Global Vegetation Dynamics And Its Relations To Precipitation And Temperature Among During 1982-2015

As we know,vegetation plays critical roles in global water and carbon cycles,while climate change directly influences the spatial distributed patterns and growing rates of vegetation.Therefore,the study about vegetation dynamics and its relationships with temperature and precipitation helps better understanding of dynamic processes of vegetation growth under the interactions between biosphere and atmosphere,and also functions significantly in predicting of vegetation responding to future limate change.Previous studies about vegetation-climate were limited by low temporal-spatial resolution of the data,so most of them focused on regional or single type of vegetation with short-time scales.Recent techniques of remote sensing help us finding vegetation dynamics in a global view and in long-time scales,distinguishing different plant functional types and spatial patterns and deeply analyzing the relationships between vegetation and climate.By appling GLASS-LAI(Global LAnd Surface Satellite Leaf Area Index)dataset,CRU temperature and precipitation datasets from 1982 to 2015,this thesis used simple linear regression to analyze annual growing trends of global vegetation LAI,and analyzed different scatter distributions of hydrothermal conditions in thirty-four years with annual mean LAI,precipitation and temperature.Then,before-detrending and after-detrending data were used,together with partial correlation and correlation methods,to detect the contributing ratios of temperature and precipitation in different regions and find their inter-annual correlations.Finally,by applying seasonal adjustment,regression and correlation ananlysis,the instant and lagging relationships between LAI and temperature,LAI and precipitation can be found.Main conclusions are as follows:(1)Global significant increasing trends of annual mean and max LAI were widespreadly observed in North America,northern South America,Sahel,Middle southern Africa,and northern Eurasia northern Austrilia.Among nine plant funcational types,grasslands,croplands,open shrublands and woody savannas showed greater effects by climate change,human activities and land use and land cover change on these plant growths.(2)The partial correlation between precipitation and LAI changed significantly before and after detrending,especially in the northern hemisphere cold zone and sub-frigid zone.After detrending,partial correction between LAI and temperature was no longer significant in cold zone and sub-frigid zone in the northern hemisphere,while southern Amazon rainforest was more strongly restrained by increasing temperature.(3)The results of annual correlation between LAI and precipitation showed that significant positive correlation was mainly distributed in south central North America,east South America,south central Eurasia,southern Africa,Sahel and Australia.Under different hydrothermal conditions or human impacts,grasslands showed significantly positive correlation between LAI and precipitation in some large regions,and also presented significantly negative correlation in some other regions.After detrending,the positive correlation between LAI and temperature disappeared in most regions,especially grasslands.(4)Long-term mean values of LAI in evergreen broadleaf forests,mixed forests and grasslands,were increased by instant-month precipitation and temperature.The lagged regression coefficients between temperature and LAI of mixed forests,woody savannas and grasslands were negative,which might be explained by the fact that the rising temperature in the first two months promoted the instant enzyme activity of photosynthesis,but the accelerated material consumption in the early stage inhibited the growth of plants two months later.(5)The instant correlation between long-term month-to-month temperature and LAI was more significant than lagging correlation,and the significantly negative correlation took larger proportions than the positive correlation.Compared with the annual correlation,monthly correlation was found to occupy larger significant areas between LAI and temperature,as the proportion of positive correlation were increased in the west of the Amazon Rainforest and Central Africa,and the proportion of negative correlation were increased in the south of Mexico,the east of Brazil and Australia.Vegetation in these areas were closely related to short-term temperature.