The mountain hemlock is abundant on high, rocky ridges, but the best stands are on cool, moist soil at the heads of ravines, on flats, and on gentle slopes with a northern exposure.
This tree seeds every year. In good seed years the upper branches are laden with a profusion of beautiful, deep-purple cones, often in such abundance as to bend down the branchlets with their weight. The reproduction is slow. In the high mountains the trees are buried in snow from October to late in June, and the growing season is very short.
WHITE-BARK PINE (PINUS ALBICAULIS).
Fig. 20.—A gnarled, wind-swept mountain hemlock (Tsuga mertensiana), near the upper limits of tree growth, Spray Park, Mount Rainier National Park.
Photograph by A.H. Denman.
The white-bark pine ([fig. 21]) grows close to timber line in the mountains of the Pacific coast from British Columbia to southern California. In the Canadian Rockies it extends north to the fifty-third parallel. It is the most alpine of all the pines. Its lower limit on Mount Rainier is about 5,000 feet above sea level. In sheltered places where the soil is deep the trees are sometimes 30 to 40 feet high and 20 inches in diameter. The trunks are free from limbs for 8 or 10 feet. The outer bark, from which the tree derives its name, consists of thin, light-gray scales.
As the white-bark pine advances up the mountain its habit changes rapidly. The stem shortens and becomes gnarled and twisted. The tough, flexible branches reach the ground and spread over it to a great distance from the tree. On rocky summits and the bleak crests of wind-swept ridges the twisted trunk and branches are quite prostrate and the crown is a dense flattened mass of foliage.