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 yellow-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 light 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 light, 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 yellow pine. 
The bark of yellow pine in this region is not particularly thick at 
the base, and surface fires find no difficulty in eating through it and 
getting at the inflammable wood of the butt. A careful cruise of 
every tree on 154| sample acres in typical yellow-pine stands in 
several localities 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 
likely 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 full scale of 
the defective logs) was lost and had to be deducted from the full 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 yellow-pine tree here and there by gnaw- 
