Spatio-temporal Evolution Of Vegetation LAI And Its Driving Forces In Guizhou Province

Vegetation is an important part of the global ecosystem,and its growth depends on climate change and human activities to a large extent.Under the circumstance that global climate change is more drastic and human activities are more frequent,the growth of vegetation is also affected to some extent,which makes the change of vegetation cover more diverse and complicated.Guizhou Province is a typical karst region,so it is very necessary to analyze the temporal and spatial changes of vegetation cover and explore the response mechanism of vegetation growth to climate change and human activities.However,in previous studies,the quantitative analysis of vegetation changes at different time scales and the relative effects of human activities on vegetation changes in Guizhou Province is still lacking.Therefore,based on MODIS LAI data of vegetation index,different climate factors and different underlying surfaces,and combined with Theil-Sen media trend method,Hurst index analysis and path analysis methods,this paper explores the spatio-temporal variation characteristics of vegetation cover on different underlying surfaces affected by climate factors in Guizhou Province during 2001-2020.In addition,residual analysis method and relative action analysis method were used to quantitatively analyze the relative effects of climate change and human activities on LAI of vegetation in the study area.The main conclusions are as follows:(1)At different time scales,the vegetation cover in Guizhou showed a significant upward trend on the whole,and the spatial distribution showed a higher trend in the east and lower trend in the west.The vegetation growth was better in summer,but slower in winter.In the past 20 years,vegetation LAI in Bijie region of western Guizhou Province showed an upward trend under different time scales,while it showed an insignificant downward trend in southeast Guizhou Province,and the improvement trend of spring LAI was the most obvious.The future variation trend of LAI of different vegetation types in different seasons was mainly anti-sustainability improvement,The area of seasonal variation from large to small is spring >Growing season >Autumn >Summer> Winter.(2)The temperature and precipitation in different seasons in the study area showed a gradual increasing trend from west to east.The spatial variation trend of precipitation in spring and winter was the most significant,while the temperature in summer increased the fastest and the temperature in winter increased the slowest.In Guizhou Province,the sensitivity of vegetation to precipitation was slightly stronger than that of air temperature,and the response of vegetation LAI to precipitation and air temperature was mainly delayed by one month.At slope grade 1,the correlation between vegetation LAI and temperature and precipitation at different time scales was the strongest,and the correlation gradually decreased with the increase of slope.Under different geomorphic types,the largest proportion of correlation area was mainly distributed in the peak cluster valley,followed by the peak forest lysogen,and the spatial distribution of all kinds of correlation was different for geomorphic types4 and 6.Except spring,vegetation LAI showed no significant positive correlation and no significant negative correlation with temperature and precipitation at other time scales,and all the correlations between vegetation LAI and temperature and precipitation at different time scales were mainly distributed in areas with moderate karst development intensity.(3)In the past 20 years,spring temperature had a significant promoting effect on vegetation LAI,and precipitation had a slightly greater inhibiting effect than promoting effect on vegetation LAI.There was no significant difference between the comprehensive effects of summer temperature and precipitation on vegetation growth.The promotion effect of autumn and winter temperature on vegetation growth was stronger than the inhibition effect.Precipitation in the growing season mainly promoted vegetation growth,while the comprehensive positive and negative effects of temperature on vegetation LAI were basically unchanged.Overall,human activities had a significant positive effect on vegetation growth in the study area.The area of different land use types changed into forest type was the largest,and the area of farmland also increased.The changes of LAI of different vegetation and actual vegetation under the influence of human activities mainly showed an insignificant upward trend,and the influence of simple human activities on LAI of different vegetation was greater than that of climate factors.The relative effect of human activities on vegetation cover in the vegetation cover improvement area of Guizhou province is stronger than climate change,and the relative effect of climate change on vegetation cover in the vegetation cover degradation area of Guizhou Province is stronger than human activities.(4)The relative effects of climate change and human activities on vegetation cover increase with the increase of slope.When the slope is less than 5°,human activities show obvious inhibition on vegetation growth.The relative effect of human activities on the actual LAI improvement under different geomorphic types was higher than that of climate change,and the peak forest valley was the geomorphic type with the strongest relative effect of human activities on vegetation cover.Human activities had the greatest effect on the actual LAI improvement in the area of moderate karst development intensity improvement,while the actual LAI degradation in the area of strong karst development intensity degradation was more affected by climate change.