Decline Of Nitraria Tangutorum Shrub Dunes In Minqin Desert-Oasis Transition Zone Ecological Landform Characteristics

Scrub dunes are widely distributed in the desert-oasis transition zone,which play a barrier role for the agricultural production and ecological security of the oasis and are a natural barrier to protect the oasis.However,with the influence of environmental factors and human destruction,scrub dunes gradually enter the decay stage,and the decline of scrub dunes causes wind erosion of dunes,which inevitably leads to the intensification of wind and sand threats to the oasis on the desert-oasis transition zone.The paper selects the extensively distributed white thorn scrub dunes at the edge of Minqin Oasis,and analyzes the morphology,sediments and vegetation of various types of dunes with different degrees of decline through field survey,unmanned aircraft measurementt and sampling analysis,and explores the ecological-geomorphological process of the decline of white thorn scrub dunes at the dune-inter-dune scale to provide scientific basis for the recovery and conservation of white thorn scrub dunes in this area.The following conclusions were drawn from the analysis:(1)Based on the morphology,wind erosion site,white thorn distribution area,wind channel and the number of dunes after wind erosion,the scrub dunes were classified into three types of decay:crumbling decay type,layer stripping decay type and wind channel decay type.Based on the number of crumbling surfaces,white spur cover,and the percentage of windway depth,3-4 typical decay patterns were further divided into each decay type,and the decay process of each type of white spur scrub dune was initially revealed.There are differences in the scale and decay types of white thorn scrub dunes supplied by different sand sources in Minqin desert oasis area.The dunes supplied by drifting sand are the largest in size,and the dunes mainly decay by stripping,with occasional crumbling decay;the dunes supplied by agricultural soil+drifting sand are the second largest in size,and all three types of decay occur on these dunes;the dunes supplied by agricultural soil are the smallest in size,and stripping decay is the only type of decay for these dunes.The type of dune decay may be related to the variability of sediment grain size composition on dunes due to different dune scales and sand sources.(2)The rate of white spurge dieback tended to increase,and the cover,new growth,and plant number of white spurge tended to decrease with the increase of dieback,while the number of plant species tended to increase with the increase of dieback on the mounded surface of the crumbling dune and the wind eroded surface of the stripped dune(crumbling)and to increase and then decrease(stripping),and the number of first-and second-year herbaceous plants and perennial herbaceous plants tended to increase and decrease with the increase of dieback.Herbs and perennials gradually replaced white spurge as the dominant species on the dunes.(3)Soil physicochemical properties differed among different decaying types of white spurge scrub dunes.The coarse gravel content of the surface soil(0-3 cm)of the wind erosion surface and the original surface is higher than that of the mounded surface,and the soil moisture and nutrient content of the mounded surface is slightly higher than that of the original surface,the wind erosion surface and the interdune area;the powder content of the sediment of the layer stripping type is higher than that of the crumbling type,but the soil moisture and nutrient content of the mounded surface is higher than that of the crumbling type.Soil water nutrient content was not significantly different between the two sides of the dune where vegetation growth was significantly different,and it was judged that wind erosion on the dune might be the main reason for the difference in vegetation growth conditions between the two sides of the dune.In this study,the decay form and degree of scrub dunes in Minqin desert-oasis transition zone and the corresponding geomorphological-ecological processes were studied,and the decay processes of three decay types of white spur scrub dunes were initially revealed,which not only help to understand the ecological-geomorphological evolution of desert scrub dunes and their response to environmental changes,but also provide important reference values for judging the degree of desert edge desertification and taking effective control measures.