Purus Varzea forests
Purus Varzea forests are a unique type of flooded woodland found along the western tributaries of the Amazon River Basin, including notable rivers like the Solimões and Juruá. This biome is characterized by its seasonally inundated environment, which creates an interface between freshwater and terrestrial ecosystems, resulting in extraordinary species diversity, particularly among birds and fish. The area supports a range of wildlife, including endangered species like manatees and giant otters, while also serving as a critical resource for Indigenous peoples who rely on it for their livelihoods.
During the dry season, terrestrial animals such as giant armadillos and anteaters inhabit the forest, but they are displaced during floods, which can raise water levels by up to 20 feet. In contrast, the flooded conditions create a rich habitat for large fish species, many of which are sought after in aquariums. The forests are also home to various primates, with certain species, such as white uakari monkeys, uniquely adapted to life within this biome. However, the Purus Varzea faces significant threats from human activities such as deforestation, overfishing, and climate change, which complicate conservation efforts. Protected areas like the Mamirauá and Amanã Sustainable Development Reserves are in place to help safeguard these vital ecosystems.
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Subject Terms
Purus Varzea forests
- Category: Forest Biomes.
- Geographic Location: South America.
- Summary: Among the most extensive of the Amazon flooded forest biomes, the Purus Varzea offers intense species abundance and diversity.
The Purus Varzea Forests biome is a swath of flooded woodlands that line the western tributaries of the Amazon River Basin, including the Solimões River, much of the Juruá, central Purus, and Japura-Caquetá Rivers. The Purus varzea biome represents the flooded forests of the seasonally inundated river basins of the central Amazon. Bird and fish diversity are extraordinary, but terrestrial mammal diversity is low, due to the periods when the entire area is underwater.
This biome, because it encompasses aquatic super-highways where boats are the primary transportation method, is increasingly more affected by human activities than surrounding rainforests. Varzea biomes share a single common trait—that they are an interface between freshwater and terrestrial ecosystems, where seasonally a tree can be either on dry land or completely submerged in water. This unique and threatened area supports not only a plethora of endangered species such as manatee and giant otter, but also provides for many Indigenous peoples who have become largely displaced from elsewhere.
Biodiversity
In the dry season, the Purus varzea is used by some of the giants of the Amazon: the giant armadillo and the giant anteater. However, when the region floods, all such terrestrial animals seek higher ground, as the river can rise as much as 20 feet (6 meters), making the varzea forest a submerged aquatic environment. During these flood stages, another set of giants replaces the mammals—some of the largest fish in the Amazon call these forests home. These include the pacu (Metynnis and Mylossoma), tambaqui (Colossoma macropomum), pirarucu (Arapaima gigas), sardinha (Triportheus angulatus), and the piranha (Serrasalmus spp.).
Many aquarium fish that are familiar to hobbyists around the world originate from these flooded forests, including discus, many cichlids (Cichlasoma genus), tetras, and catfish. Fish greatly outnumber birds and mammals here, and often fill the ecological role as seed dispersers and grazers.
Two primates are almost entirely restricted to this biome: the white uakari monkeys (Cacajao calvus calvus) and blackish squirrel monkeys (Saimiri vanzolinii). Monkeys are able to take refuge in the trees even during the flood season, and thus remain permanent residents. Other primates include monk sakis (Pithecia albicans), endangered black-chinned emperor tamarins (Saguinus imperator), tamarins (S. mystax), night monkeys (Aotus nancymaae), and titi monkeys (Callicebus dubius).
Over 600 species of birds have been reported from this region; many of the varzea residents are familiar aquatic species like egrets, herons, ducks, ibis, spoonbills, and herons. Other birds that are adapted for water are common residents here, including kingfishers.
The largest tree in the varzea biome, kapok (Ceiba pentandra), usually forms the emergent canopy, and is propped up by enormous buttress roots. Other trees characteristic of the biome are Parkia inundabilis, Septotheca tessmannii, Coumarouna micrantha, Ceiba burchellii, Ochroma lagopus, and Manilkara inundata.
Threats and Conservation
Many threats confront the forests of these and other varzea biomes. Their accessibility to humans—especially during flooding season—makes them susceptible to both deforestation and overfishing pressures. Overharvest of aquarium fish such as the discus is likely affecting local populations. Cattle ranching, large-scale logging, and gold mining also threaten the forests. Climate change is also a concern; ironically, this region is not immune from drought. With entire habitats and biota having evolved around dynamic seasonal flooding, a change to a drier regime—while not certain, but a future possibility—will wreak havoc on many species here and their interrelations.
Meanwhile, along many tributaries, people have set up gold mining operations; some of these use mercury in operations and cause contamination of the water, which impacts both human and wildlife populations. Increasingly, large-scale cattle operations are expanding into margin pasture areas, and often result in deforestation of varzea forests for seasonal grazing.
Some efforts have been made at the conservation of the region. The Mamirauá Sustainable Development Reserve, Amanã Sustainable Development Reserve, and Jaú National Park help to preserve the region.
Bibliography
Daly, D. C., and J. D. Mitchell. “Lowland Vegetation of Tropical South America.” In Imperfect Balance: Landscape Transformations in the Precolumbian Americas, edited by D. L. Lentz. New York: Columbia University Press, 2000.
Del-Rio, Glaucia, et.al. "Birds of the Jurua River: Extensive Varzea Forest as a Barrier to Terra Firme Birds." Journal of Ornithology, vol. 162, pp. 565-77. Apr. 2021, doi.org/10.1007/s10336-020-01850-0. Accessed 30 Nov. 2024.
Ducke, A. and G. A. Black. “Phytogeographical Notes on the Brazilian Amazon.” Anais da Academia Brasileira de Ciências 25 (1953).
Junk, Wolfgang J., et. al. “The Várzeas of the Brazilian Amazon River: Living With the Flood Pulse.” River Culture: Life As A Dance to the Rhythm of the Waters, 2023, 469-95, doi.org/10.54677/BVVB3482. Accessed 30 Nov. 2024.
Prance, G. T. “Notes on the Vegetation of Amazonia III. The Terminology of Amazonian Forest Types Subject to Inundation.” Brittonia 31 (1979).