Biomes: An Introduction (1989)

[Music] [Music] We're going to keep going. [Music] A biome is a community of living things that occupies a large geographical area. A stable community whose composition of plants and animals is primarily influenced by their success in adapting to a particular climate. Because of different climates around the world, there are a number of major biomes. This is an introduction to them. Two major factors determine the location and nature of the Earth's biomes. The first is light. The sun's energy provides the power for each biome while seasonal changes in temperature and daylength regulate the lives of its inhabitants. The second factor is water. Water's abundance and seasonal changes in its availability determine which plants and animals can live within a biome. The Arctic tundra, the northernmost biome, is a level treeless plane. The tundra is found in the northern regions of North America, Europe, and Asia, fringing the ice covered Arctic Ocean. Here, solar energy and water are both in short supply. Water locked up year round in a thick, permanently frozen layer of soil called the perafrost blocks the roots of plants, so tall trees that need deep roots cannot grow here. Only a few animals live here year round. Two layers of fur insulate the muskox, while limmings stay active under the snow and depend on the insulation the snow provides. In the tundra's brief summer, annual flowers rush through their life cycles, blooming and growing seeds within a single month. [Music] Increased food supply attracts migrating animals like the caribou and many shore birds and water fowl. For a brief period, the tundra is full of life, but the approach of months of cold and darkness will limit the number of animals that can survive here. Immediately south of the tundra is the coniferous forest biome, sometimes called the tiga. Here are the largest continuous forests in the world. They form a belt across North America, Europe, and Asia. Because this biome is south of the tundra, conditions are different here. There is no perafrost. Winters are shorter and the growing season longer. These trees create shelter for yearround residents like the moose and for other animals that migrate here in winter. In spring, melting snow and ice feed the rivers and lakes that make possible the vast stands of coniferous trees. Because there is a very small range of habitats here, there are fewer species of animals and plants in the coniferous forest than in other kinds of forests. [Music] But to the south in the deciduous forest biome, there are many more habitats for a greater variety of plant and animal species. This biome occupies irregular areas in the temperate regions of the world. Here the growing season is longer. Precipitation is more abundant and evenly distributed throughout the year. The branches of trees here spread a canopy of broad green leaves. Translucent and widely spaced. They allow light to filter down to other plants on the forest floor. Deciduous trees grow leaves in the spring, keep them through the summer, drop them in the fall, and stand bare in winter. In the deciduous forest, all life is governed by the change of seasons. [Music] In the tropical rainforest, as in the deciduous forest, trees also spread a canopy of broad leaves. But these trees stay green all year round. This biome is found in scattered regions near the equator in Central America, South America, Africa, and Southeast Asia. Here there is very little change in day length from one time of year to another. Every day is a summer day with plenty of light and warmth. There is also plenty of water since rain falls almost daily. Because of the rain and sunshine, the growing season lasts all year. A greater variety of species of plants and animals has developed in this biome than in any [Music] other. More tree dwelling mammals inhabit this canopy than in any other forest. [Music] [Music] In some tropical areas, the rains are seasonal, causing a dry season deciduous forest. But in some tropical and temperate regions, there is not enough water to support a forest. In these regions, the dominant plants may be grasses. Grasslands are found on every continent except Antarctica. Vast open plains feed two kinds of planteing animals. Some, like the wilderbeasts of Africa, are grazers who feed off the grass itself. Other planteaters are browsers like the African dick dick that eats twigs and shrubs or the giraffe that eats leaves from the tops of the few trees that grow in the grasslands. The movements of these herbivores are governed by alternating wet and dry seasons. Sharing the grassland with the herbivores are lions and other carnivores. Their eating habits allow the scavengers to survive. While rain in the grassland is seasonal, rainfall in the desert biome is much less predictable and there is much less of it. Global winds have created two bands of desert, one above and one below the equator. In the desert biome, only a few inches of precipitation fall in a year. Not every desert is sandy. Some are rocky or mountainous or barren plains. In all deserts, there are extremes of temperature from day to night. Desert plants have adapted to the extremes of temperature and the scarcity of water. Cactuses, for example, store water in their stems. Desert animals have also adapted. They get their water from their food, seeds, and other plant parts. The hottest places on Earth are the deserts at midday. Except for the hottest periods, many cold-blooded animals are active in the daytime. But most warm-blooded animals rest or sleep. This conserves moisture and helps them avoid overheating. In the cool night, when temperatures can fall below freezing, many small, warm-blooded animals come out of their burrows to hunt and forage. The desert biome, like the other major biomes of the earth, is a distinct community of living things. But no community is unchanging, and so the borders between the adjacent biomes are not distinct. For example, grasses often grow along the edge of desert areas. Similarly, a few stunted trees grow in a transitional zone between the coniferous forest and the tundra. Human activity can also produce changes that affect plants and animals of a biome. When habitats are destroyed, some species may become endangered. Major changes in one biome can cause changes in others. For example, large parts of the tropical rainforest have been cut down in recent years. Without these millions of trees to absorb carbon dioxide, increasing amounts of the gas in our atmosphere may accelerate the greenhouse effect and cause the warming of our planet with future changes that are hard to predict. The fact is that all biomes affect one another and the plants and animals that live there. All biomes are united as part of the Earth's biosphere. All contribute to the number and variety of life forms on Earth. [Music] Heat. Hey. Hey. Hey. [Music]