Carbon Sequestration Capability Of Forest Vegetation In Beijing

In local and global contexts of attempting to mitigate climate change, carbon sequestration by the world's forests is a focus of global climate change researches. At present, estimated values of carbon storage by mountain forests and urban landscape in Beijing are derived from forest inventory data and models developed pastly. However, there is significant uncertainty in these estimations because of lacking correspondingly basic parameters suitable for the Beijing region, including biomass conversion and expansion factors and allometric models, and thus a useful technique framework for estimating and monitoring carbon sequestration by Beijing's forests is now lacking.The major research objects of this study are mountain forests and trees in urban green spaces in the whole Beijing area. Diameter-based aboveground biomass equations were developed for twelve tree species using a non-destructive method, named as the nested sampling method, in Beijing, and biomass conversion and expansion factors and TM-based models for estimating carbon stored by eight major forest types, including Platycladus orientalis forest, Robinia pseudoacacia forest, Betula forest, Broad-leaved forest, Quercus forest, Larix principis-rupprechtii forest, Populus forest and Pinus tabulaeformis forest, on the basis of data from the program "Beijing plant germplasm resources survey" (2007-2009) and TM images acquired in 2009. Then, carbon stock in mountain forests in 2004 and 2009 were estimated based on 2005 Beijing forest inventory data and TM images acquired in 2009, and carbon storages by trees in urban green spaces in Chongwen District in 2005 and 2009 and in the whole study area in 2005 were also estimated, respectively, based on 2005 Beijing City urban green space census and 2009 tree survey data in Chongwen District's urban green spaces. Carbon sequestered by Beijing's forests from 2011 to 2015 was projected depending on Beijing's forest carbon storage estimates of this study. The main results include as follows:(1) Beijing's mountain forest carbon stocks in 2004 and 2009 were 5 240 490.8 tonnes carbon and 6 158 970.6 tonnes carbon (including above- and belowground carbon storage), respectively, with mean carbon storage densities of 12.03 tC·hm-2 and 14.14 tC·hm-2. Among the eight forest types, carbon storages were higher in Quercus forest, Populus forest and Pinus tabulaeformis forest and lower in Robinia pseudoacacia forest and Larix principis-rupprechtii forest. According to four carbon storage densities of 0-10,10-20,20-30 and >30 tC·hm-2, Beijing's mountain forest carbon storage densities mostly varied from 10 tC·hm-2 to 20 tC·hm-2 in 2009, mainly found in the northern mountains.(2) Urban trees in Chongwen District in 2005 and 2009 stored 8 022.09 and 8 541.29 tonnes carbon, respectively, with average carbon densities of 14.86 tC·hm-2 and 15.82 tC·hm-2 based on the district's green space area of 539.96 hm2 in 2005.(3) Urban trees in Beijing's 16 districts and counties stored roughly 1 220 700.00 tonnes carbon with mean carbon density of 31.40 tC·hm-2, and average carbon densities of the 16 cities were not directly proportional to their carbon stocks. Among the 16 cities, urban trees in the cities belonging to urban capability expansion region stored the most carbon accounting for 70% of total carbon storage.(4) Based on an pool-difference method, it was estimated that carbon sequestration rates of Beijing's mountain forests (from 2004 to 2009) and Chongwen District's urban trees (from 2005 to 2009) were 0.42 tC·hm-2·year-1 and 0.24 tC·hm-2·year-1, respectively. Mountain forests and urban trees in the whole study area will sequester 914 550.00 tonnes carbon and 46 453.08 tonnes carbon from 2011 to 2015, respectively, amount to 961 003.08 tonnes carbon, with average carbon sequestered per year of 182 910.0 tonnes carbon and 9 330.62 tonnes carbon.