AND AIR 277 



of California, and some of the unfortunate effects of overuse of campgrounds. 

 General evidence indicates that the Colorado blue spruce of the central 

 Rocky Mountains is also highly susceptible to the type of injury which has 

 caused damage to the redwood. On the other hand, except at its lower 

 altitudinal limits where the never-ending struggle is waged between tree 

 growth and open prairie, ponderosa pine is relatively resistant to the effects 

 of concentrated occupancy of its environment by man. 



These are largely western problems. To the East, the birches suffer from 

 the obeyed impulse of thousands to peel off their bark as mementos of a 

 forest outing. "Give me of your bark, O Birch-tree!" Research to amend 

 such habits must enter the field of applied psychology, and be grouped, 

 perhaps, with studies of persuasion in fire prevention such as were noted in 

 chapter 10. 



Physical data as to the effects of new roads, trails, and recreational 

 structures upon the tree growth and water yield is accumulating, but still 

 is inadequate. The removal of large quantities of soil where cuts are made on 

 sloping terrain disturbs and often quite radically changes the movement of 

 water within the soil. Trees standing above a cut may find themselves with- 

 out the supply of moisture which they demand and without which they 

 cannot survive. A fill banking new soil about the base of a tree may result 

 not only in changes in the soil moisture by alteration of the rate of percola- 

 tion of surface water, but may also prevent proper aeration of the soil levels 

 in which the feeding roots of the tree occur. To cut long swaths of timber 

 through forests of even a moderate degree of density for road construction 

 may cause profound modifications of the micro-climate to which the tree is 

 accustomed. Violent changes in the local direction and velocity of air cur- 

 rents may result, and trees which otherwise might have stood for centuries 

 may suddenly be blown down. 



The precise causes of many such effects are as yet little understood. 

 Definite studies and analyses will enable the road engineer and forest 

 administrator to prevent defacement and waste. Obvious causes of deteriora- 

 tion and destruction, such as mechanical injury, can be controlled by 

 administrative regulation. But to guard against the more deeply seated 

 dangers involving slow changes in the relation of each kind of organism to 



