The Atlantic Coastal Formation (Formação Costeria Atlantica)

Dr Waldir Mantovani

Jardim Botânico do Sao Paulo
Instituto de Botânica, Av. Miguel Estefno 3031, Caixa Postal 4005, 01051 Sao Paulo, Brazil.

Abstract

The Brazilian coastline is more or less regularly followed by mountains, sometimes over 200m high. from the north of Rio Grande do Sul to the state of Espirito Santo, around Vitoria, there are a number of mountain ranges formed by crystalline massifs along the coast, now nearing the ocean and forming rough coasts, now receding and producing broad salt marshes where several isolated hills remain to attest to their past existence.

From Vitoria (SE) up to Rio Grande do Norte, granites and gneisses of the crystalline are replaced by the Barreiras Formation sandstones making up the physiognomy called Tabuleiros (Mesas).

Mountains forming the coastal ranges either from the crystalline or the Barreiras Formation are made up of rocks bearing several ores. These ores give rise to soils with diverse physical and chemical features. The cliff-like or mountainous topography, in turn, conditions their development, with the occurrence of deep soils at the bottom of valleys and on hillsides, and of shallow soils near the mountain tops.

The whole Brazilian coastline is subject to steam-saturated air currents from the Atlantic which meet the mountain barrier, causing orographic rains. In some areas, annual rainfall exceeds 600 mm. These topography-related rains cause natural slippages and landslides, making it a dynamic, mosaic-like landscape of various vegetation extensions in various successive stages.

In addition, due to the presence of shallow soils, there are a large number of springs on these ranges forming streams all along them and an intricate drainage network.

The down-slopes under which coastal forests grow filtrate a diffuse light which, added to the high rainfall, favours the development of many tree, shrub, grass and epiphytic species in copses. The forest composition comprises several formations. In the North East it includes species common to the Amazon forests. In the South there are the same species as found in the Upper Uruguay Basin, and the flora along them includes species found in the Central Region forests.

Under this set of conditions, there grows an extremely complex and little-known vegetation, broadly described as the Mata Atlantica (the Atlantic Forest). Such a complex make-up is due to its latitudinal distribution, since climates vary widely from Rio Grande do Sul up to Rio Grande do Norte, as well as from the foothills up to the ridges and over the mountains. In addition to these variations, soils also differ on the exposed sides of the mountains, with changes caused by the watersheds as well. It should also be stressed that past climates in Brazil favoured both forest retraction and expansion, with the resulting increase in the wealth of species either due to speciation processes or to the contribution of different floras.

These climatic changes, although fairly well studied in the Amazon and the Middle West, show little evidence of their effects on coastal forests. As a result, just as in the Amazon, different kinds of forest may be said to exist along the Brazilian coastal ranges. Related factors prompt the occurrence in these forests of many plant and animal species with few individuals, causing them to be richer and more diversified in tropical areas.

Current estimates indicate that approximately 5% of the whole area originally covered with these forests are maintained on the steeper hillsides. They are associated with the low human population rates which make it urgent to attempt an interdisciplinary effort to acquire further knowledge about these forests.

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