| The Bohai Rim region,situated along the Pacific Ocean on China’s west coast,comprises Beijing,Tianjin,Hebei,Shandong,and Liaoning provinces.It is the country’s third-largest economic center after the Yangtze River Delta and Pearl River Delta.To investigate the spatio-temporal evolution of vegetation in the Bohai Rim region,this study utilized the Modified Soil Adjusted Vegetation Index,based on climate,terrain,and socio-economic data,ground on the GEE platform and geographic information software,analyzed the changes in vegetation MSAVI in the Bohai Rim region from1984 to 2021 in terms of time and space by trend analysis,future trend analysis and stability analysis,and identified the driving forces from the perspectives of natural climate and human activities by correlation analysis,random forest model,geographical detector model.Finally,the study presented the predicted results of vegetation MSAVI distribution in the Bohai Rim region in the future.The main research findings are as follows:(1)From a temporal perspective,vegetation MSAVI in the Bohai Rim region showed a fluctuating upward trend from 1984 to 2021,with an average value of 0.4677.The mean value of vegetation MSAVI from high to low is as follows:summer(June-August),growing season(April-October),autumn(September-November),spring(March-May),winter(December-February).(2)From a spatial perspective,the distribution of MSAVI in the Bohai Rim region is significantly different.Vegetation is primarily in the middle(0.3-0.45)and middle-high(0.45-0.6)grades.The distribution of MSAVI in the northeast and southwest is higher than that in the middle.The high-value areas are mainly located in the Changbai Mountains in the east of Liaoning Province and Taihang Mountains in the north of Hebei Province,while the low-value areas are mainly distributed in alpine grasslands,large urban gathering areas,coastal areas,and rivers in the northwest of Hebei Province.From 1984 to 2021,vegetation MSAVI showed an overall upward trend with good stability,weak dispersion,and an average coefficient of variation of0.1164.In the future,vegetation MSAVI is expected to mainly distribute in northwestern Hebei Province,eastern and western Liaoning Province,and northern Shandong Province.(3)The average annual temperature in the Bohai Rim region increased from 1984to 2019,with a 0.595 average correlation coefficient between temperature and vegetation MSAVI.Positive correlation was mainly found in northwestern Hebei Province,northern Liaoning Province,and central Shandong Province.The average correlation coefficient between annual precipitation and vegetation MSAVI was 0.504,with positive correlation primarily concentrated in northern Liaoning Province,northern Beijing and Tianjin,and central Shandong Province.Population density and GDP output value exhibited rapid growth,with both positive and negative effects on vegetation MSAVI change.Urban areas with high population levels and developed economies,including Beijing,Tianjin,the central part of Hebei Province,and the eastern part of Shandong Province,were the main drivers of vegetation MSAVI change.In contrast,grassland and mountain areas with sparse populations and lush vegetation,such as northwest Hebei and northwest Liaoning,showed inhibitory effects.(4)Based on the random forest model,the ranking results of the driving factors of vegetation MSAVI change in the Bohai Rim were as follows:annual precipitation>land use type>average annual temperature>population density>soil type>GDP>elevation>distance from residential area>distance from national highway>slope>distance from water system>slope direction.The results of geographic detector showed that soil type and land use type had the highest explanatory power to the spatial differentiation of vegetation MSAVI,and the interaction types among different factors were nonlinear enhancement or double enhancement,and each factor had the most suitable range or specific type to promote vegetation growth:The soil type was eluvial soil,the land use type was woodland,and the annual precipitation was586.33mm-686.35mm.The average annual temperature is 7.45℃-8.97℃,the population density is 138.63 people/km~2-255.01 people/km~2,the GDP output value is7.2839 million yuan/km~2-13.32 million yuan/km~2,the elevation is 401m-581m,and the distance from the residential area is 2846.09m-3498.09m.(5)The simulation and prediction results based on the CA-Markov model showed that,compared with 2021,the proportion of low vegetation MSAVI area in 2031 in the Bohai Rim would increase by 0.33%to 2.73%.The proportion of low and middle vegetation MSAVI area would decrease by 1.22%to 4.08%,while the proportion of middle vegetation MSAVI area would be 20.69%.The MSAVI of middle and high vegetation would account for 44.75%(a decrease of 0.99%),and the MSAVI of high vegetation would account for 27.75%(an increase of 8.59%). |
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