Grasslands of the World.pdf - Disasters and Conflicts - UNEP

S.G. REYNOLDS
The Tibetan Steppe 313
Plate 8.4
Elymus nutans .
litwinowii , Helictotrichon tibeticum , Brachypodium sylvaticum , Stipa aliena ,
Festuca rubra , F. ovina and Deschampsia cespitosa . Large areas of productive
pasture are dominated by Elymus nutans (Plate 8.4) in the alpine meadow,
especially in northwestern Sichuan, southwestern Gansu and eastern Qinghai.
In swampy depressions in the alpine meadow there is hummock vegetation
dominated by Kobresia spp. (30-cm tall K. royleana and K. schoenoides). Shrub
communities of plants such as Salix spp. , Caragana jubata , Potentilla fruticosa
and Rhododendron spp. are common on northern aspects in alpine meadow.
Most Tibetan pastoralists and their stock are found in the alpine meadow
region. Livestock densities can be high; in eastern Qinghai, stocking rates are
28-70 animals/km 2 , and heavy grazing and trampling, together with solifluction,
have disturbed the sod layer, causing extensive rangeland degradation
(Schaller, 1998).
Alpine steppe
The alpine steppe comprises almost 29 percent of the area and is found between
3 500 and 4 600 m in the central and western steppe. Unlike the alpine meadow ,
there is no sod layer, and the soil is often gravel and coarse sandy loam; it is a
variant of the temperate steppe under the cold conditions of the Tibetan plateau
(Huang, 1987). Grasses of the genus Stipa dominate, often accompanied
by cushion plants, with S. purpurea and S. subsessiliflora as the dominant
grasses. Associated species are mainly xeric and meso-xeric grasses: Poa alpina
(Plate 8.5), P. crymophila , P. dolichachyra , Roegneria nutans , R. thoroldiana ,
Agropyron cristatum , Stipa aliena , Orinus thoroldii , Calamagrostis spp. , Festuca