Integrated Farming Systems at Different Scales 463Soil erosion
Soil erosion in the Yangtze River Basin is caused by both natural and man-made
causes. The natural causes in the Yangtze River watershed include fragile mountain
environments, high intensity, long duration rainfall, high stream density, steep
stream gradients, mass movements, debris flows and landslides. The causes induced
by human activities include deforestation, inappropriate land management prac-
tices, road construction in fragile lands, improper water collection, transportation
and use of water. According to statistics, the total discharge of the Yangtze River
reaches 5.02 × 10^8 tons per year, or 19.1 per cent of the national total. At present,
the water flow of every tributary in the upper reaches is decreasing, but the content
of silt is increasing. For example, in Sichuan Province, the average silt content of
water flowing in the Three Gorges area was about 5.1 × 10^8 tons in the 1970s, and
increased to 6.8 × 10^8 tons in the late 1980s. The general status of soil erosion in
different provinces of the Yangtze River Basin is given in Table 18.18.
Since 1954 natural water bodies in the middle and upper reaches of the Yangtze
River have declined by some 12,000km^2. For example, the surface area of Poyang
Lake has decreased by 36 per cent. In the Dongting Lake area 166,000ha have
been reclaimed for farming. Some 10,000ha of land in the Taihu Lake area were
also turned into polders between 1969 and 1974. In the Jianghan Plain the number
of lakes with a water surface area over 50ha has dropped by 40.36 per cent from
the 1950s to the 1980s and the total water surface area shrank by 43.67 per cent
(The National Conditions Investigation Group under the Chinese Academy of
Sciences, 1992).
Construction of protective forests in the upper and middle reaches of the
Yangtze River
In 1989 the state approved the ‘Overall Plan for the Construction of the Protec-
tion Forest System in the Middle and Upper Reaches of the Yangtze River’. The
objectives were not only to reduce water and soil loss, but also to improve the eco-
logical environment for agriculture and to accelerate development of the economy
in mountain areas. Under the guidelines of IFS, a multipurpose and comprehensive
Table 18.18 Variation of soil and water erosion areasRegion 1957 1987 Increasing
Area (km^2 ) Proportion (%) Area (km^2 ) Proportion (%) Area (km^2 ) (%)
Total 363,790 20.2 739,376 41.0 375,586 103.2
Jiangsu 1850 3.8 6100 12.3 4250 229.0
Anhui 13,686 21.3 19,263 30.0 5577 40.7
Jiangxi 11,000 6.6 38,360 23.0 27,360 248.7
Hunan 55,880 27.6 56,640 27.9 760 1.4
Sichuan 93,380 16.1 382,000 67.3 288,620 309.1
Guizhou 12,816 11.3 35,300 31.2 22,484 175.4