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Biological Importance of Indochina
Geography, Climate, and History
As a result of a high diversity of landforms and climatic zones, Indochina supports a wide variety of habitats and thus high overall biodiversity. This diversity has been further increased by the development of areas of endemism as a result of the region's geological and evolutionary history. Fluctuating Pleistocene sea levels and the resulting repeated isolation and reconnection of ecosystems and plant and animal populations have helped to promote speciation (van Dijk et al. 1999), while fluctuations in the relative extent of evergreen forest during glacial episodes have allowed evergreen forest species to evolve in isolation, and further contributed to the high levels of endemism in the region (Baltzer et al. 2001). Centers of plant and animal endemism in the region include the Annamite Mountains and the highlands of southern China and northern Vietnam.
Most parts of the region experience a strongly seasonal climate, with the climate of the south and west of the region dominated by a southwest monsoon season of variable duration and the climate of the northeast of the region dominated by the northeast monsoon in the northern summer. During the northern winter months, drier conditions prevail throughout much of the region under the influence of stable continental Asian high-pressure systems. Within the region, however, a complex array of microclimates exists, with mean annual precipitation varying from under 800 mm in coastal areas of central Vietnam (Nguyen Khanh Van 2000) to almost 8,000 mm in some parts of the central Annamite Mountains (WWF/EC 1997).
Habitats and Ecosystems
Lowland evergreen forests are among the most species-rich in plants in the whole region, and are characterized by significant plant and animal endemism. Lowland evergreen forests formerly covered large areas of peninsular Thailand, as well as smaller areas elsewhere in the region, including the Annamese lowlands of Vietnam. However, due to the abundance of commercially valuable timber species in these forests, they have been among the most heavily exploited of all habitats. Large areas have been cleared and much of the remaining forest is threatened with conversion to cash crops and subsistence agriculture.
Montane evergreen forests are distributed in mountainous areas throughout the region, including the Annamite Mountains of Lao P.D.R. and Vietnam, the Cardamom mountains of Cambodia and the highlands of southern China and northern Vietnam. Relative to most other habitats in the region, these forests support high levels of endemism in amphibians, birds and plants, although less so in mammals. Lower montane evergreen forests have similar plant species richness to lowland evergreen forests, while upper montane evergreen forests are less species rich, and dominated by members of the Fagaceae, Lauraceae and Magnoliaceae families. At higher elevations, on summits and ridge crests, stunted, xerophytic formations dominated by Rhododendron spp. and other members of the Ericaceae family are found. Relative to lowland evergreen forests, montane evergreen forests in Indochina are generally less threatened by overexploitation. However, conversion to cash crops and other land uses is leading to extensive clearance of lower montane evergreen forest in many areas.
Semi-evergreen and mixed deciduous forests are widely distributed in lowland and hill areas throughout the region. Semi-evergreen and mixed deciduous forests are less rich in plant species than lowland evergreen forests and generally support lower levels of plant and animal endemism. These forests support a number of commercially valuable timber species and are targeted for logging in many areas.
Deciduous dipterocarp forests are open forests with grassy under stories, which occur in areas with a prolonged dry season. These forests support relatively few tree species, although they support distinctive plant and animal communities. Formerly these forests covered much of the center of the region, but intact tracts are now largely restricted to western Thailand, and the plains of northern and northeastern Cambodia and adjacent areas of Lao P.D.R. and Vietnam. In these areas, deciduous dipterocarp forests frequently occur in mosaics with patches of semi-evergreen forest, grassland and wetlands, many of which are subject to seasonal monsoon inundation. Until recently, these landscapes supported such impressive herds of large ungulates that they were considered one of the "great gamelands of the world" (Wharton 1957).
The limestone karst formations that are distributed throughout the region, in some places as extensive belts and in other places as isolated outcrops, support highly distinctive ecosystems rich in endemic species. Although, to date, taxonomic groups such as primates and orchids have received the greatest amount of conservation investment and scientific study, limestone ecosystems are of equal, if not greater, significance for other, generally less well-known groups, including cave fish, land snails, and deep-soil invertebrates. While the unsuitability of limestone karst for agriculture means that forest on limestone is generally less threatened by clearance than other forest types in the region, the animal and plant species of limestone ecosystems are often threatened by overexploitation, while the karst formations themselves are, in places, severely threatened by quarrying (L. Deharveng in litt. 2003).
Seasonally inundated swamp forest ecosystems surround Tonle Sap Lake in Cambodia. Formerly these ecosystems were also extensive in the deltas and lower floodplains of the Mekong and Chao Phraya rivers but are now restricted to isolated fragments. These ecosystems are important for a number of globally threatened species, notably large waterbirds.
Mangrove forests were once distributed widely in coastal areas, particularly near estuaries, but are now greatly reduced, as a result of fuelwood extraction and conversion to aquaculture. Other important coastal habitats in the region include intertidal mud- and sandflats, which are the key habitat for many migratory shorebirds. The largest and ecologically most important intertidal ecosystems are found near large rivermouths, most importantly in the Red River and Mekong Deltas of Vietnam, the Inner Gulf of Thailand and the Pearl River Delta in southern China.
Grassland ecosystems range from small, seasonally wet meadows within dry forest landscapes, to the extensive, seasonally inundated grasslands that characterize the inundation zone of Tonle Sap Lake. Seasonally inundated grasslands, which support distinctive assemblages of species, including several globally threatened species, are one of the most threatened ecosystems in the region. They were formerly well distributed in central Thailand and the Mekong Delta, from where they have almost completely disappeared through conversion to agriculture, aquaculture and forestry.
Freshwater ecosystems range from the fast-flowing rocky mountain streams to wide, slow-flowing lowland rivers, such as the Mekong and San, braided by large, partly vegetated sand and rock bars. Expansive open freshwater lakes include Tonle Sap Lake in Cambodia. Rapids are particularly notable as sites of high species diversity, endemism and periodic congregations of fish. Freshwater ecosystems support a large number of globally threatened species, including some of the most threatened species in the region, and provide for the livelihoods of a substantial proportion of the region's human population. However, they are frequently subjected to high levels of human use, often with negative implications for biodiversity. Specific threats to freshwater ecosystems include unsustainable fishing practices and changes to river flow patterns, such as blasting of rapids for navigation channels and hydropower dam construction.
Species Diversity and Endemism
Different estimates put the total vascular plant diversity of Indochina somewhere between 10,000 and 20,000 species, and even apparently conservative estimates suggest that as many as 50 percent of the angiosperms and gymnosperms are endemic to the region (Davis et al. 1986, Campbell and Hammond 1989, Davis et al. 1995, van Dijk et al. 1999). Irrespective of their precision, these figures indicate that Indochina has extraordinarily high plant diversity, and is a major center of plant endemism (Davis et al. 1995). The complex merging of floras in the highlands of Southeast Asia (a region approximately equivalent to Indochina) has no parallel in any other part of the world (de Laubenfels 1975); it represents the convergence of several distinctive temperate, tropical and subtropical floristic regions: the Indian, Malesian (Sundaic), Sino-Himalayan and Indochinese (Schmid 1989). Forest ecosystems support the highest levels of plant species richness, among which montane forests and lowland evergreen forests are the most species-rich. Plant families particularly notable for their high species diversity in the region include the Orchidaceae and Dipterocarpaceae.
On the basis of current knowledge, the Indo-Burma Hotspot harbors about 430 mammal species, of which more than 70 species and seven genera are endemic (Mittermeier et al. 2004). A minimum of 1,200 bird species have been recorded in the hotspot, of which approximately 10 percent are endemic; the majority are resident within the hotspot but a significant proportion are highly migratory, most being species that spend the northern winter in the region and breed further north. Reptiles number nearly 520 species in over 140 genera, of which 12 genera and more than 200 species are endemic. Of the minimum 280 amphibian species (in approximately 40 genera) known to occur in the hotspot, more than 150 are endemic (Mittermeier et al. 2004). Although precise figures are unavailable, Indochina harbors the majority of vertebrate species that occur in the Indo-Burma Hotspot.
Freshwater biodiversity in Indochina is still very poorly known. In 1989, more than 900 freshwater fish species were known from mainland Southeast Asia (a region with a large overlap with Indochina) (Kottelat 1989, Kottelat and Whitten 1996), of which about half might be expected to be endemic (van Dijk et al. 1999). The Mekong Basin has more than 500 fish species, exceeded only by the Amazon and Congo Basins (Dudgeon 2000a). Overall, knowledge of freshwater biodiversity is still at the exploratory stage, with numerous taxonomic uncertainties, large areas unsurveyed, and many species known only from a single locality (Kottelat and Whitten 1996, Baltzer et al. 2001). The large number of fish species newly described in recent years (e.g. Kottelat 1998, 2000, Vidthayanon 2003, Vidthayanon and Jaruthanin 2002, Vidthayanon and Kottelat 2003) suggests that many more fish species may await discovery and description. In general, other freshwater taxa remain significantly less studied than fish. One exception is the Pomatiopsidae, a family of aquatic gastropods, for which the Mekong Basin represents a remarkable centre for radiation, with more than 110 species; this suggests that similarly high diversities might be found in other aquatic invertebrate taxa.
While it is abundantly clear that Indochina supports extraordinary vertebrate species diversity, detailed data on the diversity of many plant, invertebrate, and fish taxa are lacking. Even among mammals, birds and turtles, new species for science are still being regularly discovered in the region, including saola (Pseudoryx nghetinhensis) (Vu Van Dung et al. 1993), large-antlered muntjac (Muntiacus vuquangensis) (Do Tuoc et al. 1994, Timmins et al. 1998), Annamite muntjac (M. truongsonensis) (Pham Mong Giao et al. 1998, Timmins et al. 1998), Annamite striped rabbit (Nesolagus timminsi) (Averianov et al. 2000), Laotian rock rat (Laonastes aenigmamus) (Jenkins et al. 2005), golden-winged laughingthrush (Garrulax ngoclinhensis) (Eames et al. 1999a), chestnut-eared laughingthrush G. konkakinhensis (Eames and Eames 2001), black-crowned barwing (Actinodura sodangorum) (Eames et al. 1999b), Mekong wagtail (Motacilla samvaesnae) (Duckworth et al. 2001), and Zhou's box turtle (Cuora zhoui) (Zhao et al. 1990). The continued discovery of new species and new records for the region, combined with recent advances in taxonomy that are resulting in single widespread species being split into several different species (e.g. Fritz et al. 1997, Alstrom 1998), are leading to continued increases in known species richness and endemism.
Globally Threatened Species
Mammals
Indochina supports three Critically Endangered, four Endangered and eight Vulnerable primate species (IUCN 2002a). Eight globally threatened primate species are endemic to the region: pygmy loris (Nycticebus pygmaeus), yellow-cheeked crested gibbon (Nomascus gabriellae, pileated gibbon (Hylobates pileatus), Delacour's leaf monkey (Trachypithecus delacouri), white-headed leaf monkey (T. poliocephalus), red-shanked douc (Pygathrix nemaeus), black-shanked douc (P. nigripes) and Tonkin snub-nosed monkey (Rhinopithecus avunculus). Unresolved taxonomy within primates, especially in the genera Nomascus/Hylobates, Trachypithecus/Semnopithecus, Pygathrix and Nycticebus, may result in several additional species being recognized, some of which will qualify as globally threatened (e.g. Feiler and Nadler 1997, Nadler 1997, Groves 1998, discussion in Duckworth et al. 1999, Groves 2001).
Other globally threatened, endemic mammals include the recently described saola, which is confined to the evergreen forests of the Annamite Mountains of Lao P.D.R. and Vietnam (Schaller and Rabinowitz 1995). Eld's deer (Cervus eldi) occurs in isolated populations recognized as four different subspecies, two of which are endemic to Indochina: C. e. siamensis and C. e. hainanus (Wemmer 1998). Another enigmatic mammal is a form of otter civet known only from a single specimen from northern Vietnam (Osgood 1932) and unconfirmed reports from northeastern Thailand and southern Vietnam (Schreiber et al. 1989); some authorities (e.g. Corbet and Hill 1992) consider that this form warrants specific status as Lowe's otter civet (Cynogale lowei), distinct from otter civet (C. bennettii), which is otherwise known from the region only from peninsular Thailand.
Several globally threatened mammals with more widespread global distributions occur in the region, including tiger (Panthera tigris), Asian elephant (Elephas maximus), banteng (Bos javanicus), and gaur (B. gaurus) (e.g. Duckworth and Hedges 1998). These species are all severely threatened by overexploitation, and require species-focused conservation interventions. Several of these species remain widely distributed in the region but only as small, isolated groups or individuals, and only some of the larger, more intact blocks of natural habitat support potentially viable populations. For instance, the only known tiger populations likely to represent long-term hope for the species' survival in the region are in western and peninsular Thailand, the Annamite Mountains in Lao P.D.R. and adjacent areas of Vietnam, and Nam Et and Phou Louey protected areas in northeastern Lao P.D.R. (see Duckworth and Hedges 1998). For wild cattle and Asian elephant conservation, Mondulkiri province, Cambodia and contiguous parts of Vietnam, and the Western Forest Complex in Thailand represent the best long-term prospects.
At least one mammal species that occurred in the region is believed to have already gone extinct globally: Schomburgk's deer (Cervus schomburgki), which inhabited the lowland plains and swamps of central Thailand; the last known individual was killed in 1938 (Lekagul and McNeely 1977). A second species that may have gone extinct globally is kouprey Bos sauveli, a magnificent large ungulate that, at least formerly, inhabited the dry forest landscapes of central Indochina (Wharton 1957). Other large mammals now on the verge of extinction regionally include lesser one-horned rhinoceros Rhinoceros sondaicus (a single remnant population is confirmed at a single site in southern Vietnam; Polet et al. 1999) and Sumatran rhinoceros, also known as hairy rhinoceros (Dicerorhinus sumatrensis) (a remnant population is confirmed in Indochina at a single site in southern Thailand).
A number of mammal species in the region currently not assessed as globally threatened are under very high levels of threat. Among those in urgent need of conservation action are Chinese pangolin (Manis pentadactyla), sunda pangolin (M. javanica), and, perhaps, some lorises Nycticebus spp. and Oriental small-clawed otter (Amblonyx cinereus), which are heavily exploited to supply the wildlife trade. There is a need to reassess the global threat status of such species.
Birds
The region's rarest and most enigmatic bird is white-eyed river-martin (Eurychelidon sirintarae) known from wetlands in central Thailand, of which there are no confirmed records since 1978; the species is Critically Endangered (BirdLife International 2001).
Among the most charismatic globally threatened birds are two Critically Endangered species: giant ibis (Thaumatibis gigantean) and white-shouldered ibis (Pseudibis davisoni), once relatively widespread in Indochina, but now largely confined to the open deciduous dipterocarp forests and wetlands of Cambodia's lowland plains (Davidson et al. 2001). Together with a suite of other species, particularly storks, they form a bird mega-fauna unique to the region, including greater adjutant (Leptoptilos dubius) (Endangered), lesser adjutant (L. javanicus) and sarus crane (Grus antigone) (both Vulnerable), which require species-focused interventions at the landscape scale to conserve viable populations. Globally significant numbers of greater adjutant and lesser adjutant, together with spot-billed pelican (Pelecanus philippensis) and milky stork (Mycteria cinerea) (both Vulnerable), contribute to one of the region's most impressive natural phenomena: the biggest breeding colony of large waterbirds in the whole of Asia, in the flooded forests of Prek Toal in the northwestern corner of Tonle Sap Lake. Unfortunately, competition with lucrative commercial fishing concerns and mass collection of waterbird eggs are major threats to this colony (Goes and Hong Chamnan 2002).
Indochina supports a significant number of globally threatened migratory waterfowl and shorebird species. For these species, coastal ecosystems are particularly important, although some also use freshwater wetlands. Intertidal mudflats and coastal lagoons are the key habitats for black-faced spoonbill (Platalea minor), spotted greenshank (Tringa guttifer) and spoon-billed sandpiper (Eurynorhynchus pygmeus), species that breed in northeast Asia and occur as passage migrants and/or winter visitors to the region's coasts. The Pearl River Delta in China, the coastal zones of the Red River and Mekong Deltas in Vietnam and the Inner Gulf of Thailand are all of known global importance for some or all of these species (BirdLife International 2001).
Other globally threatened bird species requiring species-focused conservation action at the landscape scale include birds of prey. The recent population crash of Gyps vultures in the Indian Subcontinent resulted in their global threat status being revised from near threatened to Critically Endangered. Two species, slender-billed vulture (Gyps tenuirostris) and white-backed vulture (G. bengalensis), occur in the region, and their populations in the plains of northeastern Cambodia are now of the highest conservation significance, as the decline in these populations does not appear to be linked to the precipitous decline of populations in the Indian Subcontinent (BirdLife International 2001, Pain et al. 2003).
The Endangered Bengal florican (Houbaropsis bengalensis) is a flagship for diminishing grassland ecosystems in Cambodia and Vietnam. The majority of the known global population breeds in the inundation zone of Tonle Sap Lake, dispersing to surrounding areas in the wet season (Goes 2000, BirdLife International 2001). This area contains the largest remnant tracts of semi-natural floodplain grassland in the region.
Another Endangered bird species requiring species-focused conservation action is white-eared night-heron (Gorsachius magnificus). The global range of this species is restricted to southern China and northern Vietnam, although it extends outside of Indochina. There are very few recent records of this species, and vastly improved information is required to better understand its distribution, status and ecology and to formulate appropriate conservation action.
Galliforms are another group of birds that feature prominently in the IUCN Red List: four species occurring in Indochina are Endangered and a further seven are Vulnerable (IUCN 2002a). These include six species endemic to the region: Hainan partridge (Arborophila ardens), chestnut-headed partridge (A. cambodiana), orange-necked partridge (A. davidi), Edwards's pheasant (Lophura edwardsi), Vietnamese pheasant (L. hatinhensis) and Germain's peacock pheasant (Polyplectron germaini) (Stattersfield et al. 1998). The galliform species that is apparently undergoing the most significant decline in Indochina is green peafowl (Pavo muticus), which once occurred almost throughout the region but has been eradicated from many areas as a result of overexploitation (BirdLife International 2001); perhaps the most viable population remaining is in the dry forest landscapes of northern and northeastern Cambodia, and contiguous areas of Lao P.D.R. and Vietnam (Tordoff et al. 2004a).
Threatened forest passerines fall into two discrete categories: lowland species and montane species. Lowland forest specialists are chiefly distributed in the evergreen forests of peninsular Thailand, close to the region's terrestrial southern boundary, delineated by the sharp transition from seasonal to aseasonal wet climates, where the Sundaic biogeographic influence in the region is at its strongest (Hughes et al. 2003). The Critically Endangered Gurney's pitta (Pitta gurneyi) is the best known of these, although the best prospects for its survival may now lay outside of Indochina, in the lowland forests of Tanintharyi division, Myanmar (Anon. 2003).
Globally threatened montane passerines include collared laughingthrush (Garrulax yersini) and grey-crowned crocias (Crocias langbianis), which are endemic to the southern Annamite Mountains of Vietnam, and golden-winged laughingthrush, chestnut-eared laughingthrush and black-crowned barwing, which are endemic to the central Annamite Mountains of Lao P.D.R. and Vietnam (BirdLife International 2001). All globally threatened montane passerines are restricted to montane evergreen forest ecosystems that are threatened by habitat loss and fragmentation. The extremely restricted ranges of some of these species compound these threats.
Reptiles
The region supports the most diverse non-marine turtle fauna in the world. In 1999, a re-evaluation of the global threat status of Asia's turtles concluded that 75 percent were globally threatened, with over 50 percent meeting the criteria for Endangered or Critically Endangered. The distributions and habitat requirements of most species in Indochina remain less than perfectly understood, as many recent records stem from wildlife markets (van Dijk et al. 2000, Stuart et al. 2001, Stuart and Thorbjarnson in press). However, overexploitation to supply the wildlife trade is clearly the major factor driving the decline of most turtle species in the region, with some species fetching several thousand U.S. dollars for a single animal. Given the naturally slow reproductive rates of many turtle species, many wild populations may not be able to recover from overexploitation on this scale, and conservation action is urgently needed to prevent a wave of extinctions through the region's turtles.
No snake or lizard species in Indochina is currently assessed as globally threatened. However, the IUCN Species Survival Commission recently initiated a global reptile assessment. Reptiles make up a significant proportion of traded wildlife entering China from Cambodia, Lao P.D.R., and Vietnam, and a number of snake and lizard species with a high value in trade may qualify as globally threatened. Also of great concern are species with highly restricted ranges, such as Chinese crocodile lizard (Shinisaurus crocodilurus), a large lizard species known only from a few sites in southern China and northern Vietnam. The conservation of most globally threatened reptile species requires strategic, coordinated regional and global initiatives to combat the over-riding threat to their populations: overexploitation for trade.
Amphibians
While the need for conservation action for amphibians is becoming increasingly apparent, there is insufficient information to allow appropriate action to be taken. Even the most obvious action, habitat protection, is hampered by a lack of information on distribution of key sites for most species. In addition, inferring from other regions of the world, key threats to globally threatened amphibians may differ significantly from other vertebrate groups for which more information is available, and include pollution and climate change (Blaustein and Wake 1990, Dunson and Wyman 1992, Pounds and Crump 1994). At this stage, amphibian conservation efforts might best be focused on centers of endemism, such as the Huanglianshan/Hoang Lien Mountains.
Fish
A shortage of available data, combined with a lack of emphasis on conducting the assessments, has left the global threat status of the vast majority of the region's fish species unassessed. Incidental observations suggest very depleted and fragmented populations, particularly among lowland species, which are affected by intensive agriculture, pollution and problems of urbanization, notably channelization (Dudgeon 2002a,b), while upland populations are impacted by dam construction and destructive fishing practices, such as electrofishing, poisoning, and dynamiting (Roberts 1995, KFBG 2002, Chen 2003). Thus, there is an urgent need for conservation assessment of fish species, beginning with groups that are relatively well known taxonomically. Smaller-bodied, less commercially valuable species, especially those occurring outside of the Mekong mainstream, are particularly in need of re-assessment in respect to their global threat status (R. Shore in litt. 2002), for example the fish Hemigrammocypris lini, which is known only from Hong Kong, where it has not been recorded since the 1980s (Fellowes et al. 2002).
Plants
Of the plant species already assessed as globally threatened, the majority are high value timber species threatened by overexploitation. The family with the highest number of globally threatened species is the Dipterocarpaceae, which includes three threatened species of Anisoptera, 12 species of Dipterocarpus, 20 species of Hopea, two species of Parashorea, 14 species of Shorea and seven species of Vatica. Other globally threatened plant species in the region include four species of Aquilaria, which are threatened by overexploitation of agarwood, an aromatic non-timber forest product.