Tundra

I

Introduction

Tundra, Arctic plains encompassing most of Earth’s terrain north of the coniferous forest belt, dominated by cotton grass, heath, lichen, moss, sedge, and willow. Similar plains, called alpine tundra, occur above the timberline in the high mountains of the world. The Antarctic region has a few areas of tundra as well.

II

Climate and Land Formation

Tundra climate is characterized by harsh winters, low average temperatures, little snow or rainfall, and a short summer season. The Arctic tundra, in particular, is influenced by permafrost, a layer of permanently frozen subsoil in the ground. The surface soil, which tends to be rocky, thaws in summer to varying depths. The combination of frozen ground and flat terrain on the tundra impedes the drainage of water. Held at the surface or saturating the upper layer of soil, the water forms ponds and bogs that provide moisture for plants, thereby counteracting the low precipitation.

In relatively well-drained locations, the periodic freezing and thawing of the soil forms cracks in the ground in regularly patterned polygons. Poorly drained areas produce irregular landforms such as hummocks, or knolls, frost boils, and earth stripes. Thawing of slopes in the summer may move soil downslope to produce solifluction, or “flowing soil” terraces. All of these patterns, clearly visible on the Arctic tundra, also appear on a smaller scale on the alpine tundra. Common to the alpine tundra is bare rock-covered ground, called fell-fields, supporting a growth of lichens. The numerous microhabitats provided by these landforms give variety to the tundra landscape.

III

Plant Life

The number of plant species on the tundra is few, and their growth is low, with most of the biomass concentrated in the roots. The growing season is short, and plants are more likely to reproduce vegetatively by division and budding than sexually by flower pollination.

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Typical Arctic vegetation comprises cotton grass, sedge, and dwarf heath, together with associated mosses and lichens. These plant communities are adapted to sweeping winds and to soil disturbance from frost heaves. They carry on photosynthesis at low temperatures, low light intensities, and long periods of daylight. Alpine plant communities consist of mat-forming and cushion-forming plants, rare in the Arctic. These plants are adapted to gusting winds, heavy snows, and widely fluctuating temperatures. They carry on photosynthesis under brilliant light in short periods of daylight.

IV

Animal Life

Arctic wildlife is circumpolar; the same or closely related species are found around the world. The variety of animal life is also limited in the challenging environment. Musk-ox, caribou, and reindeer are the dominant large grazers, feeding on grass, sedge, lichen, and willow. Arctic hare, or snowshoe rabbit, and lemming feed on grass and sedge. Predators include the wolf, arctic fox, and snowy owl. Polar bears, and sometimes brown bears, are seen. Many birds nest in the tundra shrubbery in summer, migrating to milder climates before the winter season sets in. Invertebrate life is scarce, but insects such as black flies and mosquitoes are abundant. Alpine animal life includes the mountain goat, big-horned sheep, pika, marmot, and the ptarmigan, a grouselike bird. Flies are scarce but butterflies, beetles, and grasshoppers are abundant.

The tundra ecosystem is extremely sensitive to disturbance with little ability to restore itself. Disruption of vegetative cover causes permafrost to melt deeply, with consequent collapse of ground and loss of soil. Vehicular tracks cause deep gullies that persist for years. The tundra wildlife is vulnerable to habitat destruction, to overhunting, and to extinction through loss of any of the animal or plant species that make up the fragile, highly interdependent tundra community of life.

Recent studies have demonstrated that global warming is impacting areas of tundra, particularly the Arctic tundra. Impacts include the melting of permafrost and the expansion of the timberline, which in turn decreases the areas of tundra. Both impacts contribute further to global warming, creating a so-called positive feedback loop that makes it more difficult to halt the warming trend. Permafrost melting contributes to this feedback loop by releasing methane, a greenhouse gas, from the soil into the atmosphere. The expanded timberline results in more sunlight being absorbed by trees, which warms the Earth’s surface. Trees have a low albedo compared with the tundra. The tundra tends to reflect sunlight back into space, especially when it is snow-covered and has a high albedo, thereby cooling Earth’s surface. An expanded timberline and decreased areas of tundra therefore lead to more heat being absorbed at the surface.

Shrinking areas of tundra also have a negative impact on the animal life that depends on tundra vegetation. Some studies have indicated that areas of tundra are disappearing more rapidly than expected due to global warming.

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