Remote Sensing Monitoring And Vegetation Restoration Experiments On Aeolian Sandy Land In The Yarlung Zangbo River Basin On The Tibet Plateau

Based on a large amount of data acquired from both in situ field surveys andfour sets of remote-sensing images from1975,1990,2000and2008, the types,status and spatial distribution of aeolian sandy lands, as well as the dynamics andresponse mechanisms of this land to climate change over the past34years, werestudied in the Yarlung Zangbo River basin. The population structure, spatialdistribution and association of several psammophyte populations were studied usingpoint pattern analysis, the purpose was to provide theoretical foundation forvegetation restoration on sand dunes. The plant species for artificial seeding andbest sowing period was tested and determined by field artificial seeding trial from2008to2011on sand dune in the alpine valley, and the habitat stress factorsinfluenced on seed germination, emergence and plant growth greatly were discussed.The purpose of this study was to provide a scientific basis for ecological securitybarrier construction and vegetation restoration and reconstruction of aeolian sandyland on the Tibetan plateau. The results showed:(1) There was a total of273697.54hm~2of aeolian sandy land in the YarlungZangbo River basin currently. Aeolian sandy lands in the basin were relativelyconcentrated in various wide valleys and exhibited a decreasing trend from theMaquanhe wide valley in the headwater area to the middle and lower reaches of theriver basin. The Maquanhe wide valley contained the largest proportion of aeoliansandy land (50.28%or137622.94hm~2). During the period from1975to2008,aeolian sandy land in the basin exhibited a slow increasing trend, which increased by10.5%over34years. The total area of aeolian sandy land around Lhasa Airport andShigatse Peace Airport in2008was42462.38hm~2and49871.61hm~2respectively.The Aeolian sandy lands in the basin were found to increase further due to theslow natural desertification process under the arid and windy climate conditions ofthis region, and the combined effects of natural and anthropogenic factors, thesefactors stimulate and promote the processes of anthropogenic acceleration andaggravation.(2) The annual temperature presented a significant increasing trend and thechange rate was0.27/10a from1957to2007in the middle reaches of the YarlungZangbo River. It was more significant than the lower altitudes in other parts of Tibet.The warming trend was more obvious in autumn and winter than in summer. There were obvious periodic oscillation of15-20years for the seasonal and annual meantemperature variations. The abrupt climate change point was about in1987, and thetemperature belonged to the lower period before that time, and higher period afterthat time. The minimum precipitation occurs in1980s. Mean annual precipitationfrom2000to2007is roughly equal to that in1990s or1960s. Inter-decadal andannual variations of precipitation are similar in summer and autumn. Annualprecipitation increases from1957to2007, while it is not significant.(3) Artemisia wellbyi, A. younghusbandii and Sophora moorcroftiana are themajor psammophyte populations on the aeolian sandy land in the riparian ecotone ofthe middle reaches of the Yarlung Zangbo River. We selected four representativeplant communities under different habitat conditions in the riparian ecotone,measured the position, height and crown diameter of each individual in a20m×30m plot and studied the population structure, spatial distribution and association ofthese psammophyte populations using point pattern analysis. The objectives were todetermine how spatial scales are related to population patterns and how speciesspatially adapt to semi-arid conditions in the riparian ecotone, as well as to providetheoretical foundation for vegetation restoration on sand dunes in the study area.(4) The field artificial seeding trial results of northern psammophyte species arebetter than that of native psammophyte species. A. sphaerocephala, Hedysarumscoparium, Calligonum mongolicum, H. fruticosum var. mongolicum and S.moorcroftiana exhibits good adaptability to moving sand land in the alpine valley. A.sphaerocephala begans to flower and seed in the second years, H. scoparium and C.mongolicum begans to flower and seed in the third years, and A. sphaerocephala, H.scoparium and C. mongolicum are all able to complete life cycle. However, thereproducibility of A. sphaerocephala is weak, while H. scoparium and C.mongolicum present strong reproducibility.The morphological characteristics and different parts of sand dunes influencedthe trial results of field artificial seeding greatly. The approach of artificialbroadcast sowing to footprints trampled by feet following the contours proves to be agood way to improve the trial results. The habitat conditions of precipitation, soiltemperature of sand dune, soil moisture content and sand movement affected seedgermination, emergence and plant growth in the alpine valley greatly. The bestsowing period is before and after late June, as the habitat conditions are suitable forseed germination and seedling growth, and it could provide enough growing seasonfor plant growth before winter coming.