Evaluation Of The Resources Structure And Cooling Function Of Urban Forest

Urban forest,mainly composed of all the green vegetations of primary woody plants in or around the urban areas,is an important part of ecosystem in the city,which is also a significant role in improving the urban ecological environment,promoting co-ordination between man and nature,meeting the needs of social development and improving people's health and levels of culture and living.Previous researches on urban forest were mainly confined to the urban forestry landscape structure,on how to improve the urban green coverage rate or how to allocate a reasonable urban forestry green structure,which is one of the fundamental issues of urban forest construction.With further exacerbated pollution of environment,the significance of urban forestry ecological functions is highlighted.Therefore,it becomes another fundamental issue that giving pronominence to ecological functions of the urban forest construction.In this study,the urban forest of Harbin was evaluated on two aspects:the urban forestry landscape structure and ecological functions.The main research carried out as follows:1.Methods for monitor and investigation were studied according to the characteristics of urban forest.Then the sub-sampling method was proposed for urban forest investigation in this paper,which was very suited.The greenlands of Harbin were identified from high-resolution aerial photograph,combining with some measured sample plots which were selected by subsampling method.The investigated factors of the plots are mainly including tree species compositions,canopy densities,tree heights,breast diameters,crown widths and so on.Then, vegetation quantity,biomass and carbon storage for evaluating forestry ecological functions were calculated and transformed to green patches to build spatial database for Harbin greenlands.Last,the spatial landscape structure of Harbin was analyzed based on it.2.The green coverage area of Harbin city is about 19777.311 hm~2,accounted for 30 percent of the total city areas.And the afforestation levels of the six municipal districts were uneven that the largest green coverage is Xiangfang,the other five areas from large to small are Nangang,Daowai,Daoli,Songbei and Pingfang.3.Thermodynamic field landscape index was retrieved for thermodynamic field analysis based on Landsat data.By using the principle of Normalization Building Index(NDBI) and false color composite image for visual interpretation,it was found that the space of Harbin city zone has been expanded rapidly during the last 11 years.The city boundaries of Harbin in 2001 and 1989 were identified for overlay analysis and the impervious surfaces in the city boundary were extracted.After that,the impervious surface index was retrieved from the image by spectral mixture analysis principle. 4.The urban forestry function of Harbin was evaluated by analyzing vegetation quantity, biomass and carbon storage.The results showed that:if vegetation quantity Was less than 2000m~3,the temperature would decrease one degree for every increased 120m~3 of vegetation quantity;or else the temperature would decrease one degree for every increased 980m~3 of vegetation quantity.If biomass was less than 10000kg,the temperature would decrease one degree for every increased 760kg of biomass;or else the temperature would decrease one degree for every increased 1650kg of biomass.Therefore,the urban temperature can be reduced effectively by properly increasing vegetation quantity and biomass of the urban forest. Analysis of the carbon storage showed that abilities of carbon fixation and oxygen release of larch and elm were the strongest,the weakest were manchurian walnut and mongolian oak.It draw a conclusion that the landscape structure of Harbin urban forest is reasonable, especially Xiangfang district and Nangang district.But Daoli and Daowai districts are poor in landscape structure due to unreasonably planning.The vegetation quantity,forest biomass and forest carbon storage of Harbin are 89114863m~3,41601009kg and 18720454kg respectively. The forestry ecological functions of Harbin did not play perfectly through analyzing the factors above.Even though city temperature can be reduced by proper forest vegetation quantities and biomass,it is very small in Harbin because of the more greenlands with less vegetation quantities and biomass.From the aspect of carbon fixation and oxygen release functions,the best species for carbon fixation and oxygen release in Harbin are elm and larch.