| In arid and semi-arid areas,the wind carries away the nutrient-rich soil particles from the surface layer,resulting in the decrease of soil fertility and desertification caused by wind erosion.Plant sand control is the most ideal measure to control wind erosion.There are many studies on the effect of plant cover and overall allocation on the wind and sand resistance,which provides an effective method and scientific basis for measuring the sand resistance ability of the community,but because the arid and semi-arid areas can not meet the water requirements of afforestation,it is particularly important to study the wind and sand resistance benefits of some sparse vegetation and single vegetation brush.At present,there is a lack of research on the ability of wind and sand resistance of plants by considering the morphological characteristics of single vegetation elements.In order to solve this problem,through the field investigation,choose the Ulan Buh Desert 4 kinds of typical of the 3～4 years per plant shrubs,respectively is a natural vegetation Nitraria tangutorum,artificial vegetation Calligonum mongolicum,Hedysarum mongolicum and Haloxylon ammodendron,combined with wind tunnel experiments,the effects of individual shrub in growing season on wind velocity flow field,sediment transport rate and surface erosion characteristics were studied,compared for selecting the shrub species with the best protect effect,providing theoretical basis for the construction of windbreak and sand-fixation in sand system.The results showed that:(1)When the airflow passes through a single shrub,a blocking deceleration zone is formed at2H～1H of the windward surface,which speeds up the loss of wind energy.Wind speed reaches the lowest value 1H after plant,and increases gradually with the distance from plant,and recovers standard wind speed after 5H after plant.Compared with the four shrubs in the growing season,the Nitraria tangutorum with low morphology and low porosity were more effective than other plants,and the effective distance of protection was the largest.(2)The vertical protection range of a single shrub has a great relationship with its canopy profile area.The shape of Nitraria tangutorum is low,the crown shape is altar shape and the profile area can reach 2244.56 cm~2at 10～30 cm,and the close surface effect is the best in the range of vertical protection height.The crown shape of Haloxylon ammodendron and Hedysarum mongolicum was fusiform,and the profile area reached the maximum at the vertical height of 30～60 cm,which was3058.68 cm~2and 1728.85 cm~2respectively.Them on this level to achieve the best effect of wind protection.Calligonum mongolicum in 60～100 cm profile area is maximum,2371.41 cm~2,its vertical height above 60 cm with good windbreak effect.(3)The increase of wind speed on both sides of the plant led to the increase of near-surface sand transport rate.The near-surface wind speed around the plant was proportional to the plant thinness and the height under the branches.Large height under branches and sparse plants between branches will lead to channeling effect in the flow field space formed between branches and the surface,which will accelerate surface wind erosion.Therefore,in the future vegetation construction,reasonable allocation among plants should be carried out to prevent the occurrence of channeling effect,so as to make it play a better wind proof and sand resistance effect.(4)In the 1 m~2area around a single shrub,sand accumulation in the front of the plant was more obvious,while wind erosion was mainly observed in the lateral and rear areas.There were significant differences in the influence of four planting plants on the surface morphology,among which the surface morphology changed more after Nitraria tangutorum,and the sand accumulation was more obvious.(5)The wind and sand resistance benefits of 4 shrubs were compared.We can choose N.tangutorum or H ammodendron for windproof.We should choose N.tangutorum for preventing sand;Considering both,we must choose N.tangutorum. |
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