Várzea Forests
A várzea forest is a seasonal floodplain forest inundated by whitewater rivers that occurs in the Amazon biome. Until the late 1970s, the definition was less clear and várzea was often used for all periodically flooded Amazonian forests.
Along the Amazon River and many of its tributaries, high annual rainfall that occurs mostly within a rainy season results in extensive seasonal flooding of areas from stream and river discharge. The result is a 10–15 m (33–49 ft) rise in water level, with nutrient rich waters.
The Iquitos várzea ecoregion covers the margins of the upper Amazon and its tributaries. Further down are the Purus várzea in the middle Amazon, the Monte Alegre várzea and Gurupa várzea on the lower Amazon and the Marajó várzea at the mouth of the Amazon. The Marajó várzea is affected by both freshwater and tidal flows.
Várzea forests can be split into two categories: low várzea and high várzea. Low várzea forests can be categorized by lower lying areas where the annual water column has an average height of more than 3 m (10 ft), where the period of flooding is greater than 50 days per year. High várzea forests are categorized as the areas where the average annual water column is less than 3 m (10 ft) high and flooding periods are less than 50 days per year. Amazonian várzea forests are flooded by nutrient rich, high sediment whitewater rivers such as the Solimões-Amazon, the Purus, and Madeira rivers. This makes the várzea areas distinct from igapós, floodplains from nutrient poor blackwater. The water level fluctuations that the várzea experiences result in distinct aquatic and terrestrial phases within the year. Amazonian white water river floodplains cover an area of more than 300,000 km2 (120,000 sq mi), and várzea forests cover approximately 180,000 km2 (69,000 sq mi) of the Amazon basin. 68% of the Amazonian river basin is located in Brazil, with the remaining areas located in Bolivia, Colombia, Ecuador, French Guiana, Peru, Suriname, and Guyana. The várzea extends from this basin upward into the land before reaching slopes into the terra firme forests.
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