长三角地区植被覆盖演变城乡差异及其原因

城市生态环境和城市化之间的关系是城市可持续发展的关键。研究不同城市化水平下植被覆盖的长时间演变趋势，对理解城市化过程对植被生长动态的影响，城市更新以及推进城市绿化的科学管理具有重要意义。然而，目前对城市内部沿城乡梯度植被生长趋势差异的认识还比较有限。以我国城市化发展最为强烈的长三角地区为研究对象，基于2000-2020年长三角归一化植被指数数据，采用趋势分析和地理探测器方法，探究了长三角地区城市内部植被覆盖演变城乡差异，并从土地利用/覆被变化和城市化发展的角度解析其成因。研究结果表明：（1）2000-2020年长三角地区植被总体呈绿化趋势，植被明显绿化占最大比例（52.06%），轻微绿化与稳定不变地区占31.68%，零星分布的褐化区占6.82%。（2）城市老城区植被覆盖变化总体呈现返绿趋势（0.016/10 a），新城区褐化明显（-0.019/10 a），农郊区绿化突出（0.023/10 a）。在上海、南京和杭州等人口城市化水平较高的城市中，老城区土地利用变化强度最高，其绿化趋势也最高，体现了城市更新过程对绿地空间的促进作用；而在人口城市化水平相对较低的宣城、蚌埠和阜阳等城市，土地利用变化强度相对较低的农郊区也呈现明显的绿化趋势，更多的是受到区域生态保护的影响。（3）土地城市化是长三角地区老城区和新城区植被覆盖变化的主导因子，而城市化因子对农郊区解释程度总体不显著。从长三角总体区域看，城镇人口比重、不透水面积/总面积以及地区生产总值三者对植被覆盖演变存在显著影响，其中城镇人口比重影响最大。

Urban and rural differences in vegetation cover evolution and its causes in the Yangtze River Delta

The relationship between urban ecological environment and urbanization is a key to sustainable urban development. Studying the long-term evolutionary trends of vegetation cover under different levels of urbanization is important for understanding the effects of urbanization processes on vegetation growth dynamics, urban regeneration, and advancing scientific management of urban greening. However, the understanding of the differences in vegetation growth trends along urban-rural gradients within cities was still relatively limited. Based on the MODIS-NDVI data of the Yangtze River Delta (YRD) from 2000 to 2020, this study investigated the urban-rural differences in vegetation cover evolution within the cities of the YRD using trend analysis and geographic probe methods, and analyzed the causes from the perspectives of land use/cover change and urbanization development. The results showed that (1) the vegetation in the Yangtze River Delta region showed a greening trend in general from 2000 to 2020, with the largest proportion (52.06%) of vegetation being significantly green, 31.68% being slightly green and stable unchanged areas, and 6.82% being sporadically distributed in browning areas. (2) The change of vegetation cover in the old urban areas of the region showed a general trend of returning to green (0.016/10 a), browning in the new urban areas was obvious (-0.019/10 a), and greening in the agricultural suburban areas was prominent (0.023/10 a). In cities with a high level of population urbanization, such as Shanghai, Nanjing and Hangzhou, the old urban areas with the highest intensity of land use change also had the highest greening trend, reflecting the promotion of green space by the urban renewal process; while in cities with a relatively low level of population urbanization, such as Xuancheng, Bengbu and Fuyang, the agricultural suburban areas with a relatively low intensity of land use change also showed an obvious greening trend, more influenced by regional ecological protection. (3) Land urbanization was the dominant factor of vegetation cover change in old and new urban areas in the Yangtze River Delta, while the urbanization factor was generally insignificant in explaining the degree of suburban areas. From the overall region of the Yangtze River Delta, three factors, namely the proportion of urban population, impervious area/total area and gross regional product, had significant effects on the evolution of vegetation cover, among which the proportion of urban population has the greatest influence.