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.
BirdLife International (2020) Important Bird Areas factsheet: Nakai-Nam Theun. Downloaded from http://www.birdlife.org on 07/04/2020.