10 BULLETIN 418^ U. S. DEPARTMENT OF AGRICULTURE. 



spreading fires that form a blaze not more than 2 or 3 feet high and 

 that burn chiefly the dry grass, needles, and underbrush start freely 

 in yeUow-pine forests, because for several months each summer the 

 surface litter is dry enough to burn readily. Practically every acre 

 of virgin yellow-pine timberland in central and eastern Oregon has 

 been run over by fire during the lifetime of the present forest, and 

 much of it has been repeatedly scourged. 



It is sometimes supposed that these hght surface fires, which have 

 in the past run through the yellow-pine forests periodically, do no 

 damage to the timber, but that they "protect^' it from possible 

 severe conflagrations by burning up the surface debris before it 

 accumulates. This is a mistake. These repeated fires, no matter 

 how Hght, do in the aggregate an enormous amount of damage to 

 yellow-pine forests, not alone to the on-coming young trees, but to 

 the present mature merchantable timber. This damage may be 

 classified under several headings : 



(1) The fire-scarring of the butts of merchantable yeUow pine. 

 The bark of yellow pine in this region is not particularly thi6k at 



the base, and surface fires find no difiiculty in eatmg through it and 

 getting at the inflammable wood of the butt. A careful cruise of 

 every tree on 154 J sample acres in typical yeUow-pine stands in 

 several locahties in the Blue Mountains showed that 42 out of every 

 100 trees were fire-scarred — i. e., the wood was exposed because the 

 bark had been burned off. Their susceptibility to fires is aggravated 

 by the work of the red turpentine beetle (Dendroctonus valens) , which, 

 by working in the cambium at the base of the tree, loosens patches 

 of bark and stimulates the flow of pitch. These fire-scarred trees 

 may easily fall a prey to the next fire that runs through the forest, 

 and some of them are so deeply scarred at the base that they are 

 hkely to be windthrown. It is noticeable that especially the larger 

 (and therefore the older) trees are fire-scarred, because they have 

 been exposed to more of these periodic fires. A record of 1,184 

 representative trees cut in a logging operation in Grant County shows 

 that 22.8 per cent of the butt logs were fire-scarred (still more of the 

 trees may of course have had scars which did not show on the log 

 because the stumps were cut high enough to avoid them), and that 

 18.6 per cent of the butt logs were so badly fire-scarred that about 

 46.1 board feet per log (equivalent to 14 per cent of the fuU scale of 

 the defective logs) was lost and had to be deducted from the fuU scale. 



(2) The killing of occasional trees by the burning through of the 

 base. 



^ Though these surface fires kill very few trees outright by tne 

 intensity of their heat, yet each fire — even the lightest grass fire — 

 is apt to cause the death of a yeUow-pine tree here and there by gnaw- 



