Location and General Description
The Northern Annamites Rain Forests [IM0136] ecoregion lies largely in Laos but with a significant area across the crest of the Annamite Range in Vietnam. Geological substrates are varied over this ecoregion, but there are notable large areas of limestone karst topography. Climatic conditions often change abruptly along the mountain crest. Lower moisture input from the northeast monsoon winds produces mean annual rainfall in montane habitats of this ecoregion in Laos that are lower at 1,500-2,500 mm and more seasonal than those of the Northern Vietnam Lowland Rain Forests [IM0141]. However, higher elevations produce cooler temperatures and thus distinct conditions for plant growth. This ecoregion shows strong floristic relationships with the mountains of northern Vietnam and southern China and with more southern areas of the Annamite Range. Vascular plant levels of endemism are high.
Mesic lower montane forests at 800-1,200 m in the northern Annamite Range generally consist of a two-tiered forest canopy reaching to about 15-25 m in height. The dominant floristic elements in this forest are the Myrtaceae, Fagaceae, Elaeocarpaceae, and Lauraceae, with high endemism. Also notable in this forest community is the presence of species of Podocarpaceae. Epiphytes, particularly orchids, are abundant and rich in endemic species. The dense canopy structure of undisturbed humid montane forest allows little light to penetrate to ground level, so understory vegetation is sparse. However, the understory in open areas of forest often supports thick stands of woody bamboo (Chimonobambusa and Dendrocalamus). It has been suggested that typhoons that regularly reach this area provide a natural disturbance regime that continually opens the canopy and promotes bamboo growth.
Less mesic sites with thin, acid soils at elevations up to 1,500 m often support pine forests with Pinus kesiya as the dominant species. Under reasonable growing conditions, P. kesiya reaches 20-30 m in height. The most common tree associates of P. kesiya are Keteleeria evelyniana, Pieris ovalifolia, Schima wallichii, and Tristania merguensis. Frequent fire seems to promote the establishment and maintenance of these pine forests at the expense of hardwoods. A second community of open conifer forest in montane areas of northern Laos is dominated by Keteleeria evelyniana, which may occur in pure stands or mixed with Pinus kesiya and species of Fagaceae. Keteleeria may reach up to 35 m in height and occurs from subtropical areas of southern China southward into Laos and Vietnam.
Humid montane forests at about 1,200-1,800 m may support a rich forest dominated by Fokienia hodginsii, Podocarpus imbricatus, and Cunninghamia lanceolata. Fokienia can reach 40-50 m in height and 1.5 m in diameter in this community. The cool and moist conditions of these Fokienia forests often promote lush growth of cryptogamic epiphytes and an accumulation of organic litter on the forest floor.
Long histories of human impact in the northern Annamite Range of Laos and Vietnam have led to the degradation of large areas of what were once montane evergreen forest. Such forests have been replaced by thickets or savannas with diverse structure depending on the degree of degradation and the time for successional recovery since major disturbance. Thickets may include diverse assemblages of woody species or be dominated by pure stands of a single colonizing species.
Further floristic and faunal surveys are needed to assess the biological potential of this ecoregion, especially in Laos. However, the Vietnamese portion of this ecoregion contains high species diversity and is notable for its significant endemism.
This treasure trove of biological diversity is still divulging its true riches. Each new survey turns up new species of mammals, birds, fishes, herptiles, fishes, butterflies, and plants. Of the 134 mammals now known from the ecoregion, three are near-endemic species and four are endemic (table 1). More than half of these are recently described species; therefore, it is very likely that several species could be added to this list as surveys continue.
Table 1. Endemic and Near-Endemic Mammal Species.
Cercopithecidae Semnopithecus francoisi
Hylobatidae Hylobates gabriellae
Bovidae* Pseudoryx nghetinhensis*
Cervidae* Megamuntiacus vuquangensis*
Cervidae* Muntiacus truongsonensis*
Cervidae* Muntiacus (Buhouang muntjak)*
Cercopithecidae Pygathrix nemaeus
An asterisk signifies that the species' range is limited to this ecoregion.
The mammal assemblage also includes several threatened species, including the endangered Douc langur, tiger (Panthera tigris), Asian elephant (Elephas maximus), gaur (Bos gaurus), banteng (Bos javanicus), serow (Capricornis sumatraensis), and particoloured flying squirrel (Hylopetes alboniger) (IUCN 2000).
The ecoregion overlaps with a Level I TCU and two Level II TCUs (Dinerstein et al. 1997), but the prey base necessary to maintain tigers is declining rapidly because of hunting pressure. Most of the habitat in the ecoregion is too steep for elephants, which are limited to the lower elevations. But as these more accessible midmontane forests are cleared for agriculture, elephants are becoming pocketed in small forest patches.
The bird fauna in the ecoregion is estimated at more than 525 species, including 3 near-endemic and 3 endemic species (table 2). The imperial pheasant (Lophura imperialis) and Edwards's pheasant (L. edwardsi) are critically endangered, and the Vietnamese fireback (L. haitensis) and white-winged duck (Cairina scutulata) are endangered species found in this ecoregion. Not surprisingly, the ecoregion overlaps with an EBA, Annamese Lowlands (143), which contains nine restricted-range bird species (Stattersfield et al. 1998).
Table 2. Endemic and Near-Endemic Bird Species.
Family Common Name Species
Phasianidae Imperial pheasant* Lophura imperialis*
Phasianidae Edwards's pheasant Lophura edwardsi
Phasianidae Vietnamese fireback* Lophura haitensis*
Phasianidae Crested argus Rheinardia ocellata
Timaliidae Short-tailed scimitar-babbler Jabouilleia danjoui
Timaliidae Sooty babbler* Stachyris herberti*
An asterisk signifies that the species' range is limited to this ecoregion.
More than half of this ecoregion has been cleared or degraded. However, the forests in the northwest part of the ecoregion are still in fairly good condition. A large block of montane forest straddles the Laos-Vietnam border. There are nine protected areas that cover about 12,200 km2 (26 percent) of the ecoregion (table 3). Of these, five-Pu Mat in Vietnam and Nam Kading, Phou Xang He, Nakai-Nam Theun, and Khammouane Limestone NBCAs in Laos-exceed 1,000 km2.
Table 3. WCMC (1997) Protected Areas That Overlap with the Ecoregion.
Protected Area Area (km2) IUCN Category
Ho Ke Go [IM0141] 180 PRO
Nam Kading 1,600 VIII
Pu Mat 1,400 ?
Dong Phong Nha 440 IV
Phou Xang He 1,170 VIII
Nakai-Nam Theun 3,710** VIII
Hin Namno 865 VIII
Vu Quang 850 IV
Khammouane Limestone NBCA* 2,000 VIII
Ecoregion numbers of protected areas that overlap with additional ecoregions are listed in brackets.
*Now commonly called Phou Hin Poun NBCA (Phou Hin Poun = limestone mountain).
**Currently undergoing redelineation of boundaries, so the area will differ.
Because of the high elevations and steep slopes of this ecoregion, human population density is moderate (MacKinnon 1997). However, shifting cultivation and logging in the submontane forests are major sources of deforestation (IUCN 1991). The resultant erosion in the steep slopes exacerbates degradation and drives shifting cultivation into higher and more remote areas (IUCN 1991). Cleared forests usually regrow as grasslands of Imperata cylindrica or bamboo forests (Bambusa, Thyrsostachys, and Oxytenanthera) (FAO 1981).
Types and Severity of Threats
Both Laos and Vietnam have begun or are planning to develop several major hydropower schemes that will inundate large areas of habitat and provide ready access to intact forest areas, thus increasing the probabilities of further habitat degradation. Major illegal and legal logging and local and transboundary wildlife poaching and trade (Laos into Vietnam) still occur. The presence of unexploded ordnances similarly poses a severe threat to wildlife, researchers, and protected area staff.
Justification of Ecoregion Delineation
In a previous analysis of conservation units across the Indo-Malayan realm, MacKinnon (1997) included both lowland and montane tropical moist forests along the northern Annamite mountains within a single sub-biounit, the North Annam subunit 05c. In keeping with our rules for delineating ecoregions, we separated the montane and submontane forests from the lowland forests using the 1,000-m contour from a DEM. The southern boundary to separate the northern from the southern Annamites was based on the Hai Van Pass, widely recognized as a boundary between the northern and southern flora. Thus, the moist forests that lie along the spine of the northern Annamite Range, above 1,000 m in elevation and between 19(N and the low hills between Hue and Da Nang were placed in the Northern Annamites Rain Forests [IM0136].
References for this ecoregion are currently consolidated in one document for the entire Indo-Pacific realm.
Indo-Pacific Reference List
Prepared by: Ramesh Boonratana, Philip Rundel, and Eric Wikramanayake