Global Enviroments

Global Enviroments - Global Env 1 Global Environments...

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Global Env.: 1 Global Environments Terrestrial Biomes We are going to finish up the semester with a look at the major environmental regions of Earth. To do this, we will bring together aspects of climate, geomorphology, soils, hydrology and biogeography. In fact, we are going to orient this material around biogeographic realms, known as biomes . These are large ecosystems characterized by particular types of plants and animals. We will concentrate on terrestrial biomes, but realize that marine ones exist as well. Biomes are based on natural vegetation, but keep in mind that people can profoundly affect the characteristics of a biome. And, while we can map out biomes, the lines on the map hide the fact that there is often a broad transition zone from one biome to another. The map of biomes is similar to a map of climate zones, because of the strong influence of climate on plant and animal evolution. Tropical Rainforest Along the Equator, there isn’t much in the way of seasons, temperature is high and so is rainfall. Rain comes most days as afternoon thunderstorms. The high rainfall causes much leaching in the soils, depleting them of nutrients. The soils are oxisols. These areas were not glaciated during the Ice Age, so there has been little interruption of the environment for, perhaps, millions of years. This may be why there is such a tremendous diversity of life–there may be hundreds of species of trees found in a square kilometer, not to mention hundreds of species of insects and other forms of life. Typically, the tropical rainforest is structured in three layers. One of the main resources that plants compete for is sunlight. The middle layer contains the most biomass and may be twenty to forty meters above ground. This layer forms a nearly complete canopy, letting little light pass through. The top layer is less dense and is made of the tallest trees protruding above the middle layer. These trees can reach sixty meters. The lowest layer is made of young trees and herbs are often only exists if there is a break in the canopy, letting light down to the surface. The forest floor is pretty dark and relatively open because dead plant material is rapidly decomposed–it doesn’t form a litter layer like we see in mid latitude forests. Because of the competition for light, many plants, like vines and epiphytes, live out of the soil, getting their physical support from trees. Some of these get their food by catching leaves and insects and getting nutrients from the decomposing material. We often think of tropical rainforests as very dense
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Global Env.: 2 jungles, but that image comes from early explorers who traveled by river, where light can get into the forest near the stream bank. Tarzan movies helped perpetuate this misconception. The result is dense jungle, but only close to the stream. If they had walked into the forest a few hundred meters, they would have seen typical tropical rainforest. The highly diverse animal life is adapted to the
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Global Enviroments - Global Env 1 Global Environments...

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