FOREST RANGERS' CATECHISM 39 



well illustrated by the hundreds of thousands of acres of worthless 

 brush range along the borders of the great interior valleys. 



8. What effect has light burning on the productivity of the soil? 

 The humus or vegetable litter is destroyed, the soil is left exposed 



to rain, erosion follows, and the mineral salts necessary for plant 

 growth are washed away. 



9. Does the Forest Service ever use fire to reduce the hazard in the 

 forests? 



Yes. On timber-sale areas, all of the litter and slash resulting 

 from logging is piled and burned after rains or snow. Snags and 

 accumulations of inflammable litter of all kinds are being burned 

 to reduce the hazard from fires along highways, roads, and trails, 

 or wherever there is a danger of fires starting. 



NATURAL ENEMIES OF THE FOREST 



1. What are the principal natural enemies, other than fire, of the 

 forests of California? 



Insects, animals, tree diseases, and drought. 



2. How serious are insect infestations? 



All of the important forest insects of California are native to the 

 national forests. They have been killing trees for centuries. Every 

 year a certain percentage of the forest stand succumbs to insects. 

 Estimates indicate that in the West the annual loss of western 

 yellow pine from insects, principally the western pine beetle, ex- 

 ceeds 300,000,000 board feet, or enough timber to keep several mod- 

 ern sawmills in continuous operation. 



Periodically conditions become particularly favorable for in- 

 sects. Their enemies are reduced in number; the resistance of the 

 trees is lowered by drought ; or a large quantity of favorable breeding 

 material is available for them, and they become very abundant and 

 for several years kill more timber than will be replaced by normal 

 growth in many years. Such a condition is termed an epidemic infes- 

 tation, and in western yellow pine forests, over limited areas, as 

 much as 10 per cent of the stand may be killed in a single year, and 

 50 per cent of the stand during the course of the epidemic. 



3. How are insect infestations controlled? 



The methods of control which have been successfully used in 

 destroying the pine bark beetle are as follows : 



(a) Felling the trees and burning the infested bark, (b) Peeling 

 the infested bark from the trees either with or without felling the 

 trees, (c) Felling the trees and placing the bark so that it will be 

 exposed to the direct rays of the sun, either with or without peeling 

 it from the tree, (d) Felling the trees and submerging the infested 

 logs in water, (e) Preparing trap trees to attract the beetle broods 

 and later destroying them by one of the above-mentioned methods. 

 (/) Logging the infested area and removing the beetles either in the 

 logs or destroying them in the freshly cut limbs and tops. 



