金沙江干热河谷区攀枝花市土地退化初探

A PRELIMINARY STUDY ON LAND DEGRADATION IN PANZHIHUA CITY ON JINSHA RIVER DRYHOT VALLEY AREA

金沙江河谷区由于河谷深切、焚风效应显著、气候干热、生态环境脆弱，加上人类活动的强烈干扰，使水土流失加剧及土地退化甚至荒漠化的发生和发展。位于金沙江干热河谷的攀枝花市土地退化面积占本市总面积的４９．１％，轻度、中度、强度和极强度退化土地面积分别占总土地面积的３７．２％、８．２％、３．２％和０．５％。土地退化使土层变薄、肥力下降、土地生产力降低，破坏水利设施、影响水利工程效益，加剧自然灾害。土地退化的防冶对策为：制定正确的土地退化防治政策；严格控制人口增长；加强宣传，提高农民群众的生态意识；保护现有森林，加强植树造林；巩固与加强农田水利基本建设。

In the arid and semiarid areas of northern China, winderosion land desertification is very severe. But in the humid and semihumid areas of southern China, watererosion land degradation shouldnt be called desertification. So the concept land degradation' is used here.On Jinsha River valley area, because of deepcut valley (gully), remarkable foehn effect, dryhot climate and fragile ecoenvironment,as well as the intensive human activity, soil erosion is being aggravated, which causes land degradation. The area of degraded land of Panzhihua city located on Jinsha River dryhot valley makes up 49.1% of the total area of the city. Among them, light degraded,moderate degraded,severe degraded and extremly severe degrated land respectively makes up 37.2%,8.2%,3.2% and 0.5% of the total area. On one hand soil erosion makes the soil layer of cultivated land thinnerd, fertility lowered, soil texture coarsened, and land productivity decreased. Every year, water erodes 1 5 mm thick of the soil, which equals to 0 3 m thich of soil layer of 1 220 hm 2 is washed away. On the other hand soil erosion makes great amounts of sediments silt up the river bed and reservor, which lessens drainage ablility, causes severe flood disaster and inperils the people and cultivated land in the velley. Over 60% of the ponds, canal bed and reservor in the city are severely silted up, and lots of manpower are need to dig the sediments every year. Land degradation maybe also bring about disasters such as landslides and debris flow. The influencing factors of land degradation are composed of natural ones and anthropogenic ones. Natural factors mainly include complicated landscape and geological tectonics, easy wheathering rock, high temperature and evaporation, dry climate, concentrated precipitation and frequent rainstorm; anthropogenic factors include rapid population increasing, high population density, high cultivation rate, simpleextensive cultivation, deforestation denudation, mining and wastes discharge etc.. The countermeasures of land degradation are as follows: formulate correct policy to prevent and control land degradation;strictly control the increase of population; strengthen propaganda to heighten the peasants ecological consciousness;preotect existing forest and strengthen treeplanting;consolidate and strengthen the capital construction of farmland and water conservancy. 