370 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1941 



FIRE AND INSECT RELATIONS 



Insect outbreaks are occasionally of more importance because of 

 the fire menace they create than because of the value of the timber 

 killed. This condition is described in "A National Plan for American 

 Forestry" (Senate Document 12, 1933), as follows: 



When extensive outbreaks of insects develop in forest types composed chiefly 

 of one species of tree, a high percentage of the stand may be destroyed. These 

 standing dead trees go dovpn in the course of a few years, making an almost 

 impenetrable tangle of logs and tops. Under proper conditions a flash of 

 lightning may set off the mass, resulting in a widespread conflagration almost 

 impossible to fight. Past experience has shown that epidemics of the mountain 

 pine beetle in lodgepole have been followed by fires more often than not. 

 [PI. 5, fig. 1.] 



The old snags of insect-killed trees scattered throughout our mature forests, 

 which average for some areas as many as 10 per acre, stand for many years 

 and greatly increase the cost, diflSculty, and danger in fire control. Snag 

 felling is required in many sales of national forest timber, and many private 

 operators have already adopted this regulation. The increased cost of control 

 of fires which have spread from burning snags within fire lines would alone 

 justify insect control even at a high cost. 



It should be understood that in making any comparisons between 

 losses from insects and from fire, a certain percentage of this destruc- 

 tion by insects occurs in what are called normal or endemic in- 

 festations in timber stands of such low commercial value that an 

 expenditure for control would not be warranted. Such losses are 

 inevitable and are in most cases offset by the annual increment of the 

 stand. Also, as stated in Senate Document 12, 



Forest fires, beside destroying variable amounts of mature timber, kill all 

 the smaller trees and reproduction, and repeated fires leave the land in a 

 totally unproductive condition for generations to come. Forest insect epidemics, 

 on the other hand, destroy only the mature timber and not only leave the 

 regeneration already existing in a better condition for rapid growth but 

 frequently induce copious reproduction. 



SCENIC AND PROTECTIVE VALUES 



The preceding citation of insect damage in commercial timber is 

 only a part of the picture. To quote again from Senate Document 

 12, 



The importance of the forest cover in national parks, game preserves, and 

 recreational areas cannot be estimated in monetary values. Here aesthetic 

 and protective values far outweigh those of commercial timber. One of the 

 greatest attractions in these areas is a green forest cover on which much of 

 the natural beauty of the parks is dependent. The trees also give protection 

 to the birds and animals. 



Insect depredations which mar the scenic value or destroy the 

 protective values of the forest cover in these parks and recreational 



