Study on the Spatiotemporal Evolution of the “Contraction–Expansion” Change of the Boundary Area between Two Green Belts in Beijing Based on a Multi-Index System

Abstract

In serving as a pivotal strategy for curbing urban sprawl, large-scale urban green belts, being a significant constituent of the urban green space, have been ubiquitously employed in the scheming and fabrication of green space systems in global megacities. Nevertheless, the disregard for research into the independent alteration mechanism of urban green space, coupled with the reactive approach of planning and construction and the singularity of quantitative indices, has engendered challenges in the creation of urban green belts. This paper presents an investigation into the juncture zone of two green belts in Beijing as a case study, erecting a “contraction–expansion” flux model of its green space and gauging the transformational traits of the green space in light of its spatial–temporal evolution with regards to its quantity, space, and connectivity among others. Findings reveal that between 2005 and 2012, the green space in Beijing underwent an approximately 20% alteration, with the green belt intersection zone’s green space area experiencing a dual trajectory shift of “expansion-contraction”. This shift was primarily characterized by expansion before 2015 and contraction from 2015 onwards. Concerning spatial attributes, patterns of expansion and aggregation were discernible in scattered distribution, whereas contraction and aggregation were evident in mass and spaced distribution. Spatial stability was influenced by the change model, marked by a shift in the center of gravity from a “north-south-east” orientation to a “northwest-southeast” direction. At the connectivity stratum, noticeable variations were witnessed in both the overall and local connectivity levels pre- and post-2015. Regarding individual connectivity, three vital nodes of stable linear connectivity were identified, playing a decisive role in defining the dispersion of crucial corridors within the area of study.