中国东西部中小城市景观格局及其驱动力

Landscape dynamics of medium-and small-sized cities in eastern and western China:a comparative study of pattern and driving forces

中小城市的数量及其所承载的城市人口迅速增加是当今和将来全球城市化的最为显著的特征之一。因此,对中小城市的发展规律及其城市化带来的生态和环境影响的研究日趋重要。然而,迄今为止的大多数有关城市化的研究聚焦于大型城市。通过对长三角地区和新疆地区24个中小城市的景观格局分析,结合人口经济数据,探究这两个地区总体城市景观格局的变化,城市间景观格局变化的变异性,以及城市景观格局变化的驱动力,并在此基础之上进行两地区间的对比分析。结果表明,1986年至2000年15a间,长三角地区和新疆地区中小城市的总体景观格局变化基本相似,景观的破碎化程度均不断上升,斑块形状更趋于不规则,景观多样性呈小幅增加;长三角地区中小城市间景观格局变异性下降,而新疆地区中小城市间景观格局变异性上升。长三角地区中小城市景观格局变化的驱动力主要是人口的增加和流动所导致的城市景观变化,新疆地区则为人口的增加和流动所导致的耕地景观面积增加。研究结果有助于解决我国中小城市急速发展所带来的一些生态和环境问题,以及通过土地利用规划来改善我国中小城市的可持续发展。

Urbanization is an important aspect of land use and cover change, which profoundly affects ecosystem composition, structure and function as well as regional landscape pattern and processes. The rapid development of small- and medium-sized cities is a significant characteristic of global urbanization today, and is expected to remain so for decades in the future. During the last 50 years, the fastest growing cities in China are small- and medium- sized cities with populations ~〈 500 thousands. Thus, small- and medium-sized cities are important for regional social development and urbanization, which has significant impacts on the sustainability of the regions and the entire nation. In the past 20 years, because of the rapidly rising number of small- and medium-sized cities, their urbanization effects have received increasing attention. Understanding the generalities and idiosyncrasies of the urbanization patterns and processes of these cities is crucial for sustainable development. However, much of the current research on urbanization has focused primarily on thelarge cities with populations 〉 500 thousands. Few studies have investigated the complexity and dynamics of small- and medium-sized cities, including the relationship between urban landscape patterns and urban ecosystem functions. In this study, we selected 24 small- and medium- sized cities in Xinjiang and the Yangtze River Delta region to quantify landscape change and underlying driving forces in the two regions using a comparative approach. Based on the results of our study, we concluded： （ 1 ） In the two regions, urban land type had the highest growth rate with a mean annual increase of 〉 5 % , suggesting a rapid urbanization process from 1986 to 2000. However, the specific changes of land use and land cover types differed in the two regions. In the Yangtze River Delta, cropland declined in area significantly more than other types, with a mean annual decrease rate of 62.87 km2. In the Xinjiang region, the areas of unused land and grassland declined substantially during the study period. The mean annual decrease rates of these two land-use types were 123.6 km2 and 90.2 km2, respectively. （2） The overall pattern of landscape change in the two regions was similar during the 15 years. The level of landscape fragmentation, landscape diversity, and patch shape complexity all increased. However, the urban landscape pattern among different cities in the Yangtze River Delta region became more homogeneous compared to the Xinjiang region. （3） Our comparison of the main forces driving landscape change in the two regions indicated that the changes in croplands contributed significantly to the changes in the overall landscape pattern of small- and medium- sized cities. In the Yangtze River Delta, the main driving forces of landscape change were associated with population growth and rural-to-urban migration of people. A large quantity of cropland was used for urban construction and became increasingly fragmented as urbanization unfolded. In contrast, the main driver of landscape change in the Xinjiang region was related predominantly to the increase in croplands due to population growth and immigration. In this case, the increased human activity resulted in the increase in cropland. Urban sprawl contributed relatively less to landscape pattern change in Xinjiang than in the Yangtze River Delta. In addition, the expansion of croplands not only took up a large amount of grassland resources, but also intensified land use on the grasslands, consequently leading to degradation of the grassland ecosystems. These findings provide useful information for dealing with ecological and environmental problems induced by rapid urbanization, and for sustainable development of small- and medium-sized cities in China. Further studies are needed to investigate the processes and mechanisms of how urbanization affects biodiversity and ecosystem services in these small- to medium-sized cities.