| Fractional vegetation cover plays an important role in assessing regional soil and water conservation,ecological environment protection and sustainable development,as one of the important indexes to assess regional soil erosion,land desertification and stand quality.Mengyin County is one of the typical counties for the dynamic monitoring of soil erosion in key management areas of Yimeng Mountains,is the "national soil erosion dynamic monitoring and announcement(2013-2017)" project to carry out the monitoring of the typical county,it is of great significance to study the dynamic characteristics of vegetation coverage of forest and grass.Based on the Landsat remote sensing images and land use data in 1996,2005 and 2016,explores the regression relationship between the actual measured values of vegetation coverage and the extracted values of remote sensing by field investigation.This paper takes Mengyin County as the research area,based on the Landsat remote sensing images and land use data in 1996,2005 and 2016,explores the regression relationship between the actual measured values of forest vegetation coverage and remote sensing extraction value through field investigation.Compared and analysis the dynamic change characteristics and the center of gravity migration of forest and grass vegetation in different years,the main conclusions are as follows:1.According to the characteristics of vegetation in Mengyin County,and the industry needs to study on soil and water conservation,according to the different use of vegetation,the vegetation in the study area is divided into farmland vegetation and vegetation,vegetation is further divided into protection forest,economic forest,timber forest and shrub grassland.In the 20 years,the area of forest grass vegetation increased first and then decreased.In 1996,the vegetation coverage area was 840.79 km2;In 2005,the vegetation coverage area increased to 842.77km2,grassland was the main type,mainly distributed in the northern part of Yedian and Mengyin County;In 2016,the area of forest and grass decreased to 783.76km2,mainly in economic forest.It was because of the development of economic forest in Mengyin county during the past 20 years,different years between the main vegetation changes in the direction of the grass to the economic forest and agricultural vegetation transfer and agricultural vegetation to other land and Economic forest transfer.2.Based on the vegetation index constructed by Landsat,the normalized difference vegetation index NDVI,the ratio index RVI,and the modified soil adjustment index MSAVI have a good correlation with the vegetation coverage of different vegetation types.Among them,NDVI and RVI have good correlation with coverage degree of shelterbelt and economic forest cover,and the regression equations were y= 0.493NDVI+0.023RVI+0.46 and y=0.939NDVI-0.026RVI+0.37;NDVI and MSAVI are the main factors affecting the timber forest vegetation cover change,the establelishment of the regression equation is: y=0.4NDVI+0.137MSAVI+0.46;and NDVI,RVI and MSAVI are the influencing factors of grassland vegetation coverage changes,the establelishment of the regression equation is y=0.873NDVI+0.329MSAVI-0.073RVI+0.36;in a word,NDVI and RVI are main factors of vegetation cover change,on this basis,the establelishment of forest and grass planting total regression equation is y=0.857NDVI0.03RVI+0.43.3.In this paper,between 1996 and 2016,the average of forest vegetation coverage increased slowly with time over the past 20 years.The vegetation coverage rate of forest and grass in 1996 was 0.72,and increased to 0.73,in 2005 and 0.77 in 2016.The overall performance was grade I(Low vegetation cover,0-30%),grade II(medium to low vegetation cover,30%-45%),grade III(medium vegetation cover,45%-60%),While the coverage area of forest and grassland in the IV grade(medium high vegetation cover,60%-75%)and V grade(high vegetation cover,75%-100%)continued to increase,and the coverage of forest vegetation in different years was increased Mainly in the IV and V level,mainly distributed in the northern part of Mengyin town of economic forest and southern mountain shelterbelt.4.The focus of vegetation coverage at different grades in different years is mainly from north to south.The vegetation center of I and II forest and grassland migrated from northeast to southward,and the focus of vegetation coverage of grade III forest and grass was shifted from northwest to southwest,and vegetation coverage of grade IV forest migrated northward and southward.The vegetation coverage of the vegetation is gradually shifted from south to north,indicating that the vegetation coverage in the northern part of Mengyin County is gradually increasing with the passage of time,which is closely related to the development of economic forest in the northern part of Mengyin County. |
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