LIFE HISTORY OF LODGEPOLE PINE IN ROCKY MOUNTAINS. 



19 



Table 5. — Effect of thinning ; average diameter growth of lodgepole pine trees 

 left after cutting, etc. — Continued. 



Paet II. [Based on the 54 trees which showed an increased growth.] 



Diam- 

 eter 

 breast 

 high. 



Trees. 



Periodic annual diam- 

 eter growth for 20 

 years. 



Time required to grow 

 1 inch in diameter. 



Rate of 



increase in 



volume 



growth 



after 



thinning 



Before 

 thinning. 



After 

 thinning. 



Before 

 thinning. 



After 

 thinning. 



Inches. 

 3 

 4 

 5 

 6 

 7 

 8 

 9 

 10 



Number. 

 5 

 6 

 7 

 8 

 13 

 9 

 4 

 2 



Inch. 

 0.029 

 .030 

 .023 

 .029 

 .038 

 .047 

 .027 

 .022 



Inch. 

 0.045 

 .050 

 .049 

 .039 

 .061 

 .072 

 .042 

 .047 



Years. 

 34 

 33 

 43 

 34 

 26 

 21 

 37 

 45 



Years. 

 22 

 20 

 20 

 25 

 16 

 14 

 24 

 21 



Per cent. 

 140 

 169 

 127 

 59 

 112 

 98 

 70 

 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 to 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 

 debris 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-killed timber does not Completely decay until from 

 60 to 120 years after the fire. Such debris, 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 debris 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. 



