Ecology/Tundra

Tundra is one of the biomes discussed in the Ecology event

Overview
The tundra is a biome where tree growth is hindered by low temperatures and short growing seasons. There are two types of tundra covered in the Ecology event: Arctic and Alpine. Arctic tundra occurs at extreme northern latitudes and alpine tundra occurs at high altitudes. A third kind of tundra, Antarctic, is not found in North America, so should not be tested in the Ecology event. By definition, the tundra is too inhospitable to support trees, therefore, the only vegetation is shrubs, sedges, grasses, mosses, and lichen.

Climate
The tundra has one of the most inhospitable climates of any biome on planet Earth.

Temperature
The tundra temperature is cold year round and it is not uncommon for the temperature to drop below freezing even in the summer. In addition to the high latitude of the tundra, the Arctic tundra is further cooled by Polar Cells that carry frigid air from the north pole south across the biome. A 1,000 m increase in altitude up a mountain corresponds to the same temperature change produced by an 880 km increase in latitude.

Precipitation
The biome receives very little precipitation and rivals the dryness of the desert biome, usually around 150-250 millimeters per year. Most of the precipitation comes in the summer. The reason the tundra receives so little precipitation is that the air is very cold and cold air can carry less moisture than warm air. Permafrost prevents effective drainage in much of the Arctic tundra, so when temperatures do rise above freezing, a great deal of standing water and soggy soil results.

Sunlight
Because the Arctic tundra only exists at extreme northerly latitudes, the sun's rays always strike the biome at a highly oblique angle. This means that the radiation must pass through more of the Earth's atmosphere, which stifles the amount of radiation that reaches the surface of the Arctic tundra. Because the axis of the Earth is tilted 23.5 degrees from the normal line to the orbital plane, seasonal variation occurs in the tundra. If the sunward facing part of the earth is tilted away from the Arctic tundra, as is the case in winter, the sun never even rises above the horizon. Whereas in summer, the sun can stay above the horizon for 24 hours of the day. At some latitudes of the tundra the sun can shine constantly for two months, however it never rises very far above the horizon.

Wind
There is generally a very high level of wind in the tundra. Wind speeds often reach 48–97 km/h. Cold air rushes down from the North Pole and sweeps through the tundra. The tundra does not have any trees to slow down the winds.

Plant Adaptations
Plants must have extreme adaptations to survive in the cold, dry, windy climate of the tundra. Many tundra plants are chamaephytes, these plants stay very low to the ground to avoid the high winds of the tundra. The plants are perennials with buds that remain in hibernation until conditions are suitable for growth. There is not enough energy to support Annual plants because the tundra does not provide very much energy or nutrition. Because the plants are perennial, they do not have to use a great deal of energy to re-grow to a fertile size in one year. They can re-use their growth each year, which allows them to grow slower.

The leaves are usually glossy to minimize loss of water. They are also dark colored to absorb as much energy as possible and some are shaped like satellite dishes and will actually swivel around to follow the sun.

Some plants also use antifreeze proteins to prevent the recrystallization of ice inside the plant cells.

Differences Between Arctic and Alpine Tundra
Arctic tundra covers a much greater percentage of the Earth than alpine tundra, so it makes sense that most Ecology tests focus primarily on arctic Tundra. However, questions about alpine tundra do arise and it is important to know the differences between the two.
 * Because alpine tundra only exists on mountains, the soil is always very well drained, as opposed to the often soggy soil of arctic tundra.
 * alpine tundra exists because of high altitude, this means that the biome can exist at many different altitudes, so long as there are mountains. This means that alpine tundra that is farther south may receive much more solar radiation than arctic tundra which leads to greater evaporation rates.
 * As global warming continues, the biomes are shifting. Organisms in arctic tundra can generally migrate north to find the conditions they are adapted to. However organisms that live in alpine tundra are trapped on 'islands' of suitable habitat. They are adapted to a tundra climate and can not effectively compete with organisms in habitats lower down on the mountains. This traps the organisms on their mountains and does not allow them to migrate to other mountains. As global warming progresses, these organisms are pushed higher up onto their mountains. In some cases, the mountains may not extend any higher, and organisms are pushed to local extinction.
 * Alpine tundra generally has a lower oxygen concentration due to the thinning of the atmosphere as you rise in altitude.