Location and General Description
The Irrawaddy River flows into the Bay of Bengal, and its delta is made up of mangroves and freshwater swamp forests of this ecoregion. This ecoregion is an extremely fertile area because of the riverborne silt deposited in the delta. The southern portion of the ecoregion transitions into the Myanmar Coastal Mangroves [IM1404] and is made up of fanlike marshes with oxbow lakes, islands, and meandering rivulets and streams.
Topographically the region is primarily flatlands. The western part of the region is bounded by the Rakhine (Arakan) Yomas, with the highest elevation at about 1,287 m to the north, tapering down to the south to 428 m.
The geological formation in the west is composed of shale and sedimentary rocks. The soil is yellow brown to gley soil, and to the east it is sandy loam and calcareous. To the north the soils are lateritic. The region is rich in limestone. Along riverbanks there are loamy sands deposited by the rivers. Toward river mouths the soil is more loamy as the result of tidal actions and marshes.
The region is made up of a mix of deciduous forests. The forests to the north support teak, Xylia kerri, Salmalia malabrica, S. insigni, Milletia pendula, Dalbergia kurzii, Spondias pinnata, Lannea grandis, Terminalia balerica, Anogeissus accuminata, Eugenia spp., Terminalia tomentosa, T. chebula, Vitex spp., Schleichera oleosa, and Manglietia insignis. The forests to the south are made up of Xylia keri, Salmalia malabrica, S. insigni, Dalbergia kurzii, Lannea grandis, Teminalia balerica, T. chebula, Eugenia spp., Anogeissus acuminata, Terminalia spp., Vitex pubescens, Adina cordifolia, and Spondias pinnata.
Bamboo breaks of Melocanna bambusoides also are prevalent. Melocanna bambusoides is found extensively on the eastern aspect of Arakan Yomas. Other species are Dinochloa m'clellandi, Oxytenanthera albo-ciliata, Bambusa tulda, Dendrocalamus longispathus, Cephalostachyum pergracile, and Bambusa polymorpha. Bamboo associates to the north are Melocanna bambusoides, Bambusa polymorpha, Cephalostachyum pergracile, and Bambusa tulda.
Large mammals have been largely extirpated from this ecoregion. According to a survey conducted by Richard Salter in 1982, he found only fifteen Asian elephants in this ecoregion. Deep species such as sambar (Cervus unicolor), hog deer (C. porcinus), and wild boar (Sus scrofa) appeared to be numerous. Tigers and leopards were once abundant as well. Today, however, this ecoregion harbors very little of its original biodiversity. There are no endemic mammals in this ecoregion.
This ecoregion is an important wetland for migratory birds. These birds arrive by the thousands every year and include plovers (Mongolian plover [Charadrius mongolus]), sandpipers (spoon-billed sandpiper [Eurynorhynchus pygmeus]), black-tailed godwit (Limosa limosa), Eurasian curlew (N. arquata), Temminck's stint (C. temminckii), and Asian openbill stork (Anastomus oscitans). Unfortunately, their populations have been steadily declining. There are also numerous resident and wintering waterbirds. These include common waterbirds such as bitterns (cinnamon bittern [Ixobrychus cinnamomeus]), herons and egrets (Indian pond-heron [Ardeola grayii], Pacific reef-egret [Egretta sacra]), storks (woolly-necked stork [Ciconia episcopus]), ibis (black-headed ibis [Threskiornis melanocephalus]), ducks (spot-billed duck [Anas poecilorhyncha]), jacanas (pheasant-tailed jacana [Hydrophasianus chirurgus]), pratinoles (oriental pratincole [Glareola maldivarum]), and terns (black-bellied tern [Sterna acuticauda]). There are no endemic birds in this ecoregion.
Reptiles such as the estuarine crocodile (Crocodylus porosus) may still exist, but the population probably is low. In 1982 the population was estimated to be about 4,000, but they have been exploited since 1978 by the Pearl and Fishery Corporation, which reared hatchlings at a farm in Rangoon. The hatchery is still in existence.
The Irrawaddy is one of the most heavily silted rivers in the world. The sedimentation rate was 299 million tons/year, and it ranked fifth behind the Yellow, Ganges, Amazon, and Mississippi in silt deposition. Today the sedimentation rate is worsening as deforestation and agricultural erosion continue at a phenomenal rate.
The future survival of wildlife in this ecoregion is bleak. There are no large mammals of sizable populations because of habitat fragmentation. The situation for birds is no better. Birds do not receive much attention from the staff of the Forest Department or the Nature and Wildlife Conservation Division. There are no protected areas in this ecoregion.
Types and Severity of Threats
The ecoregion has experienced agricultural expansion, firewood extraction, commercial logging, fish and prawn culture, and other development works. It is highly degraded, and the future threats remain the same as those that have destroyed the habitat to this point.
Justification of Ecoregion Delineation
MacKinnon divided the Indochina bioregion into fifteen biogeographic subunits nested within seven major biounits. Each of these biounits and biogeographic subunits contains a mix of biomes. For instance, the Burmese coast biounit (04) is made up mostly of tropical wet evergreen forests but also includes tropical montane evergreen forests, semi-evergreen rain forests, dry dipterocarp forests, and large areas of freshwater swamp forests and mangroves in the Irrawaddy River delta. We assigned these distinct habitat types into separate ecoregions. Thus MacKinnon's Burmese coast biounit is represented by four ecoregions: the Myanmar Coastal Rain Forests [IM0132], Irrawaddy Freshwater Swamp Forests [IM0116], Myanmar Coastal Mangroves [IM1404], and Mizoram-Manipur-Kachin Rain Forests [IM0131].
This region does not correspond well to Udvardy's biogeographic provinces. The Irrawaddy Freshwater Swamp Forests [IM0116] and Myanmar Coastal Mangroves [IM1404] are contained within Udvardy's Burman rain forest.
References for this ecoregion are currently consolidated in one document for the entire Indo-Pacific realm.
Indo-Pacific Reference List
Prepared by: U Saw Han and Saw Tun Khaing