Part 7

The Soil, enriched by the minerals and carbon and nitrogen compounds added to it by the decomposers (and by other processes such as fire) supports new green plant growth.

Thus energy derived from the sun flows through the ecosystem in a food chain. A plant-and-animal community is a complex, interlocking web of such food chains.]

Sun Green Plants Redback Vole Garter Snake Great Horned Owl Scavengers, Decomposers Soil

Necessarily, the number of plants in an ecosystem far exceeds the number of plant eaters, and the number of prey species must exceed the number of predators. During its lifetime, a golden eagle will consume a vast number of lesser animals. The combined mass of prey animals necessary to sustain an eagle greatly outweighs the eagle itself. Ecologists refer to this proportional relationship of mass between each link in the food chain as the pyramid of numbers.

The diagram represents a numbers pyramid for the alpine zone. Because of its limiting environment, the alpine zone supports a lesser plant mass than the forest zone. As a result, the carrying capacity of the alpine is less than that of the forest.

1 Kilo

Tertiary (third-order) consumers are the predators (Golden Eagle, Swainson’s Hawk, etc.) that feed upon other predators. Because of the 90% loss of energy at each level of the food chain, there will be very few hawks and eagles in comparison to the numbers of marmots.

10 Kilos

Secondary consumers are the predators (weasels, shrews, carnivorous insects and birds, etc.) that eat herbivores. The animals at this level of the pyramid are often—though not always—larger than the animals they feed upon. But they are much less numerous, because it takes many prey animals to sustain one predator.

100 Kilos

Primary consumers (plant eaters, or herbivores) convert plant tissue into animal flesh. In the process about 90% of the energy stored as plant food is lost, mostly as heat energy. In the alpine community the herbivores include pikas, marmots, ground squirrels, and ptarmigan, as well as herbivorous insects.

1,000 Kilos

Producers are the green plants at the base of the food pyramid, manufacturing food for the animals of the alpine community. The biomass (total weight) of each level of the food chain is ten times (more or less) the weight of the stage above it: 1,000 kilos of green plants will produce only 100 kilos of primary consumers.]

As long as there is open water, the dipper suffers no hardship from the mountain winter. Then, when the land is shut down and lakes are frozen over, this little bird carries on in its mountain-stream habitat, plunging into the cold water to find food, and pausing occasionally to sing.]

Conspicuous also are many insects—including grasshoppers; flies; ants, wasps and bees; butterflies and moths; bugs; and beetles—which fulfill important roles as herbivores, carnivores, and scavengers while also acting as pollinators for flowering plants and providing an abundant food source for other animals.

Below the ground are the tunnels. Burrowing is an important means of survival on the open prairie, and life underground is extensive. Some of the animals are rarely seen—the northern pocket gopher, for example, with a diet of underground insects, grubs, worms, and roots, spends most of its life tunneling just below the surface. Others, like the badger, leave their burrows during the day to dig for rodents. Most conspicuous of the burrowing animals in the park’s grasslands is the Columbian ground squirrel. Its alert upright stance has earned it the nickname “picket pin.” When danger approaches from the air or on land, its shrill alarm whistle passes the warning to others of its kind.

Where prairie and forest meet, a never-ending struggle for dominion is waged. The isolated patches of prairie that dot the North Fork Valley near Polebridge hold the great forest of the park’s northwest region at bay.

This broad valley, floored with coarse glacial outwash and terraced downward to the deep channel of the North Fork River, presents a graphic battleground between grass and tree. Lining the upper terraces, from which they glower down on the dry, well drained grass flats like a line of warriors, are the Douglas-fir, western larch, and ponderosa pine. Seedling trees continually invade the prairie. But most perish early, their shallow roots no match for the extensive root systems of the fast-growing, moisture-greedy grasses. If encouraged by a series of wet summers, however, the young lodgepoles quickly gain stature. They had made significant inroads at Big Prairie when the disastrously dry summer of 1967 killed most of these 15-year-old pioneer trees.

These North Fork grasslands and the immediately surrounding lodgepole pine forests are an important spring range. Deer, wapiti, and grizzly—and, in the wetter areas, moose—graze or browse here. And here, low on the western slopes of the Livingston Range, are the park’s only stands of ponderosa pine, a tree that prefers warm, dry habitats. As a result, at low elevations it often merges with the prairie community.

Groves of aspen colonize the eastern prairies in areas where there is sufficient water and protection from wind. These aspen parklands are important havens for animals. Wherever two differing communities interact, a phenomenon known as “edge effect” occurs. Here wildlife exists in abundance; the animals that favor forest cover mingle freely with those that prefer open areas. Aspen groves—supporting grasses, herbs, and shrubs beneath their thin canopies—are favored haunts for grouse, varying hare, deer, and wapiti, all of which find among the trees abundant food, shelter and concealment. Populations of insects, small mammals, and birds, which are high for the same reasons, attract a wide range of predators.

Isolated aspen groves are characteristically dome-shaped. Because aspens are capable of reproducing themselves vegetatively, the grove slowly expands outward from the parent tree. As a result, most of these groves are either exclusively male or exclusively female.

Since quick-growing aspens provide a bountiful food source for beaver, streams near these trees are often dammed by the rodents flooding lowlands and creating additional habitat in the form of willow flats. Another “edge effect” is established, attracting animals found near water. Waterfowl, marsh birds, moose, mink, muskrat, skunks, amphibians, and many others find such areas to their liking.

■ Before the appearance of the white man, these eastern prairies were a paradise for animals. Once, on the summit of Rising Wolf, light-headed from the climb and the view of endless prairie, I fancied that I saw that vast, undisturbed animal panorama spread before me.

Principally there were the bison, darkening the uneven land. Pronghorn bands flashed white on ridgetops, and moose moved through the long fingers of willow that extended eastward with the rivers. Caribou and wolves inhabited the shadows. Among vast cities of prairie dogs, swift fox and grizzly roamed. There were the clamorings of sandhill crane, and white clouds of trumpeter swans.

This land, endowed with a wealth of wild grass, wore its wilderness well.

The Forest

On Gunsight Pass, the rain lancing down, I found a sharpedged rock that split the continent in two. On both sides the rain rivulets ran down, a fraction of an inch determining the stream’s destination: Pacific or Atlantic.

The Continental Divide is a mighty barrier, a line of consequence that does more than determine watersheds. Its effect in Glacier is dramatic, as a look at the forests will reveal.