Indo-Burma

Biodiversity
Flagship Species
Threats
Conservation

The redefined Indo-Burma Hotspot has emerged as a result of the exclusion of the Himalayan chain and associated foothills in Nepal, Bhutan, and India (now included in a new Himalaya Hotspot, the addition of southern and western Yunnan, and an expansion of the area of southern subtropical China (southern Guangxi and Guangdong). The area covered by this redefined hotspot is at times referred to as the Indo-Chinese Subregion and can be described as Tropical Asia east of the Ganges-Brahmaputra Lowlands, excluding the Malesian region. The Indo-Burma Hotspot begins at the evergreen forests in the foothills of Chittagong in Bangladesh and extends through the Garo and Khasi Hills of Meghalaya, India, then eastwards through the States of Manipur, Mizoram, and Nagaland to encompass most of Myanmar (except the extreme northern alpine areas), a part of southern and western Yunnan, China, all of the Lao People's Democratic Republic (P.D.R.), Vietnam, and Cambodia, the coastal lowlands of southern China, Hainan Island, the vast majority of Thailand, a small fraction of Peninsular Malaysia, and the Andaman Islands of India. As redefined here, the original extent of the hotspot is 2 373 000 km².

The transition to the Sundaland Hotspot occurs on the Thai-Malay Peninsula. The boundary between the two hotspots is here taken to be the Kangar-Pattani Line, which cuts across the Thailand-Malaysia border, marking the transition between the Indochinese and Sundaic floras (Van Steenis 1950; Whitmore 1984). However, other analyses indicate that the phytogeographical and zoogeographical transition between the Sundaland and Indo-Burma biotas may lie just to the north of the Isthmus of Kra, associated with a gradual change from wet seasonal evergreen dipterocarp rainforest to mixed moist deciduous forest (Woodruff 2003). For example, more than half of the 544 forest bird species present on the Thai-Malay Peninsula have their species limits north of the Isthmus at 11°-13°N (Hughes et al. 2003).

Indo-Burma has a complex geological and evolutionary history. The Indian intrusion into the Asian continental landmass has been responsible for the formation of most of the hotspot's topography, including the general north-south orientation of the mountains and main rivers. The wide variation in land form, climate, and latitude within the hotspot has led to the development of diverse natural habitats that support a high diversity of plant and animal species. This diversity is enhanced by a significant endemic element, which may largely derive from habitat isolation caused by periods of high sea level and vegetation changes during the glacial episodes of the Pleistocene. Consequently, the hotspot contains many localized centers of endemism, particularly montane isolates, but also areas of lowland wet evergreen forest that were isolated at some stage, and river basins.

At present, much of Indo-Burma is characterized by distinct seasonal weather patterns. During the northern winter months, dry, cool winds blow from the stable continental Asian high-pressure system, resulting in a dry, cool period under clear skies across much of the south, center, and west of the hotspot (the dry, northeast monsoon). As the continental system weakens in summer, the wind direction reverses and air masses forming the southwest monsoon pick up moisture from the seas to the southwest and bring abundant rains as they rise over the hills and mountains. In northern Vietnam and southern coastal China, the dominant weather pattern is the north or northeasterly monsoon during the northern winter and east or southeasterly monsoon in the summer.

Originally, nearly all of Indo-Burma would have been dominated by broadleaf forests. The complex composition and distribution of the hotspot's principal vegetation formations are determined by the seasonality of rainfall, soil characteristics, temperature, and history. The richest forests —in terms of tree diversity and overall plant species numbers— are the lowland mixed wet evergreen forests, which occur in climates with one to four dry months. The southern mixed wet evergreen formations comprise the Parashorea stellata association, characteristic of zonal yellow-red clay loams, and the Dipterocarpus costatus association on yellow sandy soils, with low nutrient levels and high sensitivity to erosion, which occurs locally as islands within the widespread clay loams. The former were once widespread in Tenasserim south of Tavoy, Peninsular Thailand from Chumphon to northwestern Malaysia, and on the lower slopes of granite outcrops in southeastern Thailand, as well as south of Da Nang and in the hills north of Hue in Vietnam, but now survive only as a few fragments. The forests of D. costatus have been severely degraded, although significant stands remain on the southern slopes of the Cardamom and Kamchay ranges, and isolated patches in the Thai-Malay Peninsula. The northern mixed wet evergreen forest association is at present fragmented by mountain ranges and habitat conversion, and remnant patches are restricted to the northern part of the hotspot (northern Myanmar; southern China, including southern Yunnan and also Hainan; the Lao P.D.R.; and northern Vietnam).

In lowland areas where rainfall is more limited and the dry season lasts for five to seven months, the Dipterocarpus turbinatus dry evergreen forest formation is the natural climax stage in many lowland and hill regions. In the driest areas, it is confined to galleries in stream and river valleys, in areas otherwise dominated by deciduous forest types. This dry evergreen forest type is still widespread across substantial areas of Indo-Burma.

Deciduous forests occur in areas with five to nine dry months. The Dalbergia-Lagerstroemia mixed deciduous forest formation is widespread on yellow clay soils throughout the hotspot. Teak (Tectona grandis) may be a major component where soil and climatic conditions are right. On sandy and shallow lateritic soils, mixed deciduous forest is replaced by deciduous dipterocarp forest, which generally forms a low, broken canopy. Several factors contribute to the formation and maintenance of this forest type, including high frequency of fire (probably anthropogenic). In the dry, central Ayeyarwady Plain of Myanmar, a variety of semidesert thorn communities occur (Stamp 1925), which support fewer species than most other deciduous forest types but have relatively high levels of endemism. Some deciduous forests contain highly valuable timber species (e.g., teak, rosewood). Their leafless period and often broken canopy permit enough light to reach the ground and stimulate a dense undergrowth of grasses and herbs, making these forests excellent feeding areas for large herbivorous mammals. Historically, these forests supported some of the most diverse and abundant mammal and bird megafaunas in Asia.

Throughout the hotspot, montane forests extend on humus-rich soils from about 800 masl. These forests are lower in stature with fewer emergents; oaks (Fagaceae) dominate, while laurels (Lauraceae) and magnolias (Magnoliaceae) become notable constituents. Montane tree species composition is generally less diverse than that of lowland forests, but it contains proportionally more endemic species. Diverse edaphic, topographic, and microclimatic conditions at higher elevations give rise to a range of mixed coniferous and broadleaf evergreen forest formations. On dry hills and plateaus subject to fire, conifer-dominated savanna forests occur (typically dominated by Pinus merkusii or P. kesiya). At the highest elevations, on ridgelines and ridge crests, stunted, xerophytic formations, characterized by the presence of Rhododendron spp., occur. In general, the diversity and richness of shrubs, herbs, epiphytes, and acid-loving species increase at higher altitudes, as tree diversity declines. Among them are many endemic species.

Heath forest occurs on some raised beaches in coastal areas. This evergreen forest type is less speciesrich, but probably contains the highest proportion of endemics of any regional evergreen forest type. A related forest occurs on similar soils above 800 masl in association with sandstone mountains. Limestone karst outcrops support distinctive shrub and woodlands on their summits, as well as rich, mostly herbaceous floras on sheltered cliffs. Limestone karst formations can support relatively high levels of endemism, particularly in groups such as orchids (Orchidaceae). In addition, a wide variety of distinctive, localized vegetation formations occur in Indo-Burma, including lowland floodplain swamps, mangroves, seasonally inundated grasslands, and successional assemblages, as well as croplands and plantations.

The hotspot is home to a wide diversity of ethnic groups, cultures, and languages. Several language groups, including Mon-Khmer, Austroasiatic, and Tai-Kadai, originated and developed in the hotspot, and were later joined by the Hmong-Mien and Sino-Tibetan language groups. Agriculture developed very early in the hotspot, and gave rise to different land-use forms, including both semi-nomadic and rotational swidden cultivation, and irrigated floodplain rice cultivation. Among the human population of the hotspot, there is a broad spectrum in terms of the degree of integration with the global economy, from the Paleolithic lifestyles of certain ethnic groups in the Thai-Malay Peninsula and the Jarawa, Onge, Sentinelese, and Andamanese tribes of the Andaman Archipelago, to the urban life-styles of the residents of Bangkok, Hong Kong, and other major cities.

Attempts to estimate species diversity and endemism for Indo-Burma are hampered by uneven knowledge of taxonomy and distribution of species and groups. New, locally endemic species are regularly discovered, while advances in taxonomy continue to reveal that single widespread “species” actually comprise complexes of separate species, many of which are local or regional endemics. Socio-political divisions have also complicated biodiversity assessments because populations in neighboring countries may be independently described as locally endemic species, although an independent revision would consider such pairs to represent just a single species. Nevertheless, reasonable estimates of species diversity and endemism can be made for some groups in the hotspot.

The total plant diversity of the former Indo-Burma Hotspot was estimated at about 13 500 species of flowering and gymnosperm plants, of which about 7 000 were estimated to be endemic to the hotspot (Dijk et al. 1999). A reassessment of the revised Indo-Burma Hotspot results in similar estimates for numbers of hotspot species and endemics: the modest losses of species restricted to the Himalayan chain and associated foothills being compensated for by the species gained in southern China. These estimates are, however, quite conservative: Davis et al. (1995) estimated that there are 12 000-15 000 species of vascular plants (i.e., including ferns) in Cambodia, Laos, and Vietnam combined. This flora includes a profusion of orchid (Orchidaceae) and ginger (Zingiberaceae) species (for example, there are more than 1 000 orchid species in Thailand alone), as well as the variety of fine tropical hardwoods.

The vertebrate fauna of the hotspot is quite diverse. Mammals number 430 species in 171 genera and 37 families, of which 71 species and seven genera (six monotypic) are endemic to the hotspot. In addition, there is a single endemic family, the Craseonycteridae, which is represented by one species, Kitti's hog-nosed bat (Craseonycteris thonglongyai), which is no larger than a bumblebee, and among the world's smallest mammals.

Over the last 12 years, the hotspot has witnessed the discovery of six large mammal species. Five of these were discovered in the Annamite Mountains: the saola (Pseudoryx nghetinhensis, EN), large-antlered muntjac (Muntiacus vuquangensis), Annamite muntjac (M. truongsonensis), grey-shanked douc (Pygathrix cinerea), and Annamite striped rabbit (Nesolagus timminsi) (Do Tuoc et al. 1994; Vu Van Dung et al. 1994; Nadler 1997; Giao et al. 1998; Timmins et al. 1998; Averianov et al. 2000). The sixth species, which was discovered in the mountains of northern Myanmar, is the leaf deer (Muntiacus putaoensis) (Amato et al. 1999).

The bird fauna is also very diverse, with some 1 277 species, of which 74 are endemic. There are also three endemic genera, all represented by single species: the golden-crested myna (Ampeliceps coronatus), shorttailed scimitar-babbler (Jabouilleia danjoui), and wedgebilled wren-babbler (Sphenocichla humei). Six Endemic Bird Areas (EBAs), as identified by BirdLife International (Stattersfield et al. 1998), are found within the hotspot, namely the Andaman Islands, the Irrawaddy Plains, Hainan Island, the Annamese Lowlands, the South Vietnamese Lowlands, and the Da Lat Plateau. The Eastern Himalayas and the Assam Plains EBAs are shared with the Himalaya Hotspot.

The non-marine reptiles number at least 519 species in 151 genera, of which 189 species and 12 genera are endemic. Nine of the endemic genera are represented by single species, among them a recently described form of pit viper from Vietnam (Triceratolepidophis sieversorum) (Ziegler et al. 2000). The rich amphibian fauna contains some 139 endemics among a total of around 323 species; yet, of the 57 genera represented, three (Ophryophryne, Bufoides, and Glyphoglossus) are endemic to the hotspot. Bufoides and Glyphoglossus comprise single species: the Khasi Hills toad (B. meghalayanus, EN) is known from only a few sites in northeastern India, while the last-mentioned (G. molossus) is more widespread in the hotspot.

The hotspot's inland fish fauna is remarkably diverse, with 1 262 documented species or 10% of the world's fishes that enter fresh water. The total may ultimately approach 2 000 species. The 566 fishes that are restricted to the region amount to more than half of the hotspot's endemic vertebrates, and constitute an obvious priority for conservation efforts. Endemism is also considerable at higher phyletic levels, with 30 endemic genera and an endemic family, the Indostomidae, or armored sticklebacks. This family of strange fishes is an extraordinary element to be found in tropical fresh waters, and may be remotely related to the marine seamoths. Diversity of freshwater fishes is particularly high on the lower to middle flanks of mountain ranges, where riffle and pool habitats in small streams have been the sites for extraordinary diversification, particularly in the loach families, Cobitidae and Balitoridae.

First on the list of flagship mammal species is the saola. The known distribution of the saola is restricted to the Annamite Mountains, along the border between Vietnam and the Lao P.D.R., and outlying hills to the east. Although the ecology of the species is little known, it is believed to be largely restricted to wet evergreen forests at elevations below approximately 1 000 masl. This habitat has been extensively degraded, fragmented, and converted throughout the species' known range, and most remaining areas are subject to high levels of human use. While the saola is not a species in particular demand in the wildlife trade, it is susceptible to indiscriminate snaring, which may be expected to increase in some parts of its range with the ongoing construction of the Ho Chi Minh National Highway and associated road network. Despite the global attention that was focused on the species following its discovery, none of its populations has been placed under effective conservation management, and the very real possibility exists that this enigmatic species may become extinct within a decade.

Other flagships include the Vietnamese population of Javan rhinoceros (Rhinoceros sondaicus, CR), estimated to number only a handful of individuals at Cat Tien National Park, and the kouprey (Bos sauveli, CR), a large bovid formerly found in forest areas of northern and eastern Cambodia and adjacent countries, but which may now be extinct. Also of special significance are the endemic primates, a number of which are included on a list of the world's top 25 most threatened primates prepared by Conservation International and advisors: the eastern black-crested gibbon (Nomascus nasutus, CR), Tonkin snub-nosed monkey (Rhinopithecus avunculus, CR), grey-shanked douc, white-rumped black leaf monkey (Trachypithecus delacouri, CR), whiteheaded black langur (T. poliocephalus leucocephalus, CR), and Tonkin hooded black langur (T. p. poliocephalus, CR) (Mittermeier et al. 2002).

Flagship bird species include Gurney's pitta (Pitta gurneyi, CR), a lowland evergreen forest specialist endemic to Peninsular Thailand and adjacent parts of southern Myanmar. During the twentieth century, the species underwent a dramatic decline due to extensive clearance of its habitat to the point that, by the end of the century, it was known to persist only at a single locality: Khao Nor Chuchi in Thailand. However, it has recently been rediscovered in the Tanintharyi division in Myanmar, which potentially supports a very significant population (BirdLife International 2004). Although not endemic, the majority of the world population of green peafowl (Pavo muticus, VU) is found within the hotspot. This species has undergone a dramatic decline over the last century as a result of hunting and expansion of human populations into natural landscapes, particularly the spread of human settlements along permanent water sources. Edwards' pheasant (Lophura edwardsi, EN), a species endemic to the lowlands of central Vietnam, is, like the saola, a flagship for the lowland wet evergreen forests of the Annamite Mountains and foothills. The Bengal florican (Houbaropsis bengalensis, EN) is a flagship for the threatened grassland ecosystems in Cambodia and Vietnam.

Tortoises and freshwater turtles collectively form a flagship group. The hotspot's non-marine turtle fauna is probably the most diverse in the world, with at least 40 (and, depending on taxonomic opinions, up to 52) species in 31 genera. This represents one-sixth of the world's turtle species and over one-quarter of the genera; about two-thirds of the species are endemic to the hotspot. Noteworthy also are the endemic Siamese crocodile (Crocodylus siamensis, CR), now greatly reduced in the wild with a severely fragmented population; and the Chinese crocodile lizard (Shinisaurus crocodilurus). Although the latter is not quite endemic (occurring in northeastern Vietnam and southern China), it deserves mention for being the sole member of the family Shinisauridae, which has its closest relatives in the lizards of the genus Xenosaurus in southern Mexico and Guatemala.

Flagship amphibians are considered as groups rather than individual species. Numerous remarkable and endemic frog species occur, but several groups such as the Rhacophorus gliding frogs, the megophryid litter toads, and various ranid groups stand out for their local evolutionary radiations, conservation concern, and eyecatching appearance. Salamander diversity is not very high in the hotspot, but the salamanders contain a high proportion of species with very restricted ranges and of high conservation concern, including four endemic species in the genus Paramesotriton, two of which are globally threatened: the Vietnamese salamander (P. deloustali, VU) from Vietnam and the Guangxi warty newt (P. guangxiensis, VU) from Guangxi Autonomous Region, China, and northern Vietnam.

Indo-Burma's streams and rivers are inhabited by fish species that are not only of global conservation significance, but also include some of the extremes of size among freshwater fishes. The Tonle Sap Lake and deep pools of the Mekong River, up to 60 m deep, are critical habitats for some of the world's largest freshwater fishes: the Mekong giant catfish (Pangasianodon gigas, CR), giant carp (Catlocarpio siamensis), and giant freshwater stingray (Himantura chaophraya, proposed CR). Other flagship fishes include the dragonfish (Scleropages formosus, EN), a relict of a Gondwanan group that is rapidly being depleted by illegal collecting of its juveniles for the aquarium trade.