32 BULLETIN 149 
extreme temperatures, frost, winter killing, and sleet and snow break- 
age; also poor stock and careless planting, and competition with 
other growth. 
FIRE 
A fire, if allowed to run through a young plantation, will almost 
surely kill all the trees in the area. Protection from lire is pecul- 
iarly essential in the northern Lake States for the success of a for- 
est plantation, for such plantations must occupy areas where there 
is more or less grass and brush to dry out to high inflammability 
during the dry periods of spring and fall. 
The protective measures must provide for preventing fires from 
entering the plantation from outside as well as for the suppression 
of those fires which may start within. The- detection of fires is now 
provided for in much of the forest region of the Lake States by the 
State or Federal Governments, or by associations of private owners, 
through a system of lookout towers, telephone lines, and observers. 
Supplementing this, there should also be some one on the ground defi- 
nitely responsible for keeping fires out of the planted area. 
The use of fire lines for the protection of plantations is desirable 
and sometimes necessary. They may be single or double. Single 
lines are plowed 10 to 20 furrows wide on land-subdivision lines, or 
along old logging railroads, or roads through the center of a strip 
on which the brush or tree growth is cleared to a width of 14: to 30 
feet. Before plowing, it may be necessary to pull or blow out the 
stumps. The lines are then disked or harrowed periodically to pre- 
vent growth of grass or other vegetation. Double fire lines consist 
of two plowed strips of 6 to 10 furrows, 7 to 12 feet wide, located 30 
to 50 feet from and on each side of a section or other subdivision line, 
or parallel to a traveled road. (PI. 3, B.) The brush is usually cut 
on the strip between the lines so that the strip may be burned over 
each year and kept as free as possible from inflammable material. 
Fire lines serve chiefly as barriers to the spread of surface fires, or. 
in case of brush or crown fires, as base lines from which back fires 
may be safely started. Experience has shown that straight fire lines 
are of the greatest value because, in fighting fire, a straight line from 
which to back-fire means the shortest line to watch and one least apt 
to cause fire fighters to become confused. Straight fire lines may also 
better serve as roads. Single fire lines are about half as expensive 
as double lines, but because of overhanging branches from adjoining 
planted areas they are not as valuable for fire protection. Single fire 
lines cost from $25 to $100 per mile where the amount of brush and 
stumps to be removed is not large. Double lines cost from $50 to 
$200 per mile under similar conditions. If single fire lines are con- 
structed around every 40 acres, as they have been in the plantations 
on the Michigan State forests, where the fire protection is intensively 
organized, they come to 1 mile of line for every 80 acres. The acre 
cost for construction is then 30 cents to $1.25, and this is probably the 
maximum cost for this form of protection. Ordinarily, fire lines are 
more widely separated and the costs per acre are correspondingly 
lower. 
The cost of disking or replowing fire lines annually varies with the 
age of the lines. Usually the lines are gone over twice in a season, 
