Indochina mangroves
Mekong Delta viewed from space. Source: National Aeronautics and Space Administration
The Indochina mangroves ecoregion is a disjunctive coastal forest biome located on parts of mainland Southeast Asia. Among the most diverse and extensive mangrove ecosystems in the world, this ecoregion hosts a total of 528 vertebrate taxa; furthermore , it provides very important habitat for some of the Earth's rarest waterbirds. The largest block of Indochina mangroves in the Mekong River delta suffered habitat degradation from defoliants sprayed during the Vietnam War. The approximate areal extent of this mangrove ecoregion is 10,400 square miles.
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) damaged 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 mudflats have lower diversity than mangrove [[habitat]s] in the south. This low mangrove species 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 the Api-api mangrove tree (Avicennia alba). Next, along a gradient of decreasing exposure and submergence by seawater are Tall-stilt Mangrove (Rhizophora apiculata) andSmallflower Bruguiera (Bruguiera parviflora), the latter tree which becomes established after about five years and grows to displace Avicennia after aprroximately twenty years. Higher ground, subject to conditions of brackish water rather than seawater, is dominated by White Mangrove (Avicennia officinalis),Crabapple Mangrove (Sonneratia caseolaris), Nipa Palm (Nypa fruticans), and Mangrove Date Palm (Phoenix paludosa).
Biodiversity Features
With a remarkable biodiversity, especially for mangrove ecoregions, there are a total of 528 vertebrate taxa recorded in this ecoregion. There is a diverse mammalian fauna, including numerous large framed species and a plethora of bat taxa. Among avifauna, the ecoregion holds a number of rare waterbirds. There are only two amphibian species occurring in the Indochina mangroves, both of which are anuran taxa; however, there is a large array of reptiles found here. Furthermore, the Mekong Delta supports a valuable fishery, especially for shrimp.
Tbe endangered Siamang. Source: Suneko
Mammals
There are no endemic mammals in the ecoregion, but many mammalian species are known to inhabit this mangrove ecoregion, including the Tiger (Panthera tigris), Malayan Tapir (Tapirus indicus), and Siamang (Hylobates syndactylus).
Avifauna
Numerous waterbirds use the remaining parts of these mangroves, and many of them are endangered. Included in this assemblage are the Lesser Adjutant Stork (Leptoptilos javanicus VU), Storm's Stork (Ciconia stormi EN), White-winged Duck (Asarcornis scutulata EN), and Spot-billed Pelican (Pelecanus philippensis NT).
Amphibians
Only two amphibians are found in the Indochina mangroves, including the Spectacled Toad (Duttaphrynus melanostictus), found expecially on backshores and river banks; Asian Brackish Frog (Fejervarya cancrivora), found in estuarine settings.
Reptiles
There are several reptile species of conservation significance in this ecoregion, including the Monitor Lizard (Varanus salvator), the False Gavial (Tomistoma schlegelii), and the Saltwater Crocodile (Crocodylus porosus).
Current Status
This ecoregion is highly threatened in nearly every locale of its occurrence. About half of the mangroves in southern Vietnam were destroyed by Agent Orange, tank movements, Viet Cong movements, and bombing during the war. Since then, however, the country 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 kilometres) cover a mere 820 km2 (three percent) of the ecoregion-the majority of the ecoregion is threatened by a multitude of ongoing human activities (table 1).
Table 1. Protected Areas That Overlap with the Ecoregion.
|
Protected Area |
Area (km2) |
IUCN Category |
|
Do Son |
30 |
UA |
|
Unnamed |
60 |
unknown |
|
Xuan Chuy |
40 |
unknown |
|
Con Dao |
190 |
II |
|
Botum-Sakor |
250 |
II |
|
Dong Peng |
200 |
VIII |
|
Peam Krasop |
50 |
IV |
|
Total |
820 |
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
Indochina mangroves. @ WWF-Canon / Peter Denton 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.
References
- S. Gebhardt, L. D. Nguyen, and C. Kuenzer. 2012. Mangrove Ecosystems in the Mekong Delta. Overcoming Uncertainties in Inventory Mapping Using Satellite Remote Sensing Data. In (eds.): Renaud, F. and C. Kuenzer, 2011: The Mekong Delta System - Interdisciplinary Analyses of a River Delta. Springer, ISBN 978-94-007-3961-1, pp. 315–330
- P. Leinenkugel, T. Esch, and C. Kuenzer. 2011. Settlement Detection and Impervious Surface Estimation in the Mekong Delta Using Optical and SAR Data. In: Remote Sensing of Environment 115 (12) 2011, pp. 3007–3019.
- F. Renaud and C. Kuenzer. 2012. Introduction. In (eds.): Renaud, F. and C. Kuenzer 2012: The Mekong Delta System - Interdisciplinary Analyses of a River Delta. Springer, ISBN 978-94-007-3961, pp. 3–6
- A. Royan. 2010. Significant mammal records from Botum-Sakor National Park, Southwest Cambodia. Cambodian Journal of Natural History, 2010 (1): 22-26.
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