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General Facts
PHYSICAL FEATURES The topography is generally
mountainous with a network of many permanent rivers and streams
dividing the area into valleys and lowland plains. The
sanctuary's distinguishing feature is a large central grassland
plain, from which it takes the name of Thung Yai (meaning 'big
field'). Within the catchment area are four importantrivers:
the Mae Khlong, which flows into the Kwai Yai (of "Bridge over
the River Kwai" notoriety) and feeds into the Sri Nakarind Dam;
Kwae Noi, which feeds into Khao Laem Reservoir; and Mae Kasart
and Mae Suriat which, respectively, flow into Mekathat and
Huang Tharaw rivers in Myanma. Red-brown earths and red-yellow
podzols are the predominant soils, the former derived from
limestone and found in the level uplands and Mae Chan Valley,
whilst the latter is found in the Huai Kha Khaeng Valley. A
physical feature that is important for wildlife is the presence
of mineral licks. These occur throughout the sanctuary as
either wet or dry, and most appear to be located on, or around,
granite intrusions in areas with red-yellow podzolic soil and
may be associated with the massive faults or lineaments in the
intensely folded geomorphology of this area. Small lakes, ponds
and swampy areas occur, some being seasonal whilst others are
perennial; these are important wildlife habitats. Limestone
sink holes are found; most are only about 20m in diameter and
10-12m in diameter, but some are more than 2km long, 250m wide
and drop as much as 30m depth (ONEB, 1990). VEGETATION The principal vegetation types, and their estimated cover is as follows: hill evergreen forest (54,900ha); dry evergreen forest (112,900); mixed deciduous forest (164,100ha); dry dipterocarp forest (3,600ha); savanna forest (9,900ha); grassland (3,900ha); and areas of swidden agriculture (15,400ha) (Anon., 1991). The highest ground is generally covered with hill evergreen forest, also known as tropical lower montane rain forest, but slopes above 600m generally support dry evergreen forest (seasonal evergreen forest). This latter formation is tall, dense, stratified and always dominated by Dipterocarps, and may appear to be evergreen in wet areas such as the central uplands of the sanctuary. In some areas, particularly broad valleys, there is often a mosaic of vegetation types. At lower altitudes mixed deciduous and bamboo forests predominate, with dry deciduous dipterocarp forest occurring in areas with poor or shallow soil. Mixed deciduous forest is the most predominant formation, probably dominated by Lagerstroemia calyculata associations, although pure stands of Xylia xylocarpa are found. Dry dipterocarp forest, also referred to as dry deciduous dipterocarp, is unique to mainland South-east Asia. It is dominated by five xerophilous dipterocarps and is confined to the poorest and most porous soils where fire occurs. Savanna forest and grassland, both very similar formations, occur at every elevation, although the 'thung yai' covers 14,000ha. Some 17 trees occur in the savanna forests, of which L. macrocarpa, Stereospermum nueranthum, Terminalia chebula and Dalbergia cultrata are amongst the most common. Trees within grassland are smaller, of generally the same genera, but not exceeding 5m, and stunted either by fire or other edaphic constraints. In particularly moist areas along rivers and streams, evergreen gallery forest is present. This is noticeably lusher than other formations, and harbours many more creepers, climbers and epiphytes, with emergents as high as 40m. The gallery forest sustains a higher than usuallevel of biological diversity in comparison to the more widespread but drier habitats, especially during dry season fires. The most important wetlands are those along the upper Khwae Yai and is tributaries, the Mae Klong and Mae Chan, both deep, fast flowing rivers with steep banks, muddy bottoms and frequent rapids and rocky ravines. Secondary forest on areas of
former swidden agriculture are found in the Mae Chan Valley and
central uplands towards the east. Swidden agriculture has been
practised in areas of the most fertile soils which indicates
that some of the richest forest has been destroyed but also
that there is a good chance of regeneration. Characteristic
species are those that grow in the surrounding forest,
including L. macrocarpa, Vitex peduncularis,
Bauhinia acuminata and Albizia odoratissima. FAUNA The fauna of both Thung Yai and Huai Kha Khaeng includes an unusual mix of species with primarily Sundaic, Indo-Chinese, Indo-Burmese and Sino-Himalayan affinities, many of whose ranges do not overlap. Most species are either characteristic of the Oriental/Indo-Malayan region or more specifically associated with the Indo-Chinese province of that region, but with a strong Sundaic element included. A small proportion is Palaearctic. Thung Yai has not been comprehensively surveyed, but it is known to support a significant proportion of Thailand's fauna (Nakasathien et al., 1987). It is big enough to support several of the larger and increasingly rare mammal species, such as tiger Panthera tigris (E), leopard P. pardus, clouded leopard Neofelis nebulosa (V), Elephas maximus (E), tapir Tapirus indicus (E), Sumatran rhinoceros Didermocerus sumatraensis (E), gaur Bos gaurus (V), mainland serow Capricornis sumatraensis (I) and hog deer Cervus porcinus. A herd of 50 gaur was seen in 1985, making it the largest herd recorded in Thailand (P.D. Round, pers. comm.). Neither banteng B. javanicus (V), nor wild water buffalo Bubalus arnee (E) has yet been reported from Thung Yai, although both occur in neighbouring Huai Kha Khaeng Wildlife Sanctuary. The Javan rhinoceros Rhinoceros sondaicus (E) is said to have existed in the area and a track was photographed in 1988 (J.Thorsell. pers. comm., 1991). Notable bird species include white-winged wood duck Cairina scutulata, Kalij pheasant Lophura leucomelana, Burmese peafowl Polyplectron bicalaratum and green peafowl Pavo muticus (V) (Round, 1988). A detailed summary discussion of the fauna of the combined Thung Yai-Huai Kha Khaeng sanctuaries is given in ONEB (1990) and species lists have been compiled. This includes some 120 mammals, 400 birds, 96 reptiles, 43 amphibians and 113 freshwater fish as confirmed occurrences, with a number of species suspected as being present but not confirmed. Thirty-four internationally threatened species are also found within the confines of the two sanctuaries (ONEB, 1990). CULTURAL HERITAGE It is certain that Thung Yai contains several sites of great archaeological interest, possibly dating back to the Pleistocene era when early hominids are thought to have migrated east and southwards through the area. Stone artifacts have been found which reinforce this supposition, but the area has yet to be properly investigated (B.J. Stewart-Cox, pers. comm.). CONSERVATION VALUE Watershed protection in both Thung Yai and Huai Kha Khaeng is conservatively estimated to be worth some US$ 13.8 million annually (Dobias et al., 1988). Both Thung Yai and Huai Kha Khaeng are considered key sites for the conservation of lowland and montane bird species (Round, 1988) and Thung Yai contains the largest and least disturbed expanse of riverine forest in Thailand (Round, 1985). The justification for the inscription of the Thung Yai-Huai Kha Khaeng sanctuary complex on the World Heritage List (ONEB, 1990), argues that the site is biogeographically unique, capable of sustaining flora and fauna indefinitely, of exceptional natural beauty and scientific value, and includes very high biological diversity. Being located in a transition zone between the tropics and sub-tropics and, perhaps, because it was a Pleistocene refugium, a number of species of birds and mammals are found to be sympatric here. Few other areas of dry tropical forest in the region are as large, as well protected or as pristine. The complex also contains outstanding examples of the rock formations which distinguish the western edge of mainland South-East Asia from the more stable continental core, and is probably one of the best modern examples of the impact of the Pleistocene epoch on the distribution and dispersal of South-East Asian fauna. The impact of geological activity on an area of pristine dry tropical forest is exemplified better than elsewhere. SCIENTIFIC RESEARCH AND FACILITIES Very little scientific research has been undertaken and there are no facilities.
Source: Protected Areas
Programme
Map Wildlife Protection Stations
List of chief in command of wildlife sanctuary Officers
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