中国土地荒漠化的概念、成因与防治

CONCEPT, CAUSE AND CONTROL OF DESERTIFICATION IN CHINA

荒漠化是指人类历史时期以来，由于人类不合理的经济活动和脆弱生态环境相互作用造成土地生产力下降，土地资源丧失，地表呈现类似荒漠景观的土地退化过程。在中国北方荒漠化形成因素中过度放牧占30．1％，过度农垦占26．9％，过度樵采占32．7％，水资源利用不当占96％，工矿交通建设中不注意环境保护占0．7％，在地区上以北方农牧交错及旱农地区荒漠化最为严重。要采取因地制宜措施和建立健全而完善的治理实施系统以达到生态、经济和社会三个效益的目的。

Desertification is one of the most serious environmental problems on the globe. It is of concern to 900 million people in over 100 countries and regions covering 3.6billion ha of land or one-fourth of the total terrestrial area. It is still in the process of expansion. The convention to combat desenification signed in Paris in 1994 indicated that this problem has been placed as one of the important agendas in the international society. Desertification is also an essential environmental problem in China. The expansion of desertified area constitutes an essential factor for the gradual shrink of land resources. With regard to the sandy desertified area in the farming-pastoral region of northern China, the affected area increased from 30 percent of the total land area in the 1970s to 40 Percent in the mid 1980s. China is situated in Asia / Pacific region, according to Convention and its Annex for Asia and in the light of viewpoints of Asia / Pacific region and actual conditions of China, we think that 'Desertification means the process of land evoluting towards desert-like conditions and reduction of land productivity and even loss of land resources resulting from interactions between irrational human activities and vulnerable environment'. Therefore, desertification in China should not include original desert such as sandy desert, rocky of gravel desert (gobi), salt desert, wind-erosion related yardan relief and frigid desert resulting from pure natural factors. With regard to bedrock-exposed stony hills (bare rocky relief), only the naturally formed bare rock landscape such as karstic fenglin (Peak forest) and fengcong (cluster forest) is differentiated from top soil washed-off and bedrock exposed rocky slopeland resulting from human activities such as steep slope reclamation and cultivation, can the latter be referred to as rocky desertification. In terms of warer erosion related desertification, it merely means serious land degradation marked by bad land or rocky (fragmental)slopeland occurred due to serious decline or even loss of land productivity resulting from serious fluvial erosion caused by human activities rather than simply referring to all that related to soil and water loss as desertification. Since desertification is closely related to human activities, in terms of concept of bine, it refers to land degradation forming desert-like landscape caused by human activities since recorded history rather than taking the deserts formed and developed in natural process during prehistorical or geological period as desertfication. Therefore,desertification combating can not be equated to sandy desert prevention and control, or even simply take areas with drought index ranging between 0.05～0.65 as desertified area. According to implications of desertification described in Chapter 1 and indicators and features shown above, in light of generalization of major research achievements gained in China, the existing desertified land area in China is 861 600km2, accounting for 8.97 percent of the total land area, of which desertified land area induced by water erosion covers 394 000km2, making up 45.7 percent of the total desertified area;wind-erosion induced desertified area is 379 600km2, or 44.1 percent; and desertifiedarea caused by physical and chemical actions (such as secondary salinized land)occupies 88 000km2, or 10.2 percent. Though land desertification takes human excessive economic activities as an inducing factor, yet the unfavourable physical factor serving as the basis for its formation and development also exists. Land desertification can be formed and developed only by the combination of the two factors. Desertification can thus be regarded as the product of interactions between intense human activities and vulnerable eco-environment, the product of manland conflict. The types of human factors for land desertification under wind effect in northern China are listed in following: overgrazing occupied 30. 1% of desertified land,overfarming occupied 26.9%, excessive firewood gathering occupied 32.7%, irration