Changes In Phenology And Their Main Factors In The Grassland Of China-Mongolia Border

Vegetation phenology refers to natural phenomenon that occur on a yearly cycle of vegetation affected by the environment,including processes such as budding,branching,leaf spreading,flowering,fruiting and leaves falling.The change of vegetation phenology is closely related to global climate change.The thesis takes the grassland of China-Mongolia border as a study area.By using the MODIS vegetation NDVI data from 2001 to 2017,the start of growing season(SOS),the end of growing season(EOS)and the length of growing season(LOS))in the grassland of study area are obtained by S-G filtering and the cumulative NDVI based on Logistic curve curvature(CUM).Combined with meteorological data,land surface water and heat data,elevation data and statistical data,the main influencing factors of vegetation NDVI and phenology in the grassland of China-Mongolia border from 2001 to 2017 were analyzed.The main conclusions are as follows:1.The overall distribution of NDVI in the study area was high in the east and low in the west.NDVI increased significantly during the whole growing season and in different seasons.By country,the vegetation NDVI of Inner Mongolia was slightly higher than that of Mongolia.The SOS in the study area increased with the latitude and the SOS in the southwest of the study area had an obvious advance trend.The EOS in the study area decreases with the latitude and a significant advance trend was showed in the central area.The LOS decreases with the latitude and a decreasing trend was showed in the middle of the study area and near Hulun Lake.2.Precipitation was the main meteorological influence factor of grassland vegetation NDVI and phenology in the study area.Vegetation NDVI was positively correlated with precipitation and negatively correlated with temperature.The SOS showed a positive correlation with March precipitation and a negative correlation with April precipitation.The EOS was positively correlated with precipitation in March and August and negatively correlated with precipitation in April and May.There was a negative correlation between LOS and precipitation.There was a negative correlation between SOS and temperature,but EOS and LOS had a positive correlation with temperature.Spring NDVI was positively correlated with sunshine hours while there was a significant negative correlation between NDVI and sunshine hours in summer and autumn.Phenological periods in the study area was overall positively correlated with sunshine hour.3.Among the land surface water and temperature elements,the land surface water index(LSWI)is the main influencing factor of grassland vegetation NDVI and phenology in the study area.The mean NDVI had a significant positive correlation with LSWI and a negative correlation with daytime land surface temperature(DLST).There was a significant positive correlation between SOS and LSWI in January to March.However,there was a negative correlation between LOS and LSWI.There was a negative correlation between SOS and land surface temperature,meanwhile,the EOS and LOS were positively related with land surface temperature.4.The vegetation NDVI in the study area generally decreased with the altitude.There was no significant difference in NDVI with slopes gradient.The NDVI of shady slope was slightly higher than sunny slope.The SOS and EOS decreased with altitude,but LOS increased with altitude.SOS had an advance trend with slope,EOS had a delayed trend with slope and LOS increased with slope.The LOS of the shady slope in the study area was 1.5 days shorter than sunny slope.In general,under different altitudes,slopes and aspect gradients,the changes of vegetation NDVI and phenology are mainly affected by different land surface water and temperature conditions.5.The statistical results showed that the population in the border areas of Inner Mongolia showed a slowly increasing trend.The area of cropland and food production showed clearly increasing trend.Meanwhile,the number of large livestock was increasing.However,the number of stored sheep were decreasing.The number of stored sheep had a good synchronization with the vegetation NDVI but there was a lag time of one to two years.The number of large livestock and stored sheep in Mongolia(Dornod Aymag and Sukhbaatar Aymag)had a clear upward trend.6.The vegetation NDVI of Sample 1 was higher than sample 2 because of good water conditions.From country perspective,vegetation NDVI in Mongolia was higher than Inner Mongolia,but the growth speed of vegetation NDVI in Inner Mongolia was higher than Mongolia.The difference of phenology in sample 2 was obvious.The vegetation NDVI and phenology in Inner Mongolia were more sensitive to climate change.