The Water Conservation Benefit Of Different Vegetation Types In The Montane Forest-Arid Valley Ecotone In The Upper Reach Of Minjiang River

The article select Mountaine Forest-Dry Valley Ecotone in Xiong-er Shan Mountain of Lixian which is located in the upstream of the Minjiang River as the study area; and analyzed the water conservation effect of different vegetation types (including Bare,Shrub-grass and Pinus- Ailanthus altissima forest) from aspects in the interception of canopy and the shrub and herb layers,the interception of litter layers,the physical properties of soil hydrology,soil water evaporation,the overall storing capacity of vegetation, etc. The study of hydrological benefit of litter fall of different vegetation types was conducted Cyclobalanopsis glauca, Salicaceae broad-leaved forest,Conifer forest,Cupressus chengiana,Secondary shrub,Grassland slope.The key findings of this study are as follows:(1)With the increase of precipitation, canopy interception, forest throughfall and stem showed an increasing trend mainstream Liang Jun, and the penetration of rainfall with precipitation of relatively rapid growth. Throughfall precipitation total of 50% to 80%.(2)The holding capacity in the shrub and herb layers has close relationship with the volume of unit area,with the volume growing,the holding capacity grows too.The moisture of the shrub and herb layers remains at 85% in Minjiang River dry valley.(3)The total litter stock of the 6 modes represented a descending order as follows:Cyclobalanopsis glauca>Salicaceae broad-leaved forest>Conifer forest>Cupressus chengiana>Secondary shrub> Grassland slope.The moisture decreases with the total litter stock, water conditions deteriorates with different vegetations.(4)The analysis on the process of holding water of different vegetation type in the upstream in the Montane Forest-Arid Valley Ecotone of the Min River shows a rapid increasing process during the first two hours,and the increasing becomes smaller in the coming hours;the velocity of absorbing water reduced quickly during the first two hours,and the reducing becomes smaller in the coming hours when forest litters were submerged under water.(5)The study on the 6 modes represented shows that:the maximum interception and the modified interception of litter layer indicated a descending order as follows:Cyclobalanopsis glauca>Salicaceae broad-leaved forest>Conifer forest>Cupressus chengiana>Secondary shrub>Grassland slope.the range of the maximum interception is 10.1mm-21mm,and the range of the modified interception of litter layer is 1.59 mm-7.73 mm. (6) During the simulated rainfall, bare land runoff are much higher than the shrub grassland and woodland, and the beginning time of the runoff of the bare ground begins earlier than the shrub grassland and woodland, indicating shrub grassland and woodland as Litter cover and vegetation cover on surface runoff are effectively blocking,showing a better water holding.(7) Bulk density of woodland and shrub grassland soil is smaller but porosity greater, while bulk density of bare ground is greater but less porosity. Soil bulk density increases with soil depth gradually, and the tendency is obvious. Tree and shrub-grass on the soil porosity changes significantly and increases the permeability of the soil and increase the pore size, improves the ability of water conservation(8) The maximum water-holding capacity and effective water-holding capacity in soil layers of bare land are significantly lower than that with shrub cover; and the two capacities of soil layers under trees are in turn effectively higher than that of the two above, which indicates a better water storage capacity with better vegetation coverage.(9)The soil infiltration rate decreases with the increase of soil depth under different vegetations. As to the soil infiltration under different vegetation types, trees and shrubs can reduce the soil compaction resulted from raindrop splash for their large cover; they also decrease the surface runoff and raise the soil infiltration rate and penetration rate by improving the physical properties of soil with their roots. The bare land damaged by grazing and human activities demonstrate a poor performance in terms of soil infiltration.