Location and General Description
The Tian Shan extend 2,500 km east-to-west across Central Asia. An extensive mountain system that comprises part of the basin-and-range topography of northwestern China, the mountains were formed by faulting and uplift during the Pliocene, 7 to 2.5 million years ago. Like the Rocky Mountains of North America, the Tian Shan are thought to be one of the greatest examples of intracontinental mountain-building in the world. Ridges average about 4,000 m in elevation; the highest summits exceed 7,400 m.
To the south, the Tian Shan are separated from the Kunlun Mountains and the Tibetan Plateau by the broad, hyper-arid Tarim Basin and Taklimakan Desert. To the north are the Kazakh Shield and the broad Junggar Basin, another large desert. Despite its location in an arid part of Central Asia, the Tian Shan Range is high enough to intercept moist arctic air from the northwest, especially during winter. At the higher elevations on the northern slopes of the range, annual precipitation (400 to 800 mm) is sufficient to support large patches of subalpine coniferous forest, or smaller patches that comprise a forest-meadow mosaic complex.
The forest zone in the Tian Shan is limited to places of sufficient moisture and warmth. Thermal tree line, where the average temperature during the warmest month equals 10oC, is situated at a maximum of 2,700 m, and elevations below 1,500 m are generally too dry to support coniferous forest. Within this broad elevation belt, forest is generally restricted to north-facing slopes. Sites that fail to meet the criteria for forest cover tend to support steppe or meadow vegetation, the character of which is determined primarily by elevation and secondarily by aspect and precipitation. This formation comprises a separate ecoregion, the Tian Shan Alpine Meadow and Tundra.
Coniferous forests in the Tian Shan tend to be quite homogeneous. The system is dominated by the spruce, Picea schrenkiana, a tall tree with a narrow crown that may form single-species stands or may grow up through a layer of broad-leaved deciduous trees. At the lower elevations, spruce associates with aspen (Populus tremula), a pioneer of landslides and other disturbed sites. At higher elevations, the associated broad-leaved species include mountain ash (Sorbus tianschanica), willow (Salix xerophila), and several birch species including Betula tianschanica, B. verrucosa, and B. microphylla.
Landscape vistas reveal a park-like mosaic of cropped meadows, scattered shrublands, rocky outcrops and dense stands of narrowly conical, dark-needled spruce. Meadows serve as pastures in most locations and are dominated by the grasses Festuca spp., Poa spp., and Helictotrichon schellianum. In moist areas within the lower forest belt, a shrub understory grows beneath the forest canopy. Species here include Lonicera spp., Cotoneaster melanocarpa, Euonymus semenovii, Rosa albertii, and R. beggeriana. Some of these species are identical to those that dominate the adjacent shrub or steppe areas. In the upper forest belt, understory shrubs form "spruce thickets." The shrubs found here (Juniperus turkestonica, J. sibirica, Caragana jubata, Salix spp., Dasiphora fruticosa, and Spiraea tianschanica) include many of the same species that comprise the alpine scrub vegetation at elevations above tree line. Where grazing pressure is high, pastures tend to acquire an increasing density of thorny, unpalatable shrubs like Lonicera spp., Rosa spp., and Berberis spp.
Grasses and forbs also occur in the forest understory. Some of the important species include the grasses Brachypodium pinnatum, Calamagrostis spp., Helictotrichon pubescens, Dactylis glomerata, Agropyron tianschanicum,and Poa nemoralis and the forbs Solidago virga-aurea, Mulgedium azureum, Doronicum altaicum, Senecio soongoricus, Crepis sibirica, Aegopodium alpestre, and Cerastium dahuricum.
Like the forests of the Himalaya, the middle-elevation coniferous forests here support diverse and luxuriant carpets of moss (Thuidium spp., Rhytidiadelphus spp., Hypnum spp., and other genera) in shady locations with understory vegetation adapted to low-light conditions (Pyrola spp. and saprophytic orchids like Corallorhiza innata).
The larch, Larix sibirica, is found in a few local areas in the extreme eastern part of the Tian Shan.
The overall plant species richness of the Tian Shan (about 2,500 species of vascular plants) is very high, relative to the other desert mountain ranges in northwestern China. Of course, part of the reason is due to a species-area effect: the Tian Shan is much larger than the other desert ranges in this area. And due to its height, the range receives more precipitation and has a greater range of climate zones than the other desert ranges. Yet the protected area network is very small.
The Tian Shan lacks adequate nature reserves for its coniferous forest vegetation. Gongliu Yunshan Nature Reserve (312 km2) protects middle-elevation habitats including Picea schrenkiana forests and alpine environments. Several other small reserves are reported, but few details are available. Tuomu’er Feng Nature Reserve (1,000 km2) is a high mountain area with alpine habitat and much rock and ice, including 7,435 m Tuomu’er Peak, the highest in the range. Lower reaches of the reserve also protect some spruce forest habitat. Various other small reserves have been declared, but the protected area remains inadequate for such a large, diverse mountain complex.
The Tian Shan includes potential habitat for snow leopards (Uncia uncia) and the ungulates that serve as their prey base. Today, however, it is uncertain whether any snow leopards remain in this area.
Types and Severity of Threats
Threats include hunting and overgrazing at the higher elevations. Local people sometimes shoot animals to obtain meat and products that they can sell. Predator species like snow leopards are also hunted because they kill livestock.
Justification of Ecoregion Delineation
The coniferous forest belt occurs up to around 2,500m and is replaced by dwarf junipers at higher elevations. In China, the boundaries are based on the CVMCC (1979) Vegetation Map of China classes larch (1) and spruce/fir (2a), that fall within Mackinnon’s (1996) Tian Shan biogeographic unit. It is possible that these classes underestimate the original extent of the forests in China. In Central Asia, the ecoregion is drawn according to the coniferous forests and shrubs ecosystem in the Tian Shan region according to Pereladova’s (1998) map of Central Asian ecosystems. According to Knystautas (1987), this area also contains a belt of broadleaf forest at lower elevations.
Chinese Vegetation Map Compilation Committee. 1979. Vegetation map of China. Map (1:10,000,000). Science Press, Beijing, China.
Grubov, V.I. 1999. Plants of Central Asia, vol. 1 Science Publishers, Inc., Enfield, New Hampshire, USA. (translated from: Rasteniya Central’nov Asii, vol. 1, 1963. Nauka Publishers, Leningrad)
Knystautas, A. 1987. The natural history of the USSR. McGraw-Hill Book Company, New York.
Laidler, L. and K. Laidler. 1996. China’s Threatened Wildlife. Blandford, London.
MacKinnon, J. 1996. Wild China. The MIT Press, Cambridge MA.
Mackinnon, J., M. Sha, C. Cheung, G. Carey, Z. Xiang, and D. Melville. 1996. A biodiversity review of China. World Wide Fund for Nature, Hong Kong.
Pereladova, O., V. Krever and M. Williams. 1997. Biodiversity Conservation in Central Asia. Moscow.
Zhao, J. editor. Zheng Guangmei, Wang Huadong, Xu Jialin. 1990. The Natural History of China. McGraw Hill Publishing Company, New York.
Prepared by: Chris Carpenter
Reviewed by: In process