Brazil Eco Adventure Tours
Rainforest - Hiking & Biking - Wildlife

Geological and climatic processes a long time ago are responsible for the topographic structure of todays Amazon. The Amazon basin was formed by deposition of sediments from a lake called "Belterra" which covered the area during the tertiary period between 2 and 25 million years ago. With the rising of the Andes, those sedimental plains have been slightly modulated and modern rivers began to excavate their beds. Nowadays, three typical topographic forms can be found in the Amazon basin: highlands (planaltos) up to 200 m, plains and depressions.

Precisely the topographic structure of the Amazon basin, which decides if an area is flooded or not, together with the water quality of the Amazon rivers & streams determines the characteristics of the six principle ecosystems of the Amazon Rainforest:

Tierra Firme (dry land) constitutes the majority of the total 7 million km2 of the Amazon Rainforest. This is a forest that is never flooded, spreaded across a great plain of up to 130-200 meters of altitude, up to the bottom of the mountains. The plants of this ecosystem have countless adaptations to the clay and podzol soils, poor in nutrients. The trees that form it are capable of stocking up with nitrates through nitrogen fixing bacterias, which are linked to their roots. This part of the Amazon Forest, especially rich in epiphytal araceaes, is relatively poor in bromeliads and orchids, in comparison to the Atlantic Rainforest / (Mata Atlântica). In the sub-woods of the forest stand out especially palm trees and lianas; large ferns are rare.

Várzea is periodically flooded by the white or clouded waters, like the rivers Solimões ,Amazon and Madeira. Those rivers traverse lands rich in minerals and organic suspensions. Due to the fertility of those rivers and the alluvial soils carried by them, the Flora and Fauna of this particular Amazon ecosystem is one of the richest and highest in terms of productivity. The rivers are rich in fish and there are many aquatic mammal species to be found, such as "botos" (fresh water dolphins), "peixe-boi" (cow fish), "ariranhas" (Brazilian otters) and others. In the avifauna the aquatic birds are predominat: herons, "biguás" (cormorants), "jaçanãs", "mucurungos" and ducks. The high productivity of the Amazon "várzeas" has allowed the existence of a dense indigenous population at the time of the discovery.

Igapó is permanently flooded by either white waters which descend from the central highlands (Altiplano Central) in northern direction, such as the rivers Tapajós, Tocantins, Xingu or Araguaia or by the black waters that descend from the Guianas highlands in southern direction, like the Negro river. Both type of waters are very poor in minerals and nutrients. Consequently the flora and fauna of this ecosystem, different from the "Várzea" one is one of the poorest. Some trees have a big resistance to the prolonged flood and survive many years of permanent submersion.

Igarapé is characterized by little streams passing through the Várzea rainforest area. There the giant trees, like the "Maparajuba" with heights up to 40 m can be found.

Cerrado is characterized by small trees with twisted trunks. This forest is typically to be found in the northeast and the central Amazon Rainforest region in an area of about 200 million hectares.

Caatinga occurs in form of a brushy, thorny stratum with rough leaves, mostly located above the white sands of the "Negro" river.