Tundra in the context of "Physical geography"

The Americas, sometimes collectively called America, are a landmass comprising the totality of North America and South America. When viewed as a single continent, the Americas are the 2nd largest continent by area after Asia and the 3rd largest continent by population. The Americas make up most of the land in Earth's Western Hemisphere and constitute the New World.

Along with their associated islands, the Americas cover 8% of Earth's total surface area and 28.4% of its land area. The topography is dominated by the American Cordillera, a long chain of mountains that runs the length of the west coast. The flatter eastern side of the Americas is dominated by large river basins, such as the Amazon, St. Lawrence River–Great Lakes, Mississippi, and La Plata basins. Since the Americas extend 14,000 km (8,700 mi) from north to south, the climate and ecology vary widely, from the arctic tundra of Northern Canada, Greenland, and Alaska, to the tropical rainforests in Central America and South America.

Nomads are communities without fixed habitation who regularly move to and from areas. Such groups include hunter-gatherers, pastoral nomads (owning livestock), tinkers and trader nomads. In the twentieth century, the population of nomadic pastoral tribes slowly decreased, reaching an estimated 30–40 million nomads in the world as of 1995.

Nomadic hunting and gathering—following seasonally available wild plants and game—is by far the oldest human subsistence method known. Pastoralists raise herds of domesticated livestock, driving or accompanying them in patterns that normally avoid depleting pastures beyond their ability to recover. Nomadism is also a lifestyle adapted to infertile regions such as steppe, tundra, or ice and sand, where mobility is the most efficient strategy for exploiting scarce resources. For example, many groups living in the tundra are reindeer herders and are semi-nomadic, following forage for their animals.

Polar deserts are the regions of Earth that fall under an ice cap climate (EF under the Köppen classification). Despite rainfall totals low enough to normally classify as a desert, polar deserts are distinguished from true deserts (BWh or BWk under the Köppen classification) by low annual temperatures and evapotranspiration. Most polar deserts are covered in ice sheets, ice fields, or ice caps, and they are also called white deserts.

Polar deserts are one of two polar biomes, the other being Arctic tundra. These biomes are located at the poles of Earth, covering much of the Antarctic in the southern hemisphere, and in the northern hemisphere extending from the Arctic into North America, Europe and Asia. Unlike the tundra that can support plant and animal life in the summer, polar deserts are largely barren environments, comprising permanent, flat layers of ice; due to the scarcity of liquid water, the same is also true of the few ice-free areas. However, there is evidence of some life in this seemingly inhospitable landscape: sediments of organic and inorganic substances in the thick ice hosting microbial organisms closely related to cyanobacteria, able to fix carbon dioxide from the melting water.

Terrestrial ecosystems are ecosystems that are found on land. Examples include tundra, taiga, temperate deciduous forest, tropical rain forest, grassland, deserts.

Terrestrial ecosystems differ from aquatic ecosystems by the predominant presence of soil rather than water at the surface and by the extension of plants above this soil/water surface in terrestrial ecosystems. There is a wide range of water availability among terrestrial ecosystems (including water scarcity in some cases), whereas water is seldom a limiting factor to organisms in aquatic ecosystems. Because water buffers temperature fluctuations, terrestrial ecosystems usually experience greater diurnal and seasonal temperature fluctuations than do aquatic ecosystems in similar climates.

In geography, a plain, commonly known as flatland, is a flat expanse of land that generally has few rapid or steep changes in elevation. Natural vegetation in plains can include prairies/grasslands, forests, savanah, tundra, and desert biomes, among others. Plains occur as lowlands along valleys or at the base of mountains, as coastal plains, and as plateaus or uplands. Plains are one of the major landforms on earth, being present on all continents and covering more than one-third of the world's land area. Plains in many areas are important for agriculture. There are various types of plains, and biomes on them.

A biome (/ˈbaɪ.oʊm/, BYE-ome) is a distinct geographical region with specific climate, vegetation, animal life, and an ecosystem. It consists of a biological community that has formed in response to its physical environment and regional climate. In 1935, Tansley added the climatic and soil aspects to the idea, calling it ecosystem. The International Biological Program (1964–74) projects popularized the concept of biome.

However, in some contexts, the term biome is used in a different manner. In German literature, particularly in the Walter terminology, the term is used similarly as biotope (a concrete geographical unit), while the biome definition used in this article is used as an international, non-regional, terminology—irrespectively of the continent in which an area is present, it takes the same biome name—and corresponds to his "zonobiome", "orobiome" and "pedobiome" (biomes determined by climate zone, altitude, or soil).

The polar climate regions are characterized by a lack of warm summers but with varying winters. Every month a polar climate has an average temperature of less than 10 °C (50 °F). Regions with a polar climate cover more than 20% of the Earth's area. Most of these regions are far from the equator and near the poles, and in this case, winter days are extremely short and summer days are extremely long. They could last for the entirety of each season or longer.

A polar climate consists of cool summers and very cold winters, or, in the case of ice cap climates, no real summer at all, which results in treeless tundras, glaciers, or a permanent or semi-permanent layer of ice. It is identified with the letter E in the Köppen climate classification.