74 



THE DESTRUCTIVE AGENTS OP FORESTS. 



in February, 1910, and doubtless other regions suffered in the 

 same way. 



The breaking of limbs by winds, snows and sleets and the 

 wounding of bark and wood by falling trees and by lightning re- 

 sult, indirectly, in a great loss from diseases of various kinds. 

 Many species of wood-infesting insects and myriads of disease 

 germs find a suitable place to enter at the scars of broken limbs 

 and bark. 



Effects of Insufficient Light. 



The life of every tree in a forest is a constant struggle to get 

 to the light. Some species demand more light than others, but 

 all are dependent upon it to a greater or less degree. The trees 

 that succeed in overtopping those that are intolerant of shade 

 grow and reach maturity at the latter 's expense. Disease is sure 

 to follow a weakening of trees that have been overgrown and left 

 in the shade ; and so an insuffi^cient supply of light causes a con- 

 stant thinning out process to go on from year to year. 



Injuries Due to Smoke and Gas. 



The ill effects upon vegetation of the smoke and gas of coke 

 ovens and paper pulp mills is readily seen in the immediate 

 vicinities of these industries. Not only the grass and other small 

 vegetation about the thousands of coke ovens in West Virginia 

 are killed, but the leaves of all the trees surrounding them have 

 a withered and sickly appearance. Cone-bearing trees, especial- 

 ly white pine and hemlock, are most easily killed from the causes 

 here mentioned. Oaks, hickories, chestnut, and poplar, however, 

 are all seriously affected and many others suffer disease and 

 finally death after long exposure. 



Effects of the Wounding of Trees by Mammals. 



A number of forest-living mammals, such as bears, deer, and 

 rabbits, injure live trees by chewing, scratching, or otherwise 

 wounding the bark; and small, burrowing rodents occasionally 



