Monte Alegre várzea


The Monte Alegre várzea is an ecoregion of seasonally flooded várzea forest along the Amazon River in the Amazon biome.

Location

The várzea forests of this ecoregion extend along the low, seasonally flooded rivers of the central and lower basin of the Amazon River, including a large part of the Madeira River basin, the mouth of the Purus River, tributaries of these rives and an isolated patch of várzea along the Mamoré River between Bolivia and Brazil.
Major population centers in or near the ecorgion are Manaus, Itacoatiara, Coari and Óbidos.
The ecoregion adjoins the Madeira-Tapajós moist forests to the southeast and the Uatuma-Trombetas moist forests and Japurá-Solimões-Negro moist forests to the north.
The Purus-Madeira moist forests lie to the west of the Madeira and the south of the Amazon.
The Purus várzea is upstream along the Solimões and Purus rivers and their tributaries.
The Gurupa várzea is downstream along the Amazon.

Physical

Elevations range from in the east, where the Tapajós meets the Amazon river, to on the Madeira.
The soils are fertile sediments formed in the present Holocene epoch, carried down from the Andes.
The annual floods renew the sediments, making very rich soils compared to the higher terra firme on either side of the várzea.
The river waters, loaded with sediment, rise by each year, flooding the land for as long as eight months.
The river course through the floodplain constantly shifts over time, creating oxbow lakes, levees, meander swales and bars.
These landscape elements support diverse vegetation, predominantly seasonally flooded tropical evergeen rainforest.
Typically the levees are relatively high, formed by the deposit of sediments along the river margins.
Behind them the land slopes down, flattens out and then rises to the terra firme forest.
The area behind the levees holds canarana grassland and lakes that expand and contract with the flood cycle.

Climate

The Köppen climate classification is "Af": equatorial, fully humid.
Average monthly temperatures range from with an annual average of.
Average annual rainfall in the east is less than, while in some parts of the Madeira in the west it exceeds.

Ecology

The ecoregion is in the Neotropical realm and the tropical and subtropical moist broadleaf forests biome.

Flora

The main vegetation types are aquatic vegetation, permanent swamp vegetation, succession vegetation and forest mosaics.
Typically there are fewer tree species in the várzea than on terra firme, although many trees are common to both environments.
Trees in the várzea are usually shorter than on terra firme, with a canopy of up to.
There are some palms, and often a dense understory of plants in the genus Heliconia and families Zingiberaceae and Marantaceae.
Tree species that grow only in wetlands include Virola surinamensis, Calycophyllum spruceanum and Açaí palm.
The economically valuable palms Astrocaryum jauari and Mauritia flexuosa are common on the floodplain.
Other trees that feed the fruit-eating fish that enter the forest during flood periods are the yellow mombim, socoró and tarumã.
Grasses in the canarana areas include Echinochloa and Hymenachne species, with tall grasses along the river margin such as Gynerium sagittatum, Paspalum repens and Echinocloa polystachya.
Shrubs include Coccoloba ovata, Eugenia inundata, Ruprechtia ternifolia and Symmeria paniculata.
Slightly higher up there are early succession trees such as Acosmium nitens, Buchenavia macrophylla, Cecropia latiloba, Crateva benthamii, Ficus anthelminthica, Machaerium leiophyllum, Macrolobium angustifolium, Piranhea trifoliata, Pseudobombax munguba and Tabebuia barbata.
Higher up again, but still in flooded areas, trees include Calycophyllum spruceanum, Ceiba pentandra, Couroupita guianensis, Hura crepitans, Pirahnea trifoliata, Virola surinamensis, Genipa americana, Hevea brasilienses, Lecointea amazonica, Sterculia elata and Rheedia brasiliensis.

Fauna

The ecoregion is home to 200 species of mammals including jaguar, ocelot, South American tapir, capybara, kinkajou and white-lipped peccary.
The hairy-tailed bolo mouse, and Amazonian sac-winged bat are endemic.
Aquatic mammals include Amazon river dolphin, tucuxi and the endangered Amazonian manatee is also endangered.
The giant otter is also endangered.
Large reptiles include black caiman, spectacled caiman and green anaconda.
Primates include spider monkey, Venezuelan red howler, common squirrel monkey, bare-eared squirrel monkey and red-handed tamarin.
Endemic primates include Hoffmanns's titi, ashy black titi, Hershkovitz's titi, Santarem marmoset and white-footed saki.
Endangered primate include white-bellied spider monkey, Peruvian spider monkey, white-cheeked spider monkey, white-nosed saki, black bearded saki and pied tamarin.
681 species of birds have been reported, including herons and egrets, whistling ducks, sharp-tailed ibis '', ibis, and the roseate spoonbill.
Endemic birds include ash-throated crake, plain-breasted ground dove, red-shouldered macaw, green-rumped parrotlet, scaled ground cuckoo, and stygian owl.
Endangered birds include sun parakeet, wattled curassow, varzea piculet, green-thighed parrot and red-necked aracari.

Status

The World Wildlife Fund lists the ecoregion as "Critical/Endangered".
The ecoregion is threatened by contamination of the water and fish by gold mining, and heavy sedimentation caused by destruction of the forests. Huge areas of the floodplain forests are cleared and burned by ranchers to create pastures for livestock.
Global warming will force tropical species to migrate uphill to find areas with suitable temperature and rainfall.
Low, flat, deforested ecoregions such as the Monte Alegre várzea are extremely vulnerable.