A Unified Vegetation Modeling Approach By Integrating With 3D Volume And Leaf Area Density By Taking Built-up Areas Of Wuhan As A Case Study

In the process of rapid urbanization,urban ecological problems began to emerge gradually,and human beings began to recognize the urgency and importance of greening environment.Assessment and analysis of urban green space can help us better understand the quality advantages and disadvantages of urban green space and its ecological benefits.However,urban green space has different vegetation types and structures,so it is necessary to use three-dimensional vegetation mass to realize the assessment of urban environment quality and green space characteristics based on 3D space.Currently,research on urban 3D vegetation mass at large scale is mainly limited to two-dimensional indicators,which cannot adequately represent the distribution characteristics of vegetation community structure in vertical space.So this study intends to propose a new method for quantifying 3D vegetation mass to improve the limitations of traditional planar mass inversion to calculate 3D vegetation mass,and to shift from green coverage to green space occupancy from spatial volume to describe more reasonably the distribution characteristics and ecological benefit level.Based on the current construction status of Wuhan,this study takes the area within the Wuhan third ring road as the study area of Wuhan built-up areas(hereinafter referred to as Wuhan built-up areas).The study uses 6 m high-resolution remote sensing data to achieve spatial downscaling conversion and inversion of 1 km low-resolution remote sensing products,obtains vegetation leaf area index and canopy height with 6 m high-precision spatial resolution,and verifies accuracy of the conversion model using the measured data.And further deduced the vegetation leaf area density and 3D volume.Then,the quantification method of urban 3D vegetation mass is constructed by combining the vegetation leaf area and spatial volume in urban space,and integrating the horizontal and vertical directions of vegetation.The spatial characteristics and influencing factors of 3D vegetation mass3D vegetation mass at three different spatial scales of cities,regions and projects are analyzed by establishing a 3D vegetation mass composite model with complete spatial information in simulation,and the potential applications of this urban 3D vegetation mass model are proposed.After analysis,four points were found:(1)There are differences in the ways of quantifying 3D vegetation mass at different scales.On the urban scale,the variation of leaf area density is not obvious.So the study select vegetation volume as the quantitative index of 3D vegetation mass in the built-up area of Wuhan,and conclude that the total 3D vegetation mass in the built-up area of Wuhan was 392380605 m~3,and the average 3D vegetation mass was 0.748 m~3/m~2.On the regional and project scales,the 3D vegetation mass corresponding to different site types was quantified by combining leaf area density and vegetation volume.Among them,the total volume of vegetation at the regional scale was 10416824 m~3,with an average vegetation volume of 1.008 m~3/m~2,and the total vegetation leaf area density was 26708m~2/m~3,with an average leaf area density of 0.003 m~2/m~3.The project scale has a total vegetation volume of 912082 m~3,with an average vegetation volume of 1.733 m~3/m~2,and a total leaf area density of 2940 m~2/m~3,with an average leaf area density of 0.006 m~2/m~3.(2)The details of spatial characteristics of 3D vegetation mass at different scales are also different.On the urban scale,the spatial distribution of 3D vegetation mass spreads mainly from the east-west to the north-south direction of the city.On the regional scale,the 3D vegetation mass is mainly concentrated in major parks and residential areas with high green volume.On the project scale,the3D vegetation mass is more distributed in the space with rich vegetation species and strong enclosure.(3)The influencing factors of 3D vegetation mass at different scales are mainly divided into vegetation and spatial factors.On the urban scale,the 3D vegetation mass is mainly influenced by the vegetation cover and the proportion of land space volume.On the regional scale,the influencing factors are mainly plant growth and community level.And on the project scale,the 3D vegetation mass is closely related to the species richness of the vegetation and the planting method.(4)The 3D vegetation mass composite model has a variety of potential application scenarios.The model can be used as a basis for 3D vegetation mass quantifying and analyzing,or constructing relevant evaluation metrics based on 3D vegetation mass,or to establish the index system and calculation method of 3D landscape pattern index.The model can also be applied to the simulation of evolutionary processes in urban green space and the assessment of multiple ecosystem services in urban green space in 3D space.