PINE TREES OF ROCKY MOUNTAIN REGION. 25 



The cones mature at the end of the second season, and are then 

 from 2^ to about 3^ inches long and of a deep chocolate-brown color 

 tinged with purple. Each cone scale bears a bristlelike, very fragile 

 prickle, which easily distinguishes the cones of this pine from other 

 species of the region. Unexposed parts of the cone scales are clear 

 reddish brown. The seeds (PI. XV, a, b) are pale brown with ir- 

 regular black spots, and are shed from about the last of September 

 to the middle of October. Seed-leaves of this pine vary in number 

 from 6 to 7. 



Bristle-cone pine produces rather narrow-ringed, soft, brittle wood 

 with a thin layer of whitish sapwoocl and a pale brownish-red heart. 

 It is moderately heavy for a white pine, a cubic foot of dry wood 

 weighing about 34f pounds. On account of the poor timber form of 

 the tree the wood is not used commercially. In the region of greatest 

 abundance it is sometimes employed for fuel and mine props. 



OCCURRENCE AND HABITS. 



Pinus aristata is found on ridges and rocky ledges, but mainly on 

 south slopes, here often predominating at elevations between 7,500 

 to 10,800 feet (Map No. 8). It grows on thin, rocky soil, and fre- 

 quently on volcanic soils of cinder cones. Usually growths of this 

 tree are in isolated situations, where snow melts early and evapora- 

 tion is rapid, so that the trees are subjected to more or less prolonged 

 dryness of soil during summer., Rarely does this species form pure 

 stands, the trees being usually scattered over grassy ground of a 

 gravelly or rocky nature with little or no underbrush. It is most 

 abundant at higher levels, where limber pine is its only associate. 

 At lower altitudes it is often associated with Engelmann spruce, lim- 

 ber pine, and western yellow pine, and occasionally with white fir. 



Bristle-cone pine never forms dense stands, which indicates that 

 it is intolerant of shade during the greater part of its life. Seed- 

 lings, however, endure light shade for several years without material 

 loss of vigor. 



Trees begin to bear cones when they are about 20 years old, and 

 produce them practically every year thereafter, with specially heavy 

 crops at intervals of several years. Reproduction is always sparse 

 and much scattered. Seeding often takes place at a distance of at 

 least 600 feet away from mother trees. The large number of seeds 

 eaten by rodents and the ease with which surface fires destroy the 

 large-winged seeds and kill the seedlings and dense-foliaged older 

 plants doubtless account in great measure for the thin stands of this 

 pine. Seeds germinate best in loose, exposed mineral soil, and less 

 promptly in grass and litter. The seedlings appear to grow best 

 on slopes with little or no underbrush. 



