and autumn to prevent the spread of fires started by careless 

 campers or by lightning. Airplanes and. permanent lookout 

 stations on mountain peaks aid in this work. 



In recent years almost as much forest has been destroyed by 

 fire as has been cut into merchantable timber, and the fires have 

 consumed not only the trees but also the forest humus or '' duff," 

 and made the areas unfit to establish valuable forests for genera- 

 tions to come. 



Irrigation. Most of the large irrigation projects of the United 

 States are located in the semi-arid regions adjoining the lower 

 forest borders. Through the construction of dams and canals 

 the water from the mountains is made available throughout the 

 growing season. The soils of these areas are highly fertile, and 



