Southeast Tibet shrub and meadows
Tibetan Plateau, Sichuan, China Photograph by Tsahi Hod
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. This region, like the rest of the Plateau, is treeless except in southeasterly river valleys. It 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 meters (m). It is a center of diversity for several alpine taxa such as Kobresia, Pedicularis, Mecanopsis, and Primula. This ecoregion supports potential habitat for endangered mammals such as snow leopards (Uncia uncia), lynx (Felis lynx), and Himalayan wolves (Canis lupus). Their prey species include the endemic white-lipped deer (Cervus albirostris) and blue sheep (Pseudois nayaur). While the vegetation across this ecoregion is mostly intact, mammal populations have been adversely affected by anthropogenic activities, primarily grazing of domestic livestock, particularly yaks and goats.
Location and General Description
This ecoregion includes the eastern part of the Tibet-Qinghai Plateau and the higher elevation areas that finger out along mountain crests in the river gorge area of southeastern Tibet and western Sichuan. It is defined as those areas too cold to support forest vegetation (generally above 4,000 m) but with enough moisture to support a closed vegetation cover (more than 500 millimeters (mm) per year). Generally, the vegetation consists of meadow in places that are either snowfree and exposed to wind during winter or that are prone to flooding. Dense shrublands occur in those places that are sheltered and well drained. Northwestward, the climate becomes drier and this ecoregion gives way to Tibetan Plateau shrublands and meadows. Southeastward, complex ecotones occur where the relatively flat Tibetan Plateau falls away into a landscape of river gorges and steep mountain ridges.
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 no more than 10o Celcius. 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 region, 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.
This moist, cold habitat is similar to the alpine regions of the Eastern Himalaya. Meadows are dominated by the sedge (Kobresia pygmaea) in association with many dicotyledenous forb species, most of which belong to genera common throughout the Himalayan alpine region. Potentilla, Pedicularis, Primula, Lancea, Gentiana, and monocots such as Allium are some of the more abundant forbs. Places subject to heavy grazing support unpalatable species like Stellera chamae-jasme.
Aspect has a strong effect on the stature and taxonomic composition of the vegetation, primarily due to differences in snow retention. In general, places that hold snow support more luxuriant scrub vegetation because the snow acts as a protective blanket in the winter, prevents the damaging effects of grazing and trampling by livestock early in the season, and may ameliorate the effects of summer drought. North-facing slopes support evergreen sclerophyllous shrubs like the small-leafed Rhododendron species R. anthopogon, R. setosum, and R. nivale. Slopes with a southern aspect often have no shrubs at all, and those with vegetation tend to have deciduous species like Salix, Potentilla, and Caragana. In swampy locations, Kobresia may form tussock mounds.
As climate becomes drier to the west, mesic forbs become less important and meadows are almost pure Kobresia. Rhododendon is replaced by Juniperus as moisture decreases, again a pattern typical of the moist alpine scrub of the Eastern Himalaya.
Biodiversity Features
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Yaks (Bos grunniens), Tibetan Plateau, Sichuan, China (Photograph by Peter Snow Cao/ BikeChina) The Kobresia sedge meadows of the Southeastern Tibetan Plateau are floristically and ecologically distinctive, due to the combination of cold temperatures and high precipitation that occur here. Although it is dominant over much of eastern Tibet, the genus Kobresia is nearly endemic to the Tibetan Plateau and the surrounding mountains of Central Asia. (Some disjunct species occur in the Rocky Mountains of North America.) Its center of species diversity is located in southeastern Tibet as well.
The moist alpine [[region]s] of the Tibetan Plateau and Eastern Himalaya support some of the richest alpine landscapes on Earth. It is a center of diversity for several alpine taxa including Pedicularis, Mecanopsis, and Primula. "Characteristic orders [sic] which are well represented are Ranunculaceae, Papveraceae, Rosaceae, Saxifragaceae, Umbelliferae, Compositae, Primulaceae, Gentianaceae, Scrophulariaceae, and Liliaceae, while the following genera present a richness of species I have never seen equaled elsewhere: Rhododendron, Gentiana, Saxifraga, Meconopsis, Primula, Pedicularis, and Corydalis".
This ecoregion supports potential habitat for endangered mammals such as snow leopards (Uncia uncia), lynx (Felis lynx), and Himalayan wolves (Canis lupus). White-lipped deer (Cervus albirostris), endemic to the Tibet Plateau, occur in small numbers throughout this ecoregion, frequenting scrublands and meadows, both above and below tree line. They can also venture into the high alpine to elevations above 5,000 m. Blue sheep (Pseudois nayaur) is an ungulate widespread in the eastern part of the Tibetan Plateau. Tibetan argali (Ovis ammon hodgsoni) is recorded in the literature for this area and may still occur here, but recent records are confined to areas further west. Similarly, Tibetan gazelle (Procapra picticauda) has historically ranged here, although its current status this far east is not well-known.
Current Status
While the vegetation across this ecoregion is mostly intact, mammal populations have been adversely affected by anthropogenic activities, primarily grazing of domestic livestock, particularly yaks and goats. Tibetan brown bears (Ursus arctos) occurred here in the past century, but have probably been hunted to extinction in this part of Tibet.
Types and Severity of Threats
Hunting, even of those species strictly protected by the laws of China and by international treaty, continues in this region. In certain parts of Sichuan, such as Songpan County, snow leopard pelts are displayed for sale on the street. In Songpan, during September 1999 and June 2000, more than 12 pelts were observed for sale on the main street; others were on sale at scenic tourist locations like Munigou, near Songpan.
Grazing pressure is difficult to quantify, but may be excessive in some areas.
Justification of Ecoregion Delineation
This ecoregion encompasses the plateau just north, and in some cases between the Hengduan and other north-south trending ranges of the Yunnan province in China. The northern line coincides with the northeast extent of dispersed evergreen needleleaf forests in a one kilometer resolution map of global land cover produced by University of Maryland. The southern boundary is defined by the limits of alpine meadow on the CVMCC map of actual vegetation in China.
Additional information on this ecoregion
- For a shorter summary of this entry, see the WWF WildWorld profile of this ecoregion.
- To see the species that live in this ecoregion, including images and threat levels, see the WWF Wildfinder description of this ecoregion.
- World Wildlife Fund Homepage
Further Reading
- Chinese Vegetation Map Compilation Committee. 1979. Vegetation map ofChina. 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.
- Fleming, Robert L. 1998. A summary of biodiversity: the great river ecosystems of Asia Trust Region. Future Generations.
- 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: 0199206082
- 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.
- MacKinnon, J. 1996. Wild China. The MIT Press, Cambridge MA. ISBN: 0262133296
- Schaller, G.B. 1998. Wildlife of the Tibetan Steppe. The University of Chicago Press, Chicago. ISBN: 0226736539
- Ward, F. K. 1913. Land of the Blue Poppy. London: Edward Arnold.
- Zhao, J., editor. Zheng Guangmei, Wang Huadong, Xu Jialin. 1990. The Natural History of China. McGraw Hill Publishing Company, New York. ISBN: 0002190435
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