INSECTS AND FOREST MANAGEMENT — CRAIGHEAD 377 



artificial control. Definite suggestions along these lines were 

 expressed very early by Hopkins (1909a) : 



The desired control or prevention of loss can often be brought about by the 

 adoption or adjustment of those requisite details in forest management and 

 in lumbering and manufacturing operations, storing, transportation, and utiliza- 

 tion of the products which at the least expenditure will cause the necessary 

 reduction of the injurious insects and establish unfavorable conditions for their 

 future multiplication or continuance of destructive work. 



Curiously enough the principles for growing or handling forests 

 to avoid insect attack are best learned from the study of the insects 

 themselves. As mentioned previously, insect losses are only serious 

 when they interfere with man's need. For generations certain types 

 of forests have been destroyed by insects and rebuilt through growth, 

 and this process is still going on unnoticed and of little concern to 

 man in the more remote areas. Nature also uses msects for the 

 removal of certain shade-intolerant or temporary species of trees 

 from the forest, thus hastening the arrival of the climax type. 



Many excellent examples of such activities have been observed and 

 recorded. The first might be illustrated by the activities of the Black 

 Hills beetle on the Kaibab Plateau, an area relatively undisturbed by 

 man. To quote Craighead (1924) : 



This beetle has been present in this forest, killing enormous quantities of 

 timber, probably since the forest has been in existence, although absolute 

 records can only be dated back 400 years. The activities of these beetles have 

 been almost continuous with intermittent periods of greater epidemicity * * * 

 Generally speaking, the forest consists of a densely stocked immature stand. 

 Stands of old mature timber are very limited in extent * * * These beetles 

 have in reality been putting into effect a form of management — cutting by a 

 group system the annual increment of the forest for hundreds of years in the 

 past and providing at the same time good conditions for reproduction. But 

 little study is needed to convince one that this system has been higlily successful 

 from the standpoint of producing rapid growth and fully stocked stands. 



An illustration of the action of insects in effecting natural forest 

 succession is provided by the 1910-20 spruce budworm outbreak in 

 eastern Canada and the northeastern part of the United States, as 

 described by Swaine and Craighead (1924) and by Graham and Orr 

 (1940). This outbreak was one phase of a slow process of natural 

 forest succession over extensive areas. The temporary types, com- 

 posed largely of aspen and birch, were gradually replaced by mix- 

 tures of balsam fir, spruce, and red and white pine. The forest tent 

 caterpillar {Malacosoma disstr-ia Hbn.) probably aided in this con- 

 version by killing some of the aspen and birch and thus releasing 

 the coniferous understory. By the time the fir and spruce reached 

 maturity they formed a considerable part of the upper crown canopy 

 and thus made conditions favorable for an outbreak of the spruce 

 budworm. The budworm killed most of the mature fir and some of 



