Temporal And Spatial Evolution Of Grassland Phenology And Analysis Of Its Climate Influencing Factors In Xilingol League

As the main ecosystem of land,grassland is closely related to climate change.The phenology of grassland vegetation can reflect environmental conditions,vegetation growth process and local climate change.It is of great scientific significance to discuss and analyze the relationship between the temporal and spatial evolution of phenology and climatic factors in order to guide the production of animal husbandry and formulate the corresponding measures for grassland ecological protection.In this paper,based on the MOD13Q1 NDVI data from 2001 to 2016,the starting period(SOS),the ending period(EOS)and the length of growing season(LOS)of grassland in the study area are extracted respectively by the method of cummulative NDVI based Logistic regression curves and dynamic threshold.The site monitoring data is used to verify the extraction results.Comparing the two extraction methods,the extraction results with higher accuracy are analyzed and discussed using the spatial analysis and statistical methods based on pixels.The conclusions are as follows:(1)The accuracy verification is performed by calculating RMSE,MAE,and correlation coefficients.The results show that the extraction results of cummulative NDVI based Logistic regression curves method are better than the dynamic threshold method.(2)The three phenological parameters of SOS,EOS,and LOS all show insignificant changes.They are concentrated in 105~150 days,270~300 days,and120-180 days,respectively.The percentage of the area they occupy in the total area is83.9 %,62.6 % and 74.3 %.Further analysis based on different grassland types found that except for the SOS of the temperate desert steppe,the temperate meadow steppe,temperate steppe,and lowland salinized meadow steppe all showed an advance trend.And the trend of EOS of the four grass types is in advance.And LOS showed a shortening trend.(3)The mean temperature and sunshine hours from 2001 to 2016 generally show a trend of decreasing from west to east,while the annual cumulative precipitation shows an increasing trend from west to east.With the passage of time,the temperature and sunshine hours in spring show an increasing trend,while the temperature and sunshine hours in other three seasons show a decreasing trend;the precipitation in all fourseasons shows an increasing trend.(4)Correlation analysis of grassland phenology parameters and climatic factors at different time scales in the study area found that grassland SOS is mainly affected by temperature and sunshine hours,and the increase of temperature in March and the decrease of accumulated sunshine hours in April to May will promote the advance of SOS;the temperature is the key factor affecting EOS,and the decrease of temperature in September will promote the advance of EOS;the precipitation in July is the main factor affecting the LOS of grassland,and the increase of precipitation will lead to the shortening of the growth period(5)Further discuss the response of different grassland types to climatic factors.Except for the temperate desert steppe,SOS of the other three grassland types were the most sensitive to the temperature in March and the cumulative sunshine hours from April to May.EOS of the temperate meadow steppe and lowland saline meadows steppe have the most obvious response to the temperature in September,EOS of temperate steppe was the most sensitive to the accumulative temperature in autumn,and EOS of temperate desert steppe was the most sensitive to the accumulative temperature in summer.All the four grassland types LOS had the most obvious response to the precipitation in July,among which the temperate desert steppe LOS had the strongest correlation with the precipitation in July.