Among the most diverse and extensive mangrove ecosystems in the world, this ecoregion provides extremely important habitat for some of the world's rarest waterbirds. The largest block of Indochina Mangroves in the Mekong River delta suffered large-scale habitat loss from defoliants sprayed during the Vietnam War.

Location and General Description

Mangrove forests occur in coastal areas of regular flooding by tidal or brackish water and develop on saline gleysols. The extent of mangroves in coastal areas of Thailand, Cambodia, and Vietnam was once high, but much of this area has been destroyed. Extensive mangrove forests once occurred around Pattaya in Thailand and in the areas of Veal Renh and Kompong Som Bays in Cambodia. The absence of more extensive mangrove stands in Cambodia is strongly related to the rocky coastline and lack of major estuaries or river deltas. In Vietnam, the largest area of remaining mangroves is around Camou Point at the southern tip of Vietnam, with smaller areas in the Mekong delta region, in south central Vietnam around Cam Ranh Bay, and in northern Vietnam in the Red River delta area. The central coast of Vietnam is largely free of mangroves because of the exposed coastline, absence of major river deltas, and low tidal fluctuations in this area. Far more extensive stands of mangroves once occurred around the Red River delta in northern Vietnam. The extensive military use of defoliants and napalm during the Vietnam War (1962-1972) destroyed a major part of mangrove forests in southern Vietnam, but these areas are slowing recovering under active reforestation programs today.

Mangrove diversity in the Indochina Mangroves ecoregion is high, with the presence of approximately 60 percent of the mangrove species known from anywhere in south and southeast Asia and Indonesia. The most diverse mangrove communities occur in areas that are inundated at high tide but are otherwise influenced by freshwater flows. Mangrove forests in the Red River delta and associated estuaries and mud flats have lower diversity than mangrove habitats in the south. This low mangrove diversity in the Red River delta area is the result of a combination of cooler growing conditions and a longer and more intense period of human impact.

Mangrove forests typically exhibit strong patterns of zonation. The pioneer species along the open coastline is typically Avicennia alba. Next along a gradient of decreasing exposure and submergence by sea water are Rhizophora apiculata and Brugiera parviflora, which become established after five or six years and grow to replace Avicennia after about twenty years. Higher ground subject to conditions of brackish water rather than seawater is dominated by Avicennia officinalis, Sonneratia caseolaris, Nypa fruticans, and Phoenix paludosa.

Biodiversity Features

There are no endemic mammals in the ecoregion, but many species are known to use mangroves, including the tiger (Panthera tigris), tapir (Tapirus indicus), and siamang (Hylobates syndactylus). Numerous waterbirds use the remaining parts of these mangroves, and many of them are endangered. Included in this assemblage are the lesser adjutant (Leptoptilos javanicus), Storm's stork (Ciconia stormi), white-winged wood duck (Cairina scutulata), and spot-billed pelican (Pelicanus philippensis).

There are several reptile species of conservation significance in this ecoregion, including the monitor lizard (Varanus salvator), the false gavial (Tomistoma schlegeli), and the estuarine crocodile (Crocodylus porosus). The Mekong delta supports a valuable fishery, especially for shrimp.

Current Status

This ecoregion is highly threatened in nearly every site where it occurs. About half of the mangroves in southern Vietnam were destroyed by Agent Orange, tank movements, and bombing during the war. Since then, however, the government has launched a large-scale reforestation program. Although protected areas have been created to conserve these mangroves-seven small protected areas (average size of only 117 square kilometers (km²)) cover a mere 820 km² (3 percent) of the ecoregion-the majority of the ecoregion is threatened by a multitude of human activities (table 1).

Table 1. Protected Areas That Overlap with the Ecoregion.

Mangrove forests often are treated as wasteland to be cleared for development. In Thailand, large areas of the ecoregion have been logged, primarily to produce charcoal to supply the domestic market and markets in Malaysia, Singapore, and Hong Kong . Fifty percent of the mangrove habitat in Thailand was lost between 1975 and 1991. The species most heavily exploited for charcoal are Rhizophora apiculata, R. mucronata, Avicennia marina, and Xylocarpus spp. Thailand's mangroves are also severely affected by prawn farming.

Types and Severity of Threats

In addition to exploitation for the domestic and international commercial markets, trees are cut or lopped for domestic consumption as fuelwood. In Vietnam and in Thailand, large areas are cleared for aquaculture, salt ponds, and agriculture. Poaching and illegal trade of animal products are another important threat, especially to estuarine crocodiles and monitor lizards. Fishing with explosives and trawlers with drag-nets has also caused extensive damage to this sensitive ecosystem.