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The Tocantins-Araguaia-Maranhão Moist Forests ecoregion spills across the eastern extreme of the Amazon basin, its edges rimmed by abundant waters. Along one side, the forest meets the shore of the Atlantic Ocean and the mouth of the Amazon River. The Tocantins River carves the forest’s western edge, while the Mearim River marks the border to the south. During five months of the year, a dry season settles over the region, with less than 4 inches (101 mm) of rain falling during each of those months. With the arrival of the wet season, however, an intricate web of streams and rivers weaves through these forests, sculpting the landscape as waterways swell and flood across the flat land. A large mangrove ecosystem borders the region to the north, winding along the mouth and banks of the Amazon River. Annual rainfall in this northern portion is about 100 inches (2,540 mm). To the south, where the climate becomes drier and annual rainfall is only about 60 inches (1,524 mm), the moist forest gives way to cerrado shrublands.
Trees as tall as 100 feet (31 m) rise from dense evergreen communities to meet the sky here. This includes both terra firme, or dry land, and both igapó and várzea flooded forest types. Igapó forests appear where blackwater rivers flood. These rivers are so named because dark tannins stain the water. With such acidity and lack of a sediment load, trees such as Ficus and Clusia thrive in the nutrient-poor, white sands. Várzea forests grow in nutrient-rich soils deposited by the floods of whitewater rivers, whose milky current churns with sediment from the Andes. Várzea forests host diverse tree species such as palms and the important legumous timber tree acapú. Many other rare or threatened trees grow in this ecoregion, including mahogany, jaborandi, and Dicypellium--a timber tree whose bark contains a pleasant-smelling essential oil.
As the first indigo shadows of dusk settle on the trees, the night drama of the forest begins. Red-handed howler monkeys call to each other as they swing through the branches on their way to a tree where they’ll sleep. The threep, threep, threep of a channel-billed toucan echoes in the approaching darkness. Many species of bats wake from their daytime slumber to feast on abundant insects, whose droning reverberates through the rainforest canopy. By day, a sudden commotion begins as a swarm of army ants marches across the forest floor, stirring up other insects and small mammals. Birds such as the black-faced antthrush and the ocellated antbird follow the ants’ march, feasting on insects that flee the path of the charging army. The nocturnal two-toed sloth sleeps high in the canopy, its back covered with a greenish tint from the mold that helps to camouflage the defenseless mammal. Along the water’s edge of a nearby river, a tricolored heron sits poised to strike a small mosquito fish, while in a nearby palm tree a yellow-crowned night heron rests with its head tucked in the shade of its wing. A bounding frog does not go unnoticed as the tricolored heron snatches it midleap.
Human settlements and agricultural conversions pose the primary threats to this ecoregion byse fires to clear the forest for crops and cattle ranches. For more information on this ecoregion, go to the World Wildlife Fund Scientific Report. All text by World Wildlife Fund © 2001
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