The remarkable development of the forests about the base of Mount Rainier results from climatic conditions peculiarly favorable to tree growth. The winters are mild and short. The ocean winds that pass through the gaps of the Coast Range are laden with moisture which falls in the form of rain or snow on the west slope of the Cascades. The trees are nourished by this moisture through a long season of annual growth, and form an evergreen forest which is, in some respects, the most remarkable in the world. This forest, distinguished by the extraordinary size and beauty of the trees and by the density of the stand, extends into the deep valleys of the rivers which have their sources in the glaciers. On the dividing ridges and in the upper stream basins the composition and character of the forest change with the increasing severity of the climate.
The distribution of the different species of trees according to the intervals of altitude at which they occur separate the forests of the Mount Rainier National Park into different types. The lines of separation are to some extent also determined by complex conditions of slope, exposure, and moisture. The successive forest belts are uniform in the composition of their central areas, but blend and overlap where they come together.
The low valleys of the main and west forks of White River, of the Carbon, the Mowich, the Nisqually, and the Ohanopecosh are covered with a dense and somber forest of fir, hemlock, and cedar. The trees, pushing upward for light, are very tall and free from limbs for more than half their height. Their tops form a continuous cover which the sunshine rarely penetrates, and on which the light snows of early winter fall and melt, without reaching the ground. Even in midsummer tIme light is soft and shaded, and the air cool and humid. In the wintertime the young growth is sheltered from wind and the severity of the cold is tempered by the protecting mountain ranges. Saved from fire by the uniform dampness of the air the trees grow until they decay and fall from old age. They are succeeded by the suppressed younger trees. The forest remains mature, not uniformly sound and vigorous, yet not decreasing as a whole in size and volume. Individuals perish, but the character of the forest is constant. The deep alluvial soil covered with moss and decayed vegetation nourishes a luxuriant tangled undergrowth of vine maple, willow, and devil's-club. The forest floor is covered with a deep layer of decayed vegetation and is encumbered with fallen and mossy logs and upturned stumps. The explorer who leaves the trails must be a strong and active man if he can carry his pack 6 or 8 miles in a long summer day.
Ascending from the river bottoms to the lower slopes of the dividing ridges the forest becomes more open and the trees are smaller. Salal, Oregon grape, and huckleberry bushes take the place of the taller undergrowth of the valleys. up to 3,000 feet the Douglas fir and the hemlock still are the dominant species. Above this altitude new species are found intermingled with the trees typical of the lowland, but forming a distinct forest type. The noble and silver fir appear, sometimes growing in pure stands, but more often associated with the Douglas fir and western hemlock at the lower limits of the type, and with alpine fir and mountain hemlock at the upper limit.
Nearly all the trees of this type have deep and widespreading roots which serve to hold in place the surface deposit of volcanic pumice which covers the slopes of the mountain. Evidence afforded by the after effects of forest fires in other parts of the Cascades indicates that the destruction of the forest on the mountain sides is followed by erosion. Heavy rains and the melting of the upper snow banks by warm Chinook winds combine to produce a surface run-off that denudes the steeper declivities down to the underlying bedrock.
At elevations above 4,500 feet the lowland trees have disappeared entirely. Subalpine species adapted to withstand the burden of deep snow take their place. Mountain hemlock, alpine fir, and Englemann spruce grow singly and in scattered groups or form open groves, alternating with grassy parks and rocky ridges. The symmetrical outline of the slender pyramidal crowns and rapidly tapering trunks of the spruce and alpine fir trees that stand singly on the greensward of the open parks bring to mind the closely trimmed cultivated evergreens that adorn city parks and lawns. Their lower branches reach the ground and the tops terminate in slender upright spires.
As timber line is approached tree growth is confined to dwarfed and flattened mountain hemlocks, alpine firs, and the white-bark pines firmly rooted among the crevices of the rocks.
The extreme upper limit of tree growth on Mount Rainier is 7,600 feet above sea level. There is no well-defined timber line. Scattered clumps of low stunted trees occur up to 7,000 feet. A few very small and flattened mountain hemlocks grow above this elevation. A very large part of the area above 4,500 feet consists of glaciers, talus slopes, barren rocky peaks, and open parks. Basins at the heads of canyons in the high mountains are usually treeless, on account of the great depth of snow which accumulates in them during the winter. On the steep, smooth upper inclines the snow banks frequently slip and form slides, which acquire momentum as they rush down the mountain side and break and carry away large trees. Repeated snowslides in the same place keep the slopes nonforested, and their track is marked by light green strips of brush and herbage.
The transition of the forest from its lowland to its extreme alpine type is one of the most interesting features of a visit to the mountain. Entering the park at the western boundary close to the Nisqually River the road skirts the base of the lightly timbered spurs and passes into a forest of large and old Douglas Fir and western hemlock. Red cedars grow along the streams the cross the road. Little yew trees and vine maples mingle with the young conifers that form the undergrowth; the gloom of the forest is occasionally relieved by the white bark of alders and the smooth gray stems of the cottonwoods that grow on the sandy bank of the Nisqually. After the road crosses the Tahoma Creek, noble fir and silver fir appear, but the Douglas fir and western hemlock are still the prevailing species.
Above Longmire Springs the noble and silver fir, mixed with western hemlock, become the dominant type. The trees are shorter and the branches heavier. Mountain ash and Alaska cedar grow on the margin of the mountain streams. Huckleberry bushes take the place of the taller undergrowth of the valley.
Above Narada Falls the forest is more open, and the trees are still smaller. Mountain hemlock and alpine fir succeed the trees of the lower slope. Little glades and mountain meadows are seen. They become larger and more numerous and the traveler soon enters the open park of Paradise Valley, in which are but scattered groves of trees. The same successive altitudinal types are met in ascending to Moraine and Grand Parks by way of the Carbon Valley, and in following the Mowich watershed, Mowich Lake, and Spray Park routes.
Approaching the park from the east the routes pass through open western yellow pine forests and western larch stands. Since Mount Rainier is west of and apart from the summit line, these species which are peculiar to the eastern slope are not found within the limits of the park.
Last Updated: 02-Feb-2007