10 CIRCULAR 8 6 4, IT. S. DEPARTMENT OF AGRICULTURE 



trees weakened by overcrowding, fire, or lightning; and, to a lesser 

 extent, those showing signs of overmaturity, are the trees most sus- 

 ceptible to attack. The removal of these trees before they are attacked 

 not only saves a large amount of valuable timber but leaves the stands 

 in a vigorous healthy condition, and better able to resist beetle attacks. 



As a result of these studies, two valuable silvicultural tools have 

 been made available to foresters and timber managers to help solve the 

 pine beetle problem. The first is a bark beetle susceptibility classi- 

 fication, referred to as Keen's ponderosa pine tree classification, 2 

 which recognizes 16 individual classes based on age and vigor. When 

 the more susceptible classes are removed from a mature stand, a cut 

 of 40 to 60 percent of the stand volume usually results. This system 

 has been widely adopted by foresters and timber managers for mak- 

 ing selection cuts to remove the trees likely to be killed over a period 

 of 30 to 40 years. 



The second tool is a method, devised by Salman and Bongberg. 3 

 of risk-rating the current health of individual ponderosa pine trees. 

 Four classes of risk to beetle attack are set up, as follows : 1, Low-risk 

 tree — full foliage and healthy appearing crown; needles dark green, 

 long, or coarse; no weakened portions in crown: 2, moderate-risk 

 tree — moderately vigorous crown, imperfect in spots; foliage mostly 

 healthy with fair to good colored needles of average length : few twigs 

 lacking foliage, and few small weakened portions in crown ; 3, high- 

 risk tree — crown fair to poor in vigor, somewhat thin and ragged in 

 parts; foliage in parts of crown thin, bunchy, or unhealthy, and of 

 fair to poor color ; some to many weakened portions of the crown ; 4, 

 very high-risk tree — crown of very poor vigor, ragged, thin, and often 

 showing evidences of active infestation; foliage thin or bunchy; 

 needles short, sparse, or of poor color; some to many twigs and 

 branches dead or dying; large portions of crown weakened (plate 1). 



When the trees in classes 3 and 4 are removed by sanitation-salvage 

 logging (a term used to designate this method), the stand volume is 

 reduced by 15 to 30 percent. By removing this high-risk element from 

 the stand bark beetle losses have been reduced, over a 10-year period, 

 by TO to 85 percent. This type of salvage cutting can be clone at costs 

 only slightly higher than the usual utilization cutting. 



Thus, through a critical analysis of individual trees in pine stands — 

 their age, vigor, and current health — it is possible to designate the 

 trees likely to be killed by the western pine beetle in either a short or 

 a long period of time. This practice holds much promise for solving 

 the perplexing western pine beetle problem. "Beetle-proof" ponde- 

 rosa pine forests may sometime become a reality. 



2 Keen. F. P. ponderosa pine tree classes redefined. Jour. Forestry 41 : 

 249-253, illus. 1943. 



3 Salman, K. A., and Bongberg. J. W. logging high-risk trees to control 

 insects in the pine stands of northeastern California. Jour. Forestry 40 : 

 533-539. 1942. 



"fc U. S. GOVERNMENT PRINTING OFFICE; 1951 



