Part 6

From the lush redcedar-hemlock forest in the McDonald Valley to the subalpine fir, whitebark pine, and Engelmann spruce struggling for existence near treeline, the forests of Glacier reflect the conditions of temperature, exposure, soil, and drainage prevailing; and each forest has its characteristic association of understory trees and shrubs, herbaceous ground cover, and vertebrate and invertebrate animal life.]

Many physical and climatic factors determine the range of Glacier’s plant-and-animal communities. Boundaries between communities are seldom sharply defined, but rather merge together in broad zones of transition.

With elevation gain, average daily temperature drops at the rate of 5° per 900 meters. Precipitation, wind velocity, and evaporation loss increase. Soil thins. These factors, along with others such as fire frequency, north or south exposure, and availability of moisture, combine to determine the range of each community.

In the forest community below 1,800 meters, Douglas-fir, lodgepole pine, and western larch predominate. In the valleys, Engelmann spruce and subalpine fir are found. The somewhat lower and much better watered western valleys of the park support western redcedar and western hemlock.

Treeline is the upper limit to which the tolerances of trees to environmental conditions permit them to grow. Because there are so many controlling factors (wind, temperature, exposure to sunlight, snow cover, etc.) treeline in the diagram is only approximate. In Glacier it averages 2,000 meters. Avalanche chutes or sheer cliff walls may suppress it to below 1,500 meters; on protected slopes it may be as high as 2,150 meters.

At the eastern edge of the park below 1,200 meters, the forest gives way to the prairie community, composed mostly of soft-stemmed plants adapted to the conditions of low precipitation that prevail here in the rainshadow of the mountain range. Clumps of aspen, found in the prairie in sheltered spots, occur here in the transition zone between prairie and forest.]

This diagram represents the eastward-facing slope of a hypothetical mountain near the eastern boundary of Glacier National Park. Its life communities are somewhat different from those of mountain slopes at the western edge, chiefly because of the differential in annual precipitation.

Illustration: Here, above approximately 2,750 meters, in a realm of ice, snow, and barren rock, there is little life.

Alpine tundra

Below 2,750 meters and above 2,000 meters, depending on other factors such as exposure to sun and wind and steepness of terrain, exists the alpine tundra community, with vegetation similar to that of the vast, essentially level, treeless zones of the Arctic.

Scrub-forest

Roughly between 1,800 and 2,000 meters, the dominant vegetation is scrub-forest. Trees here are stunted; except in sheltered spots they are more or less prone rather than upright. Net growth is slow, not only because of the short growing season but also because of the pruning effect of icy mountain winds. Very few tree species can survive in this harsh habitat.

Coniferous forest

In the forest community below 1,800 meters, Douglas fir, lodgepole pine, and western larch predominate. In the valleys, Engelmann spruce and subalpine fir are found. The somewhat lower and much better watered western valleys of the park support western redcedar and western hemlock. See page 54

Prairie

At the eastern edge of the park below 1,200 meters, the forest gives way to the prairie community, composed mostly of soft-stemmed plants adapted to the conditions of low precipitation that prevail here in the rainshadow of the mountain range. Clumps of aspen, found in the prairie in sheltered spots, occur here in the transition zone between prairie and forest.]

A forest is organized vertically like an apartment house or office building, with layers corresponding to stories. The canopy is the branches and foliage of tall trees that form a roof over the community. Below the canopy are the understory trees: young individuals of the canopy species; and small, shade-tolerant trees that will never become part of the canopy. Beneath the understory branches is the shrub layer, occupied by knee-high-to-man-high woody plants; beneath that is the herb layer, where most of the ferns, wildflowers, grasses, and smaller woody plants grow. The forest floor is the zone of mosses, mushrooms, creeping plants, and forest litter (leaves, twigs, needles, feathers, bits of bark, animal droppings, etc.). The forest has a “basement,” too, interlaced by plant roots, mycelia of fungi, and tunnels of myriad animals.

Each layer of the forest has its characteristic animal species, but most forage over more than one level. Some nest in one story and feed in another. The red squirrel races back and forth from the forest floor to the highest branches.

The forest community also has a socio-economic organization. Every animal (and plant) takes up space and consumes a portion of the available nutrients. Each has a place in the community food chain—as, for example, herbivore, carnivore, or scavenger. Each directly or indirectly affects all the other organisms.

The Forest Community

The role of a species in the community, like the job and social function of a person, is its niche. Similar species of animals have different niches, thus lessening competition for food and living space. Thrushes hunt close to the ground; vireos and kinglets hunt among the branches; flycatchers snap up airborne insects. The flicker feeds upon insects, excavates nesting holes that are later occupied by other species such as squirrels and owls, and is preyed upon by the great horned owl; its niche is insect exterminator / food for carnivores / homebuilder. The great horned owl, hunting mammals, birds, and reptiles by night, preys on species different from those hunted by the goshawk, and thus occupies a parallel niche. When it dies, its remains, like those of other animals, are decomposed and return to the soil.]

Canopy Great Horned Owl Yellow-bellied Sapsucker Understory Flying Squirrel Shrub Layer Ruffed Grouse Herb Layer Red Squirrel Western Toad Forest Floor Shorttail Weasel Scavenging Insects Deer Mouse Garter Snake Soil Layer Ground Squirrel Earthworm Masked Shrew

The sun is the source of energy for any plant-and-animal community. Green plants draw nitrogen and minerals from the soil, and in a process called photosynthesis use sunlight to convert raw materials (carbon dioxide and water) into carbohydrates (sugar, starch, cellulose), giving off oxygen as a by-product. Besides burning oxygen, animals depend on plants for food.

Green Plants, trees and shrubs, grasses and sedges, wildflowers, ferns, mosses, algae and lichens—are fed upon by animals, which are unable to manufacture their own food.

The Redback Vole, like other rodents, pikas and hares, seed-eating birds, grazing and browsing hoofed animals, and herbivorous insects, derives its energy from the seeds and other parts of green plants that it eats.

The Garter Snake, feeding upon the vole, is dependent upon plants even though it does not eat them.

The Great Horned Owl, preying upon the garter snake, is one more step removed from the green plants—but still dependent on them.

Scavengers such as carrion beetles feed upon the carcass of the owl; the remains are then attacked by Decomposers, primarily bacteria, that break down the animal tissues into basic organic compounds.