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 the 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 amabilis 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 wide-spreading 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 Engelmann 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 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 that 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 Rainier Fork, noble fir and
amabilis fir appear, but the Douglas fir and western hemlock are still
the prevailing species.
Above Longmire Springs the noble and amabilis fir, mixed with western
hemlock, become the dominant type. The trees are shorter and the
branches heavier. Mountain ash and yellow cypress 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, Crater
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.