Gradient and Directional Differentiation in Landscape Pattern Characteristics of Urban Ecological Space Based on Optimal Spatial Scale: A Case Study in Changsha City, China

The study on the explicit gradient change in urban ecological space helps a deeper understanding of the landscape pattern-process relationship, and could provide the support for the urban landscape pattern optimization and management. Meanwhile, rapid urbanization caused a series of ecological problems associated with the changes of urban ecological space in Changsha. In this study, remote sensing (RS), geographic information system (GIS) technology, landscape pattern index, and Fragstats 4.2 moving window method were adopted to explore the gradient and directional differentiation of landscape pattern characteristics of urban ecological space in Changsha metropolitan area at optimal spatial scale based on remote sensing images in 2013, 2017 and 2020. The results prove that: (1) The most suitable grain size is 60 m, and 1 000 m moving window is the most suitable size for analysis. (2) The increase of the construction land area came from the reduction of part of the cultivated land, and the dominant position of cultivated land was gradually weakened. The largest patch area and aggregation degree of urban green space and forest showed an overall upward trend, while the fragmentation level was weakened. Urban ecological space presented the trend of discrete development from 2013 to 2017 and agglomeration from 2017 to 2020. (3) The construction land is the dominant landscape component of the urban center, and the landscape homogeneity is strong. The construction level develops rapidly, and the urban ecological space has a high degree of fragmentation and diversity in the sub center of the city. Moreover, the urban-rural transition area has the largest landscape diversity, high degree of fragmentation and strong landscape heterogeneity, which makes it a typical area of urban expansion. The cultivated land and forest constituted the ecological barrier of ecological conservation area in Changsha metropolitan area. (4) From 2013 to 2020, the ecological space of the metropolitan area, as a whole, had a north-east and south-east shift trend, while the spatial center of gravity showed an east-west shift trend, and the construction land spread from the city center to all directions, especially in the north-south, east-west and north-east directions. The landscape of cultivated land has been seriously impacted. The largest patch area of forest increased and the degree of fragmentation decreased in the north, north-east, south-east and south. The ecological function of the east and west sides of the central Xiangjiang River has been significantly enhanced.