Remote Sensing Estimation Of Urban Forest Biomass In Shanghai

Monitoring and quantifying the biomass and its distribution in urban trees and forests are crucial to understand the role of vegetation in an urban environment.Because of the distinctiveness of management and distribution in urban forest,it is a challenge for efficiently and accurately calculating urban forest biomass and its distribution patterns at a regional scale in technology and methodology.In this study,an urban forests biomass estimation method which combined regression analysis and spatial analysis in Shanghai,China was explored.Based on the measured data of biomass from June 2011 to June 2012 and a variety of remote sensing data,an analysis of the biomass distribution characteristics of urban forest,Cinnamomum camphora trees and forest leaf biomass were carried out.Meanwhile,the spatiotemporal dynamics of urban forest biomass between 2005 and 2012 were also analyzed.Results show that:(1)The higher densities of forest biomass concentrated mostly in the urban areas,e.g.in districts of Jing'an and Huangpu,mostly ranging from 35 to 70 t/ha.Suburban localities such as the districts of Jiading and Qingpu had lower biomass densities at around 15 to 50 t/ha.The spatial biomass distribution of urban forests displayed a tendency of higher densities in northeastern areas and lower densities in southwestern areas.(2)The density and amount of urban forests biomass,Cinnamomum camphora trees biomass and leaf biomass across Shanghai was 33.37 t/ha,48.31 t/ha,2.55 t/ha and 3.57 million tons(Tg),1.33 Tg,0.3 Tg.The overall forest biomass was also found to be distributed mostly in the suburban localities with a fraction of 93.9 %,whereas the urban areas shared a fraction of only 6.1%.In terms of the areas,the suburban and urban forests accounted for 95.44% and 4.56%,respectively,of the total areas in the Shanghai metropolis.(3)The spatiotemporal dynamics of urban forest biomass between 2005 and 2012 indicated that the density and amount of forest biomass in Shanghai maintained a steady increase.The mean biomass density across Shanghai increased from 34.82 t/ha in 2005 to 37.12 t/ha in 2012,and the amount raised from 3.02 Tg in 2005 to 3.42 Tg in 2012.The spatial distribution of the urban forest biomass shows a tendency towards higher densities in the urban areas and northeastern areas versus lower densities in the suburban localities and southwestern areas.(4)It was found that the root-mean-square error(RMSE),mean absolute error(MAE)and mean relative error(MRE)of the model for estimating urban forest biomass in this study were 8.39,6.86 and 24.22%,respectively,decreasing by 57.69%,55.43% and 64% compared to the original simple regression model and by 62.21%,58.5%,65.4% compared to the spatial analysis method.Results indicated that a more efficient way to estimate urban forest biomass in the Shanghai metropolis might be achieved by combining spatial analysis with regression analysis.In fact,the estimated results based on the proposed model are also more comparable to the up-scaled forest inventory data at a city scale than the results obtained using regression analysis or spatial analysis alone.