Study On The Structure Characteristics And Environmental Benefit Of The Shahe Corridor Plant Community In Chengdu

Cities should be in harmony with the nature in the 21st century, and urban river should coordinate the relation between development of urban and environment. As an important part of urban ecosystem, river corridors play an important role on improving ecological environment of city. The current quantitative studies of ecological benefits are almost conducted in the green plots.The objectives of the present study are providing a scientific foundation for rational allocation of river corridor's tree species and quantitative evaluation of environmental benefits in Chengdu, and providing references for construction and renovation of urban forest in the future, particularly for the artificial plant community along the river. The study area in this study is Shahe corridor of Chengdu. On the basis of analysis of structural characteristic through investigating its community, environmental benefits of tree species which was the main of Shahe corridor were measured by LI-6400XT photosynthesis instrument. The main results in the present study were stated as follow.(1) Cinnamomum japonicum var. chekiangense, Ginkgo biloba, Metasequoia glyptostroboides, C. camphora, Salix babylonica, Osmanthus fragrans, Ficus virens and Elaeocarpus sylvestris were the main tree species. The accumulative number of the eight tree species account for over fifty percent in the study area.The distribution of these trees in DBH and stratum shown a tendency of "great number ones in middle and small in both sides". The average of DBH and the height of trees were 12.53cm and 6.29m, respectively. The biodiversity index of species for different stratum in the study area shown the trend of shrub stratum>herb stratum> tree stratum, which between three to four. It means that the construction of community is simpleness relatively. Among of the measured species, the tridimensional green biomass and leaf area per tree of S. babylonica are both much higher than others, which were 42.86 m3 and 49.71 m2 respectively, E. sylvestris is the lowest which were 3.12 m3 and 8.69 m2 respectively.(2) Most of daily varation of the photosynthesis and transpiration of the main trees pecies were single-peak type, and the trend of seasonal change was summer> autumn>spring. The order of capacity of photosynthesis from strong to weak was S. babylonica, O. fragrans, C. camphora, F. svirens, E. ssylvestris, G. biloba, C. japonicum var. chekiangense, and M. glyptostroboides. The capacity of transpiration from strong to weak was S. babylonica, M. glyptostroboides, E. sylvestris, F. virens, C. japonicum var. chekiangense, C. camphora, G biloba and O. fragrans. The daily change curve of transpiration rate of O. fragrans and G biloba were single peak, but the photosynthesis rate were double peak.(3) The order of capacity of carbon fixation, oxygen release, temperature drop and humidity increase per unit leaf area of the trees pecies during the whole growth period was summer>autumn>spring. The capabilities of daily carbon fixation and oxygen release per unit leaf area of the trees pecies from strong to weak was O. fragrans, S. babylonica, C. camphora, F. virens, E. sylvestris, G biloba, C. japonicum var. chekiangense and M. glyptostroboides, and the capabilities of annual from strong to weak was S. babylonica, C. camphora, F. virens, G biloba, O. fragrans, C. japonicum var. chekiangense, M. glyptostroboides and E. sylvestris. The capabilities of daily temperature drop and humidity increase per unit leaf area of the trees pecies from strong to weak was S. babylonica, E. sylvestris, M. glyptostroboides, C. japonicum var. chekiangense, F. virens, C. camphora, G biloba and O. fragrans. It was estimated that the total amount of annual carbon fixation of trees in Shahe was about 5.87×104t and the oxygen release was about 4.27×104t. Based on the analysis of capacity of carbon fixation, oxygen release, temperature drop and humidity of the main tree species, shown that S. babylonica, O. fragrans, E. sylvestris, C. camphora were the preferred tree species. G. biloba was lweaker which could not be virescenced in a large area, but could be used as a longevous and ornamental tree species,.The overall planning of Shahe corridor in Chengdu should be strengthened such as optimization the proportion in compound structure of tree, shrub and grass properly, choosing the native tree species to replanting for build a complex layers and high biodiversity community structure; Moreover, according to the average tridimensional green biomass and leaf area and the environmental benefits of different species, larger leaf area per plant, stronger cability of photosynthesis and transpiration of trees can be used to purify air, reduce noise, balance carbon and oxygen, drop temperature and increase humidity,and so on.