The Study Of Disposition Optimization For Water Conservation Forest Of The Loess Area In Western Shanxi Province

The social ,natural and economical conditions of loess plateau in western Shanxi province are investigated.The analytic hierarchy process and grey system theory have been applied to the analysis of the hydrologic functions of forest canopy, litter and soil layers.Based on the study of vegetation disposition of water and soil conservation forests, the optimum structure of forest type in this catchment is established.Compared to the current forests condition, the rational suggestions for forest stand are discussed.Firstly, the water environment character of the watershed is summarized and analysed.It includes the distribution trend of monthly precipitation in a year and annual amount of precipitation and the storm character analysis in the area. The area belongs to warm temperate zone continental climate , the arid and windy climate in spring and the high tempetature in summer. Rainfall occurring in June, July and August accounts for 80.6% of the total in a year.A continuous decreasing tendency ,with a linear-change-rate-21.9mm(10a)-1 ,during 1950s-1990s could be detected . The amount of precipitation between 10mm to 30mm is the principal rainfall type in the area, and surface runoff is produced under the condition of precipitation more than 30mm.Secondly, the hydrologiacal functions of forest canopy, litter and soil layers for different forest vegetations are compared and assessed. Based on the observation data through runoff plots, function of conservation water of different forsets stands, including conifer,hard wood, mixed forest, shrub, economical forest are evaluated. On the basis of the grey related result, six factors including forest canopy density, canopy water-holding ability, litter height, litter water-holding ability, soil non-capillary porosity, soil water-holding ability have been selected as the indexes to assess the water conservation function. The relation according to the grey correlative degree : soil water-holding ability > canopy water-holding ability >forest canopy density> soil non-capillary porosity> litter height>litter water-holding ability.At last, using analytic hierarchy process, the spatial disposition of forest of water and soil conservation is established. Water conservation function is the final object, which is objective level; the hydrological functions of forest canopy, litter and soil layers determining function of conservation water is strategic level; rational vegetation structure...