| Desertification is the significant global environmental problem that current mankind is faced with, which puzzles the survival and development of human society. China is the one of serious desertification countries in the world. According to the basic principle of wind-sand physics and aerodynamics, this paper compared bare sandy land and desertification grassland, which are two kinds typical land surface pattern, study of wind-sand physics, sand driving wind, wind profile,surface roughness, sediment discharge,wind-sand flow structure. On the summary of ecological vegetation construction projects and existing vegetation distributed patterns in Yanchi county in recent years, serial researches was carried out in this paper. First of all, using common plant salix mongolia shrub in sandland as experiment material,simulated study the wind-fields of single plant and clustered growing which has different allocation form. Then using introduced trees scotch pine,s young trees as experiment material, research different protective effect to ground surface with uniformity model, stochastic model and banding collocate; At last, artificial layout simulating no-leaf stage of different rows, different space between plants. Mechanism between different vegetation arrangements and soil wind erosion was studied on the protective range and wind energy attenuation two aspects. Reveal the different effect on wind protective effect of each factor in vegetation arrangements, in order to provide reference basis for vegetation construction in Mu Us sandland.The results showed:(1)When the wind-sand flow through natural shrub,it will form a wind shadow after the shrub,and cause sand grain deposition,natural shrub grass vegetations were set these effects together to enhance it,s sand fixation function,as the vegetation growing, shifting sand movement were under control gradually. Different types of clustered growing has different wind-break benefits. Diamond allocation vegetations wind-break and sand-fixing benefits is the best, triangle allocation vegetations takes second place, rectangular-shaped is the worst.(2) The wind velocity profile of scotch pine with uniformity model, stochastic model and banding collocate all follow one-variable linear regression, and velocity increased with height. The change of wind speed of banding collocate is the most drastic. The decrease range is largest inside brush with banding collocate and the stochastic model is least, the uniformity model is in the middle. As wind speed increase the surface roughness is decrease gradually in the plots. Under the same coverage degree, for the banding collocate, the surface roughness is stablest and variation rate is 0.08; For the stochastic model , the surface roughness changes sharply and variation rate is 0.56; The uniformity model is in the middle. According to windbreaking effect from 0.3m height of shelter forest, average wind prevention of stochastic model is 13.26%, average wind prevention of uniformity model is 28.04% and wind prevention of banding collocate is 36.95%. In summary, the effect of banding collocates for controlling wind erosion is best .(3) By protected range experiment analyse with different rows, we draw some conclusion: belt composition of one row, two rows and three rows, the protective distance is 4～5H, 6～7H and 8～9H respectively. According to windbreaking effect from 0.5m height of shelter forest, the results is that three rows >two rows >one row. To some extent,as the line number increasing, not only protective distance has been enlarged, but also protective effects has been enhanced everywhere simultaneous. It makes shelter forest plays a stable protection to ground surface,but the number of rows is not the more the better. Account to the limiting factor of water in sandland,so our suggestion is that choose belt composition of two rows as you can as possible, belt spacing 6～7H is suitable.(4)The effect of plant spacing to protection is obviously,comparative results of three kinds of plant spacing disposition wind-break and sand-fixing benefits is 0.5m×3.0m>1.0m×3.0m>2.0m×3.0m. As 0.5m×3.0m has the minimum shelterbelt porosity, so got the maximum protective effect, wind-break benefits is 23.89% in average, the two other are 16.43%, 11.02% in turn. When the wind-sand flow through shelterbelt, uniform distributed shelterbelt branch are distributed uniformly, the effect of friction and swing impact are strengthen, the effect of sand-fixing is obvious. While plexiform dense type formed wind gap easily among clumps, increasing wind sand activities, hence weakened the effect of sand-fixing holistic. My suggestions is that shlter forest projection should fully reflect the principle of uniform distribution in single line for future and make profits from forest belt dispersion,so as to play the effect of windbreaking and reducing erosion better from seedlings grow to forests. |
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