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Climatic Regions of the United States, Subarctic

Tundra climate zone, Subarctic climate, inceptisols, frost action, trapping animals

The Subarctic climate is found in most of interior Alaska, reaching as far north as the Arctic Circle (60° north latitude), where it gives way to a Tundra climate zone. Summer is very brief in the Subarctic climate and lasts for one to three months. Summer temperatures average about 10° C (50° F). Winter arrives as early as October. During winter some areas experience average temperatures of less than -15° C (5° F) for at least three or four months. Precipitation is usually less than 500 mm (20 in) annually, and most falls as rain during the brief summer. During the winter, when the region is dominated by cold, dry air masses, precipitation is meager. Snow may accumulate to depths of one foot or more.

Because the earth’s axis is tilted, daylight hours vary considerably in the extreme northern latitudes of Alaska. During the summer months, when the North Pole tilts toward the sun, days average 17 to 22 hours of sunlight. During the winter, when the pole tilts away from the sun, nights with 18 hours or more of darkness are the rule.

The soils of the Subarctic climate are inceptisols, which form primarily from minerals that are broken down by frost action and glacial grinding. Inceptisols are young, undeveloped soils that tend to easily lose their mineral content. Layers of peat, a dark brown organic matter composed of partially decayed vegetation, are often present between the mineral layers.

One characteristic of the Subarctic climate is permafrost, permanently frozen subsoil. Summer warmth thaws only the upper 1 to 4 m (3 to 12 ft) of frozen soil. Because surface water cannot drain into the frozen subsoil, swamp and bog conditions develop during the summer months. These wetlands become home to countless mosquitoes and black flies. Permafrost requires that buildings be constructed to prevent heat losses. Escaping heat can melt adjacent frozen subsoils, causing construction projects to slowly sink into saturated soils.

Although the ground is waterlogged during the summer, the soil is frozen much of the year, and water is accessible to plant roots only during the short warm season. Many of the region’s trees are xerophytic in nature, meaning that they have adapted to dry weather conditions by developing special features that allow them to retain water. The Subarctic contains a vast needle-leaf type of forest known as taiga. The forest consists of relatively few tree species, including the jack pine, balsam fir, white and black spruce, poplar, and willow trees. On the shaded forest floor, vegetation is meager; mosses and lichens are the most common plant forms.

Animal life is not as abundant as in the midlatitude forests further south. Caribou, wolf, bear, fox, otter, mink, ermine, squirrel, lynx, and sable inhabit the Subarctic. Trapping is an important occupation, as animals living in the cold climate tend to grow heavy fur pelts.

This area is not highly favorable for human settlement because the growing season is short and the impoverished soils of the region limit agricultural opportunities. A few crops, such as potatoes and hardy grain, are raised in this climate. The sparse population of the area supports itself by logging, fishing, and mining, and by trapping animals.

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