In physical geography, a tundra is a type of environment where trees cannot grow because of very cold temperatures and short growing seasons. There are three types of tundra: Arctic, Alpine, and Antarctic.

Tundra plants include small shrubs, grasses, mosses, and lichens. Some areas have a few scattered trees. The area where tundra meets forests is called the tree line. Tundra soil has high levels of nitrogen and phosphorus. It also holds a lot of plant material and decayed matter that is stored as methane and carbon dioxide in frozen ground, called permafrost. This makes the tundra soil a place that stores carbon. When global warming increases temperatures and causes permafrost to thaw, the stored greenhouse gases are released into the air. This process speeds up climate change and creates a cycle that worsens the problem.

Etymology

The word "tundra" comes from the Russian word "ту́ндра" (tundra). It was first used in English in 1824, spelled "toundra," which may have been taken from French. The origin of the Russian word is not certain. It might have come from the Sámi language word "tundar," which means "fell," "a type of land," or "marshy plain." This word was used as far back as the 16th century. Some sources suggest the word might have come from Finnish.

Arctic

Arctic tundra is found in the far northern part of the Northern Hemisphere, north of the taiga belt. The word "tundra" often refers to areas where the soil is permafrost, which is soil that stays frozen all year. It can also refer to the treeless plains in places like northern Sápmi. Permafrost tundra covers large areas in northern Russia and Canada. The polar tundra is home to several groups of people who are mostly nomadic reindeer herders, such as the Nganasan and Nenets in permafrost regions and the Sámi in Sápmi.

The Arctic tundra has a harsh landscape and is frozen for much of the year. The soil there is frozen from 25 to 90 cm (10 to 35 in) deep, which prevents trees from growing. Instead, the ground is often bare or rocky and supports only certain types of Arctic plants, such as moss, heath (like crowberry and black bearberry), and lichen.

The polar tundra has two main seasons: winter and summer. In winter, it is very cold, dark, and windy, with average temperatures around −28 °C (−18 °F), sometimes as low as −50 °C (−58 °F). However, temperatures in the tundra are generally not as cold as those in the taiga regions further south. In summer, temperatures rise slightly, and the top layer of frozen soil thaws, making the ground very wet. During the warm months, the tundra is covered with marshes, lakes, bogs, and streams. Summer daytime temperatures usually reach about 12 °C (54 °F), but can drop to 3 °C (37 °F) or below freezing. In Canada and Russia, many tundra areas are protected through national biodiversity action plans.

The Arctic tundra is often very windy, with winds reaching speeds of 50–100 km/h (31–62 mph). It is also a polar desert, receiving only about 150–250 mm (6–10 in) of precipitation each year, mostly during the summer. Although precipitation is light, evaporation is low. During summer, the permafrost thaws just enough for plants to grow, but the frozen soil below prevents water from draining, creating lakes and marshes. Natural patterns of fuel buildup and wildfires vary depending on vegetation and terrain. Research in Alaska shows that wildfires on the tundra typically occur every 150 to 200 years, with drier lowland areas burning more often than wetter highland areas.

The Arctic tundra has low biodiversity, with about 1,700 species of vascular plants and 48 species of land mammals. Millions of birds migrate there each year to use the marshes. A few fish species also live in the tundra. Notable plants include blueberry, crowberry, reindeer lichen, lingonberry, and Labrador tea. Notable animals include reindeer (caribou), musk ox, Arctic hare, Arctic fox, snowy owl, ptarmigan, northern red-backed voles, lemmings, mosquitoes, and polar bears near the ocean. The tundra has few species with large populations and no reptiles or amphibians.

Because of the harsh climate, the Arctic tundra has seen little human activity, even though it is rich in natural resources like petroleum, natural gas, and uranium. In recent years, this has changed in places like Alaska and Russia. For example, the Yamalo-Nenets Autonomous Okrug produces 90% of Russia's natural gas.

A major threat to the tundra is climate change, which causes permafrost to thaw. Thawing permafrost can change which species can survive there and damage infrastructure like roads and pipelines. In areas where dead vegetation and peat have built up, wildfires can occur. For example, in 2007, 1,039 km (401 sq mi) of tundra burned on the north slope of the Brooks Range in Alaska. These fires can both result from and contribute to global warming.

When permafrost thaws, it releases carbon dioxide and methane, which worsen global warming. This process creates a feedback loop, making warming worse. Increased warming also intensifies the Arctic water cycle, and warmer rain further increases permafrost thaw.

The IPCC Sixth Assessment Report estimates that permafrost thaw could release the equivalent of 14–175 billion tonnes of carbon dioxide per 1 °C (1.8 °F) of warming. For comparison, in 2019, human activities released about 40 billion tonnes of carbon dioxide annually. A 2018 study suggested that if global warming reaches 2 °C (3.6 °F), permafrost thaw could add an additional 0.04–0.16 °C (0.07–0.29 °F) to global temperatures by 2100.

Antarctic

Antarctic tundra is found in Antarctica and on some islands near Antarctica, such as South Georgia, the South Sandwich Islands, and the Kerguelen Islands. Most of Antarctica is too cold and dry to support plants, and much of the land is covered by ice or cold deserts. However, parts of the Antarctic Peninsula have rocky soil that can support plant life. The plants found there include about 300–400 lichen species, 100 moss species, 25 liverwort species, and around 700 species of algae that grow on exposed rock and soil near the coast. Two flowering plants, Antarctic hair grass (Deschampsia antarctica) and Antarctic pearlwort (Colobanthus quitensis), grow on the northern and western parts of the Antarctic Peninsula.

Unlike the Arctic tundra, the Antarctic tundra does not have large mammals because Antarctica is physically separated from other continents. Sea mammals and seabirds, such as seals and penguins, live near the shore. Some small mammals, like rabbits and cats, were brought to certain subantarctic islands by humans. The Antipodes Subantarctic Islands tundra, which includes the Bounty Islands, Auckland Islands, Antipodes Islands, Campbell Islands, and Macquarie Island, is home to species found only in this region. These include the windswept helmet-orchid (Corybas dienemus), the grooved helmet-orchid (Corybas sulcatus), the royal penguin, and the Antipodean albatross.

There is debate about whether Magellanic moorland, located on the west coast of Patagonia, should be classified as tundra. Edmundo Pisano, a Chilean scientist, called it tundra (Spanish: tundra Magallánica) because he believed cold temperatures limited plant growth. More recent studies classify it as a temperate grassland, limiting the term "tundra" to coastal Antarctica and its islands.

The plants and animals in Antarctica and its islands (south of 60° south latitude) are protected by the Antarctic Treaty System.

Alpine

Alpine tundra does not have trees. This is because the climate and soil at high altitudes prevent trees from growing. The cold climate of the alpine tundra is caused by low air temperatures and is similar to the climate found in polar regions. Alpine tundra soils are usually better drained than arctic soils. Alpine tundra changes into subalpine forests below the tree line. Stunted forests in the area where forests and tundra meet are called Krummholz. Alpine tundra can be affected by the spread of woody plants.

Alpine tundra is found in mountains around the world. The plants of the alpine tundra grow close to the ground and include perennial grasses, sedges, forbs, cushion plants, mosses, and lichens. These plants are adapted to the harsh conditions of the alpine environment, which include low temperatures, dryness, strong ultraviolet radiation, and a short growing season.

Climatic classification

Tundra climates are usually classified as ET in the Köppen climate system. This means the area has at least one month with an average temperature above 0°C (32°F), enough to melt snow, but no month with an average temperature higher than 10°C (50°F). The coldest parts of the tundra climate meet the EF climate, which includes areas covered in permanent ice and snow. The warmest parts of the tundra climate are near the edges of where trees grow, such as in areas with subarctic climates labeled Dfd, Dwd, Dsd (found in parts of Siberia), Dfc (common in Alaska, Canada, mountain regions of Scandinavia, European Russia, and Western Siberia). These subarctic climates have very cold winters with months of freezing temperatures.

Although the ET climate category includes many different types of weather, such as varying amounts of rain, snow, and temperature extremes, it is not usually divided into smaller groups. Rain and snow are generally light because the cold air holds little moisture. However, because plants use very little water, wet areas like swamps and bogs can form even in places that receive the same amount of rain as deserts in other parts of the world. The amount of plant life in tundra areas depends more on temperature than on how much rain or snow falls.