Dynamics Of Vegetation Biomass And Its Environmental Factors In Alashan Plateau

Alxa League is located in the westernmost region of the Inner Mongolia Autonomous Region.The ecological environment is relatively poor.Although its vegetation coverage is low,its role in resisting the Siberian cold current and northwest wind and sand invasion is still not to be underestimated.Therefore,it is of great significance to study and analyze the effects of vegetation coverage,vegetation aboveground biomass and climate factors on Alxa Plateau.Based on the time series,this study used a combination of field investigation and data research methods,based on the 1981-2019 NOAA-NDVI and MODIS-NDVI remote sensing data and 132 ground sample data to construct a biomass-remote sensing data estimate The model completes the remote sensing estimation and prediction of the aboveground biomass of Alxa League from 1981 to 2019.The following conclusions are drawn from the Alxa League vegetation climate factor,vegetation NDVI,different vegetation types NDVI,biomass,and the relationship between biomass and meteorological factors:(1)In constructing biomass-NDVI estimation models,the correlation of power function is the best,The modeling decision coefficient is 0.321,the average relative error(REE)is 0.22,the root mean square error(RMSE)is 53.9kg / hm2,and the model accuracy is 78%,which can be applied to the actual remote sensing estimated output;(2)From 1981 to 2019,the annual precipitation and average annual temperature of Alxa League showed an upward trend with time.Among them,the annual precipitation increased significantly.The rising rate of precipitation reaches 6.5mm/10 a,the fluctuation range is between 32-180 mm,and the 39-year average is 115.6mm;The spatial distribution pattern of precipitation is high in the southeast and low in the northwest.The annual precipitation gradually increases from northwest to southeast,and the spatial distribution is in the form of a strip.Alxa Left Banner has the highest annual precipitation,with an average annual rainfall of 132.4mm for many years;Alxa Right Banner is next,with an average annual rainfall of 124.6mm;Ejin Banner has the lowest annual precipitation of 52.2mm.The annual average temperature rise rate is 0.24 ? / 10 a,the fluctuation range is between 8-12 ?,the annual average temperature value in 39 years is 9.9 ?;the area with higher annual average temperature is distributed in central and southeastern Alashan,namely Tengger Desert,Ulanbuh Desert and Badain Jaran Desert.The regions with low average annual temperature are distributed in the Helan Mountains in the east of Alxa Left Banner and the central region,the eastern mountains in Alxa Right Banner and the microclimatic areas in the southern Longshou Mountain and Heli Mountains,and the western Mazong Mountain Area in Ejina Banner;(3)From 1981 to 2019,the normalized vegetation index NDVI value of Alxa League fluctuated greatly from year to year,with a fluctuation range of 0.014-0.055.The average annual NDVI value was 0.028.The average NDVI value in the best state was 0.161.The average NDVI was the largest in 1981-1989,and the vegetation coverage was higher;1990-1999 was followed by vegetation coverage;the vegetation coverage was very low in 2000 and 2001,and the growth was not good;the average NDVI growth during 2000-2009;NDVI continues to increase in 2019,which is closely related to the local implementation of the policy of returning grassland to grassland since 2002 and the policy of ecological awards and compensation from 2011.In terms of spatial distribution,Alxa League NDVI has a typical spatial distribution pattern of southeast high and northwest low.The overall vegetation coverage of Alxa League is poor,but the spatial distribution is uneven.The NDVI value of Ejina Banner is the smallest.The vegetation growth of Alxa Right Banner is slightly better than that of Ejina Banner.The vegetation growth of Alxa Left Banner is the best;(4)Vegetation types of Alxa League can be divided into 8 types: typical grassland,desert grassland,grassland desertification,typical desert,extremely dry desert,fixed dune vegetation,shrubland,and meadow.From 1981 to 2019,the NDVI values showed an upward trend with typical grasslands,grassland desertification,fixed sand dunes and shrubs.The largest increase rate was grassland desertification and shrubs,with a rate of 0.01 / 10a;typical deserts,deserts showed a downward trend For grasslands,extreme dry deserts and meadows,the largest decline rate is extreme dry deserts,with a rate of 0.009/10a;(5)8 NDVI of the planted cover types are all negatively correlated with the average annual temperature,of which extreme drought deserts are significantly negatively correlated with annual average temperature;extreme drought deserts and meadow NDVI are negatively correlated with annual precipitation,but not significant The NDVI of the remaining 6 planted types are positively correlated with annual precipitation,and except for typical deserts and shrubs,the correlation is significant;(6)From 1981 to 2019,Alxa League's biomass fluctuated greatly from year to year.The average biomass in 39 years was 122.59 kg / hm2,ranging from 80-200 kg / hm2.The average biomass was the largest in 1981-1989,followed by 1990-1999,during which the interannual fluctuation of biomass was the most intense.After entering the 21 st century,the biomass change shows a steadily increasing trend,indicating that the vegetation growth of Alxa League has improved,which is mainly related to the "returning grazing to grass" project implemented in 2002 and the "ecological award" policy implemented in 2011 Relationship.The grassland biomass of Alxa League has a spatial distribution pattern of high in the east and low in the west.With the passage of time,the biomass in the western region has a downward trend,while the biomass in the eastern region has a tendency to increase and improve.The biomass of Alxa Left Banner has Obvious and continuous improvement;(7)There is a significant positive correlation between the biomass of Alxa League and annual precipitation,and there is no significant negative correlation with the annual average temperature.Overall,the correlation between precipitation and biomass is higher than that between temperature and biomass.Alxa League has a special geographical location,extreme climate,sparse vegetation and relatively scarce species,and low vegetation coverage.After entering the 21 st century,the “Returning Grazing to Grass” project and the “Ecological Awards and Compensation” policy implemented by the government in the 21 st century With a series of grassland protection and management measures,the vegetation growth status of Alxa League has gradually improved.In future research,more data resources can be used,combined with the current development results of remote sensing and geographic information,to carry out comprehensive vegetation coverage estimation.To provide a scientific basis for the protection of vegetation in Alxa League and the restoration of the ecological environment.