Yellowstone Autumn

September, 2013. The season has turned. Autumn gains strength by the day. Winter begins to waken.

Following is an excerpt from the book Snow Country by Jeremy Schmidt and Steven Fuller.

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A bull bison pauses on a boardwalk in morning mist at Mud Volcano.

Summer in Yellowstone is a tumultuous flowering that lasts a bare three months. From mid-June to late August, everything seems to happen at once as living things rush to recover from and prepare for winter. While the sun shines warmly and the days are long, plants grow and produce blossoms. Insects feed on the nectar of flowers, transferring pollen from one to another. Calf elk and bison, born amid the late snows of May and June, grow fat on mother’s milk and the rich grasses of summer. In the forests, marshes, and waterways, young birds are hatched. Well-fed on insects and vegetation, they grow quickly. To survive, their adult feathers must replace the down of infancy before the snows fall. For waterfowl such as swans, summer is a race against the seasons. The birds do not always win. It takes four months for a young swan to develop so he can fly. If the lake where he was hatched freezes before he fledges, the ice-bound bird becomes one of winter’s first casualties.

September 21 marks the autumnal equinox. From then until the spring equinox, March 21, the nights are longer than the days. Each morning the sun rises farther toward the south, its arc shorter and nearer the horizon. This explains the cold. Though the earth is actually closer to the sun during the northern hemisphere winter than at any other time in its year-long orbit, the tilt of the planet results in shorter exposure to low-angle sunshine.

In deciduous trees and shrubs photosynthesis stops, chlorophyll breaks down, leaf nutrients are absorbed into the plant and the leaves are dropped. To the plants, the value lies in retrieving what it can from leaves which will surely die during winter and then shedding them to make room for the growth of next year’s buds. The bright colors are incidental. They result from the removal of chlorophyll which has masked already present carotenoid pigments. Gradually the reds and yellows become visible. They are intensified by the addition of anthocyanins, bright pigments produced by the last conversion of remaining sugars before the leaf dies. In cool wet weather free of killing frosts the leaves will live longer, produce more anthocyanins and create brilliant displays.

Along stream beds and rivers and on mountain slopes especially in the north part of Yellowstone, aspen and cottonwood trees, shrubby willows, mountain ash, chokecherry, alder buckthorn, mountain alder and other shrubs turn brilliant. In meadows, fireweed breaks open its seed pods; together with salsify seeds the silky parachutes float sunlit against the blue sky. Coneflower leaves dry into husks which rattle loudly as deer walk through the plants. Wild rose bushes bear shiny red fruits. The leaves and stalks and dried flower heads of hundreds of herbs — columbines, buttercups, sunflowers, parsley, glacier lilies and others — turn delicate shades from gray to orange.

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A warm stream flows through the bare trunks of thermally killed lodgepole pine. Yellowstone’s autumn colors draw from a simple palette.

Yellowstone is mostly coniferous. Lodgepole pine is by far the most common tree and at first glance the forest seems unchanged in autumn — evergreen and never yellow. But there is change here, perhaps on a small scale but no less brilliant. Strawberries, high-bush huckleberries, bracken ferns, grouse whortleberries, beargrass, lupine and fireweed combine with other small plants to carpet the forest floor with color.

The nesting territories of birds break down as the young are fledged. Flocks begin to form as the time nears to fly south. Some will remain — the ravens and jays and chickadees and geese and a small variety of others capable of enduring the winter.

Of special note is the annual fall gathering of swans along the Yellowstone River between Lake and Canyon. Between 300 and 450 birds, mostly trumpeter swans but some whistlers, move in during October and stay until the river begins to freeze. Many then move to Henry’s Fork of the Snake River in Idaho where there is open water all year. Yellowstone’s winter swan population fluctuates with changes in the weather.

Autumn has a fragrance all its own of sun-dried grass, thermal sulphur and wet soil churned by frost. The scent of pine is especially pervasive. To one who has known previous Yellowstone autumns, it is an instantly recognizable and pleasing smell.

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Three bison stand quietly beside a hot spring on the first subzero day of November.

In most years, there is a snowstorm by late September. Beginning as a cold rain, it turns as night falls into huge, wet foreboding flakes. These melt on first contact with the ground, but by morning several inches of accumulation create a dripping white landscape. In two or three days the snow is gone and the sun again feels warm, but high on the peaks the white dusting remains.

 

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