Seasonality of the rainfall is the main reason for the spatial variation in types of vegetation found throughout the Amazon Basin. Most of the lowland evergreen rainforest is found near the Equator where it experiences a double maximum rainfall. It experiences rain in two seasons when the sun is directly overhead. As the sun moves north or south so the ITCZ (Inter tropical Convergence Zone) moves with it bringing heavy daily rain. There is a very short dry season and plants are not under any stress to lose their leaves. Rainfall annually exceeds 2 000 mm. Evergreen montane rainforests are found in a thin strip along the foothills of the Andes. South East Trade winds in June, July and August carry moist air to the Andes, which acts as a barrier producing orographic rainfall. Rain occurs almost every day in this zone of rising air. In the centre and east of the Amazon, away from the influence of the Andes and the ITCZ, there is a reduced annual rainfall and rain occurs in only one season. There is a marked dry season of between 3 and 4 months and the forest dries out. This is where the seasonal rainforest is located. Rainfall here totals between 1 500 and 2 000 mm annually. On the edges of the seasonal rainforest are found savanna and thorn forests. The main reasons for their
existence are lower rainfall, a dry season lasting up to six months and fires caused by lightning. Annual arainfall here ranges from 900 to 1 060 mm.

Montane forest is found in the western high country because it needs a high rainfall. In the west, the
rain can be up to 4000mm per year. This rain is due to orographic rainfall from the prevailing westerly winds off the Tasman Sea. Winds are forced to rise over the Southern Alps. As the air rises, it cools, condenses, forms clouds, and rains. On the eastern side of the high country it is drier – less than 1500mm because of the rainshadow effect. The winds, which have now no moisture, descend and warm. These winds, known as fohn winds, have a drying effect. Grasses such as tussocks are adapted to these dry conditions and can survive lower rainfall.

Amazonia – Soils

Andes Mountains - The soils in the mountains are thin as erosion is rapid

Alluvial Soils - On the flood plains of the Amazon River and its tributaries from the Andes and therefore are found along the edge of waterways. They are deep, fertile clay soils. These have been deposited annually by floods, resulting in it because very rich in nutrients which have been eroded from the mountains and sediments from the rich decaying swamps onto the land. The poorer drained areas in pasture; the better drained areas are planted in crops, as the soil is very fertile..

Latosols - These are soils that are very deeply weathered and infertil, and therefore cannot sustain farming for very long. It is poor because of the process of leaching (nutrients are flushed out due to heavy rainfall). Often there is 4 to 5 metres of clay overlaying weathered rock. If their surface is protected e.g. covered in forest, they do not erode. The main problem with latosols is their low fertility. Many latosols have a high iron content. Red latosols contain higher amounts of iron that the yellow latosols. Both iron and aluminium reduce natural fertility.

High concentrations of aluminium tend to limit plant growth. Iron lacks in phosphorus by forming insoluble iron phosphates that is of little use to plants.

Podsols - These are sandy soils that are swampy in the wet season, but dry in the dry season. They are also infertile because of their low moisture holding content which will only support deciduous forest of savannah.

Alluvial Soils - On the flood plains of the Amazon River and it’s tributaries from the Andes, there are deep, fertile clay soils. These have been deposited annually by floods. The poorer drained areas are in pasture, the better drained areas are planted in crops.

LATOSOLS - These are soils that are very deeply weathered and infertile. Often there is 4 to 5 metres of clay overlaying weathered rock. If their surface is protected e.g. covered in forest, they do not erode. The main problem with latosols it heir low fertility. Many latosols have a high iron and aluminium contact. Red latosols contain higher amounts of iron than the yellow latosols. Both iron and aluminium reduce natural fertility.

High concentrations of aluminium tend to limit plant growth. Iron lacks in phosphorus by forming insoluble iron phosphates that is of little use to plants.

PODSOLS - These are sandy soils that are swampy in the wet season but dry in the dry season. They are also infertile but because of their low moisture holding content, only support deciduous forest or savannah.

btw ncowie i included bathymetry, can i have some browney points?