Study On Design Of Sloping Stable Forest Structure In Hilly-Gullied Area Of Loess Plateau

Landscape pattern of vegetation in watershed is analysized by making use of the technology of GPS and GIS and integrated ourside investigation. In order to study stand stabilities, the representative sloping vegetation is selected as studying object from the indexes of condition of soil moisture affecting stands stable, the productivity of stands and the function of preventing soil erosion. The paper analyzes the soil water validity by observing the soil moisture feature curve, on the basis of long-term supervising on soil water movement, and studies water consuming features of stands for the main tree species by pot experiment. At the same time the paper studies the productivity of different stands and the soil and water conservation benefit of sloping stands respectively through investigation and analysis of stand biomass and long-term data of runoff and sediment production. And the extent of influence on runoff and sediment yielding from sloping stands is judged using the method of grey correlation analysis. According to the conclusion above, sloping stable stand structures are designed, which will offer theoretic evidence and practical guidance for changing cultivation into tree planting and ecology re-construction in Loess Plateau.The result shows that, firstly, the condition of soil moisture of the natural sub-forest is the best, that of mixed forest of Robinia pseudoscacial and Platycladus orientalis in all manual stands is best of all close to the natural sub-forest, and mixed forest of Robinia pseudoscacial and Pinus tablaeformis superior to Robinia pseudoscacial forests, in Robinia pseudoscacial forests the density of 2000 trees/hm2 superior to the other densities, and mixed forests of different arbor species being better than that of arbor and herb. Providing and consuming soil water loses balance for Robinia pseudoscacial and Platycladus orientalis from Apr to Jun, and for Prunus armeniaca and Malus mila from Apr to Jun and Aug. Secondly, the biomass for natural sub-forest in all stands is the maximal, being followed by that of mixed forest of Pinus tablaeformis and Hippophae rhamnoides and mixed forest of Robinia pseudoscacial and Platycladus orientalis. Thirdly, the factors of stand and topographty affecting sloping runoff and sediment are analysed grey-relatedly, from which it is found out that influence from herb biomass, litter biomassand coverage of shrub and herb is the most remarkable, but sloping direction takes least. In all sloping stands the natural sub-forest and Ostryopsis davidina forest have the best benefit of soil and water conservation, then being followed by Robinia pseudoscacial forest, mixed forest of Robinia pseudoscacial and Platycladus orientalis, mixed forest of Robinia pseudoscacial and Pinus tablaeformis and Pinus tablaeformis forest. At the same time benefit is better for mixed planting of apple trees and crops after high-quality and big-engineering soil preparation. From the result of study it is concluded that annual average soil loss of missed forest of Pinus tablaeformis and Hippophae rhamnoides, mixed forest of Robinia pseudoscacial and Pinus tablaeformis and Ostryopsis davidina forest are about 4.29, 12.91 and 5.89 t/ hm2respectively, which are far less than permitted soil loss (200t/hm2 a).On the basis of the results of study, sloping stable stand structures are designed according to different sloping parts of weirs and moulds and gullies.