The Tundra
Tundra vegetation is composed of dwarf shrubs, sedges, grasses, mosses, and lichens. Scattered trees grow in some tundra regions. The ecotone (or ecological boundary region) between the tundra and the forest is known as the tree line or timberline. The tundra soil is rich in nitrogen and phosphorus.[3] The soil also contains large amounts of biomass and decomposed biomass that has been stored as methane and carbon dioxide in the permafrost, making the tundra soil a carbon sink. As global warming heats the ecosystem and causes soil thawing, the permafrost carbon cycle accelerates and releases much of these soil-contained greenhouse gases into the atmosphere, creating a feedback cycle that increases climate change.
The Tundra
Arctic tundra occurs in the far Northern Hemisphere, north of the taiga belt. The word "tundra" usually refers only to the areas where the subsoil is permafrost, or permanently frozen soil. (It may also refer to the treeless plain in general so that northern Sápmi would be included.) Permafrost tundra includes vast areas of northern Russia and Canada.[3] The polar tundra is home to several peoples who are mostly nomadic reindeer herders, such as the Nganasan and Nenets in the permafrost area (and the Sami in Sápmi).
Arctic tundra contains areas of stark landscape and is frozen for much of the year. The soil there is frozen from 25 to 90 cm (10 to 35 in) down, making it impossible for trees to grow. Instead, bare and sometimes rocky land can only support certain kinds of Arctic vegetation, low-growing plants such as moss, heath (Ericaceae varieties such as crowberry and black bearberry), and lichen.
The biodiversity of tundra is low: 1,700 species of vascular plants and only 48 species of land mammals can be found, although millions of birds migrate there each year for the marshes.[6] There are also a few fish species. There are few species with large populations. Notable plants in the Arctic tundra include blueberry (Vaccinium uliginosum), crowberry (Empetrum nigrum), reindeer lichen (Cladonia rangiferina), lingonberry (Vaccinium vitis-idaea), and Labrador tea (Rhododendron groenlandicum).[7] Notable animals include reindeer (caribou), musk ox, Arctic hare, Arctic fox, snowy owl, ptarmigan, northern red-backed voles, lemmings, the mosquito,[8] and even polar bears near the ocean.[7][9] Tundra is largely devoid of poikilotherms such as frogs or lizards.
Due to the harsh climate of Arctic tundra, regions of this kind have seen little human activity, even though they are sometimes rich in natural resources such as petroleum, natural gas, and uranium. In recent times this has begun to change in Alaska, Russia, and some other parts of the world: for example, the Yamalo-Nenets Autonomous Okrug produces 90% of Russia's natural gas.
A severe threat to tundra is global warming, which causes permafrost to thaw. The thawing of the permafrost in a given area on human time scales (decades or centuries) could radically change which species can survive there.[10] It also represents a significant risk to infrastructure built on top of permafrost, such as roads and pipelines.
In locations where dead vegetation and peat have accumulated, there is a risk of wildfire, such as the 1,039 km2 (401 sq mi) of tundra which burned in 2007 on the north slope of the Brooks Range in Alaska.[11] Such events may both result from and contribute to global warming.[12]
There is some ambiguity on whether Magellanic moorland, on the west coast of Patagonia, should be considered tundra or not.[35] Phytogeographer Edmundo Pisano called it tundra (Spanish: tundra Magallánica) since he considered the low temperatures key to restrict plant growth.[35]
Alpine tundra occurs in mountains worldwide. The flora of the alpine tundra is characterized by plants that grow close to the ground, including perennial grasses, sedges, forbs, cushion plants, mosses, and lichens.[39] The flora is adapted to the harsh conditions of the alpine environment, which include low temperatures, dryness, ultraviolet radiation, and a short growing season.
Despite the potential diversity of climates in the ET category involving precipitation, extreme temperatures, and relative wet and dry seasons, this category is rarely subdivided. Rainfall and snowfall are generally slight due to the low vapor pressure of water in the chilly atmosphere, but as a rule potential evapotranspiration is extremely low, allowing soggy terrain of swamps and bogs even in places that get precipitation typical of deserts of lower and middle latitudes.[43] The amount of native tundra biomass depends more on the local temperature than the amount of precipitation.[44]
The Arctic tundra, where the average temperature is -30 to 20 degrees Fahrenheit (-34 to -6 degrees Celsius), supports a variety of animal species, including Arctic foxes, polar bears, gray wolves, caribou, snow geese, and musk oxen. The summer growing season is just 50 to 60 days, when the sun shines up to 24 hours a day.
The relatively few species of plants and animals that live in the harsh conditions of the tundra are essentially clinging to life. They are highly vulnerable to environmental stresses like reduced snow cover and warmer temperatures brought on by global warming.
The Arctic tundra is changing dramatically due to global warming, a term that falls within a wider range of trends scientists now prefer to call climate change. The impacts in this region are broad and somewhat unpredictable. Animals that are typically found further south, like the red fox, are moving north onto the tundra. This means the red fox is now competing with the Arctic fox for food and territory, and the long-term impact on the sensitive Arctic fox is unknown.
This map shows the major regions where tundras are most common; tundras are in yellow. Tundras are often located near permanent ice sheets where during summer the ice and snow recede to expose the ground, allowing vegetation to grow.
Other tundra denizens, such as the wolf spider, are growing bigger and thriving. Shrubs are getting taller, contributing to declines in the sensitive groups of lichen that caribou and other species depend on for food. Lakes and ponds are evaporating or draining away.
Another major concern is that the melting of the permafrost is contributing to global warming. The frozen ground contains about one and a half times the amount of carbon already in the atmosphere today, as well as large amounts of methane, another potent greenhouse gas. Until recently, the tundra acted as a carbon sink and captured huge amounts of carbon dioxide from the atmosphere as part of photosynthesis. That process helped keep the amount of this greenhouse gas from accumulating in the atmosphere.
Today, however, as the permafrost melts and dead plant material decomposes and releases greenhouse gases, the tundra has flipped from a carbon sink to a carbon contributor. That means not only is the planet less capable of preventing greenhouse gases from accumulating, but the tundra is also contributing to their buildup. Scientists are still learning about what else the permafrost harbors, and what could be released as it thaws. Recently a study found that it is also the largest store of mercury on the planet and could release the toxic heavy metal into the environment, to harmful effect.
Arctic tundra is located in the northern hemisphere, encircling the north pole and extending south to the coniferous forests of the taiga. The arctic is known for its cold, desert-like conditions. The growing season ranges from 50 to 60 days. The average winter temperature is -34 C (-30 F), but the average summer temperature is 3-12 C (37-54 F) which enables this biome to sustain life. Rainfall may vary in different regions of the arctic. Yearly precipitation, including melting snow, is 15 to 25 cm (6 to 10 inches). Soil is formed slowly. A layer of permanently frozen subsoil called permafrost exists, consisting mostly of gravel and finer material. When water saturates the upper surface, bogs and ponds may form, providing moisture for plants. There are no deep root systems in the vegetation of the arctic tundra, however, there are still a wide variety of plants that are able to resist the cold climate. There are about 1,700 kinds of plants in the arctic and subarctic, and these include:
Alpine tundra is located on mountains throughout the world at high altitude where trees cannot grow. The growing season is approximately 180 days. The nighttime temperature is usually below freezing. Unlike the arctic tundra, the soil in the alpine is well drained. The plants are very similar to those of the arctic ones and include:
For most of the year, the tundra biome is a cold, frozen landscape. This biome has a short growing season, followed by harsh conditions that the plants and animals in the region need special adaptations to survive.
Atop the food chain are tundra carnivores, such as arctic foxes (Vulpes lagopus), arctic wolves (Canis lupus), snowy owls (Bubo scandiaca), and polar bears (Ursus maritimus), which move into the tundra during the summer when prey is plentiful and their usual hunting grounds on sea ice diminish. Many animals, both predator and prey, develop white fur or feathers in the winter months for camouflage in ice and snow.
Though the tundra is remote, it is increasingly threatened as people encroach on it to build or drill for oil, for example. Perhaps the greatest danger, however, comes from climate change. Warming temperatures could disrupt the cold tundra biome and the life in it, as well as thaw its underlying permafrost, releasing greenhouse gases that would further accelerate global warming.
The tundra is the coldest of the biomes. It also receives low amounts of precipitation, making the tundra similar to a desert. Tundra is found in the regions just below the ice caps of the Arctic, extending across North America, to Europe, and Siberia in Asia. Much of Alaska and about half of Canada are in the tundra biome. Tundra is also found at the tops of very high mountains elsewhere in the world. Temperatures are frequently extremely cold, but can get warm in the summers. 041b061a72