Southeastern Asia: Southern Cambodia stretching into Thailand and Vietnam

The Cardamom Mountains Rain Forests [IM0106] ecoregion sits astride the Cardamom Mountains (locally known as Kravanh) and the Elephant Range (locally known as Dom rei) in southwestern Cambodia and extends slightly across the border into southeastern Thailand. It is separated from the nearest other rain forest by the vast, dry Khorat Plateau in central Thailand to the north and east and by the Gulf of Thailand in the west. The Cardamom Mountain rain forests are considered by some to be one of the most species-rich and intact natural habitats in the region, but they are also one of the least explored. Although scientific explorations have begun to reveal the unique biological riches in other intact and hitherto unexplored rain forests such as in the Annamite Mountain Range, the Cardamom Mountains have been neglected until recently (Fauna & Flora International 2000). It would not be surprising if this ecoregion, which contains the essential ingredients for speciation (i.e., isolation, moist and stable conditions, intact and undisturbed habitat, and rugged terrain), yields a number of new species that will add to its biological diversity.

  • Scientific Code
  • Ecoregion Category
  • Size
    17,100 square miles
  • Status
    Relatively Stable/Intact
  • Habitats

Location and General Description
The ecoregion represents the original extent (see MacKinnon 1997) of the wet evergreen forests that cover the Cardamom and Elephant mountains in southwest Cambodia and along the mountains east of Bangkok, in Thailand. The small Dao Phu Quoc Island, which belongs to Vietnam but is just off the southern coast of Thailand, is also included in this ecoregion.

The mountain range rises from sea level to more than 1,500 m to intercept and extract the moisture from the monsoon winds. The orientation of their topography along the Gulf of Thailand produces unusually wet conditions of 3,000-4,000 mm annual rainfall on the southwestern slopes of these ranges, and only a short dry season occurs. The mean annual rainfall total exceeds 5,000 mm in the Emerald Valley near Bokor in the Elephant Range, whereas Kirirom, more distant from the coast in this range, receives about 2,000 mm annually. These ranges are largely Mesozoic sandstone, with localized areas of limestone and volcanic rock. Younger basalts in these ranges have produced rich supplies of gemstones (rubies, sapphires, and zircons). Also included in the ecoregion is the northeastern part of this mountain unit, composed of granite ridges that reach a maximum elevation of 1,813 m at Phnom Aural, the highest point in Cambodia. These ranges rise rapidly from the coast, leaving only a narrow coastal plain. They gently grade down into the interior lowlands to the north and northeast.

The ecological and floristic composition of these wet evergreen forest communities is poorly studied, and there would undoubtedly be recognizable communities within this association were it better known and investigated. From limited available data, local endemism appears to be significant. One of the most abundant canopy species in wet evergreen forests is Hopea pierrei, a small tree of limited distribution outside of this area. Other dipterocarps once formed the dominant canopy elements of a tall evergreen forest in coastal area, with Shorea hypochra, Anisoptera costata, Dipterocarpus costatus, and Hopea odorata all abundant. Also important as canopy trees in this area were Parkia streptocarpa, Heritiera javanica, Swintonia pierrei, and Syzygium cinereum. These forests have largely disappeared today.

In addition to typical lowland evergreen rain forests, the southern slopes of the Elephant Mountains support an unusual dwarf rain forest community reaching no more than 12 m height in areas of poorly drained depressions. The dominant species in these waterlogged sites typically are Dacrydium elatum and Podocarpus neriifolius, with a scattered distribution of P. (Nageia) fleuryi and P. (Dacrycarpus) imbricatus.

Upper elevation areas above about 700 m in the Cardamom and Elephant Mountains contain a distinct montane forest community. These forests are structured with dense evergreen tree canopies reaching up to 30 m in height. The Fagaceae are notably dominant, including Lithocarpus cambodienseis, L. guinieri, L. farinulenta, L. harmandii, and Castanopsis cambodiana. Also important are species of Lauraceae (Cinnamomum and Litsea) and Myrtaceae (Syzyngium and Tristania), whereas legumes are less common. There is a rich understory in these habitats, with shrubs of Rubiaceae and Euphorbiaceae, palms (Arenga pinnata and Pinanga cochinchinensis), arborescent ferns (Cibotium, Cyathea, and Oleandra), Pandanus, and Araliaceae. Epiphytes, most notably orchids, may often be abundant, particularly in sites that receive frequent fogs or mists.

A distinctive dwarf forest 5-10 m in height is present on the acid and skeletal soils on the sandstone plateau of the southern Elephant Mountains. This community typically is dominated by Dacrydium elatum, with another conifer, Podocarpus (Dacrycarpus) imbricatus, also commonly present. Other important associates in this dwarf forest are a variety of Fagaceae and Myrtaceae, Vaccinium viscifolium, and Schima crenata. On ridgelines or other areas habitually exposed to strong winds, this community reaches no more than 5 m height. Sphagnum bogs are also present.

A prominent area of Pinus merkusii occurs on the Kirirom Plateau in the Elephant Range, where P. merkusii grows with Dipterocarpus obtusifolius, Rhodomyrtus tomentosa, Phyllanthus officinalis, and a variety of Melastomataceae and Rubiaceae.

Biodiversity Features
The Cardamom Mountains Rain Forests [IM0106] ecoregion is one of the few ecoregions in Indochina with intact rain forests that still have potential for landscape-level conservation actions. Natural disturbance regimes and large predator-prey interactions still occur. Much of the ecoregion's biota probably remains intact. This combination of factors makes the ecoregion unique in Indochina.

The ecoregion is considered to harbor more than 100 mammal species. There are no known ecoregional endemics. Nevertheless, there are several threatened species, including the endangered tiger (Panthera tigris), Asian elephant (Elephas maximus), clouded leopard (Pardofelis nebulosa), dhole (Cuon alpinus), gaur (Bos gaurus), banteng (Bos javanicus), khting vor (Pseudonovibos spiralis), pileated gibbon (Hylobates pileatus), and serow (Capricornis sumatraensis). It is possible that several large mammals that have disappeared from Indochina's forests-the Sumatran (Dicerorhinus sumatrensis) and Javan rhinoceros (Rhinoceros sondaicus) are examples-may still find safe haven in these forests.

The elephant population in the Cardamom and Elephant ranges is widely considered to be the most important in Cambodia and among the largest in Indochina, although surveys are necessary to confirm this assertion. These intact forests were also recognized as a Level I TCU (Dinerstein et al. 1997), where the large habitat areas allow the predator-prey dynamics associated with tigers to occur under undisturbed conditions. The Cardamom Range probably harbors the highest density of pileated gibbons throughout the species' distributional range (Boonratana 1999a).

The bird fauna is estimated at more than 450 species and includes 2 strict endemic species (table 1). However, in all probability many more endemic species will be added to this list after more comprehensive surveys.

Table 1. Endemic and Near-Endemic Mammal Species.

  Family Common Name Species
Phasianidae Chestnut-headed partridge* Arborophila cambodiana*
Phasianidae Siamese partridge* Arborophila diversa*

An asterisk signifies that the species' range is limited to this ecoregion.

Recent surveys conducted by the Flora and Fauna International (FFI) have found a population of the critically endangered Siamese crocodile (Crocodylus siamensis) and several other small mammals and amphibians (Fauna & Flora International 2000).

Current Status
Because of the low human population of this ecoregion, the forests in Cambodia are relatively intact; however, the areas in southeastern Thailand have been greatly reduced and now exist only in a few protected areas in hilly regions (IUCN 1991). Sixteen protected areas cover about 14,500 km2 (33 percent) of the ecoregion (table 3). Six of these protected areas-Aural, Phnom Bokor, Botum-Sakor, Roniem Daun Sam, Khao Ang Ru Nai, and Phnom Samkos-are larger than 1,000 km2. Phnom Samkos National Park exceeds 3,000 km2.

Table 2. WCMC (1997) Protected Areas That Overlap with the Ecoregion.

  Protected Area Area (km2) IUCN Category
Aural 2,420 IV
Kirirom 250 II
Phnom Bokor 1,580 II
Ream 140 II
Botum-Sakor [IM1402] 1,520 II
Dong Peng [IM1402] 150 VIII
Peam Krasop [IM1402] 80 IV
Roniem Daun Sam 1,980 IV
Khao Ang Ru Nai 1,030 IV
Khao Soi Dao 720 IV
Khao Chamao-Khao Wong 80 II
Khao Khitchakut 70 II
Samlaut 630 VIII
Namtok Phlui 100 II
Phnom Samkos 3,170 IV
Mu Ko Chang 660 II
Total 14,580  

Ecoregion numbers of protected areas that overlap with additional ecoregions are listed in brackets.

Types and Severity of Threats
Despite this high level of formal protection, very few reserves have effective management and workforces; they are paper parks. Several are now under threat from illegal logging operations and from adjacent concessions that encroach on the unprotected protected areas. The wildlife trade has also resulted in widespread hunting throughout Cambodia and Thailand, exacting a heavy toll from endangered wildlife populations. The widespread presence of antipersonnel landmines pose severe threat to both wildlife and humans (including researchers).

Justification of Ecoregion Delineation
The large Indochina biounit (10) identified by MacKinnon (1997) in his analysis of conservation units in the Indo-Malayan realm comprises three subunits that represent the vegetation in the tropical lowland plains, subtropical hills, and temperate montane areas. The largest of these subunits, Central Indochina (10a), is a mix of tropical moist and tropical dry forests. Adjacent to this is the Cardamom Mountains subunit (05d), which also includes the freshwater swamp forests and mangroves of the Chao Phraya river and estuary (MacKinnon 1997). We extracted the tropical wet evergreen vegetation that covers the Cardamom and Elephant mountain ranges (included within MacKinnon's subunits 10a and 05d) and represented it with the Cardamom Mountains Rain Forests [IM0106]. The swamp forests, dry forests, and mangroves were assigned to separate ecoregions.

References for this ecoregion are currently consolidated in one document for the entire Indo-Pacific realm.
Indo-Pacific Reference List

Prepared by: Ramesh Boonratana, Philip Rundel, and Eric Wikramanayake
Reviewed by:


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