Chapter 17 Biomes

Chapter 17 : Biomes. Biomes are biological communities on a global, or continental scale. Major Biomes of North America Many of these biomes are also found on other continents. Tundra Tundra makes up about 20% of the land surface of the earth. Tundra has very short trees (less than 2ft) or no trees at all. It also has permafrost (soil that is frozen year round under the surface), very little rainfall and a short growing season of 2-3 months. The main plants in the tundra are small shrubs, grasses, lichens and mosses. Most animals are small, such as voles and lemmings, with the exception of polar bears on the coast and caribou (reindeer) inland. In North America the tundra is found only in northern Canada and Alaska. Fig 26.2. Taiga Taiga is also called northern coniferous forest, the dominant trees are pine and fir. Temperatures can get very cold in the winter and there is a lot of snow, but in the summer the soil is not frozen. There are many perennial plants here, but few annuals. Large animals like moose and deer are common. Taiga covers much of Canada, parts of Alaska and the northwest coast. Fig 26.3. Temperate Deciduous Forest Most of trees here are deciduous, such as maple, oak and hickory. Many of the larger trees have been logged since Europeans arrived, and much of the original forest has now been converted into farmland and towns. Temperatures are typically above freezing in the winter, and warm in the summer. A wide variety of animals are found here, including snakes, squirrels, racoons, possums and many birds. The temperate deciduous forest is found mainly east of the Mississippi river, and south of the Great Lakes. Fig 26.4. Grassland Grasslands are obviously dominated by grasses, with very few trees (typically there is not enough rainfall to support trees). Temperatures can range widely. Fig 26.5. Most natural grasslands are found west of the Mississippi, and originally supported huge herds of bison. Now, most grassland is used as pasture for cattle, or has been converted into farmland growing cereal crops, particularly corn and wheat. Desert Deserts typically have less than 5 inches of rain a year. The dominant plants are CAM plants, such as cacti and other succulents that have no leaves, just photosynthetic stems. Desert plants also have thick cuticles to reduce water loss and they store water in their stems. Annual plants are also common. They grow rapidly after any rain, bloom and then survive for months or years as seeds until the next rain. Fig 26.7. Most animals in the desert are nocturnal, because the temperature is much cooler at night. They include mice and rats, snakes and lizards. Deserts are found in the Southwest United States. Mountain and Coastal Forest The dominant trees are large conifers, such as fir and redwood, which grow very tall, partly due to the large amount of rainfall. However in the summer the climate is fairly dry, so wildfires are common. These forests are found in the Rocky mountains and California. Fig 26.8. A wide variety of animals live here, including bear, mountain lion, bobcat and elk. Wetland Wetlands can be loosely categorised as: Marshes: water covered for much of the year and with adequate nutrients in the soil; these ecosystems are productive; the characteristic plants are grasses and related grass-like monocotyledons (reeds). In Florida the dominant marsh grass in saltmarsh around rivers and estuaries is Spartina (cord grass). In the water crabs, shrimp and oysters are common, and many types of wading bird like herons and egrets are found here. Marshes are found along the coast of Florida. Swamps: waterlogged soil inland, with seasonal flooding; the characteristic plants are trees such as swamp cypresses (Taxodium) and pines. The water and soil are typically low in nitrogen, so insectivorous plants are common, like pitcher plants (Sarracenia) and sundews (Drosera). Alligators and several species of snake are found in swamps, along with a variety of birds. Swamps are found along rivers, and form most of the Everglades. Tropical Rainforest This covers 5% of the earth's surface, and is found in Central America and some islands such as Cuba and Haiti. It is found wherever there is high rainfall, high temperatures and no dry season. Humidity is usually above 80% year round. Tropical rainforest consists of a huge variety of species, dominated by large broadleaved evergreen trees. Epiphytes (plants growing on other plants, like orchids) are common but the soil has relatively few nutrients. This makes it unsuitable for farmland. A wide variety of animals are found in the rainforest including tapirs, anteaters, treefrogs, monkeys, bats and ants. Birds are also abundant. Fig 26.9.