| Vegetation is the main component of the ecosystem.It plays a key role in the substance circulation,energy exchanges and biogeochemical circulation.Vegetation is sensitive to climate change,its dynamics and response to climate change have been considered to be one of the core issues of global changes.However,on the background of the rapid changes in the global climate and the ecological environment,it is unclear that the trend,area,rate,degree and influencing factors of vegetation greening and browning in the past few decades.Based on Leaf Area Index(LAI),this study uses the Mann-Kendall mutation test,Theil-Sen median trend analysis,Mann-Kendall significance test and Hurst index to quantify the characteristics of global vegetation evolution.The pixel-based Pearson correlation,partial correlation and residual analysis are utilized to investigate the influencing factors of vegetation.This study draws the following main conclusions:(1)The global vegetation has improved significantly in the past 34years.On the annual scale,the overall LAI rises at a rate of 0.0045/a(R~2=0.7954),there is no significant mutation point,and the area of significant LAI improvement trend(50.31%)is much greater than the significant degradation trend(9.48%).On the monthly scale,except September,the area of LAI showing improvement in other months was larger than the area of the degradation area.(2)There will be a significant trend of global vegetation degradation in the future.LAI may degenerate on 53.27%of the world's land,and only 28.89%may be improved.Trends remain unchanged and uncertain areas account for 1.50%and 16.33%respectively.(3)Temperature affects vegetation more than rainfall.Globally,97.90%and 56.44%of the regions showed an upward trend in temperature and rainfall,respectively.The correlation and partial correlation between them and LAI are complementary to each other to some extent.The influence of temperature in the current month on LAI in the growing season was greater than that in the previous month,and the influence of rainfall in the previous month on LAI was greater than that in the current month.(4)The impact of human activities on vegetation is greater than natural factors.68.70%are more susceptible to human activities,among them,54.78%of them may be increased,and 13.92%of them may be decreased.Only 31.30%of the regions are greatly affected by natural factors.(5)LAI and NDVI data have a certain consistency.Both of them proved that the vegetation improvement area was larger than the degraded area,and the area affected by temperature was larger than that affected by rainfall.Overall,global vegetation has improved in recent decades,but serious degradation is likely to occur in the future.The influence of temperature on vegetation is greater than that of rainfall.LAI and NDVI data have a certain consistency in representing the overall change trend and influencing factors of vegetation. |
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