Abstract:

Urbanization and land use change are two processes with farreaching consequences at both global and local scale. Vegetation is an important characterization of terrestrial ecosystem function. Analysis of spatialtemporal change of vegetation greenness is an effective way to reveal the degree of vegetation degradation. Urbanization reduces the amount of vegetation by clearing natural and semi-natural vegetation for construction over large tracts of land. To study the impacts of land use on vegetation coverage is of significance to direct regional urban planning and land use planning. The Normalized Difference Vegetation Index (NDVI) can be used as a proxy for vegetation productivity and vegetation greenness. The Yangtze River Delta (YRD) is one of the most developed regions with highest urbanization speed in China. Rapid urbanization has occupied a large area of arable land and forest in this area, with a significant decrease in greenness and in vegetation productivity. Based on SPOT NDVI data from 2000 to 2010, land use data in 2000 and 2010, taking YRD as a study case, this paper studied the distribution of decrease in NDVI, and the relationships between land use change and vegetation degradation. Ordinary Least Squares was applied to analyze the negative trend of NDVI in 11 years. We analyzed the effect of land use change and construction land growth on NDVI by using 1-km area grid data. In 2000-2010, the highvalue region of NDVI was concentrated in mountain area of Southeast and West Zhejiang and the northern plain of Jiangsu. The low value area was mainly in and around big cities such as Shanghai, Hangzhou, Nanjing, Suzhou, Wuxi, Changzhou, Ningbo and so on. Spatial Differentiation of NDVI reflected the diversity of landscape. The vegetation cover in 14% of the study area decreased significantly. Vegetation degradation was mainly distributed in the south of the Yangtze River and in the north and east of Taihu Lake, around Hangzhou Gulf, or around big cities, such as Nanjing, Nantong, Taizhou (Zhejiang Province) and so on. Land use change was one of the main causes of vegetation degradation. About 35% of the region where vegetation cover significantly degraded was related to conversions of cultivated land and forest to construction land, and about 301% of areas of degraded vegetation are attributed to the transformation from paddy fields to fishponds. While the dominant land cover type in each grid still unchanged, the proportion of construction land increased at a different degree. We conclude that large areas are being continually and heavily impacted by the high levels of human use and unplanned urban development over the last decade. Our results indicate that varying patterns and processes can be detected using changes in NDVI values. UGBs (urban growth boundaries) should be used to contain future development, and protect farmlands and open space from development. We argue that metropolitan areas adopt compact-development policies. The local governments are urged to draw “red line” for farmland protection and ecological protection. There is an urgent need for the authorities to introduce laws and policies to manage the uncontrolled urban expansion and fragmented landscapes.