LIFE HISTORY OF LODGEPOLE PINE IN ROCKY MOUNTAINS. 19 
TABLE 5.—LHjfect of thinning; average diameter growth of lodgepole pine trees 
left after cutting, etc.—Continued. 
Part II. [Based on the 54 trees which showed an increased growth. 
Periodic annual diam- 
eter growth for 20 | /imerequired to grow | Rate of 
Diam- years. 1 inch in diameter. increase in 
oter Trees volume 
breast ° a a iT at CC CLONL LL 
high. Before After Before After pce 
thinning. | thinning. | thinning. | thinning. mS: 
Inches Number. Inch. Inch. Years. Years Per cent 
3 5 0. 029 0. 045 34 2 140 
4 6 . 030 050 33 20 169 
5 7 . 023 049 43 20 127 
6 8 . 029 039 34 25) 59 
7 13 . 038 061 26 16 112 
8 9 . 047 072 21 14 98 
9 4 . 027 042 37 24 70 
10 2 . 022 047 45 21 125 
CAUSES OF INJURY. 
FIRE. 
Fire has been the most important agent in the destruction of 
lodgepole pine forests, as well as in their establishment. Though in 
some places it has enabled lodgepole to take possession of the ground, 
in others repeated fires have practically eliminated forest growth. 
Lodgepole pine is less susceptible to fire than Engelmann spruce and 
Alpine fir, but more susceptible than the other pines with which it 
grows or Douglas fir. Its susceptibility is due chiefly tq its thin 
bark, which at stump height is only from two-tenths to four-tenths 
of an inch thick. Fire is most destructive in dense young stands of 
“jack pine,” as the young trees are often called. Crown fires are in- 
frequent, but may occur with high winds or when a large amount of 
débris litters the ground. When a lodgepole stand is killed by fire 
a period of from 15 to 30 years elapses before the dead trees fall to 
the ground. Fire-lilled timber does not completely decay until from 
60 to 120 years after the fire. Such débris, of course, greatly increases 
the fire danger in a new stand. 
In comparatively open stands which have reached maturity with- 
out being burned over there is usually not much débris on the ground 
and consequently less danger of crown fires. Even here, however, 
there is in most cases a ground cover of grasses, weeds, needles, and 
similar litter to invite surface fires, which destroy reproduction, 
occasionally kill mature trees, and seriously injure the butts and 
lessen the vitality of many others. These ground fires, too, by de- 
stroying the organic content of the soil, reduce both its water-holding 
power and its productive capacity, which necessarily results in de- 
creased growth of the surviving trees. 
