Vegetation Structure Characteristics And Carbon Uptake Of Urban Built-up Area In China

With the urbanization rate riseing, urban ecology has become more closely related to human life and the environmental problems. China is one of the fastest urbanizing areas. China’s urbanization has been called the world important source of energy to promote the development in the21st century, but also one of the prominent areas of environmental issues. Study of built-up area vegetation structure characteristics and the contribution of reducing atmospheric carbon dioxide that contributes to the urban ecology theory.China is located in the southeast of climate zone, from north temperate to tropical climatic zones, from humid to arid, provides a good material for the study of the built-up area vegetation. In this study, we surveyed43cities in China with3295(400m2) plots, measuring a total of24027trees,19species424tree rings.With questionnaires garden workers getted the management of urban vegetation and garden waste. This study combined with measured data and literature and Yearbook data to study the pattern of urban gneenspace built-up area and the vegetation structure characteristics, explored the urban built-up area of vegetation carbon storage and carbon sequestration and driving factors, discussed the potential of garden waste for bio-energy production. The following conclusions:(1) The study which focused on the pattern of green space and vegetation structure characteristics in urban built-up area showed that:The area green space in built up area is growing rapidly in China, green space coverage had been increased by7.5%annually between1996-2010. Greening coverage rate grew by an average of2.8%every year. There is an uneven spatial distribution of green space coverage for286cities in China, with an obvious gradient distribution descending from the East to the West. Tree diameter at breast height (DBH) was mainly5-25cm for built-up area green space, and tree height was mainly concentrated in two intervals of5-7m and7-9m; the coverage of stratified vegetation structure was between12%-39%, with an average value of24.6%. Gleason richness index of trees in built-up area were between1.30-5.17with a higher value the south than the north.(2) The correlation analysis of community characteristics and nature and socio-economic factors showed that the average DBH and height of trees significantly related with nature-economic factors; compared to natural factors, economic factors is a more significant determinants for stratified vegetation structure; Gleason index was significantly correlated with average annual rainfall, annual temperature and PGDP (P<0.05). While Simpson index, Shannon-Wiener index and Pielous index showed no significant relationship with hydrothermal conditions and economic development The study found that the diversity of vegetation in urban green space is largely regulated by human activities, to a certain extent, landscape aesthetics is a more significant determinants of woody plants in the urban ecosystem. But the natural environment has a great impact on the selection of urban greening tree species.(3) The green vegetation carbon density of the urban built-up area in47studied cities is in the range of4.95t C hm-2to46.30tC hm-2, with an average of18.19±9.23tC hm-2. The average carbon density of the average green coverage area of the47cities in China is57%of the natural forest. The carbon uptake of the urban built-up area of the studied cities ranges from0.21tC hm"2yr-1to4.30tC hm-2yr-1, with an average of2.13tC hm-2yr-1. At this stage, in China’s built-up area, the carbon uptake of the average urban vegetation area is higher than the natural forest, approximately50%higher than the natural vegetation. The vegetation carbon sequestration of built-up area in China can offset2.5%of the carbon emissions from the energy use of the urban residents.(4) Studing the driving factors of vegetation carbon storage and uptake in built-up area in China, showed that carbon density of the urban built-up area do not have significant relation with natural factors, such as longitude, latitude, annual precipitation, average annual temperature and moisture index. Carbon pool of the natural has changed a lot dute to the impact of human activities, the vegetation carbon pool is no longer signifcantly changed with latitude and longitude, which influence the light, temperature and humidity and other factors, that means the carbon density showing convergence phenomenon; carbon uptake mainly influenced by natural factors, instead of the economic impact, and the garden management could promote the built-up area of vegetation carbon sequestration.(5) Garden waste to bio-energy production has advantages in the energy input and output. Using the garden waste of the urban green space has great prospects. Development and utilization of garden waste of the urban green space to produce bio-energy not only reduces transport costs, but also brings benefit which can compensate for the cost of collection and disposal of the waste, thus achieving the win-win effect of revenue increasing and energy savings. The total bioenergy potential of China’s garden waste can be244PJ, equivalent to20.7%of the electricity consumption of urban residents,12.6%of the energy consumption of the gasoline used in transportation of China in2008, and it can reduce17X106t CO2equivalent replacing fossil fuel. Using garden waste to produce of bio-energy contributes to the construction of low-carbon city.