Location and General Description
The Nujiang-Lancang gorge ecoregion includes the valley system through which rivers flow down from the Tibetan Plateau into the tropical hills of northern Indochina. The Nujiang (Salween) River and the Lancang (Mekong) River both originate in Southeast Tibet. The Nujiang flows into the Andaman Sea and the Lancang into the South China Sea. The Jinsha Jiang (Upper Yangtze) River also flows through this area. This ecoregion supports a wide range of habitats from semiarid river valleys to alpine ridges along an elevation and latitude gradient that ranges from near-tropical (25oN and less than 1,000 m elevation) to cold temperate (30oN and more than 6,000 m elevation). Consequently, it is difficult to characterize. The most distinctive and biologically rich parts, however, occur in the mountains and river valleys that lie in the southern part of the ecoregion. Here, intact forests support a rich assemblage of Indomalayan and Palaearctic species.
The gorge area is notably rich in temperate elevation coniferous species. The Kunming Institute of Ecology (Chinese Academy of Sciences) reports that most of the twenty mid-elevation coniferous species reported from Yunnan occur here. Some of these are endemic to the gorge area. Others have their centers of distribution elsewhere in East Asia but include no other Himalayan populations. For example, Taiwania flousiana is a rare conifer that is locally dominant at 2,200 to 2,400 m in some forests of the Nu and Gaoligong Mountain Ranges of the western Hengduan Mountains. The T. flousiana communities occur in humid areas with annual precipitation of 1,000 to 1,700 mm per year. Associated trees include Tsuga dumosa, Pinus griffithii, Cyclobalanopsis glauca, Magnolia spp., Schima spp., and members of Lauraceae (Li 1993).
Other coniferous species that are endemic to the gorge area or locally abundant here and rare elsewhere belong to the genera Keteleeria, Pseudotsuga, Platycladus, and Cunninghamia. The cedar, Cupressus ducloxiana, grows throughout dry river gorge valleys of this ecoregion, especially on basic soils derived from limestone.
This ecoregion also includes many high-elevation coniferous taxa such as Pinus spp., Larix spp., Picea spp., Abies spp., and Juniperus spp. One of the most abundant is Abies delavayi which dominates high-elevation forests at 2,700 to 4,000 m in the Cangshan, Nushan and southern Gaoligong Mountains along Yunnan’s border with Myanmar.
The gorge area supports several forest types that are azonal, i.e. forests that occur in subalpine regions that have unusual environmental conditions. Examples include sclerophyllous broad-leaved evergreen forests on sunny slopes at 2,800 to 4,200 m, dominated by subalpine oak species like Quercus aquifolioides. Secondary forests dominated by Pinus densata grow on sunny sites below 3,500 m where late-successional spruce has been removed. Secondary forests of Populus bonatti and Betula utilis stabilize steep hillsides. Some damp subalpine valleys have forests of arboreal juniper (Juniperus wallichiana), and the upper reaches of dry valleys may support forests of cypress (Cupressus duclouxiana), especially on basic soils, sometimes with an understory of scrub oak.
The Gaoligong Mountain Range, part of the southern Hengduan mountain system, forms the divide between the Nujiang River to the east and the Irrawaddy River to the west. Most of range is now protected within the recently enlarged Gaoligong Nature Reserve.
The Gaoligong National Nature Reserve is of great ecological importance. It is located along the crest (higher than 2,000 m) of the long (300 km), slender (6-12 km) Gaoligong Range. And it includes a complete vertical forest strata from subtropical evergreen broadleaf forest to subalpine conifer forest, large tracts of which are relatively undisturbed. Warm temperate evergreen broadleaf forests of oak and laurel at 2,000 m are replaced by cold temperate deciduous forests and conifer forests above 3,000 m. A precipitation gradient from southeast to northwest also affects vegetation throughout this range.
The Nujiang Nature Reserve (3,754 km2) contains a similar breadth of forest habitat and supports red pandas (Ailurus fulgens), musk deer (Moschus moschiferus) and other Himalayan forest species. Several rare, endangered or endemic mammal and bird species occur in this ecoregion. Mammals include the Gaoligong pika (Ochotona gaoligonensis) and the Yunnan snub-nosed monkey (Rhinopithecus bieti). This monkey (one of four species of "golden monkeys") is a langur (Colobinae) that is adapted to a subalpine forest habitat. It is completely endemic to the Nujiang Lancang Gorge alpine conifer and mixed forests ecoregion. The monkey forages on foliose lichen and the young leaves and shoots of trees like Betula spp. and Sorbus spp.
Birds characteristic of this ecoregion include at least two restricted-range species, brown-winged parrotbill (Paradoxornis brunneus) and Yunnan nuthatch (Sitta yunnanensis). Several species that are more widespread, but vulnerable to extinction, include giant nuthatch (Sitta magna) and white-eared pheasant (Crossoptilon crossoptilon). The rare pheasant, Sclater’s Monal (Lophophorus sclateri) is also recorded here.
Gaoligong Nature Reserve would be more effective if it were not so slender and could include more low-elevation habitat. Farmland and scrub replace forest below 2,000 m, an elevation that potentially holds very high diversity, and villages have been established up to the lower edge of the forest. Nonetheless, Gaoligong is one of Southwest China’s most important protected areas.
The Yunnan Great Rivers Project, initiated by the Nature Conservancy in partnership with the Yunnan Provincial Government, is a recent effort to establish an integrated conservation and sustainable development program for a large area that includes the southern part of this ecoregion. The project is "working to identify and promote strategies that will protect the cultural and natural resources of [the ecoregion] while encouraging the long-term economic well-being of the 3 million people who live there. Top officials in China view the project as a model for strengthening all of China's nature reserves, national parks, and protected areas.
Types and Severity of Threats
The gorge area of Yunnan has been one of China’s main regions for forestry. Until the mid 1990s, the area was intensively logged. Recent logging bans offer a strong measure of protection. The force of the ban is evident in Tengchong County, west of the Gaoligong Range, where the logging industry has been shut down. Today, much timber continues to come across the border from Myanmar.
Justification of Ecoregion Delineation
Dominant cold-temperate conifer (4a) class from the CVMCC (1979) Vegetation Map of China is the basis for the boundary, along with evergreen broadleaf (22b) and alpine shrub (27). This is comparable to the Nujiang Lancang Gorges biogeographic subunit in the Sichuan-Yunnan Highlands according to Mackinnon et al. (1996).
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Prepared by: Chris Carpenter
Reviewed by: In process