Location and General Description
This ecoregion is situated on the upper reaches of the Ping, Wang, Yom, and Nan rivers, tributaries of the Chao Phraya, and the upper Pasak River. Part of the area also lies in the Mekong Drainage. Annual rainfall throughout the region is around 1,000-1,200 m, and mean minimum and maximum temperatures are around 20°C and 32°C, respectively (Meteorological Department 1987). Most of the area is on steep hill slopes, interspersed with narrow, north-south-aligned valleys carrying alternately swift-flowing and slow-flowing rivers.
Teak (Tectona grandis) is a co-dominant of the moist mixed deciduous forest characterizing this zone. A detailed description of vegetation at one site in Mae Yom National Park, Phrae Province, Thailand is given in Center for Conservation Biology (1992). Teak contributed 27.2 percent of all tree individuals, Xylia xylocarpa 11.4 percent, and Pterocarpus macrocarpus 10.0 percent. Other important tree species in the mixed deciduous community included Millettia brandisiana (6.7 percent), Lagestroemia cochinchinensis (4.1 percent), Bombax kerrii (3.0 percent), and Afzelia xylocarpa (2.3 percent). Bamboo is common and is an indicator of high human disturbance. This vegetation type extends from the valley floors (which range from less than 200 m elevation to about 400 m elevation, depending on site) at varying distances from the montane transition (800-1,000 m).
Most large mammals were extirpated from this ecoregion by the 1960s or early 1970s, but small populations of elephants, banteng, and gaur still remain at a few sites. There are at least five banteng individuals in Sri Satchanalai National Park and a few gaur in Thung Saleng Luang National Park (Srikosamatara and Suteethorn 1995). There is very little information on carnivores. It is conceivable that tiger may be already extirpated from this region. The ecoregion overlaps with two Level I TCUs and one Level II TCU (Dinerstein et al. 1997).
The Ping River once supported important riparian bird communities, including such species as Brahminy kite, river lapwing, and river tern, associated with rapids, sand bars, and islands. Possibly the largest such area of rapids in the region, on the Ping River (McClure and Lekagul 1961), was submerged by the Bhumibol Dam in the early 1960s, so this rich river community has now disappeared from most areas (Murray 1995). Green peafowl (Pavo muticus) was once widespread. It is still represented by a few populations in this ecoregion, the largest of which are found on the northern border of Mae Yom National Park. Small populations have been found persisting at three other sites in Chiang Mai Province (Wina Meckvichai, pers. comm., 2000).
Some of the forest bird species would have been shared with those found in the Central Indochina Dry Forests [IM0202], but bird communities have been affected greatly by the gradual loss of large trees. A few green imperial pigeons (Ducula aenea) were still present in Mae Yom National Park in 1991 (Center for Conservation Biology 1992). Yellow-footed pigeon (Treron phoenicoptera) also still occurs in the region but has been reduced to near extirpation. Huge flocks of parakeets, mainly Psittacula alexandri, were recorded by Deignan (1945), and Alexandrine parakeet (P. eupatria) was once widespread. The former is still present in small numbers, along with both P. roseata and P. finschii, but P. eupatria probably is close to being extirpated.
The only non-breeding-season record of the globally threatened blackthroat (Luscinia obscura), which breeds in west and central China, was from lowland forest or secondary growth in this region (Lekagul and Round 1991). There is a subsequent sight record (March 2000) of two birds in lowland forest remnants in the newly established Mae Jarim National Park, Nan Province.
Overall, because the area supports the highest proportion of woody cover of any region of Thailand, it continues to be of great conservation importance. The continued presence of such large and sensitive species as green peafowl raises the possibility that some species of birds and perhaps large mammals may be able to recolonize regenerating secondary forest, given a likely future reduction in hunting pressure. Even in Thailand, much of this area has not been surveyed and assessed for its biodiversity attributes.
The valleys of this ecoregion have long been cultivated, and shifting cultivation has been responsible for more recent destruction of upland regions (IUCN 1991). In Thailand, previously itinerant hill tribes such as the Hmong and Yao, who cultivate upland rice and opium replacement crops such as coffee, cabbage, and ornamental flowers, have settled illegally in many areas that are ostensibly protected. The subsistence and, increasingly, commercial agricultural activities of both upland shifting cultivators and especially lowland Thai farmers have been responsible for much of the recent degradation that has occurred inside and outside Thailand's protected areas. Large areas of forest land are now occupied by cotton fields and fruit orchards. Almost all remaining forest has been selectively logged and is significantly degraded, and has been damaged by burning and other disturbances. The predominance of teak probably has been increased by burning, although most larger trees are gone. In addition, much of this area is also occupied by teak plantations rather than native forest. In Laos, teak forests have been mostly destroyed; meanwhile, shifting cultivation, regular fires, and continual erosion of the hills turn these areas into scrubland of bamboo or other grass species, preventing reestablishment of the original forest (FAO 1981). However, overall, the original habitat has been heavily altered.
Small-scale hunting is widely practiced and has greatly reduced populations of mammals and larger birds. There is a large amount of trade in wildlife and wildlife parts throughout the region. One such market specializing in wildlife is situated near the provincial forestry office in Lampang. Sale of wildlife, though illegal, continues with little or no official interference.
Riverine habitat has been greatly altered. River valleys were first settled and agriculture practiced along their banks. In silty areas, dry season cultivation follows the retreating water so that almost no undisturbed riparian habitat remains. Three of the four major rivers of northern Thailand now have hydroelectric dams. In addition, the spread of Mimosa pigra into disturbed areas has replaced areas of native riparian and floodplain scrub and low herbage. Construction of new roads and enlargement of existing roads under government development programs seem likely to further fragment the larger habitat patches.
There are fourteen protected areas in this ecoregion (table 1). For some ecoregions, we were not able to get accurate area information, so the total area reflects only those listed.
Table 1. WCMC (1997) Protected Areas That Overlap with the Ecoregion.
Protected Area Area (km2) IUCN Category
Namtok Chatrakarn National Park [IM0121] 310 ?
Doi Chiang Dao IV
Doi Pha Chang [IM0202], [IM0137] 180 IV
Doi Luang Wildlife Sanctuary 100 IV
Doi Luang National Park II
Doi Khun Tan 255 II
Wiang Kosai 440 II
Mae Yom Si Satchanalai 170 II
Thung Saleng Luang 1,260 II
Mae Ping [IM0119], [IM0202] 480 II
Khun Jae II
Jae Sorn 592 II
Mae Jarim II
Ecoregion numbers of protected areas that overlap with additional ecoregions are listed in brackets.
Types and Severity of Threats
The construction of a combined hydroelectric and irrigation dam on the Yom River inside Mae Yom National Park, which supports one of the best and most extensive remnants of teak-dominated forest, has been approved by the Thai government.
Hunting is widespread and has reduced or locally extirpated populations of mammals and larger birds. Illegal logging carried out by influential businesses in conjunction with corrupt officials and police officers is a major threat. A Thai government body, the Forest Industries Organization, is empowered to remove and sell illegally felled timber from the forest, including inside protected areas. Therefore, there is no incentive to suppress illegal logging. In addition, many villages around Mae Yom National Park and other areas also continue a thriving, small-scale, illegal timber trade, assembling teakwood houses, which can be readily dismantled and sold. Fires set by farmers and hunters sweep through the region annually.
Justification of Ecoregion Delineation
The tropical moist deciduous forests to the west and northwest of the Luang Prabang Range in northwestern Thailand and Laos are an extension of the teak (Tectona grandis)-dominated deciduous forests (Rundel and Boonpragob 1995), but the vegetation community of the moist deciduous forests in the Mekong plains near Vientiane are dominated by Fabaceae, Lythraceae, and Rubiaceae. Therefore, these forests were placed in separate ecoregions, the former in the Northern Thailand-Laos Moist Deciduous Forests [IM0139] and the latter in the Northern Khorat Plateau Moist Deciduous Forests [IM0138].
References for this ecoregion are currently consolidated in one document for the entire Indo-Pacific realm.
Indo-Pacific Reference List
Prepared by: Philip D. Round, Sompoad Srikosamatara, Nantiya Aggimarangsee, and Eric Wikramanayake