terça-feira, 29 de março de 2011

The Amazon rainforest

The Amazon rainforest is situated in northern South America occupies the territories of Brazil, Bolivia, Peru, Ecuador, Colombia, Venezuela, Guyana, Suriname and French Guiana.

It is the equatorial forest that occupies the largest in the Amazon territory. It is one of three great world's tropical forests. It is the largest rainforest in the world, though it's smaller than the Siberian Taiga Forest is a forest of coniferous trees in the shape of cones, pine trees.

The forest looks, when seen from above, a continuous layer of hearts wide, located approximately 30 meters above the ground ..

Most of its five million square kilometers, or 42% of Brazilian territory, is composed of a forest that have never flooded, on a plain 130 to 200 meters, formed by sediments of Lake Belterra, which occupied the Amazon basin between 1.8 million and 25,000 years ago. At the time when the Andes rose, the rivers dug its bed, which led the three types of forest in the Amazon.

* Amazon rainforest biome Ecosystem

The Andean mountain forests
Forests land
Forests flooded river

The upland forest, not unlike the Andean forest, except for lower density, is located in uplands rather high (30-200m) and has a soil poor in nutrients. This forced an adaptation of the roots of plants, through a symbiotic association with certain types of fungi, began to rapidly decompose organic matter deposited in the soil to absorb nutrients before they are leached.

The river flooded forest also has some adaptations to conditions such as respiratory roots, which have pores that allow the absorption of atmospheric oxygen. The areas located on low ground and subject to periodic flooding by muddy or turbid water, from rivers in regions rich in organic matter, are called the floodplain forests. And the areas flooded by black water, and running through the sandy soils poor in minerals and they assume a dark color due to organic matter, are called wetland forests. The oscillation of the water level can reach up to ten meters high.

In the Pleistocene the climate of Amazonia alternated between cold-dry, hot-humid and hot-dry. In the last phase cold-dry, about 18 or 12 thousand years, the Amazonian climate was semiarid and the maximum humidity occurred about seven thousand years. In semi-arid phase predominated open vegetation such as savannah and scrub, with refugia where forest survived. Currently the savannah subsist in shelters in the forest interior.

The Amazonian soil is quite poor, with only a thin layer of nutrients. However, the flora and fauna remain under steady state (climax) achieved by the ecosystem. The exploitation of resources is great, with minimal losses. A clear example is in the distribution of mycorrhizas by the steep ground, the roots that ensure a rapid uptake of nutrients that flow with the rain forest. Also, way into the soil a layer of decomposing leaves, twigs and dead animals quickly recovered and converted into nutrients before leaching. Such a conversion takes place because the fungi found there (and who perform the symbiosis) are saprophytic.

Beneath a layer below one meter, the soil becomes sandy and endowed with few nutrients. Therefore - and because of the almost unlimited availability of water, tree roots are short, and the process of support is based on mutual bracing of trees.

The barriers to entry imposed by the abundance of light to make the canopy vegetation is very sparse and the animals that inhabit the soil and vegetation that need. Most of the Amazon fauna consists of animals that inhabit the treetops, between 30 and 50 meters. There occur large animals, such as savannas. In the canopy, among the birds are parrots, toucans and woodpeckers and, among mammals, bats, rodents, monkeys and marsupials.

The fauna and flora have been described in the stunning Amazonian Flora Brasiliensis (15 volumes), Carl von Martius, Austrian naturalist who dedicated much of his life to research in the Amazon, in the nineteenth century. However, species diversity and difficulty of access to high tops make most of the still unknown faunal wealth.

The climate in the Amazon forest is equatorial, hot and humid due to its proximity to the equator (the continuous Atlantic Forest), with temperatures varying little throughout the year. The rains are abundant, with average annual precipitation ranging from 1500 mm to 1700 mm, sometimes exceeding 3000 mm at the mouth of the Amazon River and the coast of Amapa. The rainy season lasts six months.

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