Examining the direct and indirect impacts of urbanization on vegetation net primary productivity across Chinese cities

Abstract

China has undergone the world's most rapid urbanization, drastically altering regional climates and urban vegetation growth environments. However, the mechanisms of urbanization on carbon sequestration in both urban green spaces and surrounding vegetation remain underexplored. This study utilized buffer zone analysis to evaluate the spatial heterogeneity of urbanization’s effects on Net Primary Productivity (NPP) across 271 cities in China, focusing on different buffer distances. Through quantitative analysis of both the direct and indirect impacts of urbanization on NPP, the findings revealed that urbanization not only indirectly affects urban green spaces but also exerts significant negative indirect effects on vegetation in surrounding buffer zones due to spatial correlations. These findings underscore the importance of selecting areas unaffected by built-up zones to accurately quantify the effects of urbanization Direct effects of urbanization significantly reduced NPP by 30 % to 80 %, with impacts increasing toward northern latitudes. Negative indirect effects were in the eastern and central regions with reductions between 50 % and 100 %. 30 % of cities showed positive indirect effects. Moreover, the urban heat island effect was found to weaken regional carbon sequestration capacity significantly. In areas with favorable water and heat conditions, NPP is less likely to recover to its original productivity levels after experiencing human disturbances. In contrast, some arid cities exhibited positive indirect effects of urbanization, highlighting the critical role of human interventions, such as irrigation and fertilization, under specific ecological conditions. This study offers valuable insights into the impacts of urbanization on carbon sequestration within urban and surrounding ecosystems.