Study On Degradation Mechanism Of Sophora Moorcroftiana Shrub In Semiarid Valley Region Of Lasa

The Sophora moorcroftiana is endemic species to the Xizang plateau, a long time in windbreak and sand fixation and soil improvement and other ecosystem services play an important role, in maintaining the stability of the ecological system is also positive significance. The degradation mechanism of Sophora moorcroftiana was studied. Shrub is the basic work .There is great significance on construction of Tibet's ecological security barrier.In this thesis,collecting data from the degraded Sophora moorcroftiana in semiarid valley region of Lasa, from Sophora moorcroftiana. Seed bank, seed input, interspecific association, succession process, disturbance and other aspects of Sophora moorcroftiana and shrub degradation was discussed.The results are as follows:(1)Sophora moorcroftiana seed bank exists "dispersal stage model" and "dispersal earlier stage model" in horizontal distribution and "decline model" and"parabolic model" in vertical distribution.(2)Grazing and seed pests are important factor of affecting seed input.Seed pests reduce the seed bank input, while the moderate grazing disturbance is beneficial to the inputing seed.(3)In Sophora moorcroftiana, Seed bank, main means of lossing seed are germination, decay, physiological death and mildew. The decay which caused by insects feeding and infesting is the main reason for the soil seed bank loss.(4)The germination seeds settlement rate not very high, interspecific association and grazing impact on the natural regeneration of Sophora moorcroftiana.(5)According to the interspecific association and niche overlaps inferred that the succession process of Sophora moorcroftiana is Artemisia we1lebyi, Artemisia desertorum, Chenopodium botrys→the community of Ceratostigma minus, oxytropis, Stipa→the community of Sophora moorcroftiana. (6)Natural disturbance and human disturbance disturbance are main factors of impacting on Sophora moorcroftiana Shrub. Natural disturbances include changes in climate (extreme weather) and local geological disaster. Human disturbance was mainly due to population growth leading to over-exploit vegetation in the valley. The main useing vegetation patterns are cutting, grazing and wei-sang, in which the cutting is the most serious.(7)Sophora moorcroftiana shrub degradation is impacted on human activities, climate change and self-sustaining mechanism of vegetation. At present, main factor is human disturbance.Exclusion measures can reduce human disturbance.