Study On Spatial And Temporal Variation Of Leaf Area Index In Summer In Fuzhou City

With the development of economy and the expansion of cities,the original natural landscape is gradually destroyed in the process of urbanization,leading to major changes in land cover,which will directly affect the growth and distribution of vegetation.By studying the changes in urban vegetation and the extent of the changes,and the relationship between vegetation change and land cover change,we can better understand the feedback effect of the changes in urban ecosystem structure and function on the changes in natural environment.As an important index and ecological parameter of vegetation structure and growth condition,leaf area index can well reflect the growth and distribution of vegetation.In this study,Fuzhou,capital of Fujian province,was taken as the research Area,and Leaf Area Index(LAI)was taken as the vegetation factor.Two geographical environment factors,vegetation coverage and elevation,were introduced to construct the LAI inversion model.Landsat series remote sensing data from 2008 to 2018were used to invert 30m summer LAI time series data of Fuzhou.The temporal change trend of summer LAI in Fuzhou from 2008 to 2018 was analyzed,as well as the spatial distribution characteristics of summer LAI in Fuzhou in 2018.The variation coefficient,unitary linear regression coefficient and Hurst index were used to analyze the degree of fluctuation,variation trend and sustainability of summer LAI in Fuzhou from 2008 to2018 at the pixel scale.In addition,based on the topographic data,the differences in the distribution of vegetation LAI and LAI change types in different topographic features in Fuzhou were analyzed.At the same time,the use of 2008 and 2018,land cover data,analyzes the Fuzhou city land cover change characteristics,various land cover types vegetation LAI,the overall difference,various land cover types of mutual transformation between the profits and losses of the vegetation LAI,and the use of unary linear regression and geographically weighted regression model,respectively,to explore the relationship between different pattern of land cover and vegetation LAI.The main results are as follows:(1)After the introduction of two key geographical environment factors,the results of the accuracy of the inversion model found inversion values and measured values of decision coefficient R~2increased from 0.714 to 0.795,the root mean square error RMSE reduced from 0.49 to 0.31,shows that after the introduction of geographical environment factors can improve the accuracy of LAI inversion model,and the time series of LAI inversion in summer.Further use of the sample point data of 2011 and 2016,further verify the LAI,the inversion precision of inversion model in time series data,in 2011 and 2016,the inversion of values and measured values of R2 and RMSE were 0.781,0.44 and 0.790,0.39,LAI inversion model for time series data inversion can also obtain a good accuracy of inversion.(2)In terms of time,vegetation in Fuzhou city showed an overall trend of increasing LAI in summer,with an average increase of 0.009 per year.Spatially,vegetation LAI in Fuzhou city in summer presents a trend of gradual decrease from west to east.The results of the analysis on the fluctuation of vegetation LAI in summer indicate that the fluctuation is low in most regions of Fuzhou,which are mainly distributed in mountainous and hilly areas.The regions with high fluctuation are mainly distributed in urban areas with more intense urban development and construction.The results of trend analysis showed that the LAI in the hilly region of Fuzhou remained stable.In urban areas,vegetation LAI mainly decreases,but the spatial differences are obvious,mainly distributed in Cangshan district,Minhou county,Changle city and Pingtan county.Hurst index results calculated by R/S analysis showed that 56.81%of the regions could not be judged for sustainability,indicating that the sustainability of change trend in most regions in Fuzhou could not be judged,and the trend of continuous decrease of vegetation LAI accounted for the largest proportion.(3)The distribution characteristics of LAI at different elevations are that it first increases and then decreases with the increase of altitude.The minimum of LAI in 50m is0.85 and the maximum of LAI at 1400m is 4.12.When the altitude is greater than1400m,value of LAI decreases with the increase of altitude.The distribution characteristics of LAI on different slopes are that they increase with the increase of slope,and the minimum of LAI is 0.84 when the slope is 3°,and the maximum of LAI is 3.08when the slope is 64°.Vegetation LAI change type in different terrain factors on the distribution of the results of the analysis,in the low altitude and slope area LAI,reduce the distribution types of the vegetation types,with the increase of altitude and gradient,vegetation LAI increase large gradually become advantage distribution types,but in high altitude and high grade distribution type for vegetation LAI variant regional advantage.On different slopes,LAI reduction of vegetation on flat land is a dominant distribution type,while on other slopes,the distribution characteristics are not obvious.(4)LAI of different land cover types is significantly different,land cover ratio is significantly related to LAI,and the relationship between the two is spatial non-stationarity.Different land cover types have different impacts on LAI at different spatial locations.Comparing two unary linear regression and GWR model,unary linear regression has certain limitation,especially in Fuzhou this woodland represents a significant share of the study area,a yuan linear regression model is difficult to present in different spatial location of different land cover types change on the influence of LAI,and GWR model make up a yuan linear regression model of this respect.