Linking above-ground biomass and biodiversity to stand development in urban forest areas: A case study in Northern Italy

Over recent decades, afforestation and reforestation efforts have been conducted in and around European cities for environmental and socioeconomic reasons. These efforts have led to acquire knowledge of the key components of forests (e.g., above-ground biomass [AGB], biodiversity) in relation to forest growth with implications for ecosystem management. Our hypothesis is that urban forest plantation diversity and above-ground biomass significantly change during stand development. In this study, we chose three (young to older) forest stands (three sub-plots for each stand age) to explore the relationships between AGB, tree biodiversity and community structure in the urban forest of Parco Nord Milano, Milan, Italy. Results showed that the community structure and plant species composition differed among the stands. During forest growth AGB significantly increased, whereas the Richness (S), Shannon Diversity index (H), Shannon Evenness (J) and total density values decreased. Interestingly, the AGB was positively correlated with tree height and density at species and stand scale, but was negatively correlated with total density at stand scale. As a result, we found changes in species composition. The level of dynamic competition did not significantly differ among species in stands younger than 25 years, but increased with intraspecific competition among single trees over time. Our results further suggest that disturbance (i.e., thinning) does not largely affect above-ground carbon accumulation, but over the long-term likely influences biodiversity during forest growth. Predicting AGB-biodiversity relationships could represent a supportive method for improving management services and increasing biodiversity in urban and peri-urban forest areas.