荒漠绿洲的形成条件和过程

绿洲分为天然绿洲和人工绿洲两大类型；绿洲的形成条件以水为基本、地形为制约、土壤为载体、植被为体现；天然绿洲的形成过程有沼泽化过程和草甸化过程，人工绿洲的形成过程有建立人工植被过程，培养优质高效农业过程及发展工业和城镇建设过程；绿洲的建设措施有：（１）巩固现有绿洲，保护山区水资源，内陆河流域上、中、下游合理分配用水，防治土壤次生盐渍化，防止土地风蚀沙化，（２）扩大和发展绿洲，根据现有水资源潜力扩大绿洲面积，外调水源发展新绿洲，加强绿洲工业和城镇建设。

FORMATION CONDITONS AND PROCESSES OF DESERT OASES

Oases are the regions with plentiful water source and lush grasses,or developedagriCulture and prosperous society in the desert areas.Conceptionally, an oasis has suchconditions:(1)it is situated in the desert(including semidesert)areas;(2)it has irrigationcondition;(3)there are luxuriant mesophytes and hygrophytes or aquatic plants growingthere or there are humankind engaged in agricultural production(including forestry,animalhusbandry and other sidelines),industrial production and social activities. The development of desert oases can be rotighly divided into three stages,namely,nat-ural oasis stage for natural vegetation growth→agricultural oasis stage dominated by man-made cultivation of plants→industrialization and well-developed townifying stage. As for the classification of the oasis types,they are first divided into natural oasis andanthropogenic oasis(first class)in accordance with the anthropogenic states of the oasis e-cosystem and the degree of human activities,then they are divided into desert oasis andsemidesert oasis(second class)in accordance with the geographical zones;thirdly they aredivided into alluvial plain oasis,piedmont oasis,fan-margin depression oasis,valley oasisand lake basin oasis(third class)in accordance with topographic sites;finally they are di-vided into agricultural oasis, pastoral oasis,forestry oasis,industrial and townified oasis(fourth class)haccordance with the functions and economic characteristics of the oases.They can be further divided in accordance with the vegetation conditions and soil types aswell as the names of the administrative regions and natural zones. It may be thought that the oases were formed with water source as their basic condi-tion, terrains as their restrictive condition, soil as their carriers and vegetation as theirmanifestation. The formation processes of the natural oases include swampy process, meadowy pro-cess,anthropogenic oasis process including the establishment of artificial vegetation,theprocess of estabilshing fine-quality and high-efficiency agriculture as well as industrialand townifying process. The evolutional patterns of anthropogenic oasis follow such a basic line:small andscattred agricultural oasis→patchy and high-efficiency agricultural oasis→industrial andtownifying oasis.During the formation processes of the anthropogenic oases,the environ-ment conditions of the desert areas occurred a series of changes:(1)natural stream systemtuned into artificlal canal;(2)natual soils truned into artificial soils;(3)natural vegetationturned into artificial vegetation;(4)microclimate altered;and(5)new industries and tawnsappeared. Measures for oasis construction include:(1)consolidation of existing oases,to con-serve lnountain water sources, to rationally distribute and use water resources in the up-per,middle and lovver reaches of the inland river basins,to prevent soil secondary saliniza-tion,to halt soil wind erosion and sandification;(2)expansion and development of oases,toexpand Oasis area in accordance with existing water resource potential,to divert water fromadjacent region to develop new oases and strengthen the construction of industries andtowns in the oases.