From city to countryside: Unraveling the long-term complex effects of urbanization on vegetation growth in China

The urban environment is the “natural laboratory” of the global ecosystem, and it has complicated effects on vegetation growth, including direct effects (land use transformations) and indirect effects (climatic environment changes). However, the long-term responses of vegetation to urbanization and its associated controlling factors across different spatial scales, from pixels to regions, remains unknown. Here, we unraveled the dual influence of urbanization on vegetation growth and its potential drivers along the urban development gradients in China with satellite observations of leaf area index (LAI) during 2000–2020. The results showed that 65.68 % of pixels in whole China exhibited an increasing trend in vegetation growth, with prominent greening (as indicated by LAI increases) in rural background areas (0.198/10a), significant greening in urban core areas (0.0343/10a), and significant browning in suburban areas (−0.0391/10a). As the process of urbanization intensified, the relationship between urbanization and vegetation growth became increasingly complex, transitioning from linear to non-linear interaction. The overall direct effects of Chinese cities were negative and increased annually. Meanwhile, the positive indirect effects of urban environments on vegetation growth initially declined and then recovered. Cities with high urbanization level (urbanization rate, ULp >70 %) had higher indirect effects (0.24 %) and growth offsets (0.98 %) than that with moderate (ULp = 60 %–70 %) and low urbanization levels (ULp <60 %) (0.18 %, 0.10 %). In economically developed cities, land use changes from construction to vegetation, influenced by urban policies and management strategies, positively impacted urban greening. Overall, more urbanized cities (ULp >70 %) experienced vegetation growth enhancement due to more intense land use changes, whereas less urbanized cities (ULp <70 %) showed the opposite trends. Understanding the direct and indirect effects of urbanization on vegetation growth is crucial for devising effective urban planning and environmental conservation policies. It can help guide future urbanization processes and minimize adverse effects on the natural environment.