Characterization of selected soils from the Lhasa region of Qinghai-Xizang Plateau, SW China

Soils along an elevational gradient in the Himalayas from the Lhasa River Valley bottom at 3700 m in elevation through subalpine (4200 to 4600 m) and alpine (>4600 m elevation) vegetation zones were described, sampled and classified according to the USDA soil taxonomy. Active flood plain soils were classified as Aridic Ustifluvents or, on more stable valley slopes and stream terraces, as Aridic Ustochrepts. Limited soil temperature data suggest these temperate valley bottom and lower valley slope soils have a mesic soil temperature regime. Soils within the subalpine zone were estimated to have a frigid temperature regime and sample sites were classified as Typic Haploborolls or Typic Ustochrepts, depending on parent material and degree of aeolian influence on epipedon properties. At elevations above 4600 m elevation under alpine sedge and forb turf, soils were classified as Typic Cryumbrepts. Soils above 4600 m elevation showed evidence of cryogenic soil structures (platy and fine subangular blocky) presumably formed as the result of extended periods (more than 300 days per year) of freezing and thawing and vein ice formation. Although permafrost may be expected to occur at depth at these elevations, no permafrost was observed within 2 m of the soil surface within the elevational range sampled.