Effect Of Different Vegetation Types On The Soil Water Cycle On Steep Land

One of the main problems for vegetation restoration in Loess Plateau is the uncompatibility between vegetation water requirements and soil water supplement. The abilities of soil water consumption for different vegetation types will influence the storage, transportation, and transformation of soil water on sloping land. Especially for the sloping land, precipitation is not only the chief sources to maintain plant growth, but also one of the main powers for soil erosion. One of the problems that are needed to be solved in Loess Plateau is how to plan and manage the artificial vegetation efficiently according to natural precipitation conditions.In this paper, the native grass, Hippophae rhamnoides, Pinus tabulaeformis, Platycladus orientalis and the mixed forests were taken as the research materials. The variation of leaf area index, soil water dynamics, the differences of sediment, runoff and evapotranspiration were measured and collected during the study period in 2013 and 2014. Hydrus model was used to simulate the soil water cycle processes of grass, Hippophae rhamnoides, Pinus tabulaeformis, and Platycladus orientalis to analyze the components of water balance for each vegetation type. The main conclusions are as follows:1. In the growing season, LAI increased at first, then showed a decreasing trend after reaching a maximum value and remained for a period of time. The LAI of different vegetation types showed a declining order as: mixed forests of arbor, mixed forests of arbor and shrub, arbor forests, shrub forests, grassland.2. Seasonal variation of soil water was related to the rainfall amount and seasonal distribution, and it was quite different in different years. Vertiginous layer and active layers in grassland were shallower than the forests. The vertiginous, active, transitional layers under woodlands were distributed at the depth of 0~70 cm, 70~120 cm, and 120~200 cm, respectively. The relative stable layer of the soil moisture under woodlands were located at the depth of below 200 cm.3. The runoffs of different vegetation types showed a declining order as: arbor forests, mixed forests of arbor, mixed forests of arbor and shrub, shrub forests, grassland. The order of erosion modulus for different vegetation types was accordance with the order of runoff coefficients.4. Hydrus model was used to simulate the soil water cycle of four vegetation types. The root mean square errors(RMSE) between simulated and measured values were among 0.015 ~ 0.063 cm3 / cm3. Compared the water balance components of four vegetation types, we found that the amount of runoff was affected by KS value. The declining order of the four different vegetation types was: Platycladus orientalis, Pinus tabulaeformis, Hippophae rhamnoides, and grassland. The interception was related to the LAI. The decling order was: Pinus tabulaeformis, Hippophae rhamnoides, Platycladus orientalis, Grassland. The declining order of evapotranspiration was: Hippophae rhamnoides, Pinus tabulaeformis, Platycladus orientalis, Grassland. Evapotranspiration played a dominant role to control water balance in the semiarid region. In order to keep sustainable ecosystem, the water consumption for different vegetation types should be considered before planted an artificial vegetation type for controlling soil erosion in the semiarid region of the Loess Plateau.