Variation Of Land Use And Vegetation NDNI And The Driving Factors In The Middle Reaches Of The Yangtze River

The middle reaches of the Yangtze River(Hubei,Hunan,and Jiangxi)are the central areas of the Yangtze River Economic Belt.Studying the land use pattern change,vegetation dynamic evolution and driving factors in this area is of great significance for the socio-economic and environmental sustainable development.This paper uses many data including the Landsat TM land use type map,MODIS NDVI image,meteorological data,DEM data and statistical yearbook data in this area.With the support of Arc GIS,Fragstats,Matlab,SPSS and other analytical software,this paper adopts landscape pattern analysis,Sen+MK trend analysis method,Hurst index method and correlation analysis method.The land use change patterns in different periods from 1990 to 2015 are studied.The spatial and temporal variation characteristics of vegetation cover from 1999 to 2015 are discussed.Then the study explores the correlation between vegetation NDVI and climate(temperature,precipitation,relative humidity,sunshine hours),topography(altitude,slope,aspect)and human activities(population density,GDP,urbanization).Finally,Aiming at the problem of regional ecological development,put forward the countermeasures for sustainable development of land and vegetation ecology.The main findings are as follows:(1)The area of forest land was the largest,accounting for 49.82%,followed by cultivated land,which was 30.41%.Shrubs,waters,grasslands,construction land,orchards,and unused land accounted for 7.03%,4.61%,3.92%,2.81%,and 1.08%,0.32% respectively in 2015.Compared with 1990,the area of cultivated land and forest land in the area decreased by 1.06%and 0.49%,respectively,while the area of construction land and orchard increased by 1.08% and 0.54% respectively.From the perspective of the landscape pattern index,with the urbanization process,the landscape of the study area tended to be fragmented,the plaque tended to be complicated,and the landscape diversity increased.Economic and industrial development,urbanization and national implementation of ecological protection projects and restoration policies were the driving factors for changes in landscape patterns.(2)In the urban-rural gradient,the proportion of forest land occupation increased,while the cultivated land and construction land showed opposite trends;the construction land and cultivated land fragmentation level increased,while the forest land fragmentation level decreased.However,in the landscape level index,the increase of plaque density,the decrease of the average area of plaque,and the increase of the fractal dimension of the perimeter area showed the characteristics of landscape agglomeration in urbanized areas.These results indicated that the development of the integration of the middle reaches of the Yangtze River may be the driving factor of this spatial pattern.(3)The vegetation NDVI in the middle reaches of the Yangtze River increased significantly from 1999 to 2015,and was higher than that of other important urban agglomerations(for example,the Yangtze River Delta,Pearl River Delta,etc.).On the regional scale,the vegetation NDVI is characterized by the spatial distribution of “west high east low,north high south low”.In the past 17 years,the area of vegetation NDVI increased by about 90%,and the degraded area accounted for about 7%.The severely degraded area was located in the center of capital city.According to the Hurst index,the vegetation improvement area accounted for about 35%,mainly distributed in the western mountainous areas;the vegetation continuous degraded area accounted for about 3%,mainly distributed in more developed urban areas.Moreover,the NDVI of different vegetation types was ranked as natural forest(0.81)>grassland(0.78)>plantation(0.77)>cultivated land(0.75);in the past 17 years,compared with other vegetation types,cultivated land and planted forests were degrading and may be further degraded.Further reasons and countermeasures need to be explored.(4)In the past 17 years,the interannual variation of NDVI in the middle reaches of the Yangtze River had not responded strongly to the climate during the same period.The correlation coefficients had not reached a significant level(p>0.05).The vegetation NDVI was positively correlated with temperature and precipitation,and was negatively correlated with relative humidity and sunshine hours.In the past 17 years,the NDVI of each vegetation type was slightly positively temperature and precipitation,and was significant correlated with the annual variation of relative humidity.Cultivated land and precipitation were significantly positively correlated.On the spatial scale,the proportions of the study area that were significantly correlated with temperature,relative humidity,precipitation,and sunshine hours were: 7.53%,7.31%,4.12%,and 3.76%,respectively.Vegetation NDVI had the highest proportion of significant correlation with temperature,indicating that temperature was the main climatic factor affecting the interannual variation of vegetation growth in this area.(5)From the monthly correlation between vegetation NDVI and climatic factors in each month,the vegetation NDVI in this area from January to April was affected by precipitation and sunlight,and there was a significant lag;vegetation NDVI in July was affected by the precipitation lag in May;August vegetation NDVI had significant correlation with temperature,relative humidity and sunshine hours.From this point of view,the monthly precipitation and sunshine hours were the main climatic factors affecting the seasonal variation of vegetation NDVI in this area,and the summer temperature and relative humidity had a significant impact on the vegetation growth in this area.(6)The topographical factors drived the vegetation NDVI in this area.When the altitude was less than 2500 m,the vegetation NDVI increased with the elevation,while when the altitude was greater than 2500 m,the NDVI value decreased.With the increase of the slope,the vegetation NDVI gradually increased,however the rate of increase was slower and slower;the relationship between vegetation NDVI and slope direction was the directional pattern of south high and low north.When the transition from south to north,the NDVI of vegetation was gradually reduced.(7)The human factor drived the vegetation NDVI in this area.With the increase of population density,the vegetation NDVI gradually decreased and the decreasing range increased;with the increase of GDP grade,the vegetation NDVI gradually decreased;Urbanization was also a driving factor for the decline in vegetation NDVI.With the increasing afforestation area,NDVI was gradually increasing,and the two were significantly correlated,indicating that the national implementation of ecological afforestation and other projects had improved the regional vegetation coverage.The research results are of great significance to the development of the Yangtze River Economic Belt,the construction of the "three screens and two belts",and the transformation of low-efficiency forests,as well as guiding the sustainable development of the economic and ecological environment of urban agglomerations in the region.