The IBA is located inside Nakai-Nam Theun National Protected Area, in central Lao P.D.R. The topography of the IBA is very rugged, and dominated by the main ridge of the Annamite mountains, which runs along the east of the IBA, forming the international border with Vietnam. The highest point on this ridge is Phou Laoko, at 2,286 m asl. The vegetation of the IBA is dominated by dry evergreen forest up to 1,800 m asl, with upper montane forest above this elevation. In addition, Fokienia forest is distributed between 1,400 and 1,700 m asl, (Thewlis et al. 1998). Furthermore, wet evergreen forest occurs in the east of the IBA, close to the international border with Vietnam (Timmins and Evans 1996). To the east, the IBA is contiguous with Vu Quang IBA (VN022) in Vietnam. The IBA supports a rich montane avifauna, including the globally threatened Beautiful Nuthatch Sitta formosa, although the total area of upper montane habitat is lower than that at a number of other sites in the Annamite mountains and Northern Highlands. The extensive, relatively undisturbed forest within the IBA is important for the conservation of a number of species of hornbill. Most notably, the IBA supports what is probably the largest population of Rufous-necked Hornbill Aceros nipalensis in Indochina (R. J. Timmins in litt. 2002). The IBA receives high levels of precipitation, with some areas being wet all year round, as a result of which the fauna of the IBA shows a number of affinities with that of wet evergreen forests on the eastern flank of the Annamite mountains. For example, the IBA is thought to support populations of at least two of the restricted-range species found in the Annamese Lowlands Endemic Bird Area: Crested Argus Rheinardia ocellata and Short-tailed Scimitar Babbler Jabouilleia danjoui, although, given the much larger populations of these species in parts of Vietnam, the populations at the IBA are of low global significance. Furthermore, the IBA is one of the few sites in Lao P.D.R. known to support Saola Pseudoryx nghetinhensis (Duckworth et al. 1999). Moreover, it has the most species-rich documented large mammal community in Lao P.D.R., and, while this partly reflects survey coverage, the site is unquestionably of exceptional international importance for mammals, especially those with large area requirements (Duckworth 1998).
A fairly good impression was obtained of the avifaunas of the Cypress forests and other areas above 1000m in the central mountains (Timmins and Evans 1996).
Non-bird biodiversity: Timmins and Evans (1996) recorded Back-striped Weasel Mustela strigidorsa in the IBA. Timmins and Evans (1996) also recorded Asiatic Black Bear Ursus thibetanus, Clouded Leopard Pardofelis nebulosa, Leopard Panthera pardus and Tiger P. tigris in the Central Mountains of Nakai-Nam Theun, but is not clear whether any of these records are from within the IBA. Tobias (1997) recorded Hodgson's Porcupine Hystrix brachyura at the IBA in 1997.Gibbons, presumed to be White-cheeked Crested Gibbon Hylobates leucogenys, were heard on three occasions in montane evergreen forest between 1,500 and 1,600 m asl in 1997 (Tobias 1997). Timmins and Evans (1996) also heard gibbons calling in the IBA. They also recorded Slow Loris Nycticebus coucang, Pygmy Loris N. pygmaeus, Rhesus Macaque Macaca mulatta, Bear Macaque M. arctoides, Douc Langur Pygathrix nemaeus, and, provisionally, Assamese Macaque M. assamensis in the Central Mountains of Nakai-Nam Theun but it is not clear if any of these species occur within the IBA.The IBA supports cypress forest dominated by Fokienia hodginsii.Timmins and Evans (1996) recorded Asian Elephant Elephas maximus, Gaur Bos gaurus and Southern Serow Naemorhedus sumatraensis in the Central Mountains of Nakai-Nam Theun but it is not clear if any of these species occur within the IBA.
Pressure/threats to key biodiversity
One of the major threats to biodiversity at the IBA is hunting, which is a particular threat to populations of certain large mammal species, hornbills and, possibly, Crested Argus. However, large parts of the IBA are very remote, and separated from human habitation by large areas of primary forest. Hunting pressure in these areas appears to be relatively low, and most visitors appear to be NTFP collectors (Tobias 1997). In 1994, the valuable timber species Fokienia hodginsii was being selectively extracted from some parts of the IBA using helicopters, and a logging road was under construction into the area. By 1996, however, both Fokienia extraction and road construction had ceased (Thewlis et al. 1998). As of 1997, the impacts of these activities appeared to have been minor (Tobias 1997). Another major threat to biodiversity at the IBA is clearance of forest for shifting cultivation, which is progressively expanding in the south and north-east of the IBA, where the IBA is bordered by agricultural areas, but most rapidly in the north-east of the IBA, where there has been a recent influx of ethnic minority migrants, creating enclaves of human settlement within the IBA (Thewlis et al. 1998). During the mid-1990s, there existed plans to build roads to all enclave villages, which, if they went ahead, would facilitate natural resource exploitation (Thewlis et al. 1998), and piecemeal habitat conversion.