A full understanding of the ‘real’ conversion dynamic of green vegetation and its ecosystem service: quantity-quality and gain-loss perspectives

Abstract Contexts. To quantify the ecosystem service (ES) changes caused by the dynamic of green vegetation (GV) during rapid urbanization, it is necessary to fully understand the ‘real’ conversion pattern of GV, yet key and ‘real’ conversion patterns within specific periods and contributions to GV quality remain poorly understood. Objectives. Here we use Normalized Difference Vegetation Index (NDVI) as a mediator to represent GV quality. Land cover transfer matrix (LCTM) and urban greenspace dynamic index (UGDI) were employed to fully understand the GV dynamic from quantity-quality and gain-loss perspectives. The Pearl River Delta Metropolitan Region (PRDMR), one of the fastest urbanizing regions in the world, was selected as a case study. Results. We found that from 1990 to 2015, built-up land, forests and grasslands has the most dynamic conversion, and also has the most significant impact on NDVI. The NDVI value of the newly-built forest (0.29) was much lower than that of the lost forest (0.5), which demonstrate the value and importance of existing natural forest ecosystem, as newly-built forest does not provide the same quality of NDVI and ESs. Hence, we reconfirm and suggest that in regional ecological planning and management, in addition to creating new, higher quality GV, it is essential to protect existing natural forest ecosystems. Conclusions. The study proposed new and full perspectives, including quantity-quality and gain-loss angle of view, enhance the understanding of GV dynamic and can be used in other related analyses. Results also provide important theoretical bases for regional ecological planning and protection of existing natural forest ecosystems.