Diverse types of coupling trends in urban tree and nontree vegetation associated with urbanization levels

Cities are increasingly recognizing the benefits of incorporating urban greening strategies into their planning and design to improve sustainability and livability. However, the specific contribution of tree versus nontree vegetation has not been adequately studied in the context of urban greening and rapid urbanization. In this study, we investigated the spatiotemporal variations of urban tree and nontree coverage in China during 2000–2020 by using satellite observations. Results show the nationwide mean urban tree coverage increased by 0.073 ± 0.511% per year (mean ± 1 standard deviation), while nontree vegetation coverage decreased by 0.584 ± 1.022% per year. We found that the majority of mega- and large cities had a contrasting vegetation pattern, with significantly ascending trends in both tree and nontree coverages in urban core areas but descending trends in peri-urban areas. These trends were positively associated with multiple greenness indices, suggesting the importance of the vegetation structure for growth and productivity in urban areas. This study highlights the predominance of enhancing vegetation growth in urban areas primarily driven by significantly increasing tree cover in China, and can further serve as a reference for global vegetation study.