Abstract:
During the last few decades, urban population increased dramatically. The expansion of human population and the process of urbanization change carbon stocks and fluxes by a complex biogeochemical process, which can have significant impacts on the urban ecosystem functions and carbon cycle. In New Zealand, many studies focused on non-urban ecosystem (e.g. farming land, grassland, plantation forest and indigenous land), but pay less attention to the impacts of urbanization on urban forest soil. No literature has been found on the status of urban forest soil carbon density in New Zealand. The objective of this study is to determine Auckland (New Zealand) urban forest soil carbon density, and provide an overview of the factors that could influence soil carbon density in urban forest ecosystem. A total of 70 soil cores for three depth increments (0-10cm, 10-30cm, 30-75cm), and 32 plant litter samples were collected from ten permanent urban forest plots in Auckland. Laboratory measurements included: total C and total N concentration, soil pH, soil dry bulk density and particle size distribution. Total soil carbon concentration was high in 0-10cm depth (4.49%) and reduced to only 0.95% in 30-75cm depth. The average carbon density for Auckland forest soil was 113 t C/ha in 0-75cm depth and the data was lower than the literature data for plantation forest and indigenous forest in New Zealand. Plant litter carbon density was 4.78 t C/ha with high variability. Basal area may be used as a variable to predict soil carbon density as it was strongly correlated with carbon density (0-10cm) in this study. High soil carbon density (0-10cm depth) was found in the plots of less than 10 km to the Auckland CBD compared to the plots with the distance of greater than 10 km to the CBD. Whether the high carbon density for the plots (<10 km to CBD) was caused by the effects of urbanization, needs more data to confirm.
