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The Terrestrial Biomes
The terrestrial world can be divided into areas called biomes. A biome is a large area of land classified by its distinct plants and animals. The characteristics of each biome are dependent on its temperature and the amount of precipitation the area receives. The plants and animals found in each biome are adapted to the particular environment of the biome.
A biome is made up of many ecosystems. An ecosystem is the interaction of living and nonliving things in an environment. However, a biome is the specific geographic area in which ecosystems can be found.
For the purpose of this backgrounder we will identify major terrestrial biomes of the world based on the Whittaker biome classification scheme. It is interesting to note that not everyone agrees on the number and types of biomes.
Distribution of the Earth’s Major Biomes
The map below shows where each of the eight major terrestrial biomes are located in the world. Canada contains four biomes: temperate deciduous forest, grassland, boreal forest/taiga, and tundra. A biome has the same characteristics in any part of the world when it can be found. Therefore, the boreal forests of Canada look like the boreal forests of Russia. The characteristics of each biome are dependent on its climate, particularly temperature and the amount of precipitation the area receives.
The arctic tundra biome is the northernmost biome. It covers the lands north of the Arctic Circle up to the polar ice cap. It reaches as far south as the Hudson Bay area of Canada and the northern part of Iceland. It covers approximately 11.5 million km2. There is also an alpine tundra, which is found on mountains and Antarctic tundra, which is found on Antarctica and the surrounding Antarctic islands.
The arctic tundra is a vast, dry, rocky place that is noted for its lack of trees. In fact, the word “tundra” comes from the Finnish word tunturi, meaning ‘treeless plain.’ One important characteristic of the tundra is the permafrost. The word permafrost is short-form for the permanently frozen soil, which starts within a meter of the soil surface. In the winter almost all of the soil is frozen. In the summer the soil near the surface thaws, but the permafrost at lower depths remain frozen. The permafrost limits how far roots of plants can extend down into the soil. It also is what prevents trees from growing. The ground in the arctic tundra tends to be rocky and the soil has few nutrients. This is because the decomposition rates of plants tends to be low. Despite the lack of trees, this biome is still considered a major carbon sink as there are large amounts of organic matter found in deposits of peat and humus. Peat is decayed sphagnum moss and humus is organic matter.
Due to its northern position, the arctic tundra has a very cold climate. Temperatures range from 15.5 °C in summer to -60 °C in winter and mean temperatures are below 0°C for six to 10 months of the year. Summers are also much shorter than the winters. The northernmost part of this biome receives close to 24 hours of sunlight during parts of the summer. And it receives close to 24 hours of darkness during parts of the winter. Annual precipitation is around 150 to 250mm a year. Most of this precipitation does not evaporate due to the low temperatures. Rivers and lakes often form soil tends to be very soggy in the summer.
Plants & Animals
Due to the cold climate and short growing season, most vegetation in the tundra tends to be herbaceous. Examples of herbaceous plants found there include grasses, mosses such as reindeer moss, liverworts and lichens. The few woody plants which live in the tundra, such as dwarf willows, tend to be short and spread across the ground. This is an adaptation to the high winds that are common in this biome. Plants in this biome also tend to go dormant during the long winters. This means that they slow down their normal life functions. Most of their biomass (mass of their parts) is below ground. And they have relatively high growth rates in the short summers.
Many large mammals, such as caribou, polar bears, arctic foxes, and musk ox, are found in this biome. There are also several smaller mammals, such as lemmings and arctic hare which are prey to the larger mammals.
These prey animals have brown fur in the summer and white fur in the winter to help them camouflage with the changing landscape. During the summer many migratory birds, such as loons, snow geese and terns, come to the tundra to breed. Although there is low insect biodiversity, the insects that live in the arctic tundra, such as mosquitoes, can have large populations.
Human Impacts & Conservation
In the past, humans have had relatively little impact on the arctic tundra. Recently this has begun to change as more and more people have come to the north to extract various natural resources such as oil. Climate change has also begun to, and will continue to have a large impact on this biome. Higher global temperatures are melting the sea-ice and permafrost. This is altering and sometimes destroying the habitats of plants and animals. In an effort to protect this unique biome, efforts to reduce human impacts are being undertaken. This includes efforts to reduce levels of greenhouse gases as well as the creation of protected areas where human interference and hunting are limited.