Dynamic Characteristics Of Vegetation In Inner Mongolia From 2001 To 2016,and Its Response To Climate Change

Climate is an important part of the natural environment on which humans depend,and any form of change will have a profound impact on terrestrial ecosystems and social and economic systems.In order to further study the dynamic characteristics of vegetation in complex and diverse environments in the Inner Mongolia Autonomous Region and its response mechanism to climate change,this study extracted the vegetation in the study area based on the MODIS NDVI time series data from 2001 to 2016 and using the logistic curve curvature extremum method of cumulative NDVI The vegetation phenological parameters of greening period,yellowing period and growing season length,combined with the temperature and precipitation data of the meteorological stations during the same period,analyzed the characteristics of the dynamic changes of vegetation in Inner Mongolia and its response mechanism to climate change.The results show:(1)From 2001 to 2016,the spatial distribution pattern of Normalized Difference Vegetation Index(NDVI)in the growing season of Inner Mongolia decreased from northeast to southwest,and mainly concentrated in summer.In the past 16 years,the area with a significant increase trend of vegetation productivity accounted for 33.24% of the total area of Inner Mongolia,with a slope of 0.044/10 a,mainly distributed in the south of forest ecological area and desert ecological area;The area with a significant downward trend is only0.52% and the slope is-0.049/10 a,which is scattered in grassland ecological area and Hetao irrigation area,the main grain producing area in Inner Mongolia.Results showed that the ecosystems of forest and desert had earlier greening day than that of grassland ecosystems,with the day of 120,119 and128,respectively.In contrast,the ecosystems of forest and desert had later browning day of than that of grassland ecosystems,with the day of 275,276 and 269,respectively.Influenced by the greening and browning day,theecosystems of forest and desert had longer growing days than that of grassland ecosystems,with the day of 155,157 and 141,respectively.The area of both start and end of growing season with advancing trend is larger than that with delaying trend,but the trend of most of the area is not statistically significant.The areas with significant length of growing season extension trend in the study area are mainly distributed in the north of forest ecological area,southwest of grassland ecological area and southeast of desert ecological area,accounting for only 5.9% of the total area,with a slope of1.33d/a.The trend of length of growing season shortening is distributed in the grassland and the eastern part of the forest ecosystem,accounting for 4.8% of the area,with a slope of-1.15d/a.(2)From 2001 to 2016,the spatial pattern of annual average temperature in Inner Mongolia has the characteristics of rising from northeast to southwest.The forest ecological area,grassland ecological area and desert ecological area are 4.63 ? 2.75 ? and 7 ? respectively.The distribution pattern of annual accumulated precipitation is characterized by gradual decrease from southeast to northwest.The annual accumulated precipitation in forest ecological area,grassland ecological area and desert ecological area is 392 mm,305mm and 232 mm respectively.During the study period,the annual average temperature,the average minimum temperature and the average maximum temperature in Inner Mongolia fluctuated in the range of3.53~5.79 ?,-2.35~-0.40 ? and 10.17~12.69 ? respectively,and the annual accumulated precipitation fluctuated in the range of 235 ~421mm;There is no significant change in temperature within 16 years,and the annual cumulative precipitation has an increasing trend with a slope of 5.7/a(P<0.05).(3)The vegetation coverage during the growing season in the study area during the observation period has the characteristics mainly regulated by precipitation,which is obvious in the grassland ecological area and desert ecological area.(Vegetation coverage in the forest ecological zone in spring,summer and autumn is mainly significantly positively correlated withtemperature and negatively correlated with autumn precipitation;vegetation coverage in the grassland ecoregion in spring and summer is significantly positively correlated with precipitation and negatively correlated with summer temperature,Autumn vegetation coverage is regulated by both air temperature and precipitation;in the desert ecological zone,spring vegetation coverage is significantly positively correlated with air temperature,summer vegetation coverage is significantly positively correlated with precipitation,and is significantly negatively correlated with summer temperature,and autumn vegetation coverage is affected by air temperature,Precipitation adjustment together).(4)Length of growing season of vegetation in the study area is mainly regulated by temperature(greening day of vegetation in forest ecological area and grassland ecological area is negatively correlated with spring temperature;browning day of vegetation in the study area is positively correlated with autumn temperature;browning day of vegetation in forest ecological area and Eastern grassland ecological area is negatively correlated with autumn precipitation),which is negatively correlated with precipitation.(5)Correlation analysis between phenology and NDVI indicates that the advancing trend of greening day and delaying trend of browning day could not increase the vegetation productivity for all ecosystems.The reason is that the vegetation summer productivity accounts for larger number of annual productivity,which determines the annual productivity trend.However,seasonal scale analysis shows that the advancing/delaying trend of greening day could increase/decrease spring productivity and delaying/advancing trend of browning day could decrease/increase autumn productivity.