~N 
48 BULLETIN 1200, U. S. DEPARTMENT OF AGRICULTURE. 
3. Set the fire on a still evening, usually after sundown. 
4. Burn away from the edge toward the center all around the 
area to be burned and from the base of all green trees to 
be left. On steep slopes burning should begin along the 
top edge and be carried down through the slash by parallel 
strips along the slope. . 
5. Protect all adjacent young growth. If necessary, put fire 
lines along the edge of a young stand on slopes or where 
there is dry material among the young growth. 
6. Before burning the slash, cut all snags and unmerchantabie 
trees, except trees to be left for seed, in order that as much 
débris as possible may be consumed in the-first fire. 
. Construct fire lines between old burns and new slash where 
it is necessary in order to prevent the fire from running 
back over the old burns. , 
8. After the slash is once burned, keep out fire until the new 
stand is matured and logged. 
The application of these rules in handling mature and overmature 
Douglas fir forests is the best preparation for future forests. 
There is a definite reason for burning the slash in the night and 
while there isno wind. Usually the night air contains more moisture, 
which prevents the fire from burning so briskly as in the daytime, 
so that the green timber at the edge of the slash and the green trees 
left on the area are protected. A slash fire during a hot, dry day 
invariably kills all standing trees and, moreover, 1s apt to start a 
crown fire in adjacent timber. 
Crown fires will travel in clean young Douglas-fir stands only 
before a high wind or on steep slopes, and will scarcely ever travel at 
night. Consequently a stand of young growth at the edge of the 
slash is fairly well protected if the burning is done at night. The 
trees left after logging are generally not killed by overheating of the 
base or trunk, but'the needles are either dried or burned by the heated 
air or flame rising through the crowns. If the bark is unbroken and 
there are no pitch pockets on the trunk, a mature Douglas fir will 
withstand the heat of a slash fire. Experiments have shown that bark 
4 inches thick on a mature Douglas fir resisted, without injury to the 
growing tissue inside, a heat of 900° F. applied for 4 hours; and that 
slash fires heated the trunks from 800° F. to 1,400° F. for periods of 
5 to 20 minutes without harm. Trees 35 years old with bark 13 inches 
thick were killed after 52 minutes, and 15-year old trees with bark 
one-fourth inch thick were killed after 11 minutes ina heat of 900° F. 
Young trees 8 years old with bark 0.15 inch thick were killed in 1 
minute and 10 seconds. These figures show why it is important to 
keep all fires away from young stands and why older trees live 
through hot fires, provided the flames do not reach the crowns. 
The needles will not burn unless a great deal of water is evapo- 
rated from them, and so it is important to prevent the generation of 
sufficient heat to dry them. If fire is set at the edge of a stand of 
young growth it burns away from the young stand, and the heat de- 
veloped is not so intense as that of a fire that runs up to the stand 
and that may destroy the young growth for some distance at least, 
and even pass through it. 
~T. 
