| The Horqin region is located in the intersection zone between the eastern part of the Inner Mongolia Autonomous Region and the western part of Jilin Province and Liaoning Province.It is the interlaced zone of semi-arid,semi-humid,animal husbandry and agriculture in northern China.Due to the climate drought and the influence of human activities in recent decades,this region is exposed on the ground from autumn to spring of next year,and it is easy to be desertified sand and convert to source of dust and dust storm under the strong winds in the period,thus,the Horqin region is becoming an important dust and dest storm source in northern China.During the non-growth season from late autumn to spring,the land surface residual litter plays an important role in preventing desertification and dust in the land ecosystems such as sandy land,grassland,and farmland.It is an important parameter to measure the coverage of surface vegetation,and it is also an important indicator to indicate the change of ecological environment.In the past,the identification of dust source areas mostly focused on deserts and other bare soil areas,and neglected grasslands and farmland that covered least dry residues.Based on ground-measured hyperspectral data and the MODIS remote sensing data from November 2000 to November 2017,this paper takes the Horqin area as a case region,and uses spatial analysis,landscape index method,statistical analysis and other methods to process and calculate the data.The characteristics of the reflectance spectrum of surface residues that include different types of land use in the non-growth season of the study area and the coverage of ground surface residue were obtained in each year.And finally,the dust source areas were refined to different intensity levels to claasify the study area.It is of great practical significance to quantitatively discribing the surface litter coverage in the Horqin area,so as to quickly and accurately understanding the characteristics of the arid and semi-arid area ecosystem and to provide scientific and effective management and protection of the dust source area.The main findings are as follows:(1)There was a near perfect linear function relationship between the CAI index and DFI index of surface residuals in the grassland,farmland,and sandy lands in the Horqin area.The correlation coefficients were 0.9064,0.9511,and 0.9565 respectively.(2)There was a significant correlation between the coverage of dry land surface and the CAI index in the grassland,farmland and sand area of Horqin,the fitting regression models were y=0.1328x-1.4943,y=0.1211x-2.7299,and y=0.0807x-1.2721,respectively,which all met the linear function relationship and were positively correlated.Therefore,there was a good functional relationship between surface residue coverage and DFI index in grassland,farmland and sand regions.A model could be established to estimate dry land surface residue coverage.(3)The average coverage of surface residues in the Horqin region from 2000 to2017 was the highest in the farmland,followed by the sandy land,and the coverage of the surface residues in the grassland was the lowest among the three landscape types.The distribution of surface residues in grassland and sand areas were relatively wide.The coverage of farmland was mainly strong dust sources with 18.69%-20.57%residue coverage and strong sand and dust sources with coverage less than 18.69%.The distribution was scattered.The distribution pattern of dry surface residues in the grassland area was generally small and fluctuating.It mainly distributed strong dust sources with a coverage of 10.04%to 11.39%and medium dust sources with a coverage of 11.39%to 12.74%.The medium dust sources areaswere mainly concentrated in the northwest region and maintain relatively stable coverage.The sand region was mainly composed of medium dust sources with a coverage of13.50%-16.56%,mainly distributed in the eastern and southern regions.The distribution in other areas was relatively scattered,and the residual coverage in the sand areas had certain fluctuations in different years.(4)Based on landscape pattern index,landscape pattern analysis indicated that the coverage of surface residues in grassland areas was mainly distributed between11.39%-12.74 medium dust sources and strong dust sources between 10.0357%and11.39%,and 12.74%-14.09%weak dust sources were distributed in small quantities,it with a coverage of more than 14.09%and strong dust sources with less than 10.04%were extremely rare.On the whole,the area of the strong sand and dust source area in the grasslands has been reduced from 4913175hm~2 to 3685126hm~2,and the fluctuation of the patch number has increased from 8560 to 11314.The degree of fragmentation of the stronger source area might be further aggravated,and the degree of agglomeration was relatively strong.The average dust source in the grassland occupied a considerable proportion.The overall area has increased from 1043650 hm~2 to 2452860 hm~2,and the number of patches has increased from 5762 to 15245.This indicated that the area of the middle dust source area in the grasslands was expanding,Its fragmentation in the overall layout was also further increased.The surface residuals in the sand area were mainly concentrated in16.56%-19.61%of the weaker dust sources and 13.50%-16.56%of the medium dust sources.The distribution of weak dust sources were greater than 19.61%,strong sand dust sources were less than 10.45%,and strong dust sources ranging from 10.4%to13.50%was rare.The area of medium dust sources decreased from 6658825 hm~2 to6661521 hm~2,and there was no significant change in the number of patches,indicating that the degree of fragmentation of medium dust sources in the sand did not change much.The relatively weak source area of sand and dust sources in the sand has reduced from 1725 hm~2 to 70 hm~2,and the number of patches has decreased from 21 to2 and the degree of fragmentation has decreased.The distribution of residues in farmland was mainly strong dust sources with a coverage of 18.69%-20.57%and strong dust sources of less than18.69%.22.45%-24.32%of weak dust sources,and 24.32%of weak dust sources had a small amount of distribution.The area of the relatively strong source area in the farmland accounted for a high percentage of the remaining farmland.As a whole,the area of the strong sand and dust source in the farmland showed a decreasing trend,from 519,125 hm~2 to 489,541 hm~2.The number of patches increased from 2545 to3694,and the degree of fragmentation of the landscape increased.The area of strong dust sources increased from 7100 hm~2 to 35210 hm~2,and the number of patches increased from 125 to 734.The degree of fragmentation increased significantly. |
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