Southern Central Plains of Thailand
Location:
 13°30'-15°00'N, 99°40'-101°15'E; extending from the gulf coast of Thailand, in the vicinity of Bangkok. upstream along the Chao Phraya River to the town of Chainat; delimited to the east and west by uplands. The site encompasses the whole or parts of the provinces of Bangkok, Thonburi, Nonthaburi, Samut Songkhram, Samut Sakhon, Samut Prakan, Nakhon Pathom, Nakhon Nayok, Saraburi, Chachoengsao, Pathumthani, Ayuttbaya, Suphanburi, Singburi, Chainat and Lopburi.
Area:
 Approximately 1,900,000 ha.
Altitude:
 Sea level to 20m.
Biogeographical Province:
 4.5.1.
Wetland type:
 11, 13, 14, 15, 19 & 20.
Description of site:

A huge area of intensively cultivated land (chiefly rice paddy) dotted with numerous small lakes and marshes each of which is generally not more than a few hectares in extent, together with small patches of semi-natural woodland and bamboo. Formerly a vast area of natural and semi-natural swamps, a relatively small proportion of which was utilized for rice cultivation, the area had already been substantially drained by the construction of massive canal systems during the reign of King Chulalongkorn in the early 20th Century. The main centres of human population are in the city of Bangkok (more than 5 million inhabitants) and in 28 other towns with 10,000-200,000 inhabitants. However, much of the population is scattered evenly throughout the area in small villages and hamlets, with particular concentrations along the banks of the larger rivers and other waterways.
The plains receive water from four major rivers: the Bang Pakong, Chao Phraya, Tachin and lower reaches of the Mae Kiong. The Chao Phraya is fed by a catchment of over 100,000 sq.km in the mountains of northern Thailand, and the Mae Kiong and Bang Pakong by catchments in western and southeastern Thailand respectively. The site is well-watered throughout the year, but the river levels are highest from October to December, when run-off from the monsoon rains over the northern hills is at its peak. High tides in November and December combine with the high river levels to produce limited flooding. Water levels are regulated through releases from two major dams upstream on the Chao Phraya river: the Bhumibol Dam in Tak Province and the Chao Phraya Dam at Chainat, near the northern boundary of the site. There are also many smaller irrigation reservoirs and storage canals throughout the area.

There is both annual and seasonal fluctuation in the extent of natural flooding. More than 90% of the area was under water as recently as October 1983, when the rains were exceptionally heavy. Under normal circumstances, however, flooding is highly restricted. By December or January, little if any flooding remains apart from a few moist depressions in the lowest-lying paddy areas, and standing water is restricted to ponds, lakes and water courses. By February or March, the paddies take on the character of a huge, dry prairie. There is rarely a little salt water encroachment in coastal parts of the area.
Climatic conditions:
 Tropical monsoonal climate with an average annual rainfall at Bangkok of 1,418 mm (range 870-2,072 mm), 85.8% of which falls during the southwest monsoon (May to October). The mean annual temperature is 28.1°C (range 9.9-39.9°C).
Principal vegetation:
 The most extensive, non-cultivated swamp vegetation consists of mats of low grasses, Eleochanis sp and Cyperus spp. There are also beds of Typha angustifolia, but extensive beds of taller swamp vegetation such as Phragrnites are now rare. Small areas of a fresh or brackish water swamp woodland community still occur along the lower reaches of the Tachin River. Floating aquatic vegetation consists of Eichhonnia crassipes, Nelumbo nucifera, Nymphaea spp, Nymphoides spp and Pistia straliotes. Most of the area is occupied by rice paddy. Although standing rice supports few waterfowl or other birds, dense grasses along paddy bunds provide some habitat for wildlife.

Plant communities in adjacent areas include scattered clumps of bamboos and woodland with such native trees as Elaeocarpus hygrophilus and Terminalia spp. A few stands of Dipterocarpus alatus occur, especially in temple grounds. Exotic ornamental tree species, such as Delonix regia, are widely planted. There are also some extensive plantations of Casuarina.
Land tenure:
 Most of the wetland areas are under private ownership; surrounding areas are privately owned.
Conservation measures taken:

The following areas have been established as Non-Hunting Areas:

  1. Wat Phai Lom, Samkok District, Pathum Thani Province: 11.8 ha the site of the largest colony of Anastomus oscitans in the country; in the grounds of a temple.
  2. Wat Tarn En, Bang Pahan District, Ayutthaya Province: 16 ha an important roosting and nesting site for a variety of larger waterbirds, and also the site of a colony of Pteropus lylei.
  3. Wat Ratsattha Krayaram, Samut Sakhon Province: 7.5 ha; a roosting and nesting site for herons and cormorants.
  4. Beung Chawak, Suphanburi Province: 320 ha a lake and adjacent marsh, important for wintering wildfowl.

A great many other areas receive de facto protection because they exist in the grounds of Buddhist temples (wats) or because private farmers choose to offer sanctuary for waterbirds nesting on their land. The better known sites include:

  1. Ban Lung Jorm, Ban Thasadet, Suphanburi Province: a roosting and nesting site for herons and cormorants on privately owned farmland.
  2. Wat Jantharam, Bang Ban District, Ayutthaya Province: a breeding site for five or six pairs of Milvus migrans.
  3. Wat Kanom Tai, Bang Pa-In District, Ayutthaya Province: the site of a colony of Pteropus lylei and nesting colony of Phalacrocorax niger.
  4. Ban Lung Tuam, Nong Khae District, Saraburi Province: a roosting and nesting site for herons and cormorants on privately owned farmland.
  5. Wat Ko Loi, Nong Khae District, Saraburi Province: the site of a colony of Pteropus lylei.
  6. Wat Tha Sung, Pathum Thani Province: the site of a colony of Pleropus lylei.
  7. Wat Samo Son, Bang Len District, Nonthaburi Province: a nesting and roosting site for herons and cormorants, and the site of a colony of Pteropus lylei.
  8. Wat Pho, Bang Khla District, Chachoengsao Province: the site of a colony of Pteropus lylei.
  9. Khlong Lat Krabang, Lat Krabang District, Bangkok: an area with several nesting and roosting sites for egrets and pond herons.
  10. Dee Som Choke Housing estate, Lard Prao Road, Bangkok: an area of small ponds and marshes in the suburbs of Bangkok, ringed by middle-class housing and protected and publicized by a sympathetic landowner; an important wintering area for wildfowl.
  11. Dee Som Choke Housing estate, Lard Prao Road, Bangkok: an area of small ponds and marshes in the suburbs of Bangkok, ringed by middle-class housing and protected and publicized by a sympathetic landowner; an important wintering area for wildfowl.
  12. Suan Somdet, Muang District, Ayutthaya Province: a small pond supporting a concentration of wintering waterfowl, chiefly Dendrocygna javanica.
  13. Wat Lam Mahamek, Lard Lumkaeo District, Pathumthani Province: a nesting and roosting site for cormorants, egrets and herons.
Conservation measures proposed:

Formal protection should be extended to the above sites, where practicable. In addition, the following sites should receive legal protection:

  1. Khan Haaxn, Uthai District, Ayutthaya Province: a newly established nesting colony of Anastomus oscitans.
  2. Nong Samur, Visetchaichan District, Ang Thong Province: a colony of a few hundred Anastomus oscitans nesting in clumps of trees among farmland. Local people at present take eggs for food.
  3. Wat Samrae, Pathumthani Province: a roosting site for over 800 wintering Milvus migrans, which congregate in tall Borassus palms. Although the site is known by the name of a nearby temple, the roosting area is outside its boundaries and is therefore unprotected.
  4. Rangsit marshes, Rangsit District, Pathumthani Province: the largest freshwater swamp remaining anywhere on the outskirts of Bangkok and possibly the largest such anywhere in the southern Central Plains, covering an area of 200-300 ha. The site possesses a large Typha bed and supports a great variety of wintering and nesting waterbirds.
One of the chief constraints upon the utilization of the area by the more sensitive, larger waterbirds appears to be the lack of undisturbed, wooded nesting areas close to suitable swampy feeding areas. Efforts should be made to try and establish such a site in a wetland nature reserve. Many other species of animals would also undoubtedly benefit. More attention should be given to publicizing waterbird sites. If observation facilities and interpretive centres were established, they could have considerable value in promoting conservation awareness. The Wildlife Conservation Division should make more effort to publicize knowledge of existing legislation, with a view to appraising villagers, police and government official to the fact that most bird species are already protected in law. Many birds are still shot or trapped and their eggs or young stolen from the nest, either for food or for sale.

A detailed inventory of all known waterbird nesting or roosting sites should be carried out.
Land use:
 Chiefly rice cultivation. Most of the area produces one crop of rice per year, during the wet season. However, because of the widespread availability of irrigation, two rice crops are produced in many areas. Rice cultivation is becoming increasingly mechanized, as
buffaloes and hand rotovators used in ploughing give way to tractors and other heavy machinery. In addition, increasing areas are now being given over to alternative crops. These include a variety of vegetables and fruits such as oranges, bananas and grapes, frequently grown on bunds raised above the level of the former paddy. There are increasing areas of Casuanina plantations. In some areas, there is still a high density of the palm, Borassus flabellifer, which is a source of sugar used in local confections. The fruits are also harvested and eaten fresh. In the wetter, more marginal areas lotus Nelumbo nucifera and Ipomoea are cultivated as table vegetables. Fishing with a variety of traps and nets is almost universally practised. There is now a much increased emphasis on aquaculture, both for fish and for the giant freshwater prawn Macrobrachium rosenbergii. Macrobrachium is also caught from the wild along the main waterways, by using handlines.

Increasing areas around the edges of Bangkok and other major towns are being given over to housing and industry. Many areas support orchards of mangoes, durians and other fruits. Riverine sand and gravel deposits, and sometimes clay and topsoil, are extracted for construction purposes. There is also much small-scale brick making using clay deposits.
Possible changes in land use:
 Increasing industrialization and the intensification and mechanization of agriculture seem likely to cause a further reduction in wildlife habitat.
Disturbances and threats: The increasing mechanization of agriculture seems certain to lead to an overall increase in the size of rice paddies and the consequent loss of many marginal areas and clumps of trees which are of value for wildlife. Some key areas around Bangkok, such as Rangsit marshes, are in danger of being filled in and built upon. Firearms are widely possessed and a great many larger birds are shot illegally. So far as is known, pesticides should not present a threat to wildlife since the compounds used in rice paddies are non-persistent. Analysis of the eggs of Anastomus oscitans in 1985 did not show deleterious levels of organochlorine contamination (A. Spaans, pers. comm.).
Economic and social values: The area is of immense national economic importance. Thailand is the world's largest exporter of rice, most of which is grown in its Central Plains. The fishery is difficult to evaluate, since fishing is such a universally practised activity throughout the entire Central Plains region and makes a direct or indirect contribution to the economy of virtually every household. However, aquaculture for Macrobrachium prawns and for food fishes is of immense importance to the economy of small-holders as it becomes less profitable to grow rice. There are more than 1,500 commercial prawn breeders operating in the Central Plains and it is estimated that the net profit per hectare from prawn "grow-out" ponds is Bht.36,000 (US$1,380) per year (Johnson, 1986). The waterways of the region have long provided a means of communication and transport.
Fauna: The intensively cultivated nature of the area belies its very great conservation importance. Although most waterbirds occur at a relatively low density, the total number dependent upon the resources of the southern Central Plains is enormous. The Thai breeding poulations of Phalacrocorax fuscicollis, Ardeola speciosa, Bubulcus ibis, Egretta garzetta, E. intermedia, E. alba and Anastomus oscitans are believed to be entirely restricted to the southern Central Plains. While other sites such as Beung Boraphet may show more spectacular concentrations of wintering ducks, very few Ardeidae breed there. Some of the most important breeding colonies and roosting sites for herons, egrets and/or cormorants in the Central Plains are at Ban Lung Jorm (Suphanburi Province), Wat Tarn En and Wat Kanom Tai (Ayutthaya Province), Wat Ratsattha Krayaram (Samut Sakhon Province), Ban Lung Tuam (Saraburi Province), Wat Samo Son (Nonthaburi Province), Khlong Lat Krabang (Bangkok) and Wat Lam Mahamek (Pathumthani Province). The colony of Anastomus oscitans at Wat Phai Lom Non-Hunting Area is believed to support 16,000-20,000 individuals during the nesting season (December to April), and may be the largest single concentration of the species in Asia. There are other large breeding colonies of this species at Nong Samur in Ang Thong Province (several hundred pairs) and at Khan Haam in Ayutthaya Province.

The Oriental Darter Anhinga melanogaster is still present in the area, but is now believed to be threatened or endangered. One or two birds are still seen in most years at Wat Tarn En, but the species no longer breeds. Other nationally rare or endangered waterfowl which still occur annually in small numbers, but which may no longer breed, include Pelecanus philippensis, Myctenia leucocephala, Leptoptilos dubius and Threskiornis melanocephalus. A few P. philippensis are occasionally attracted by the concentration of kites at Wat Samrae in Pathumthani Province, and M. leucocephala occurs regularly on passage at Ban Lung Jorm in Suphanburi Province. Up to 90 T. melanocephalus have been recorded roosting at the Wat Tarn En Non-Hunting Area, and up to 70 have been recorded on passage at Ban Lung Jorm.

Concentrations of wintering Anatidae occur at several localities, notably the Dee Som Choke Housing Estate area in Bangkok (up to 20,000 ducks, chiefly Dendrocygna javanica and Anas querquedula, with occasionally one or two Sarkidiornis melanotos), Beung Chawak in Suphanburi Province (up to 1,000 D. javanica and 1,000 A. querquedula) and Suan Somdet in Ayutthaya Province (chiefly D. javanica). The total number of D. javanica wintering in the Central Plains is probably between 50,000 and 100,000 birds. This species and Nettapus coromandelianus are also widespread breeding birds in small numbers. Other species of waterbirds which breed or probably breed in the area include Tachybaptus ruficollis, Phalacrocorax niger, Nycticorax nycticorax, Ixobrychus sinensis, I. cinnamomeus. I. flavicollis, Rallus striatus, Porzana fusca, P. cinerea, Amaurornis phoenicurus, Gallicrex cinerea, Porphynio porphyrio, Metopidius indicus, Rostratula benghalensis and Vanellus indicus. From February onwards into the first half of the wet season, the area is particularly important for breeding Glareola maldivarum. A great many other species of shorebirds occur in winter or on passage.

The area supports large numbers of wintering Milvus migrans, and at a few sites, there are major roosts of several hundred birds in Borassus palms (e.g. 800 at Wat Samrae in Pathumthani Province). A few pairs of both this species and Haliastur indus nest, while Elanus caeruleus is very common. Aquila clanga is an annual winter visitor and passage migrant in small numbers, and A. heliaca has been recorded. Circus (aeruginosus) spilonotus is abundant and C. melanoleucos also occurs.

Earth banks along the course of the Chao Phraya river and in a few old oxbows support nesting Ceryle rudis. The better wooded parts are important for the rather local Pelargopsis capensis. Clumps of woodland support Tyto alba and a great variety of small insectivorous birds, including Pericrocotus cinnamomeus. There are large colonies of the flying fox Pteropus lylei at Wat Tarn En, Wat Kanom Tai, Wat Ko Loi, Wat Tha Sung, Wat Samo Son and Wat Pho. The Water Monitor Varanus salvator and Reticulated Python Python reticulatus both still occur in the area.
Special floral values: None known.
Research and facilities: The Bangkok Bird Club has conducted partial censuses of the Anastomus oscitans colony at Wat Phai Lom and a number of members maintain some record of important waterbird roosting or nesting sites. Other research on A. oscitans has been carried out by Buphar Amget of the Royal Forest Department, by Inkapatanakul (1986) and by Lauhachinda (1969). Many sites within the southern Central Plains are visited by bird-watchers whose records are on file at the Center for Wildlife Research, Mahidol University, Bangkok.
References: Inkapatanakul (1986); Johnson (1986); Kerdtham & Pumsaka (1983); Lauhachinda (1969); Lekagul et al. (1985).
Criteria for inclusion: 123.
Source:
 Jira Jintanugool and Philip D. Round.