Tenasserim-South Thailand semi-evergreen rainforests

Ecoregions (main)

Published: May 8, 2014, 2:16 pm

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Ecoregions (main) Conservation Biology (main) Rainforests (main) Biodiversity (main) Ecology (main) Geography (main) Zoology (main) Biology (main)

WWF Terrestrial Ecoregions Collection

The Tenasserim-South Thailand semi-evergreen rainforests cover the transition zone from continental dry evergreen forests common in the north to semi-evergreen rainforests to the south. As a consequence, this ecoregion contains some of the highest diversity of both bird and mammal species found in the Indo-Pacific region.

The relatively intact hill and montane forests form some of the best remaining habitat essential to the survival of Asian elephants and tigers in the Indo-Pacific region. However, the lowland forests are heavily degraded, and many lowland specialists such as the endemic Gurney's pitta survive in a few isolated reserves.

Location and General Description

This ecoregion encompasses the mountainous, semi-evergreen rain forests of the southern portion of the Tenasserim Range, which separates Thailand and Myanmar, and the numerous small ranges of peninsular Thailand.

This ecoregion also includes the extensive lowland plains that lie between the peninsular mountains and until recent decades supported extensive lowland forest.

The southern margin of this ecoregion is defined by the Kangar-Pattani floristic boundary, which separates Indochina from the Malesia.

Source: WWF

Annual precipitation increases southward as the length of the dry season and the magnitude of premonsoon drought stress declines. The southern mountain ranges receive rain from both the northeast and southwest monsoons so that, unlike in mountain ranges further north, there is no significant rainshadow. The Köppen climate system places this ecoregion in the tropical wet climate zone.

The vegetation of this ecoregion includes both lowland and montane forests. It is transitional between the drought-deciduous forests of Central Thailand at 12 degrees N latitude, where climax species include teak Tectona grandis and Xylia dolabriformis, and seasonal evergreen rain forests that occur south of about 6 degrees N. Tropical hardwood trees in the family Dipterocarpaceae dominate forests throughout the ecoregion, but species turn over with both elevation and latitude. The diverse dipterocarp forests that occur in the southern portion of this ecoregion include numerous species (Biodiversity) such as Dipterocarpus alatus, D. griffithii, D. laevis, D. turbinatus, Shorea spp., Hopea odorata, Fagraea fragrans, Bassia longifolia, Mesua ferrea, Delina sarmentosa, Tetracera assa, Dillenia aurea, and Talauma mutabilis. The mature forest trees are buttressed and draped with numerous lianas and epiphytes, including Drynaria basket ferns, and more than 700 orchid species. Distinctive, thorny climbing palms known as rattans are common in undisturbed sites, although their economic value means that they are greatly reduced in most accessible, unprotected forest locations. Lichens and algae are also speciose components of the epiphyte community.

Ao Phang Gha National Park, Thailand (Photograph by Michael Brown/Innovative Resources Management, Inc.) Karst limestone towers are evident in many locations throughout peninsular Thailand, including islands off Thailand's southwest coast. Extensive karst limestonevegetation is also found in Ao Phangnga National Park. In general, forests on limestone are more easily drought stressed and tend to be deciduous, whereas forests on granite benefit from the soil's increased water-holding capacity and tend to support a higher proportion of evergreen species.

Forests of this ecoregion support innumerable plant species that have distinctive and fascinating life histories. The insectivorous pitcher plants Nepenthes grow in high-elevation bogs and other nitrogen-deficient [[habitat]s]. Forests of this ecoregion also support Rafflesia, a curious root parasite specific to vines of the genus Tetrastigma. This plant occurs throughout Malesia. The species found here, R. kerrii, is by no means the largest-flowered member of the genus, but the flowers do attain a diameter of 70 centimeters (cm), which makes them the largest flowers in Thailand or Myanmar. Rafflesia is completely devoid of leaves and possesses very little vascular tissue. The entire plant is underground, except the large but ephemeral, rank-smelling flowers. It is thought that the smell, of carrion, attracts flies that serve as pollinators.

Biodiversity Features

Green dragontail (Lamproptera meges virescens) (Photograph by Chin Fah Shin)

This ecoregion contains one of the most intact vertebrate faunas of Indochina, including one of the richest mammal assemblages in Asia. The fauna is also distinctive, with characteristics of the islands of the Malay Archipelago as well as the mountains of China and India. The relatively intact and contiguous hill and montane habitat has potential to conserve large landscapes that will provide adequate habitat to maintain a viable populations of Asia's largest carnivore, the tiger (Panthera tigris), and the Asian elephant (Elephas maximus). This ecoregion lies within a high-priority (Level I) Tiger Conservation Units (TCU). This range of forests in conjunction with the Kayah-Karen mountains represents some of the best landscapes for Asian elephant conservation in Indochina.

Numerous other mammals are of conservation significance, primarily the elusive and endemic Fea's muntjac (Muntiacus feae) (Table 1). The population of the Malayan tapir (Tapirus indicus), the only Old World tapir representative, has been drastically reduced. It survives in the hill and montane protected areas of this ecoregion and scattered pockets throughout peninsular Malaysia and Sumatra. Several primate species are found in these forests and include the threatened banded langur (Trachypithecus melalophus) and slow loris (Loris nycticebus), a small, nocturnal prosimian. Other species (Biodiversity) of conservation concern include the Dyak fruit bat (Dyacopterus spadiceus), the endangered clouded leopard (Pardofelis nebulosa), common leopard (Panthera pardus), sun bear (Helarctos malayanus), binturong (Arctictis binturong), gaur (Bos gaurus), and banteng (Bos javanicus).

Table 1. Endemic and Near-Endemic Mammal Species.
Family	Species
Rhinolophidae	Hipposideros halophyllus
Vespertilionidae	Eptesicus demissus*
Cervidae	Muntiacus feae
An asterisk signifies that the species' range is limited to this ecoregion.

Porcupine (Hystrix brachyura), Thailand (Photograph by Sean Austin)

The diverse [[habitat]s] within this ecoregion, from deciduous forests in the north to seasonal evergreen forests in the south, lowland to montane, make it one of the richest in bird species for the entire Indo-Pacific. A total of 560 bird species have been recorded here. However, with rapid habitat loss (Habitat fragmentation) in the lowlands, many of these forest birds are threatened. One of the most critically endangered, Gurney's pitta (Pitta gurneyi), is endemic to this ecoregion (Table 2). This species, once thought to be extinct, survives in a few locations in lowland forest in the central part of peninsular Thailand. More than twenty-five pairs have been found in some of the last remaining forest, and that forest is now contained within Bang Kram wildlife sanctuary. The Malayan peacock-pheasant (Polyplectron malacense) is endemic to the hill and montane forests of this ecoregion (Table 2). The lowland, alluvial, and wetland forests also support a wide variety of waterfowl. Species range from the large and colorful purple swamphen (Porphyrio porphyrio) to several majestic egret species. The lowland, hill, and montane dipterocarp forests are home to several species of the vivacious hornbills. Hornbills prefer to nest in tall trees (usually dipterocarps) in primary forests. At least nine hornbill species are found in these forests and include the nearly extinct wrinkled hornbill (Aceros corrugatus).

Table 2. Endemic and Near-Endemic Bird Species.
Family	Common Name	Species
Phasianidae	Mountain peacock-pheasant	Polyplectron inopinatum
Phasianidae	Malayan peacock-pheasant*	Polyplectron malacense*
Pittidae	Gurney's pitta*	Pitta gurneyi*
Pycnonotidae	Spectacled bulbul	Pycnonotus erythropthalmos
An asterisk signifies that the species' range is limited to this ecoregion.

Current Status

The existing protected areas system includes twenty-two reserves that cover 11,530 square kilometers (km²⁾, or 12 percent of the ecoregion's area (Table 3). Most of these protected areas are located in Thailand. Large blocks of intact seasonal evergreen forest habitat remain in Myanmar, but most of these are not protected. Some protected areas have been designated in the portion of this ecoregion that lies within Myanmar, but their effectiveness is difficult to assess at this time because of the political instability of the region.

Table 3. WCMC (1997) Protected Areas That Overlap with the Ecoregion.
Protected Area	Area (km2)	IUCN Category
Khao Laem	530	II
Sai Yok	500	II
Kaeng Krachan	2,560	II
Pakchan	940	PRO
Unnamed	440	?
Unnamed	130	?
Unnamed	490	?
Khlong Nakha	460	IV
Khlong Saeng	1,070	IV
Khao Sok	690	II
Unnamed	260	?
Khao Luang	640	II
Khlong Phraya	60	IV
Unnamed	20	?
Unnamed	80	?
Khao Phanom Bencha	60	UA
Khao Pu-Khao Ya	710	II
Khao Banthat	1,160	IV
Hat Chao Mai	260	II
Ton Nga Chang	190	IV
Thaleban	100	II
Unnamed	180	?
Total	11,530

Overall, more than 50 percent of the ecoregion's habitat has been converted to agriculture. Despite a logging ban in the late 1980s, the extensive lowland forests of peninsular Thailand have been nearly extirpated. Only one flat, lowland area in peninsular Thailand-Bang Kram-still supports a significant amount of late-successional forest. Other areas support vast tracts of rubber plantation, monocultures of a fast-growing, short-lived tree species native to South America, and plantations of oil palm. Pineapple may be grown here for a few years as a rotation crop after the removal of senescent rubber trees. Paddy rice is also grown in some lowland areas. Unfortunately, none of these crops, with the possible exception of paddy rice, provide significant support for natural biological diversity.

Khao Chong Nature Reserve, Thailand (Photograph by Michele Depraz)

Hill slopes support more native forest than the lowland areas, and the hill forests of southern Thailand are relatively intact, although swidden (slash-and-burn) agriculture is still practiced in some hill areas in the northern part of the ecoregion. Mature forest cut for swidden agriculture generally is succeeded in this ecoregion by a grassy subclimax that supports far fewer species than the mature forest. Kaeng Krachan National Park (2910 km²) provides important protection to a variety of moist forest [[habitat]s] and is exceptionally rich for birds.

Khao Sok National Park (645 km²) is another important protected area in southern Thailand, although both of these either contain or adjoin large artificial reservoirs from which protrude the skeleton trunks of climax forest trees that have been inundated. Tarutao Marine National Park includes several large islands that support extensive stands of late-successional evergreen forest. Terrestrial mammals that occur on these islands include flying lemur and mouse deer.

Types and Severity of Threats

After Thailand banned timber exploitation in its forests in 1988, Myanmar granted large logging concessions to Thai companies, and illegal timber extraction in Myanmar by Thai loggers has become common in recent years. The soils of this ecoregion are very vulnerable to erosion once exposed, and the long-term ecological effects of large-scale clear felling would be catastrophic. This area is also subject to heavy pressure from development]], especially in Kanchanaburi Province, Thailand, where dams and highways are being constructed, and in certain areas of peninsular Thailand such as Phuket and Krabi, where coastal resort development has been proceeding with an imprudent degree of urgency. The lowland and alluvial forests are more endangered than the montane region. Large tracts of these forests are being converted to rubber and oil palm plantations. Less than 5 percent of the level lowlands still retain their forest cover, and the degradation (Habitat fragmentation) threats are slowly moving upslope to hill and montane forests.

Justification of Ecoregion Delineation

MacKinnon's subunit 05d extends into the Kayah Karen and Tenasserim mountain ranges. We extracted the montane forests along the Tenasserims to form this ecoregion.

Additional information on this ecoregion

• For a shorter summary of this entry, see the WWF WildWorld profile of this ecoregion.

Disclaimer: This article contains information that was originally published by the World Wildlife Fund. Topic editors and authors for the Encyclopedia of Earth have edited its content and added new information. The use of information from the World Wildlife Fund should not be construed as support for or endorsement by that organization for any new information added by EoE personnel, or for any editing of the original content.

Citation

Fund, W. (2014). Tenasserim-South Thailand semi-evergreen rainforests. Retrieved from http://editors.eol.org/eoearth/wiki/Tenasserim-South_Thailand_semi-evergreen_rainforests