PINE TREES OF ROCKY MOUNTAIN REGION. 9 
Pinus flexilis usually occurs interspersed among other conifers, 
singly or in small groves, the largest size being produced under these 
conditions. Occasionally, however, it forms pure, open growths of 
stunted trees on exposed slopes and ridges. It is associated mainly 
with lodgepole pine and mountain hemlock at higher elevations, 
and sparingly with white fir and Douglas fir at lower altitudes. 
Limber pine grows best only in the full enjoyment of light, never 
forming dense stands. It is similar in its requirements of sunlight 
to the white-bark and bristle-cone pines, being less able to grow in 
the shade, except when young, than other associated conifers. Lim- 
ber pine is not an aggressive tree and rarely crowds out other species. 
It is a moderate seeder, the amount of seed borne varying with the 
region and elevation. Generally it bears the largest number of cones 
in open stands at low altitudes, fruiting less abundantly in the denser 
stands and at higher elevations. The cones are produced locally 
‘about every year, while good seed years occur at intervals only of 
several years. Many of the seeds are eaten by birds and squirrels 
before they are shed. They are practically wingless and fall only 
near the trees. Flood waters distribute the seeds irregularly and 
the “hoards” of pine squirrels occasionally result in accidental 
planting of uneaten seed. Germination of the seed, which at best 
is only moderate, occurs most abundantly in moist mineral soil. 
LONGEVITY. 
Little is known now of the longevity of this pine. Trees from 18 
to 22 inches through are from 200 to 300 years old. 
WHITE-BARK PINE. 
Pinus albicaulis Engelmann. 
COMMON NAME AND EARLY HISTORY. 
This species is commonly known to lay travelers in its high moun- 
tain habitat only as “scrub pine,” because of its stunted. form in 
exposed, wind-swept places. Those who know it botanically, how- 
ever, usually call it white-bark pine, a name derived from the tree’s 
technical name, albicaulis (white stem), which has reference to the 
characteristic chalky-white color of the bark. 
Pinus albicaulis was discovered in 1851 by the intrepid Scotch 
botanical. explorer, John Jeffrey. A letter he wrote, now preserved 
at the Royal Gardens of Edinburgh,’ states that he found the tree 
“on the summit of a mountain near Fort Hope, Fraser’s River,” 
central British Columbia, at an elevation of 7,000 feet. A. Murray, 
1 Fide Sargent, Silva, XI, 41, 1897. 
