| In the desert fringe of arid and semi-arid area,in both stable and unstable dunesystem,due to the protective layer on the surface is destroyed and eroded under the joint action of human activities and natural factors to form the concave landform type,namely,the formation of Blowouts in the desert transition zone of the arid area The formation of Blowouts is a sign of the activation of fixed or semi-fixed deserts.In this paper,the degraded and sparse forest land of Xiahe County forest farm in the northern edge of the Taklimakan Desert is taken as the research area,and the Blowouts of the degraded and sparse forest land is taken as the research object,the morphological characteristics,spatial distribution,development and influencing factors of the Blowouts in the degraded woodland on the Xiahe county were studied.The results show that:(1)In the initial stage of development,the area and number of Blowouts are small, the depth of Blowouts is shallow,and new Blowouts are forming constantly.The results show that the maximum,minimum and average value of the Blowout area are 3231 m~2,31.9 m~2 and707.25 m~2 respectively.With the advance of time,there is a trend of further development.(2)At the same time,the direction of the etch pits is basically the same as the prevailing wind direction in the area,the types of Blowouts in degraded sparse forest land are strip-shaped,crescent-shaped,flower-shaped and man-shaped.The Blowout L/w value of degraded sparse forest land in Xiahe County forest farm is between 1.5 and 2.7,which indicates that the Blowout in this area is mainly of strip shape.(3)There is a significant positive correlation between the Blowout shape parameters of sample plot and sample plot B.The correlation between the area and the width of the etch pits is remarkable,which indicates that the etch Blowouts in this area have been expanding to both sides under the influence of strong wind erosion.The correlation between the length and width of the etch Blowouts and their depth in the two sample plots is significant,indicating that the depth of the etch Blowouts in the study area is shallow,the pit length,width and depth increase slowly.(4)From 2013 to 2019,the patch Pland,NP,PD and LPI of the Blowouts all in the trend of increase,it should be understood that the wind erosion area is increasing,and as the wind erosion intensifies,there is the phenomenon of merging of adjacent Blowouts,the proportion of the largest patch area is increasing,which reflects the strong human activity direction in this area.In space,the closer get to the desert,the more Blowouts there are.From north to south,the number of etch pits increases,and the long axis of etch Blowouts keeps consistent with the direction of prevailing wind.Blowouts are formed from the south of Yarkand River towards the north of the river,possibly due to secondary wind erosion of abandoned soil due to over-cultivation in the area.During 2013-2019,the Blowouts in the study area continuously expanded in space,the main moving direction of the center was NE,and the moving distance of the center was 833.71m.This indicates that the development of Blowouts in the study area tends to oasis.The formation of Blowout has great influence and harm to the ecological environment in this area,so the development of Blowout should be controlled.(5)The factors affecting the formation of Blowouts in degraded sparse forestland include natural and human factors.According to the changes of air temperature,precipitation and wind speed in the study area for many years,under the conditions of low precipitation,high air temperature,high wind speed and low vegetation cover,coupled with poor soil cementation of degenerated forest land,it has higher wind erosion.Blowouts in degraded woodlands are mainly distributed on the ancient terraces of Yarkand River.After a long period of erosion,the partial hardening of the clay sediments resulted in the collapse of the clay layer at the top,which accelerated the expansion of the Blowouts.The NDVI value of the study area is 0.09-0.14,which indicates that the vegetation coverage is very poor.From the analysis of vegetation cover in the past 20 years,it is concluded that although the vegetation cover in the study area shows a gradual increase trend,the formation of Blowouts also keeps an increasing trend,this is closely related to the irrational land use activities such as land reclamation,overgrazing and land abandonment after land reclamation.Strong human activity in the Yarkand River,River Basin has facilitated the expansion of Blowouts,various indirect factors such as seasonal floods in the lower reaches of the Yarkand River,River basin and diseases and pests of Populus Euphratica also contribute to the expansion of Blowouts.Based on the study,the spatial distribution pattern of Blowouts on the Xiahe county can be determined more clearly,it can provide decision-making basis for the researchers of desertification and the Department of controlling and preventing desertification in Xinjiang. |
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