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 intra-continental mountain-building in the world. Ridges average about 4,000 m while the highest summits exceed 7,400 m elevation.
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 is the Kazakh Shield and the broad Junggar Basin, another large desert. Despite their location in a very 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, annual precipitation of 400 to 800 mm is enough to support subalpine conifer forests in some locations and a variety of steppe and meadow communities, stratified by elevation, over extensive areas throughout the range. At the lower elevations, annual precipitation totals of 100 to 200 mm support steppe grassland vegetation.
Heavy snowpack at the high elevations is responsible for numerous oases and rivers in the dry Tarim Basin. These support the Tarim Basin Deciduous Forests ecoregion and, more recently, extensive irrigated agriculture. Despite the orogenic precipitation, the climate of the Tian Shan is strongly continental. Large seasonal variations in temperature occur due to the temperate latitude (41-45oN) and distance from the ocean. High elevation generates a large diurnal variation in temperature.
Vegetation of the Tian Shan was determined during the Tertiary when boreal and arctic species migrated southward during the uplift of the range to mingle with communities of plants on the lower slopes that are more characteristic of the steppes and deserts of Central Asia.
Today, vegetation is stratified according to elevation so that several distinct meadow and steppe communities occur along a gradient that ranges from the base of the mountains at about 1,000 m to the edge of snowline at about 3,300 to 4,200 m. Along this gradient, moisture availability is an important variable. At the lower elevations, it determines the magnitude of drought stress. At the higher elevations, it determines, among other things, the presence or absence of a protective snow cover. In general, forest (mainly spruce Picea) is restricted to more mesic sites on north-facing slopes in the subalpine zone (2,000 to 2,600 m), and forest stands are intermixed with broad swaths of sedge-meadow. Elsewhere, meadow steppe is the dominant ground cover with the character of the vegetation determined primarily by elevation and secondarily by precipitation.
A transect shows the following floristic trends. Vegetation at 800 to 1,100 m consists of wormwood Artemesia steppe with grasses and annual species more abundant in the moist western regions than in the drier eastern regions. At 1,100 to 1,500 m on south-facing slopes, desert steppe is replaced by dry, sparse grassland dominated by the grasses Stipa spp. and Festuca spp., with associated shrubs (Artemisia spp.) in the west and Reaumaria songorica and Anabasis brevifolia in the east. This "grassland-steppe" vegetation persists over a broad altitude range to merge with alpine vegetation above 2,700 m. The alpine zone here is dominated by low-growing herbaceous Kobresia spp. sedge in the meadows. These are very extensive, especially in the eastern part of the Tian Shan and support, beside the sedge Kobresia and Carex, various alpine forbs like Papaver nudicaule, Arenaria formosa, Potentilla nervosa, Aster alpinus, Leontopodium ochroleucum and numerous species of Gentiana, Androsace, Saxifrage, and Ranunculus. Floristically, the high elevations of the Tian Shan seem very similar to the Tibetan Plateau. This stands to reason as both regions have obtained their alpine flora from the Palaearctic in the recent geological past.
North-facing slopes are shrubbier at the low elevations (Caragana, Spiraea, Cotoneaster) and give way at about 2,500 m to a parklike forest-meadow mosaic in which the meadows are dominated by the grasses Festuca spp., Poa spp. and Helictotrichon schellianum. Here, shrub taxa include some of the same genera found at lower elevations, together with higher-elevation taxa like honeysuckle (Lonicera spp.), rose (Rosa spp.) and barberry (Berberis spp.), most of which are thorny and respond favorably to high grazing pressure. Forests, described as a distinct ecoregion, the Tian Shan Montane Coniferous Forests, are dominated by the spruce (Picea schrenkiana) that occurs on northern slopes from 2,700 to 3,700 m.
Like the Himalaya, alpine elevations support shrubbier vegetation on northern exposures because these hold a protective blanket of winter snow. Another important factor at the highest (sub-nival) elevations is soil stability. Soils made restive by solufluction support a restricted assemblage of plants (Saxifragaceae, Brassicaceae, and Corydalis) that are adapted to sliding on scree while stable sites support slow-growing turf-sedges, rosette plants like Saussurea involucrata, and a number of cushion growth forms.
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 of Central Asia. And due to its height, the range receives more precipitation and has a greater range of climate zones than the other desert ranges.
Mammals recorded from the Tian Shan include Asiatic wildcats (Felis sylvestris), argali (Ovis ammon karelini), goitered gazelles (Gazella subgutturosa), Asiatic ibex (Capra ibex), snow leopards (Uncia uncia), wolves (Canis lupus) and brown bears (Ursus arctos). Snow leopard populations in this ecoregion are reported to be severely diminished or perhaps extirpated.
The Tian Shan is not an endemic bird area, but two species, little bustard (Otis tetrax) and Houbara bustard (Chlamydotis undulata), occur in this ecoregion. Both of these species are widespread but rare with declining populations.
The Tian Shan lacks adequate nature reserves for its steppe-meadow ecoregion. There are a few protected areas. One is Bayin Buluke (1,000 km2) that protects habitat for waterfowl like swans Cygus spp. at foothill elevations. Another is Tuomu’er Feng (1,000 km2) a high-mountain area with alpine ecosystems, some upper-elevation forests and much rock and ice, including 7,435 m Pobeda Peak. Various other small reserves have been declared, but the protected area remains inadequate for such a large, diverse complex.
Types and Severity of Threats
Overgrazing at the higher elevations by horses, sheep and goats, and at the lower elevations by cattle have been reported as a conservation problem for this ecoregion. Hunting, for meat, for income, or in response to livestock depredation is also probably responsible for diminished populations of some mammal and bird species. The Tian Shan supports much potential habitat for snow leopards and the ungulates that serve as their prey base. Today, however, it is uncertain whether any snow leopards remain in this area. Hunting pressure from the Kazakh herdsmen whose livestock graze the high elevation meadows is probably severe.
Mining activity occurs on the slopes of the Tian Shan for coal, iron, lead and zinc
Justification of Ecoregion Delineation
The ecoregion consists of the high altitude areas in the Tian Shan that extend into Central Asia. The ecoregion is predominantly formed by the CVMCC (1979) Vegetation Map of China classes alpine meadow (68a,b) and grasslands (42,48). This is comparable to the Tian Shan biogeographic subunit in the Pamir-Tian Shan Highlands according to Mackinnon et al. (1996). In Central Asia, this ecoregion includes the cryophytic steppes and meadows of the Kashgarian-Tian Shan and North Tian Shan regions according to Pereladova’s (1998) map of Central Asian ecosystems.
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)
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: Olga Pereladova