Variations In Vegetation Cover And Phenology And Their Response To Climate Factors In Horqin Sandy Land

Vegetation as one of the components of terrestrial ecosystem,connects the atmosphere,hydrosphere and soil,and promotes the exchange and migration of materials and energy between different layers.Vegetation phenology refers to the periodic changes of vegetation affected by the environment.Climate change is the main factors that directly affect the growth and development of vegetation In this study,using GIMMS NDVI3 g and MOD13Q1 data,the temporal and spatial variation of vegetation cover(NDVI)in Horqin Sandy Land was obtained,and three vegetation phenological parameters were extracted by the cumulative NDVI based logistic curvature method:Start of Growing Season(SOS),End of Growing Season(EOS)and Length of Growing season(LOS)to discuss the impact of climate factor on NDVI and phenology.The research results show that :(1)The multi-year average NDVI of Horqin Sandy Land in growing season generally shows the spatial distribution characteristics of gradually decreasing from northeast to southwest,and the vegetation greenness of fixed and semi-fixed sandy land is the best.The annual variation of NDVI showed an overall increasing trend,and the trends of GIMMS NDVI and MODIS NDVI were the same after 2001,which was the same as that of NDVI of different sandy land types.From the perspective of spatial change,the area with increasing NDVI during 1982-2015 and 2001-2019 is larger than that with decreasing trend.On the whole,compared with GIMMS NDVI data,MODIS NDVI data has higher spatial resolution and better details.(2)Precipitation is the major factor affecting the variation of NDVI in Horqin Sandy Land.On the regional scale,the vegetation NDVI and precipitation in the two periods showed a significant positive correlation,and a significant negative correlation with sunshine hours,but no obvious correlation with temperature.On the pixel scale,the area of NDVI positively correlated with temperature in 1982-2015 and 2001-2019 was more than 53.1%,the area positively correlated with precipitation accounted for more than 85.0%,and the area negatively correlated with sunshine hours was more than 86.3% of the whole area.(3)The spatial distribution pattern of Horqin Sandy Land in 1982-2015,2001-2019 and the vegetation SOS was early in southwest and late in northeast,there were certain differences in EOS between the two periods.The spatial distribution of EOS in 2001-2019 was relatively later as a whole,and the growth season length was characterized by short in north and long in south.In the two periods,the vegetation in the shifting sandy land entered the SOS at the earliest and EOS at the latest.In time,the delayed trend of the SOS in 1982-2015 and 2001-2019 was not obvious,but the delayed rate in 2001-2019 was higher than that in 1982-2015,and the overall change trend of the EOS in the two periods was not obvious.(4)There was no significant negative correlation between the SOS and temperature and precipitation in March and April,mainly distributed in the lower altitude areas in the eastern part of the study area,while the correlation between temperature and precipitation in May and SOS was not obvious.There was an obvious positive correlation between the SOS and sunshine hours in March,April and May.The response of EOS to temperature in August,September and October was not obvious,but it has obvious negative correlation with precipitation in September and October,and the correlation between EOS and sunshine hours is different in different periods.The cumulative precipitation during EOS and the first two months of the season showed a significant negative correlation,the EOS was negatively with precipitation during the two months before the EOS.