Spatial And Temporal Pattern Of Vegetation Ecology Quality And Its Response To Climate Change In China

The rapid development of China's economy has led to the deterioration of vegetation ecology in certain areas.In order to reverse the deterioration of the vegetation ecology environment,relevant departments are restoring the damaged vegetation ecology environment through relevant measures(e.g.,returning farmland to forest,afforestation,wetland protection and water diversion).However,the contradiction between ecological protection and economic development in China is still prominent,and the ecological security situation is still serious.Therefore,it is necessary to quantitatively evaluate and analyze the evolution trend of vegetation ecology environment quality and its main influencing factors in China in the past decade or so.This paper constructed the vegetation ecology quality index that can invert the ecological quality of vegetation based on six indicators(i.e.,fractional vegetation cover,leaf area index,net primary productivity,vegetation wetness,land surface temperature and water use efficiency of vegetation)by principal component analysis.The spatial pattern of distribution,temporal changing characteristics,spatial shift,gravity migration and response to external control factors for different ecosystem of vegetation ecology quality in China from2000 to 2017 were explored by using SEN+Mann-Kendall,Hurst exponent,Markov model and so on.How climatic factors affected vegetation ecology quality over time was also analyzed.And prediction of vegetation ecology quality in the coming years was made based on BP neural networks.The conclusions are as follows.(1)The overall spatial pattern of vegetation ecology quality index in China was low in the northwest and high in the northeast and southeast.The difference between the excellent and poor vegetation ecology quality areas in China was relatively significant.And the proportion of the excellent areas was much larger than that of the poor areas.The overall ecological quality of vegetation improved with increasing longitude and decreased with increasing latitude.In terms of administrative zones,three provinces(i.e.,Fujian,Taiwan and Heilongjiang)were with the best vegetation ecology quality.While for Tibet Autonomous Region,Xinjiang Uygur Autonomous Region and Qinghai Province,the vegetation ecology quality was relatively poorer.(2)The vegetation ecology quality in China had been gradually improving in the past 20 years.The vegetation ecology quality index showed an increasing trend in both longitude and latitude directions.In terms of administrative divisions,except for Shanghai,Zhejiang,Fujian and Jiangsu,where the ecological quality of vegetation had degraded in the past 20 years,the ecological quality of vegetation in other provincial administrative divisions had been improved.(3)In terms of persistence,the future trend of vegetation ecology quality in China will be consistent with the past nearly 20 years and will maintain the trend of continuous improvement.In terms of stability,the change of vegetation ecology quality in China over the past 20 years were relatively small and stable.As for the spatial transfer matrix of vegetation ecology quality,the increase in the area of excellent vegetation ecology quality was mainly due to the transformation of the next level,while the decrease in the area of other levels of vegetation ecology quality was due to their transformation to higher level types.Regarding the migration of the gravity center,the gravity center of vegetation ecology quality in China during 2000-2017 was migrating in the northeast direction with a smaller migration.It indicated that the ecological quality of vegetation in China was getting better from west to east and from south to north.(4)The distribution and change trend of vegetation ecology quality of different ecosystems during the peak vegetation growing season were different.The vegetation ecology quality of broadleaf forest was the best.The vegetation ecology quality of shrubland and alpine grassland ecosystems was lower than other ecosystems.The vegetation ecology quality of all ecosystems showed an ameliorative trend,with the most significant improvement in mixed farmland,dryland and grassland.In addition,the ecological quality of vegetation differed in different altitudes and climatic zones.Except for desert vegetation and paddy fields,the vegetation ecology quality of other ecosystems showed a significant negative correlation with altitude.The vegetation ecology quality of the tropical zone was the highest.And the vegetation ecology quality of the plateau mountain climate zone was relatively poor.(5)During the peak vegetation season in China,overall about 71.96% of the vegetation ecology quality index was positively correlated with precipitation.About 52.75% of the vegetation ecology quality index were negatively correlated with temperature.The ecological quality of vegetation and cumulative precipitation were positively correlated in all ecosystems.Except for grassland,paddy field,dryland and mixed farmland ecosystems,the vegetation ecology quality of other ecosystems was negatively correlated with temperature.Precipitation is beneficial to healthy vegetation growth within a certain range.And too much precipitation could inhibit vegetation growth.There is a positive effect of air temperature on the ecological quality of vegetation in most ecosystems at relatively low temperatures,and a negative or uncertain effect above a certain temperature threshold.(6)Compared with the linear regression model,the accuracy of the vegetation ecology quality index predicted by BP neural network simulation was higher.It can more accurately predict the spatial distribution of vegetation ecology quality in the same year.The vegetation ecology quality index predicted by BP neural network from 2021 to 2026 showed that the vegetation ecology quality in China will continue to improve,with the most obvious improvement in forest ecosystems,followed by medium and high natural vegetation ecosystems.