The Arctic tundra is a biome representing the northernmost limit of plant growth on earth. Arctic tundra has a circumpolar distribution in the Northern Hemisphere, extending from the ice cap southward to the forested taiga of North America, Europe, and Asia. Tundra is also found on islands within the Arctic Ocean and along coastal Greenland.
The term "tundra" was derived from the Finnish word for a treeless or barren landscape. The Arctic tundra biome is located within one of the harshest climates on earth for plant growth, with winter temperatures averaging –34 degrees Celsius (–30 degrees Fahrenheit).
The climate is comparatively dry, with annual precipitation of 150 to 250 millimeters (6 to 10 inches). Locked in snow or frozen within soil, the majority of moisture is not available for plant use.
In addition to surviving extreme temperatures and dry conditions, plants must adapt to seasonal variation in available sunlight; winter nights, for example, last twenty-four hours. The tundra’s growing season is very short, extending over only about sixty days.
Continuous sunlight during warmer months, July and August, contributes to the productivity of tundra plant communities that can yield 227-454 kilograms (500-1,000 pounds) of vegetation per acre. This biomass serves as an important food source for caribou, musk ox, and migratory waterfowl.
Tundra vegetation is made up of herbaceous plants (grasses, forbs, and sedges), mosses, lichens, and shrubs that grow close to the ground, where temperatures are highest. By providing an insulating layer, snowfall is advantageous for tundra plants during cold winter months.
Rushlike tundra sedges belong to the flowering plant family Cyperacaeae. Common to the tundra, cottongrass is really a sedge within the genus Eriophorum. Perennial forbs are broadleaf plants that survive winter months as bulbs that are protected below the ground level.
During warm months the plants begin to grow rapidly and will develop flowers and seeds when temperatures climb above 10 degrees Celsius (50 degrees Fahrenheit).
Lichens and Low-Growing Shrubs
Acting as a single organism, pioneering lichens growing on rock surfaces represent a symbiotic relationship between fungi and algae. The fungi anchor to the rock, absorbing water directly into their cells, while the algae occupy this moist area, creating food through photosynthesis that is shared with the fungi.
Tundra lichens are found in fruiticose (stalklike), crustose (crustlike), or foliose (leaflike) forms. The heath (Ericaceae) family includes several species of shrub, many of which have tough, evergreen leaves.
Examples include rhododendron, cranberry, blueberry, and Labrador tea. Another heath, the alpine azalea (Loiseleuria procumbens), forms a mat or cushion where several plants clump tightly together.
Other adaptations include compact plant size that protects from cold temperatures, hairy stems that help retain heat, and dark-colored leaves that absorb sunlight.
Some plants have hollow stems that require fewer nutrients to grow. A unique adaptation made by the Arctic poppy (Papaver radicatum) and mountain aven (Dryas integrifolia) allows them to orient their flowers to track the sun’s movement across the sky, maximizing solar radiation received.
Although sunlight is usually beneficial to plant growth, some plants such as Arctic algae must implement protective measures to avoid damage from ultraviolet radiation. The green alga Ulva rigida, also called sea lettuce, produces amino acids and carotenoid pigments that absorb harmful radiation.
Cushion plants grow in tight but low-profile clumps, forming windbreaks that protect them from the cold, and may trap airborne dust and soil used as a source of nutrients.
Many tundra plants are capable of carrying out photosynthesis under relatively low light intensities. With short growing seasons, some plants reproduce by budding and division instead of by the creation of seeds. Plants may also store nutrients in rhizomes, underground stems that survive after root systems die.
Soils of the tundra are principally thin soils (inceptisols). Contributing to the lack of soil development are cold temperatures that inhibit the growth of soil-producing organisms such as bacteria. The tundra’s treeless plain may be interrupted by patterned ground made up of stone polygons, soil circles, or soil stripes.
These unusual features are formed by the thrusting action of repeated freezing and thawing in soil that overlies rock or permanently frozen ground called permafrost. Impenetrable permafrost that inhibits root system development, rather than cold temperatures, is thought to be responsible for the lack of tree growth in the tundra.
Warmer summer temperatures lead to a thaw in permafrost that extends only about a meter below the surface. Ponds and boggy areas form in places where soil above the permafrost melts and cannot move downward, creating a source of moisture for plants.
As a result of growing under harsh conditions, tundra plants are slow to recover from disturbances. Vehicles can destroy tundra plants. Other concerns include oil spillage, damage caused by pipeline construction, and other impacts tied to petroleum production.