What factors are influencing peri-urban forest carbon storage in different land use types based on permanent plots from 2009–2018

Urban forests are crucial in reducing atmospheric carbon dioxide (CO₂) concentrations. Forest structure and composition in particular are important indicators influencing forest carbon storage. In this study, a long-term survey in Chongming Island was used as a case study to examine temporally the changes in an urban forest and its assemblage of woody plant specifically during 10 years. We measured species evenness, species diversity, canopy cover, tree density and aboveground carbon storage (ACS) in three broad land use types including agriculture uses (ALU), forest land uses (WLU), and constructed land uses (CLU). Using field data from long-term permanent plots and structural equation modeling (SEM), the objective of the study was to estimate the direct and indirect effects of these metrics on ACS across these three land use types. The study showed that species evenness, species diversity, canopy cover, and tree density all increased in the ALU, WLU, and CLU. Meanwhile, the tree ACS was higher than shrub ACS. Average ACS increased by 2.07, 9.89, 4.06 MgC/ha in CLU, ALU, CLU, respectively. Both key dominant species, Cinnamomum camphora and Metasequoia glyptostroboides played critical roles in determining ACS. Vegetation density strongly directly affected on ACS in WLU, whereas canopy cover exerted the similar effect on ACS in ALU. Additionally, species evenness had a strong positive direct effect on ACS, but a strong negative direct effect of species diversity occurred. Finally, a strong positive indirect effect on ACS from canopy cover was found in CLU from 2009 to 2018. The findings can provide useful assessment indicators for managing peri-forests to improve forest carbon storage to speed up accomplishment of Sustainable Development Goals (SDGs).