White cottongrass blooms on the Arctic tundra.
Tundra is an ecological environment found in two locations on earth. Arctic tundra encircles the North Pole from latitudes 55 degrees to 70 degrees north. Alpine tundra occurs at high altitudes, above the tree line. Both are characterized by permafrost (permanently frozen subsoil), extremely low temperatures, meager precipitation, poor soils and short growing seasons. Plants and animals found in the tundra make adaptations to survive these harsh conditions.
Soil
Tundra soil is completely frozen during the winter; the upper part of the soil thaws during the brief summer. The still frozen permafrost inhibits drainage. This -- along with low air temperatures that slow evaporation -- results in summer ponds and bogs. The cycle of freezing and thawing slowly mixes the upper soil layer; it breaks rock into gradually smaller particles, causing soil formation.
Flora
Lichens and low-growing plants typify the tundra.
The nutrients and energy that support tundra plant life are available only during the short summer. Plants battle extremely low winter temperatures -- and strong, drying winds -- by growing low to the ground. Winter grazing contributes further to stunted growth. Mosses and lichens thrive. Deep snow-cover provides protection; rooted plants growing in areas that don't get a lot of snow often have aboveground parts that die or harden before winter. Many tundra plants drop seeds on the autumn snow; the wind scatters the seeds.
Resident Mammals and Birds
The musk ox is well adapted to life in a cold environment.
Extreme cold -- and the tundra's short growing season -- regulate which animals survive year round and which ones migrate. Permanent residents have adapted by developing large bodies with short limbs, by storing body fat during the growing season and by growing dense fur or feathers that thicken in colder weather. Resident populations often fluctuate cyclically. Every three to five years certain species -- in particular the lemming and its predators -- experience population surges.
Migratory Animals and Birds
Caribou migrate to the tundra during the summer.
Forest dwellers -- like bears, wolves and caribou -- avoid the tundra's harsh winter by moving south to the boreal forest. Songbirds, shorebirds and waterfowl also migrate, returning to the tundra in the brief spring and summer to breed.
Insects
Mosquitoes live successfully in the tundra.
Mosquitoes, flies, moths, grasshoppers, blackflies and arctic bumble bees all survive in the tundra. Insects adapt to the short growing season. Certain species of moths and spiders take several years to achieve all of life's stages. A mosquito successfully overwinters in the tundra because its body fills with a chemical called glycerol; the chemical keeps it from freezing. The arctic bumblebee makes its flight muscles shiver, which raises its body temperature as much as 60 F above the outside air temperature.
Carbon Dioxide Cycle
The tundra is a carbon-dioxide sink, meaning that it makes more carbon dioxide than it gives off. Plants absorb oxygen, sunlight and water in photosynthesis during the summer, but freeze quickly when winter arrives. This phenomenon traps carbon dioxide in the permafrost, where it is stored.
Tags: growing season, short growing, Arctic tundra, during summer, short growing season