Fjölrit RALA - 05.12.1999, Síða 91

JlA JlONG
89
Climate
The climate in the Ordos region is characterized by cold-dry and hot-wet seasons. The
average annual rainfall of 200-450 mm is distributed from June to September. The
fluctuation of annual rainfall is another main feature in the region. In 28.7% of the
years annual rainfall drops to 100-150 mm or lower (Table 1) (Yang et at. 1990). The
high temperature in the hot season is responsible for the high rates of potential evapo-
transpiration in relation to rainfall. The aridity ratio in Ordos rangeland ranges from
1.5-3.4 (Yangetal. 1990).
Table 1. Fluctuation of aridity ratio in Ordos. W, M, D represent wet year, median year and
drought year separately.
1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993
Otok M W M D D W M M D M D
Jungie D W D D D W M' W M W D
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Soil erosion
Chinese grassland scientists have developed advanced approaches for soil inventory in
Inner Mongolia grasslands. Remote sensing and fíeld research have shown that fea-
tures of soil erosion in Ordos include: (1) larger areas with soils transformed by “san-
dization” (shahua); (2) deterioration of the physical properties of soil components,
such as declining soil structure and soil water status; (3) decline of soil fertility and
organic matter; (4) overall increase in the area of salinization and swamping; and (5)
intensification of soil erosion (Li 1990, Jia 1995). According to Li, degradation of
grass cover is the most important cause of soil erosion in the natural grasslands. Over-
grazing and trampling by livestock are the main reasons for the loss of grass cover, but
the construction of roads, and other activities also play a role.
Population and landuse
Man has influenced the structure of Ordos rangeland vegetation through agricultural
and industrial activities and the introduction of planted woodland. Growing human
population was often accompanied by increased grazing pressure on the regional
vegetation. The rise of urbanization and industrialization during the last four decades
further intensified these activities. Open coal mining and the harvesting of plants for
the Chinese medical industry have also caused serious problems. The present landuse
pattem in Ordos rangeland is a reflection of these human pressures (Table 2).
It has been argued that all the Ordos rangeland today has been subjected to agri-
cultural practices, such that its structure and plant species composition have been al-
tered and probably greatly simplified (Gressey 1933, Shi 1991). The impact of semi-
permanent cultivation on Ordos rangeland has been greater since the turn of this cen-
tury. From 1922-1937, from 1958-1962 and from 1967-1972 about 15-20% of Ordos
rangeland were converted to cropland, most of which was abandoned in the next 5-10
years due to soil erosion and the adjusting of local policies. Frequent fluctuation of
climate together with with fragile loess and sandy soils made the surface susceptible
to erosion. Because of water and wind erosion, these abandoned croplands recover