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Arctic and Alpine Tundra
Tundra ecosystems are characterized primarily by temperature; they are extremely cold. Because of their low temperatures, they have limited plant and animal life. The Arctic tundra encircles the North Pole and extends south to the coniferous forests of the taiga. The average winter temperature is minus 30 degrees Fahrenheit and the summer temperature ranges from 37 to 54 degrees Fahrenheit. The warmer summer temperatures allow some plant life to grow, including low shrubs and lichens. Animals include caribou, polar bears, falcons, grasshoppers and trout.
Alpine tundra exists anywhere in the world where mountain elevations are so high that trees cannot grow. Alpine tundra flora is similar to the Arctic tundra and includes low shrubs, tussock grasses and heaths. Animals include mountain goats and butterflies.
Forest
Forest ecosystems include a broad range of landscapes. Rainforests, Mediterranean evergreen forests, boreal forests, temperate coniferous and deciduous are all types of forest ecosystems. Boreal forests, also known as taiga, are located just south of the Arctic tundra and stretch across North America and Eurasia. The winters are long and cold, and summers are characterized by intense growth as the winter snow melts and the sun heats up the land. Boreal forests support large coniferous trees as well as lichens and moss. Wolverines, snowshoe rabbits and moose can all be found in the boreal forests.
Grasslands and Savannas
Grasslands, as their name suggests, are covered in grasses. Well-known grasslands include the plains and prairies of North America, the pampas of Argentina and veldts of South Africa. Grassland temperatures vary greatly from winter to summer. Seasonal drought and occasional fires keep woody shrubs in check.
Savannas are grasslands with scattered, lone trees. Nearly half of the African continent is classified as savanna. They also can be found in Australia, South America and India. Savannas receive around 20 to 50 inches of rainfall a year following a long period of drought.
Desert
Desert ecosystems can be classified as hot and dry, semiarid, coastal or cold. Hot and dry deserts, like the Mojave and the Sonoran, are characterized by extremely hot days and extremely cold nights, because there is no humidity in the air to regulate the absorption and loss of the sun's rays. Semiarid deserts include Castle Valley, Utah, and the sagebrush deserts of Montana, where summers are moderately long and dry. Coastal deserts, like the Atacama in Chile, are cooler but no less dry, receiving as little as 3 to 5 inches of rain a year. Cold deserts occur in the Antarctic and Greenland and are mostly cold and dry.
Freshwater
Ponds, lakes, streams, rivers and wetlands are all freshwater ecosystems. Bodies of fresh water can vary in size from the smallest seasonal ponds to large, glacial lakes. These ecosystems can have limited species because they are isolated from each other. The ecosystem of streams and rivers can change as they flow from their headwaters to their mouths. In general, rivers and streams are cooler and clearer at their headwaters than at their mouths, so the flora and fauna vary from one end to the other. Wetlands are composed of standing water supporting a wide variety of aquatic plants. Marshes, swamps and bogs are all wetland ecosystems.
Marine
Three-fourths of the Earth's ecosystems are marine, including oceans, coral reefs and estuaries. Oceans are the largest ecosystems on the planet and vary vastly from the shallows to the depths. Coral reefs are distributed mostly in warm, shallow waters and host coral, as well as fish, sea urchins, octopus and sea stars. Estuaries are places where fresh water rivers and streams merge with the ocean. They support an interesting mix of flora and fauna including algae, seaweed, marsh grasses, mangroves, oysters and waterfowl.