The impact of urbanization process on the coupling relationship between landscape pattern and ecosystem health and its threshold effect in Cangzhou

The interplay between landscape configuration and ecosystem functionality in coastal saline-alkali zones undergoing rapid urbanization remains insufficiently quantified. Taking Cangzhou—a representative city on the Bohai Rim characterized by widespread saline soil, intensive port industrialization, and accelerated urban expansion—as the study area, we examined the nonlinear dynamics between landscape pattern evolution and ecosystem health (EH) from 2013 to 2023. The Vigor-Organization-Resilience (VOR) framework was employed to quantify EH from 2013 to 2023, the Coupling Coordination Degree (CCD) model was used to assess landscape-EH interactions, and the Modified Compound Nighttime Light Index (MCNLI) was applied to measure the urbanization level (UL). Piecewise linear regression with log-transformation was employed to detect critical transition points in the urbanization-coupling relationship, and bivariate Local Indicators of Spatial Association (LISA) were used to map geographic clusters of positive and negative urbanization effects. A bivariate spatial autocorrelation model was subsequently applied to identify regions of positive and negative effects, as well as the nature of their spatial interactions. The results showed that: (1) cultivated land and construction land accounted for more than 90% of the total area; approximately 75% of the region exhibited a healthy EH status, with notably higher values in the western zones than in the eastern areas; (2) landscape-EH coupling coordination displayed a pattern of initial increase followed by decline; although four-fifths of the study units achieved a coordinated state, the central and eastern regions exhibited relatively lower coordination levels; (3) an inverted U-shaped relationship was observed between early-stage urbanization and coupling coordination; specifically, a UL below 0.28 facilitated coordination, whereas a UL exceeding this threshold exerted an inhibitory effect; this inhibitory effect attenuated during the mid-to-late study period (2018–2023); and (4) spatial analysis identified distinct clusters: the central urban area, western region, and eastern coastal zone formed positive effect agglomerations with synergistic urbanization-landscape dynamics, whereas the southwestern and northern regions represented negative effect agglomerations characterized by spatial mismatch and antagonism.