90 WESTERN YELLOW PINE TYPE 



fall an easy prey to insects and fungi. One of the most destruc- 

 tive members of the genus Dedroctonus, or bark beetles, attacks 

 western yellow pine and if the conditions are favorable for its 

 rapid increase damage over a wide area may result. For example 

 in the Black Hills of South Dakota the numbers of this beetle 

 increased so rapidly that practically all the mature timber over 

 an area of 500,000 acres was killed and forced sales were neces- 

 sary to salvage any of it. The National Forests in California 

 are having a similar experience at the present time. Such 

 infestations get started because the beetles find weakened trees 

 in which they may breed in large enough numbers so that they 

 successfully attack vigorous trees and overcome them by sheer 

 force of numbers. In fact this habit of seeking out weakened 

 individuals where there are but few of the beetles is taken advan- 

 tage of in combating infestations in the early stages. So called 

 " trap " trees are girdled in the late summer so that the beetles 

 may lay their eggs in them. Then these trap trees are felled, 

 peeled, and the grubs destroyed before the adult beetles can 

 emerge the following spring. 



In the same way certain species of fungi, notably red rot, 

 Trametes pini, attack the western yellow pine when trees have 

 been weakened by fire or other causes and spread rapidly unless 

 the surrounding timber is thoroughly sound and healthy. 



With the great variety of climatic conditions under which 

 yellow pine grows it is natural that there should be a wide range 

 in rates of growth. The follo\ving figures are for growth under 

 favorable natural conditions but do not represent what can be 

 done under intensive management. 



GROWTH IN 100 YEARS 



Arizona. . . 

 California. 

 Oregon. . . 



Diameter 



Inches 

 14 

 20 

 13.2 



Height 



Degrees 

 48 



94 

 62 



Unfortunately no accurate figures can be presented for density 

 and yield per acre in a given time. It is only possible to state 



