Study On Ecological Effects Of Oasis-making Process In The Northeast Part Of Ulan Buh Desert

The artificial oasis of Dengkou, in the northeast of Ulan Buh Desert, has a long reclamation history. Since the founding of New China, the governments has plough into a large amount of manpower and materials for management and exploitation of sandy wastelands, a large-scale irrigated oasis has been established, leading to the great change of local eco-environment. Studies on ecological effects and dynamic changes of the artificial oasis are of great realistic significance to maintain the sustainable development of the oasis.Taking the ecological effects of artificial oasis system as starting point, serving the prevention and control of sand blown disaster, using an integrated method that combined positioning experiments, regional survey and laboratory analysis, the ecological functions of oasis system, that consist of the peripheral natural desert vegetation, in sight of sand-fix shrubs, as well as wind-break forest and farmland within oasis etc., were studied in different spatial scales, and the preliminary results of study were achieved as follows :(1) Since the founding of New China, the sandy wasteland in Dengkou Oasis has experienced several large-scale reclamations. Because of the expansion of oasis and the immoderate utilization of water resources, a series ecological problem has occurred. From 1996 to 2003, the landscape pattern of Dengkou region, related to the oasis-making and desertification, has changed significantly. The study indicates that ecological condition in Dengkou region is still deteriorated on the whole although improved partially. The area of shifting sands increased largely, and the area of natural shrub vegetation decreased simultaneously. The expansion of artificial oasis directly lead to the destruction of their natural vegetation that oasis is protected from sand blown. The potential ecological crisis is threatening the sustainable development of artificial oasis.(2) The study showed that the vegetation species composition, coverage and diversity evidently differed from each other, accordingly resulted in notable difference of their ecological function under the common background of regional arid climate whether in the Oasis and on the edge of oasis or in theperiphery of oasis, as different influencing intensity of irrigation water horizontal movement of artificial oasis. The structural difference of natural shrub and herbage and artificial vegetation cause significantly different surface roughness, consequently anti-erosion,sand blocking and sand fixing also has a marked difference. Mobile sandy land characterizes as strong wind erosion, strong deposition while natural shrub vegetation area with high coverage characterizes as weak wind erosion and weak deposition. The depositing quantity of different underlying surfaces at different levels gradients varies range from the edge of the oasis to distant desert .With vegetation coverage increasing, the dust depositing quantity significantly reduced, while the dust depositing quantity of the same underlying surface at different height changes significantly, the dust depositing quantity at 0.5m is significantly greater than that at 1.5m.(3) The research on climate ecological effects of typical artificial oasis in 3 stage of from young-late age plantation and middle-age plantation to near-maturation plantation middle age shows that (compared with the desert) : artificial Oasis can reduce air temperature and surface temperature; artificial Oasis can increase precipitation and the growth rate of precipitation of three stages were 8.3%,20.3%,67.1%; artificial Oasis can improve air humidity which respectively increases by 4.5%,4.8%,3.7%. The air humidity in oasis is higher about 6-9% than that in desert during growing season.; artificial Oasis can efficiently restrain evaporation, and the rate of evaporation fell by 40.2% in July — the hottest month of the year; artificial Oasis can reduce the speed of wind, the wind protective effect of the three phases respectively is 41.5%,47.2%,37.1%. The ecological function of a number of climatic factors decline obviously from 2003 to 2005 in artificial oasis, which indicates the mature stage of shelter-forest seems to be the appropriate updating age of farmland shelterbelts.In the process of Oasis development last over 20 years, soil quality of newly constructed artificial oasis had been remarkably improved, the total soil nutrients and available soil nutrient increased on the whole while the salt content and the PH value in the top layer of soil surface decreased significantly. The improvement of soil quality laid foundation for highly stable yielding and sustainable management of oasis agricultural industry.(4) Major disaster of artificial oasis is Sand drift in the North- East of the Ulan Buh Desert Area and farmland shelterbelts is primarily looked forward to reducing the wind speed. Study on shelterbelts (networks) with different structure and a variety of time sequence and without leaf shielding effectshows that spacing distribution for shelterbelt is the key factor to the wind protective effect of farmland shelterbelts. The wind protective effect of monospecies shelterbelts is mainly due to spacing distribution for prior shelter belt, canopy features and planting density while the shelterbelt mixed two species mainly due to combination between kinds of trees , which must be highly valued. The wind protective effect of Shelterbelt has little to do with the width, which has great significance.The shelter forest in arid desert can ensure high and stable yield of farmland , and the growth rate is between 5.0%～155.71% ; The quality and properties also improve clearly with protective forest. Shelter forest with rational structure has less effect on yield of farmland. Taking corn as example, the crop yield increase rate by shelter forest is up to 3.6%.The increase of timber volume of Alamo shelter forest(23a) is descending, while function for wind break became poor, which indicates that Alamo shelter forest is come into mature stage and should be renewal.(5) Along with implementation of the "Three North" shelter forest project, regional shelter systems can effectively restrained and weakened sandstorm. The annual average of wind days blowing sand and dust storm days totally decline from 1970 to 2000. Every index descends markedly , especially in the third stage it fell by 73.0～ 94.0%, which indicates the indices (average number of days of strong wind, blowing sand and dust storm days )is linearly related to the area and timber volume of regional shelter system .Monitoring typical artificial oasis shows that shelter system can decrease significantly the harm of disastrous weather, which accords with regional shelterbelt systems. Simultaneously, shelterblet systems can efficiently reduced sand-dust, yield at certain extent.