A dynamic assessment framework of ecological networks coupled with Graphab-PLUS model

Objective This study aimed to explore a framework for evaluating urban ecological networks that adapts to the dynamic development of cities and policy guidance, providing development guidance and forward-looking layout for the precise construction of ecological networks.

Method Taking the central urban area of Beijing as an example, based on land use data from two periods in 2005 and 2020, the PLUS model was used to simulate the land use in 2035 under three urban development scenarios. Graphab was used to calculate the landscape connectivity indicators of the ecological network under different scenarios, and a dynamic evaluation framework for the ecological network was constructed to clarify the problems and explore the direction of ecological construction in the central urban area.

Result (1) Under the overall planning development scenario, the expansion intensity of construction land was controlled, showing a trend of decentralized development, and the overall green space development status was good; under the urban expansion development scenario, construction land expanded strongly to surrounding land. (2) From 2005 to 2020, connectivity probability index (PC) in the central urban area decreased by 29.1%, and the urban ecological network degraded. The ecological network state under the overall planning development scenario improved significantly, with a PC increase of 62.6%; while the urban expansion scenario aggravated the trend of ecological degradation, with a PC decrease of 38.6%. (3) At individual level, the distribution of connectivity probability change index (dPC) grades showed a pattern of high in the northwest and low in the southeast. Under the overall planning development scenario, the overall network structure tended to be complete, with an increase in the number of higher-level elements; under the urban expansion development scenario, the overall network structure became increasingly fragmented, and the degradation of element grades was significant. (4) On the dynamic evaluation framework, the central urban area tended to have low-base characteristics, and there were significant differences in network characteristics among districts.

Conclusion The study explores the evaluation method of urban ecological networks by coupling the Graphab-PLUS model, constructs a three-dimensional dynamic evaluation framework of “base-resilience-potential”, and provides a scientific basis for clarifying regional ecological development orientation and supporting territorial space planning.