Quantifying the speed, growth modes, and landscape pattern changes of urbanization: a hierarchical patch dynamics approach

Urbanization transforms landscape structure and profoundly affects biodiversity and ecological processes. To understand and solve these ecological problems, at least three aspects of spatiotemporal patterns of urbanization need to be quantified: the speed, urban growth modes, and resultant changes in landscape pattern. In this study, we quantified these spatiotemporal patterns of urbanization in the central Yangtze River Delta region, China from 1979 to 2008, based on a hierarchical patch dynamics framework that guided the research design and the analysis with landscape metrics. Our results show that the urbanized area in the study region increased exponentially during the 30 years at the county, prefectural, and regional levels, with increasing speed down the urban hierarchy. Three growth modes-infilling, edge-expanding, and leapfrogging-operated concurrently and their relative dominance shifted over time. As urbanization progressed, patch density and edge density generally increased, and the connectivity of urban patches in terms of the average nearest neighbor distance also increased. While landscape-level structural complexity also tended to increase, the shape of individual patches became increasingly regular. Our results suggest that whether urban landscapes are becoming more homogenous or heterogeneous may be dependent on scale in time and space as well as landscape metrics used. The speed, growth modes, and landscape pattern are related to each other in complicated fashions. This complex relationship can be better understood by conceptualizing urbanization not simply as a dichotomous diffusion-coalescence switching process, but as a spiraling process of shifting dominance among multiple growth modes: the wax and wane of infilling, edge-expansion, and leapfrog across the landscape.

城市化改变了景观结构，并深刻影响生物多样性和生态过程。为了理解和解决这些生态问题，至少需要对城市化的时空模式的三个方面进行量化：速度、城市增长模式以及由此导致的景观格局变化。在本研究中，我们基于一个指导研究设计和景观指数分析的等级斑块动态框架，对1979年至2008年中国长江三角洲中部地区的城市化时空模式进行了量化。我们的研究结果表明，在县级、地级和区域级层面，研究区域的城市化面积在30年间呈指数增长，且在城市等级体系中，级别越低增长速度越快。三种增长模式——填充式、边缘扩张式和跳跃式——同时存在，且它们的相对主导地位随时间推移而发生变化。随着城市化的推进，斑块密度和边缘密度普遍增加，城市斑块在平均最近邻距离方面的连通性也有所增加。虽然景观层面的结构复杂性也趋于增加，但单个斑块的形状变得越来越规则。我们的研究结果表明，城市景观是变得更加同质化还是异质化可能取决于时空尺度以及所使用的景观指数。速度、增长模式和景观格局以复杂的方式相互关联。通过将城市化概念化为不仅仅是一个二分的扩散 - 合并转换过程，而是一个多种增长模式之间主导地位转换的螺旋式过程：填充式、边缘扩张式和跳跃式在景观中此消彼长，能够更好地理解这种复杂的关系。