Research On Ecological Benefit Evaluation System And Ecological Value Of Urban Green Space In Xi'an

With the rapid development of urbanization in China,urban environmental problems have become increasingly serious,people have realized the importance of strengthening the ecological construction of green space and improving the quality of urban ecological environment,many countries have made urban greening as an important part of the strategy of urban sustainable development.At present,the assessment system of urban green space ecological benefits is lack of systematization,urban green space ecological value measurement method is lack of unity,and the measurement method of evaluation index is chaotic.With the lack of a unified and complete research system and research paradigm,and further research is still needed.At the same time,the research on the evaluation system of urban green space ecological benefits has distinctive regional characteristics,different cities have different geographical locations,climates,urban structures and city sizes,therefore,taking a city as a unit,and combining with the local actual situation,it is imperative to build an index system suitable for local green space ecological benefit.However,the research on the evaluation system of ecological benefits of urban green space in Xi'an has not yet commenced.Therefore,in this paper,using the remote sensing image as the basic data source,combined with 3S technology,and the theoretical framework of environmental science,geographic information science,remote sensing science,landscape ecology,etc.,select the indicators suitable for the evaluation of ecological benefits of urban green space in Xi'an scientifically,and build an advanced and reasonable evaluation index system for ecological benefits of green land in line with the local characteristics of Xi'an.Combined with field measurement,evaluating the evaluation indicators quantitatively,and evaluating the ecological benefits of urban green space in Xi'an comprehensively.The study mainly carried out as the follows:?1?Based on the socio-economic-natural complex ecosystem theory,from two aspects of structure and function,selecting 9 indexes,including per capita green volume,forest coverage,green space uniformity,green coverage,per capita park green space,comprehensive ecological value?carbon fixation,oxygen release,dust retention,SO₂absorption?,and constructing the three level evaluation index system of urban green space ecological benefits,according to the actual situation of Xi'an.?2?Studying the urban forest carbon storage,carbon density,and spatial differentiation characteristics,based on the species diversity of urban forest tree species.The study found that the average carbon density in the arbor layer of forest vegetation in Xi'an City is:green area of cultural and educational areas>scenic area green space>road green area>industrial area green area>residential area green area.The average carbon density of trees in Xi'an main city area was 6.308 kg/m²,which was higher than average carbon density in Shaanxi Province.The carbon storage of forest vegetation in the main urban area of Xi'an are as follows:green land of cultural and educational area>scenic area green land>road green land>residential green land>industrial green space,the carbon stock of the green space in the cultural and educational areas was21.1×10⁴ t,which contributed 40.6%to the carbon sink of the forest layer of the forest vegetation in Xi'an city.The carbon storage of the green space in the scenic area contributed 35.1%of the carbon sink of the arbor layer of the forest vegetation in the whole city,and the carbon reserves of the road green area accounted for 14.3%of urban arbor carbon stocks,residential greenbelt carbon reserves accounted for 6.6%of urban arbor carbon stocks,while industrial park greenbelt carbon reserves only accounted for3.3%of arbor carbon stocks in Xi'an main city,and Xi'an downtown area forest vegetation tree layer carbon reserves the total amount is52.0×10⁴ t.In general,the spatial distribution pattern is uneven,showing the characteristics of high souther suburbs and low northern suburbs.?3?Based on 3S technology and high-precision 3D laser point cloud data,for the first time,a differential method was used to study the construction of single-wood three-dimensional green volume estimation model and the three-dimensional green volume of Xi'an urban forest.The results show that the three-dimensional green volume model has a high prediction accuracy of 88.07%,and the statistical parameter R is 0.89.It can be used as an inversion model for 3D green volume estimation of trees.This method is in line with the actual situation,and greatly improving the measurement accuracyof single-wood three-dimensional green.The total amount of three-dimensional green volume of green space in the main urban area of Xi'an is 3747.5×10⁴ m³,among which the three-dimensional green volume of the green space in the scenic area>the three-dimensional green volume of the green space in the cultural and educational area>the three-dimensional green volume in the road green area>the three-dimensional green volume in the residential area green space>the three-dimensional green volume in the industrial area green space.?4?Studying the ecological benefit and ecological value of Xi'an urban green space based on the three-dimensional urban green quantity.The study found that the annual absorption of carbon dioxide was 113.9×10³t in the main urban area of Xi'an,the annual amount of sulfur dioxide absorbed was 113.6 t,the annual dust holding capacity was41.2×10³t,and the annual oxygen production was 82.6×10³ t.Among them,the contribution rate of absorbing CO₂ benefit is the highest.The total value of the ecosystem service functions of absorbing CO_2,absorbing SO_2,absorbing dust,and producing O₂ in arbor forest forest in Xi'an main city in 2015 was 176.8million yuan,and its value ratios were 77.28%,0.08%,3.96%,and 18.68%,respectively.Among them,the amount of CO₂ absorbed by arbor forest in the main urban area was 113.9×10³t/a,and its currency value accounted for the largest proportion,was 136.7 million yuan.?5?Based on the ecological benefit evaluation system of urban green space,using the polygonal comprehensive index method to evaluate the ecological benefits of urban green space in Xi'an comprehensively,the results show that the comprehensive index of urban green space ecological service function in Xi'an was 0.33 in 2005,and the ecological service function was normal.In 2010 and 2015,the ecological service function was good,the comprehensive index was 0.52 and 0.65 respectively;in 2020,the comprehensive index of greenland ecological service function was 0.76,and the ecological service function is in excellent condition.