Life zones, as defined in relation to plant and animal life, are areas
inhabited by more or less definite groups of plants and animals. The
classification of these zones which is accepted by many biologists was
devised by Dr. C. Hart Merriam, who named six zones; the Arctic-alpine,
Hudsonian, Canadian, Transition, Upper Sonoran and Lower Sonoran. If one
travels from the Southwestern United States into the high country of the
Rockies or the Pacific Northwest, he will pass through all six of these
zones, beginning with the Lower Sonoran, or low desert zone, through the
Upper Sonoran, or high desert, and so on through the others until the
highest, or Arctic-alpine Zone is reached. The area immediately adjacent
to Puget Sound, for example, falls within the Transition Zone. Moving
inland toward Mount Rainier, one passes from the Transition into the
Canadian Zone, usually a short distance inside the park boundaries, and
the major portion of Mount Rainier National Park is within the upper
three zones.
Temperature is the basis for the separation of these zones, and
temperature, as we know, is affected by both altitude and latitude. In
general a difference of 1,000 feet in altitude is equivalent to a
difference of 300 miles in latitude. Variation in latitude explains the
high elevation of tree line in the southern Sierra Nevada of California
in relation to the comparatively low limit of tree growth in northern
British Columbia or Alaska. Variation in temperature explains the
tremendous difference in size and variety of tree species at 2,000 feet
and at forest line, 6,500 feet, on Mount Rainier. On a very high
mountain we might find all six of the life zones represented. The
mountain presenting such a condition, however, would necessarily be
located in a more southern latitude than Mount Rainier.
Four life zones are represented in Mount Rainier National Park: the
Transition Zone, which occupies the lower elevations of the park up to
3,000 feet; the Canadian Zone, which, with the exception of the
Transition area, extends from park boundaries to about 5,000 feet; the
Hudsonian Zone, with an altitudinal range of from approximately 5,000 to
6,500 feet; and the Arctic-alpine Zone, from 6,500 feet to the summit of
the Mountain.
As stated previously, the zones are inhabited by more or less definite
groups of plants and animals, but there is no distinct line of
demarcation between the various zones, and there is often considerable
variation in the altitudinal distribution of plants. If temperature and
moisture were uniform at a given altitude, the zones would probably be
quite distinct. However, these conditions are obviously not uniform. On
northern exposures, for example, there is less evaporation, consequently
soil moisture is increased, and lack of sunshine results in lower
temperatures. Plants which normally occur at 5,000 feet on a sunny
southern exposure may be found at a lower elevation on northern slopes,
and the reverse is true, of course, with a reversal of exposures.
Such variation is even more marked in the distribution of mammals and
birds. Many species are characteristic of one or more life zones,
depending upon the season of the year, the scarcity or abundance of
food, and other factors.
For example, deer occupy the Transition or the extreme lower limits of
the Canadian Zone in winter, but in summer range up to and occasionally
beyond the limits of the Hudsonian Zone. Goats normally range within the
upper limits of the Hudsonian and upward into the Arctic-alpine Zone in
summer, but are most commonly found in the lower Hudsonian Zone in
winter.
The general characteristics of the zones are as follows:
_Transition Zone_: This zone occupies that portion of the park which
lies below 3,000 feet. For the most part it may be more adequately
designated the Humid Transition Zone, although a limited area (roughly 4
to 6 square miles) on Stevens Creek and the Muddy Fork of Cowlitz River
is characterized by a modified plant and animal population due to
repeated fires in old Indian days. This burning favored the upward
advance of low zone elements, the destruction of the original forest
cover by fire opened the forest stand, accomplished a marked change in
conditions of temperature and moisture, thus creating a drier, warmer
site.
The Humid Transition Zone proper is one of dense, sombre forest;
magnificent trees rising from a mass of shade-loving plants with a great
number of fallen trees of huge size. Even on bright, mid-summer days the
evergreen canopy of interlaced branches permits only a little sunlight
to penetrate to the forest floor, and semi-twilight conditions exist in
the peaceful solitude of this cathedral-like serenity.
[Illustration: The Humid Transition life zone is one of magnificent
trees.]
[Illustration: The forests of the Canadian life zone afford
excellent cover for many mammals throughout the year. In summer such
retreats are favored habitats for bear families.]
Characteristic plants of this zone, though not confined to such
association, include the Douglas fir, western red cedar, western
hemlock, salal, Oregon grape, black cottonwood, bigleaf maple, and
swordfern.
Here are found the raccoon, little spotted skunk, Oregon and Olympic
meadow mice, and the mink. In this zone are seen in late spring the
new-born fawns of the black-tailed deer.
_Canadian Zone:_ This zone does not become well defined until above the
3,000-foot level. There is a considerable mixture of both Transition and
Canadian elements at the approximate area of separation. While still
heavily forested, the trees of the Canadian Zone are noticeably smaller
than those at lower elevations and the forest is more open in character.
Although common tree species include the Douglas fir and western hemlock
of the Transition Zone, the most typical trees are the silver fir,
Alaska yellow cedar, noble fir, and western white pine. Other typical
plants are the Canadian dogwood, pipsissewa, and Cascades azalea.
There are no mammals which may be considered as characteristic
exclusively of the Canadian Zone, since those occupying this zone also
range into the Hudsonian.
_Hudsonian Zone:_ At an elevation of from 4,500 to 5,000 feet the
character of the forest cover begins to change. The trees are smaller,
and the alpine fir and mountain hemlock become dominant tree species.
Ascending to higher levels the forest becomes broken, with the number
and extent of grassy parks and subalpine meadows increasing until
finally all tree growth vanishes at an elevation of about 6,500 feet.
This is the zone of beautiful summer wildflower gardens, a region of
extensive panoramas and rugged mountain scenes. The avalanche lily,
glacier lily, the heathers, paintbrushes, and the mountain phlox are
common, as well as the white-barked pine.
[Illustration: Snow blankets the Hudsonian life zone throughout most
of the year. Paradise Valley lies within this zone, the towering
bulk of the Mountain above 6,500 feet is in the Arctic-alpine zone.]
Snow blankets these highlands throughout most of the year, and the
larger mammals are usually at the lower elevations during the winter
months. Many of the permanent wildlife inhabitants are those which
hibernate or are active beneath the snow, as the Hollister chipmunk,
marmot, pika, Rainier meadow mouse, and Rainier pocket gopher.
_Arctic-alpine Zone:_ Above the forest line all plant life diminishes
rapidly in extent. This is a region of barren, rocky soils; perpetual
snow fields; and glacial ice; a bleak and forbidding expanse of
awe-inspiring grandeur where the storm king yields supremacy for only a
few brief weeks in mid-summer.
Characteristic plants, found in the lower portions of this zone, include
the Lyall’s lupine, Tolmie’s saxifrage, mountain buckwheat, and golden
aster.
Only one mammal, the mountain goat, may be considered as characteristic
of this zone.