Study On Effect On Windspeed Reduction And Sand-Break By Low Coverage Belt Caragana Korshinskii Kom. Plantation

There are a lot of large-scale afforestation work in China in order to improve the ecological environment in arid and semi arid areas. However, lack of precipitation and soil moisture reserves in the Northwest region of China limits afforestation area and often results soil degradation of the environment, causing many plantation ecosystem decline and loss of function. On the Premise of "maximum wind erosion control while minimizing excessive moisture consumption", the research discuss most optimum and reasonable coverage of Caragana windbreak using method of field observation, field simulation experiment, wind tunnel experiment and biomass survey. The research purpose is solving the problem of configuration mode and providing scientific basis for ecological construction of degraded grassland in desertification area. The results show as follows.(1) According to determination results of basic aeolian physical parameter, the main wind direction of research area in observation time is NW, WNW or NNW, wind power of research area in observation time strong and frequent. Threshold instantaneous velocity of shifting sandy land changes between 4.73～4.94 m/s,4.83 m/s; threshold instantaneous velocity of degraded grassland changes between 6.46～6.62 m/s, average value 6.54 m/s. Roughness of shifting sandy land changes between 1.61-2.57 cm, average value 0.51 cm; roughness of degraded grassland changes between 6.46～6.62 cm; average value 2.09 cm. Wind speed increases with heigt rising, and they are logarithmic correlation. Sediment transport rate increases with wind speed rising, and they are power function relative.(2) Wind field around per plant shrub is in conformity with flow around cylinder model. The best protective effect of per plant appears on the lower part of lee side. The protected range is within 2 times of plant height (2H) and the effect of shrub on wind finite on 1.5 m height. Effect on windspeed reduction and sand-break by shelterbelt with different number of row is triple rows>double rows> single row in sequence. Effect on windspeed reduction and sand-break by single row is minimum, triple rows shelterbelt is slightly better than double rows. Effect on windspeed reduction and sand-break by shelterbelt with different band spacing decreases with band spacing increasing.(3) The wind tunnel test results show that shelterbelt models with different band spacing have different protective distances. The protective distances of 4H band spacing configuration is 19H; the protective distances of 6H band spacing configuration is 15H; the protective distances of 8H band spacing configuration is 13H; the protective distances of 10H band spacing configuration is 9H; the protective distances of 12H band spacing configuration is 8H. Wind tunnel simulation experiments make up the deficiency of field simulation experiment, such as effect of atmospheric turbulence and low precision. The wind tunnel test is effective supplement and support of field simulation experiment. (4) Reliability demonstration of simulation experiment is done by field survey of wind field and sediment transport rate between shelterbelts with different band spacing, the results show that sediment transport rate increases by band spacing extension.(5) The results of biodiversity analysis between the shelterbelts with different band spacing show that biodiversity and species richness increase while band spacing extension. We should control shelterbelts with reasonable coverage and band spacing in order to promoting vegetation restoration and positive succession.(6)Low coverage belt Caragana Korshinskii kom. Plantation can reduce windspeed and break sand effectively if the shelterbelt is rational allocated.We suggest shrub afforestation in arid and semi arid areas allocates with belts. Recommended row number is 2, recommended transparence degree is 0.5 and recommended belt spacing is 8H～10H.In this study, research object is belt Caragana Korshinskii kom. plantation. Using method of field observation, field simulation experiment, wind tunnel experiment and biomass survey, making a exploration of reasonable configuration mode and coverage of belt Caragana Korshinskii kom. plantation. There is a innovative point of research method. The research results are meaningful to guide the type, configuration mode and reasonable coverage of plantation in arid and semi arid areas.