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GLACIER National Park |
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 A Mountain Profile 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 annual precipitation. 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. 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. (click on above image for an enlargement in a new window) |
 The Forest Community 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 socioeconomic 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. Forest Niches. 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, it remains, like those of other animals, are decomposed and return to the soil. (click on image for an enlargement in a new window) |
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Last Modified: Sat, Nov 4 2006 10:00:00 pm PST |