Study On Benefit Evaluation Of Vegetation Protective System In Ulan Buh Desert Oasis

Oasis is the most important eco-economic area in Ulan Buh Desert.Wind-sand disaster is severely threatening the normal function of oasis farmland.To ensure the sustainable development of oasis agriculture,research on wind-sand disaster of oasis farmland and its control mechanism was carried out with methods of field test and laboratory experiment.The main research results are:(l)From outside to inside,Wind vegetation protective system in Ulan Buh desert is made up of three layers:sand-fixing grass belt,wind-sand prevention and fixing forest,and farmland shelterbelt.(2) Study on sand-trapping efficiency of sand-fixing grass belt show that the Nitraria tangutorum shrub on the fixed dune has the function of blocking wind-sand flow.Results show that the wind-sand flow is blocked in the slope.There is a slow down area on the windward of the fixed dune,wind speed is drop 39.2%-59.8%and sand is amassed there.The sand transport rate of the different dunes is increase along with the wind speed assumes the power function form,and decreasing with high increases assumes index rule.Research indicated:The shrub may fix the shifting dune,and blocked wind-sand flow.Analysis sand transport rate of the different dunes,we can see that the rate drops 93.6%separately in fixed dune and 59.8%in sedi-fixed dune;sand transport mass in fixed dune drops 73.5%-90.5% than that in sedi-fixed dune.The effect is obvious,so sand-fixing grass belt may drop wind speed and sand transport mass,make sand amass,that wind-sand flow is blocked and Wind-drift sand is stop inflowing.(3)Study on variation of sand transport mass about different dune in different velocity show,as the wind speed reduced,the sand transport mass is decrease,the function of blocking wind-sand flow is same as the wind speed dropping.Shrub forests have better effect than woody forest,shrubs with dense branches are better than those with sparse branches.In a word,the wind defending effect of shrub forests are obvious,it can effectively control farmland wind-sand disaster.(4) Wind velocity of different farmland shelterbelt was observed;results showed that defending farmland shelterbelt can make wind speed decreased,and Wind defending effect in sandy land is the best,and Pyramidalis Bunge is smaller than mixed forests with Pyramidalis Bunge and Hedysarum scaparium or Elaeagnus angustifolia forests.Moreover,shelterbelt can reduce the sand transport mass,and the fall rate in the forest and after the forest is more than the one before the forest.The sand transport mass of Pyramidalis Bunge is smaller than the one of mixed forests with Pyramidalis Bunge and Hedysarum scaparium or the one of Elaeagnus angustifolia forests.When we make farmland shelterbelt,we should afforest mixed forests,it can decrease the sand transport mass and increases stability of the structure.