| The sandstone area, which is located in the crossing areas of Shanxi, Shaanxi and Inner Mongolia on the Loess Plateau,China, is suffering "the cancer of the Earth's environment" with serious soil erosion and poor ecological environment,. The Jungar Banner in Inner Mongolia was one of the key project areas of the national ecological construction project in Shanxi, Shaanxi and Inner Mongolia Sandstone area. Seabuckthom was one of the pioneer species used in this area for erosion control. In this paper different patterns of the artificial seabuckthorn forests were discussed and their functions and effects on soil and water conservation were analyzed. Based on these analyses, rational design of seabuchthorn forests mixed with arbors, shrubs and grasses in a proper proportion will effectively make the ecological environment better and bring the local peasants considerable economic benefits. It was hoped that this study can provide some scientific basis and enlightenment for the vegetation construction in sandstone area as well as the whole Loess Plateau.The "sample plot method" was used in this experiment. The soil and water conservation function was studied based on years of observation and research on the artificial seabuckthorn forest in the experimental region. First of all, GPS was used to specify the definite location of sample plots. And then by means of the statistical correlation analysis, regression analysis, etc. and by the aid of SPSS software, seabuckthorn's soil and water conservation function were compared in different forest age (2-8a) and in different site conditions (gully slope, gully edge and gully bottom). The ecological characteristics of the understory herb, litter layer, surface soil layer were observed as a reference. And the biodiversity of the understory herb layer, the water conservation function, soil improvement function and sediment reduction function were investigated. Besides, the economic and social benefits were analyzed as well. After the investigation and analysis, it was concluded that the artificial seabuckthorn forests in this area were short of diversity in arbors and shrubs. Finally, based on the results of the above investigation, according to the topography of a certain region and the concrete soil erosion type,4patterns of vegetation construction model for soil and water conservation are designed and put forward for the Jungar Banner sandstone area in this paper. Landscape ecology theories such as patch, corridor and matrix were used to design vegetation construction models.The main research results are as follows:1. The species richness and species diversity for understory herb layer of seabuckthorn tend to increase with forest age while Gleason richness index tends to decrease with forest age. All of these indices were evidences of seabuckthorn following the regularity of community succession and adapting itself to the sandstone area. Species richness, Gleason index, species diversity, and evenness were all calculated in the order of gully edge, gully slope and gully bottom, while the index of dominance was calculated in the opposite order. The outcomes prove that the thickness of soil layer was a critical element to influence biodiversity and that site conditions have an important effect on biodiversity. This result provided a basis on how to optimize the artificial seabuckthorn forest.2. The data showed a tendency of steady increase along the four site conditions, gully edge, sunny slope, shady slope and gully bottom by contrasting their interceptions of four-year-old seabuckthorn. On different canopies, the seabuckthorn layer intercepts far more than underwood and herb layer. Under the same site conditions, the interceptions increase with forest age. The interception of the herb layer of four-year-old seabuckthorn accounts for40%of that of seabuckthorn layer and the interception of the herb layer of seven-year-old seabuckthorn accounts for60%of that of seabuckthorn layer, which demonstrates that the two layers are getting more complementary and play a more effective ecological role as time goes by. The interception of seabuckthorn is different for different soil types, rising from loess to sandstone to alluvial soil.3. When the site conditions were the same, the older the seabuckthorn forests were, the more water holding rate and capacity the litters had. As for the seabuckthorn forests planted in2002, the ones planted in gully bottom can hold7.25t dry litter accumulation with12.62t water held, while the ones in the sunny slope can hold1.43t dry litter accumulation with3.25t water held, and the ones in shady slope can hold4.5t dry litter accumulation with5.2t water held. To sum up, the weight of litter in gully bottom is more than that in shabby slope, both exceeding that in sunny slope. The soil permeability in sandstone is better than that in sandy loam, both exceeding that in alluvial soil.4. The root of3-year-old and over seabuckthorns can expend1～2cm annually while the root suckers seedling grows up to20, with the average annual expansion rate of0.5～2.5m. The root can obviously enhance soil erosion resistance which is tightly related with density of fibrous roots that are less than1mm. If the effective root density of seabuckthorb forests aged between8～12reaches60/100cm or above, it will have significant inhibit function on the slope less than20°no matter how strong the storms are.5. In this thesis the Jungar Banner were divided into four regions:southwest Sandstone gully area, southeast loess hilly area, the northern Kubuqi desert area and the south bank of the Yellow River plain area. Different patterns of vegetation construction model are designed respectively for them. Arbors like Pinus Sinensis and poplar, shrubs like caragana and apricot, herbs like alfalfa and sweet clover, etc. are used together with seabuckthorn—the main species to construct the Soil and Water Conservation vegetation construction system, which is an effective way to control soil erosion in sandstone areas. It is suggested in this paper to purposely choose the right species of arbor, shrub or herb to design the proper model of mixed forests with seabuckthom.
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