Studies On Ecological Effect Of Soil And Water Conservation Forest In Semi-arid Region On Loess Plateau

This study attempted to present the ecological effect of soil and water conservation forest mainly based on the research of Pinus tabulaeformis, Ulmus pumila and Platycladus orientalis, three major planted trees, planted on the runoff forestry ground of the river basin in Yukou Station, Fangshan County, Shanxi Province. In the research, the transpiration observation, forestland vegetation investigation, undergrowth soil moisture and nature analysis of three forest stands are conducted on. This thesis intended to use Penman-Monteith method and ecological theory to analyse the effects of water evaporation, hydrological character of forest litter, undergrowth biological diversity, forest biomass and forest soil improvement. The results of the study indicated the following aspects:(1) In the process of ecological restoration, planted-forest-oriented model had good capacity to improve woodland ecological environment and play a positive role in constructing healthy forest ecosystem by the interaction between its growing character and environment.(2) Using the revised Penman-Monteith method to simulate the day transpiration process of Pinus tabulaeformis, Ulmus pumila and Platycladus orientalis can reaches a high precision level, while their transpiration capacity rate from higher to lower was as follows:Ulmus pumila> Pinus tabulaeformis> Platycladus orientalis. In the growing season of 2009, the research area's potential evapotranspiration was 465.08mm, while the largest one was Ulmus pumila, and the lowest one was Platycladus. The result showed that Ulmus pumila was the largest one, while the Platycladus orientalis was the lowst one not in forest water consumption but also in potential evapotranspiration. The rainfall capacity was far less than evapotranspiration in May, June and October.(3) Under the same condition, the biomass of Ulmus pumila ranked first, next came the Pinus tabulaeformis and the last one was Platycladus orientalis. On three different forest stands, undergrowth soil water content was preserved 0-30cm depth of the soil layer, which was increased in deeper layer. When it reached to 30-70cm depth, soil water content rapidly reduced. And when it came to the 70cm-90cm depth, it became basically stable. The undergrowth average soil water content of Pinus tabulaeformis, Platycladus orientalis and Ulmus pumila was 13.01%,12.29% and 11.1%, respectively. The conclusion was drawn from the above statistics that the soil water content of Pinus tabulaeformis was the largest, next came Platycladus orientalis, the lowest one was Ulmus pumila. So the effect on the soil water content made by Ulmus pumila was the most obvious. However, the result showed that Ulmus pumila had the strongest capacity to preserve and improve soil nutrient, next was Platycladus orientalis and the last one was Pinus tabulaeformis.(4) The litter amount of these three planted forest was from 13.33 t/hm2 to 42.67t/hm2. Under the very similar site condition and identical growing years, total amount from high to low by turns was Platycladus orientalis> Pinus tabulaeformis> Ulmus pumila, while their water holding capacity rate from higher to lower was as follows:Ulmus pumila> Pinus tabulaeformis>Platycladus orientalis. The litter's earlier water absorbency rate declined rapidly, and then tended to be stable. When the time was from Oh to 0.5h, the litter water holding capacity reached its maximum. On the forest stand, the litter's variable range of water-holding capacity was 28.83t/hm2～32.24t/hm2 when it reached the maximum, among which the Ulmus pumila's capacity was the largest with the amount of 32.24t/hm2. In that case, the result turned out that Ulmus pumila had advantages in water holding, water-use enhancing in the forest stand, compared with the other two planted forest.(5) Based on the staticstical method of vegetation survey and biodiversity research, undergrowth species diversity from high to low listed as Ulmus pumila> Pinus tabulaeformis> Platycladus orientalis. The types of undergrowth plants were as a whole less than those of local waste grassland.