Urban–rural gradient in vegetation changes and response to biogeochemical drivers and land use in the Guanzhong Plain Urban Agglomeration, China

A comprehensive evaluation of the long-term urban vegetation dynamics and its responses to land-cover changes and biogeochemical drivers (e.g., CO 2 concentration increase and nitrogen deposition) at the urban agglomeration scale is pivotal for better understanding of transformations in complex urban environments. In this study, we explored the vegetation change trends identified by the Landsat enhanced vegetation index (EVI) along the urban-rural gradient in 55 cities of the Guanzhong Plain urban agglomeration (GPUA) from 2000 to 2020. Additionally, we investigated the contribution of biogeochemical driving factors and land cover changes. The results showed that the EVI change trends from 2000 to 2020 exhibited a V-shaped pattern along with the urban-rural gradient, that is, EVI increased for urban cores (UC) and urban new towns (UNT), decreased for the urban fringes (UF), and increased again for rural fringes (RF) and rural backgrounds (RB). EVI changes in the city subzones (UC, UNT, and UF) showed an increasing trend with city size. The EVI change trends are influenced by urban biogeochemical drivers (UBD), background biogeochemical drivers (BBD), urban expansion or densification (UED), and urban green recovery (UGR). The significant increase in EVI in UC and UNT is mainly attributed to UBD (51.9% and 37.2%) and BBD (27.3% and 30.7%), respectively. The EVI change trend in UF is positively contributed by both BBD (29.2%) and UBD (15.8%) and weakened by UED (-51.9%). The EVI increase is dominated by UBD and BBD in UC and UNT, and decrease is dominated by UED in UF. These results help assess the impact of complex environmental changes on vegetation in urban agglomeration areas.