Amazon river dolphin (Inia geoffrensis), Brazil Photograph by WWF/ Andrea Florence   Northern South America: Northeastern Brazil Tropical and Subtropical Moist Broadleaf Forests   3,800 square miles (9,900 square kilometers) -- slightly smaller than Connecticut Critical/Endangered

· A Forest of Rushing Rivers
· Special Features
· Did You Know?
· Wild Side
· Cause for Concern
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A Forest of Rushing Rivers

This ecoregion covers the lower Amazon River basin, between the mouths of the Tapajós and Xingu Rivers. Várzea means "flooded forest," an appropriate name for the inundated area along the rivers’ floodplains. Water surges over the landscape as daily tidal fluctuations meet seasonal flooding from rainfall of close to 100 inches (2,540 mm) per year. In the less rainy season, water levels fluctuate from 6 to 10 feet (2 to 3 m) each day. At the height of the flood season, the daily fluctuations can be 13 to 23 feet (4 to 7 m)! The force of the Amazon River’s rushing floodwaters comes mainly from the sheer volume of water, not from the slope of the land. Sometimes these waters even flow uphill, as ocean tides push against the turbid river water.

Special Features

Tropical humid forests grow along the ever-shifting riverbanks and on islands created by constant sediment deposition. On the clay soils beyond these forests, patches of savanna grow right up to the edge of the terra firma, or dry land. Open lakes are abundant in the lowest parts of these savannas. These habitats rapidly cycle the nutrients that are constantly deposited by the seasonal floods, stabilize flooded soils, and host a great diversity of both terrestrial and aquatic life. The many species that flourish in this ecoregion have evolved to take advantage of the floods for the dispersal of fruit and seeds, for reproduction, or for seasonal migrations.

	The Tapajós and Xingu Rivers are said to be "black waters" because they are stained by dark tree chemicals called tannins. These rivers also lack a sediment load. The Amazon River, on the other hand, is considered whitewater because as sediment carried down from the Andes Mountains churns in the river’s current it gives the water a cloudy, milky-white color.

Wild Side

As dawn breaks, a small arboreal cat called a margay makes its way to a resting place in the trees after a nighttime feast of arboreal rats. Nearby, several titi monkeys emerge from a bed of tangled vines in their favorite sleeping tree and venture out to forage in the understory for the fruits of buriti palm trees. Soon two savanna foxes make their way to the water line, where they find a breakfast of frogs, crabs, and fruit. The quick entrance of spider monkeys swinging through the trees ends the quiet of the morning. These acrobats stir up a pair of scarlet macaws that fly off in a red streak to a quieter tree.

Cause for Concern

The main dangers to this ecosystem lie in human-induced alterations. Forests along the water "highways" of the Amazon have been cleared for timber and also to make room for pasture where livestock can graze. Large-scale agricultural projects and urban sprawl also degrade the land.

For more information on this ecoregion, go to the World Wildlife Fund Scientific Report.