Effects of Structural and Diversity Attributes on Biomass in Different Types of Urban Forests in Changchun, Northeast China, and Suggestions for Urban Forest Planning

Understanding of the relationship between structural and diversity attributes and biomass is important for plant biodiversity conservation, ecosystem service function enhancement and sustainable development of urban forest ecosystems. In this study, road forest (RF), attached forest (AF) and landscape and relaxation forest (LF) were selected as research objects. We systematically evaluated the diversity attributes and above ground biomass (AGB) at two dimensions of different diameter at breast height (DBH) grades and different tree height grades of urban forests in Changchun, Northeast China. Structural equation modeling (SEM) analyses of the correlation between structure attributes, diversity attributes and biomass among different types of urban forests were carried out. The results showed that species richness (SR) and Shannon-Wiener index (H ') of shrubs were lower than those of trees. Under the DBH grades, H ' in each forest type was highest in the 0-10 m grades and SR was highest in the 10-20 m grades. Under tree height grades, both H ' and SR of each type were at the top of the list. AGB was highest in each forest type under 5-10 m height grades. The relationship between AGB and H ' was better in LF, but with no significant relationships in the other forest types. SEM highlighted that in the overall aspect, the effect of forest type on biomass was mediated by structure and diversity attributes. Particularly in LF, there were direct and indirect effects between structure attributes and biomass mediated by diversity attributes. The improvement of the H ', evenness index (J ') and SR could enhance urban forest services, especially for the biomass and diversity of LF.