Central Tibetan Plateau alpine steppe
Too cold and sparsely vegetated to support human pastoral activity, the Central Tibetan Plateau alpine steppe ecoregion supports some of the most intact ecosystems in temperate Eurasia. Herds of wild ungulates and their predators roam across landscapes at elevations of 5000 metres and higher. Feather grasses, cushion plants and alpine forbs comprise most of the vegetation. However, plant cover seldom exceeds twenty percent.
Location and General Description
This ecoregion includes the southern part of the Changtang, a vast section of western Tibet substantially drained by the Yellow River and its tributaries, and the high, enclosed basins that extend northeast to Qinghai Lake (Koko Nor). The Changtang, thought to have been uplifted earlier than the rest of the Tibetan Plateau, consists of a lofty basin of gently rolling plains and widely scattered, brackish lakes, most of which have been losing water to evaporation throughout the Holocene. Today, lake levels may be as much as 200 metres (m) below their fossil shorelines. Unlike other places of similar elevation throughout the Himalayan region, the Changtang Plateau appears to have been hardly glaciated during the Pleistocene. The whole area possesses a cold, arid and windy climate. The northern part of the Changtang is especially cold with widespread, continuous permafrost at elevations above 4100 m where mean annual temperatures are about –3oC. The depth of the thawed layer is very shallow at the higher elevations, about 60 centimeters (cm) at 5,000 m elevation. Annual precipitation declines northwestward throughout this ecoregion from about 400 to 200 millimeters (mm).
The Tibetan Plateau, treeless except in the southeastern river valleys, supports a range of alpine vegetation types that includes meadow, steppe, cold desert and sub-nival cushion plant communities at elevations ranging from 3,500 to nearly 6,000 m. Dry, cold, and expansive, the Tibetan Plateau possesses an alpine landscape of complex zonation with a general trend from moist alpine scrub to steppe vegetation to high, cold desert along a transect from southeast to northwest.
Because the Tibetan Plateau is gently inclined, with the highest elevations in the northwest, latitude and elevation jointly define a gradient of cooling temperatures from southeast to northwest. Latitude affects temperature by controlling the angle and intensity of solar radiation. Elevation affects temperature by controlling the air pressure and hence the heat capacity of the air.
The alpine zone in Tibet includes all areas where the average temperature during July, the warmest month of the year, is not more than 10oC. In fact, almost all of the plateau except the southern river valleys--the Indus, Sutlej, and Tsangpo (including the Lhasa Valley)–falls within this "high cold" alpine zone. Within the alpine, moisture determines whether a region supports meadow, steppe or alpine desert vegetation. As precipitation decreases northwestward, vegetation changes from dense scrub to meadow to steppe to desert. In Tibet, forests are confined to valleys. Forests never occur on the plateau due to cold, continental climate and the fact that the plateau lies above the 10o isotherm.
Dominant vegetation is a sparse steppe of Purple Feathergrass (Stipa purpurea), a hardy species for which this ecoregion is the center of distribution. Plant cover seldom exceeds 20 percent. Some cushion plants and woolly alpine forbs like Leontopodium, Saussurea, Arenaria bryophylla, and Thylacospermum caespitosum also grow here and owe their distinctive morphology to the rigors of the alpine environment, including a short growing season, persistent winds, high potential evapotranspiration, and intense solar radiation. As the climate across the Changtang becomes colder and drier on a transect from southeast to northwest, dominant plant species change along a sequence of Kobresia pygmaea (a turf-forming sedge), Stipa purpurea (a grass that forms sparse groundcover), Carex moorcroftii (a sedge), and finally cushion forbs like Krascheninnikovia compacta. Communities of S. purpurea and C. moorcroftii cover the greatest area, with Carex generally replacing Stipa with increasing elevation. In general, Stipa provides better forage than Carex so that there is some correlation between vegetation and the distribution of ungulates.
High areas that receive more precipitation and are exposed to the prevailing winds tend to support a denser and more diverse community of cushion plants, while the drier locations are dominated by a single species, C. compacta. Lower-elevation areas may have dwarf shrubs like Ajania and Potentilla fruticosa as well as herbaceous legumes like Astragalus, Oxytropis, and Thermopsis.
Qinghai Lake (Koko Nor) is located at the northeastern end of this ecoregion. Situated at a lower elevation (3,200 m), the gently rolling landscapes around this lake support cold temperate meadow vegetation that differs from the steppes of the Changtang because it consists of a closed mat of Kobresia sedge and forbs rather than the thinly dispersed steppe grasses like Stipa and Festuca that characterize vegetation at higher elevations to the southwest.
The Changtang Plateau is not only too high and cold for agriculture, it is also inhospitable to the semi-nomadic pastoralists that traditionally graze livestock over much of the Tibetan Plateau. As a result, the Changtang supports some of the largest and most intact faunal assemblages in Asia, with herds of ungulates providing prey base for predators like lynx (Felis lynx), wolves (Canis lupus), snow leopards (Panthera uncia), and brown bears (Ursus arctos).
In 1992 the government of the Tibetan Autonomous Region established the Changtang Nature Reserve, a vast region of 247,000 km2 with an additional 37,000 km2 adjoining to the west. According to Schaller (1998), the actual size is about 334,000 km2, about the size of New Mexico. It is one of the largest nature reserves in the world, certainly the largest outside the polar regions.
Several ungulate species inhabit the alpine steppes of the central Tibetan Plateau. These include Tibetan antelope or chiru (Pantholops hodgsoni), the only genus of large mammal endemic to the Tibetan Plateau, well adapted to moving quickly across expanses of flat to rolling steppe. Tibetan Argali (Ovis ammon hodgsoni), the largest of the sheep occurs here, but this CITES listed species is rare. Blue sheep (Pseudois nayaur) are abundant, but hunted intensively in many areas. Tibetan gazelles (Procapra picticaudata) are distributed widely over the central steppe region of Tibet where they frequent expansive flat or rolling areas of alpine meadow or steppe. Wild yaks (Bos grunniens) were once common throughout this region but have been hunted to extinction or near-extinction by local pastoralists in all but the remotest part of the Kunlun Range, north of this ecoregion. It is not always clear whether the surviving remnant wild yak populations are truly wild, feral domestics or hybrids. Schaller estimates that about 9,000 of these animals survive on the Tibetan Plateau, mostly along the northern margin.
Although the Tibetan Autonomous Region has eleven species of deer, only three commonly occur outside the southeastern forests. Of these, only the white-lipped deer (Cervus albirostris), endemic to the Tibetan Plateau, inhabits the alpine steppes including the eastern part of the Changtang eastward into Qinghai.
Kiang (Tibetan wild asses, Equus hemionus) are still quite common in this ecoregion, although numbers have declined drastically during the past 100 years. Even so, numbers are sufficient that the species is not immediately threatened.
Like other regions of the Tibetan Plateau and Central Asia, large carnivores (snow leopards, brown bears, wolves and lynx) also occur here at low density, supported in part by their smaller prey species like Tibetan woolly hares (Lepus oiostolus), Himalayan marmots (Marmota himalayana) and black-lipped pika (Ochotona curzoniae).
Bird species that breed at Qinghai Lake include the bar-headed goose (Anser indicus), brown-headed gull (Larus brunnicephalus), the larger black-headed gull (Larus ichthyaetus), and large colonies of great cormorant (Phalacrocorax carbo) that nest on rocky pinnacles above the lake. Black-necked cranes (Grus nigricollis) and pied avocets (Recurvirostra avosetta) also breed here.
Because it remains quite pristine, the Changtang is especially vulnerable to degradation. Niao Dao (Bird Island) Nature Reserve (533 km2), actually a group of five small islands, is located near the west end of Qinghai Lake and provides important summer breeding habitat for many migratory bird species. Other sandy wetland areas lie along the lake’s eastern and northwestern shores.
Types and Severity of Threats
Though relatively numerous (perhaps 75,000), Tibetan antelopes are being slaughtered at an unsustainable rate for their high-quality wool which may be smuggled into India or bartered for other protected animal products. Argali are both very rare and poorly studied and may be subject to disease as well as hunting pressure. Hunting of blue sheep could be sustainable if well-managed.
Qinghai Lake’s shoreline is subject to heavy grazing, although the relationship between grazing and the quality of the bird habitat is not clear. Recent increases in nature tourism also need to be considered as a potential threat to the habitat quality here, since the tourist season corresponds to the birds’ breeding season. It is important to prevent the tourists from approaching too close to the nesting birds.
Justification of Ecoregion Delineation
This ecoregion covers the western part of Qinghai-Xizang Plateau, an intermontane basin surrounded by the Kunlun and Gandise mountains. The northern boundary was defined by a digital map of Tibetan rangelands separating ‘cold semi-arid high mountain rangeland’ from ‘extremely cold arid high mountain grassland.’ The southern boundary corresponds to the vegetation change transition from open shrubland to grassland as defined in the Hansen map of global land cover produced by University of Maryland. This region is comparable to class 48 (alpine meadow) on the CVMCC Vegetation Map of China.
- Chinese Vegetation Map Compilation Committee. 1979. Vegetation map of China. Map (1:10,000,000). Science Press, Beijing, China. ISBN: 7030089561
- Chang, D.H.S. 1981. The Vegetation Zonation of the Tibetan Plateau. Mountain Research and Development 1(1): 29-48.
- Commission on Integrated Survey of Natural Resources. 1992. Rangeland Types of Xizang (Tibet) (1:2,500,000). Beijing, China.
- Hansen M.C., R.S. Defries, J.R.G. Townshend, and R.Sohlberg. 2000. Global land cover classification at 1 km spatial resolution using a classification tree approach. International Journal of Remote Sensing 21(6-7):1331-1364.
- MacDonald, D. editor. 1999. The Encyclopedia of Mammals. Barnes and Noble Books. ISBN: 0760719411
- MacKinnon, J., M. Sha, C. Cheung, G. Carey, Z. Xiang, and D. Melville. 1996. A biodiversity review of China. Worldwide Fund for Nature (WWF) International, Hong Kong.
- Schaller, G.B. 1998. Wildlife of the Tibetan Steppe. The University of Chicago Press, Chicago. ISBN: 0226736539
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