724 A NATIONAL PLAN FOR. AMERICAN FORESTRY 



the spruce budworm, the hemlock looper, the gipsy moth, and losses 

 to the felled log, sawn lumber, and finished wood products in use. A 

 considerable portion of this loss is unavoidable, just as losses from 

 lightning or windstorms are unavoidable. On the other hand, much 

 of it can be prevented and will be so in the future through silvicultural 

 practices, proper management, and direct control. 



With mature timber one of the largest single items of loss results 

 from activities of bark beetles. Actual surveys in our western forests 

 indicate that 5 billion to 6 billion feet are destroyed annually by these 

 insects. In lodgepole forests in and surrounding the Yellowstone 

 National Park tremendous losses have occurred. It has been con- 

 servatively estimated that during the past 10 years these have 

 amounted to 2,620 million board feet. In one year over 12 million 

 trees were killed. During the last 20 years most of the mature lodge- 

 pole forests in regions 1,4, and 6 have been completely destroyed or 

 are in the process of destruction by the mountain pine beetle. If 

 this is an exmple of what is to be expected in the future, we can as- 

 sume that lodgepole stands, once they have reached maturity, must 

 be so managed as to be harvested before the beetles play the part of 

 lumbermen. 



A recent survey indicates that the forest losses in the State of 

 California due to bark beetles were at least 2^ times as great in 1931 

 as they were on an average for the past 10-year period. This aver- 

 age figure has been placed at 500,000,000 board feet. This would 

 indicate a state-wide loss of 1,125,000,000 board feet of merchantable 

 timber. At a purely commercial stumpage rate this represents a loss 

 of nearly $6,000,000, not taking into account the manufacturing value 

 of the lumber, which is an asset going to the region where it is pro- 

 duced. Where these losses deplete the fine old forests that are being 

 preserved as exhibits in the national parks and around recreational 

 areas, they take on a value that is less tangible but undoubtedly 

 much higher than in purely commercial timber. 



Defoliating insects likewise destroy considerable bodies of mature 

 timber. These outbreaks, however, usually appear at rather long 

 intervals and are of short duration. An exceptional instance such as 

 that of the spruce bud worm in northeastern United States and 

 Canada ravaged the spruce and fir forests for a period of 10 years 

 (from 1910 to 1920) and it has been estimated that in spruce-fir types 

 of Maine, Ontario, Quebec, and New Brunswick from 40-70 percent 

 of the timber was destroyed and that the equivalent of more than 25 

 years' pulpwood supply for current annual American paper require- 

 ments was lost. Or certain species, even if they do not kill the 

 timber, cause a cessation or reduction of growth which may increase 

 the rotation period of the stand from 5 to 10 years or more. Such 

 defoliations may be local and confined to only a single species of tree 

 or they may spread over enormous areas involving several species. 

 The most recent outbreak of the Pandora moth in the ponderosa- 

 pine stands of southern Oregon occurred between 1918-1925 and 

 covered approximately 400,000 acres. Growth measurements from 

 plots in this area showed that for a period of 11 years the normal 

 forest growth on this area was reduced an average of 32 percent or a 

 loss of increment of approximately 100 million board feet. 



The northern white pine is subject to severe insect depredations 

 during the early stages of its growth. The Pales weevil frequently 



