Grassland Change Detection Base On Remote Sensing Images In Hulunbuir Grassland Over The Past 30 Years

Grassland is one of the main land cover types and the main area of animal husbandry development in China,and it plays a significant role on the conservation of water and soil,improvement of people’s living environment and maintainance of ecological balance.Inner Mongolia grassland is the main part of warm steppe and the important ecological barrier in North China.Hulunbuir Grassland,locates in the northeast of Inner Mongolia,takes distinctive geographical characteristics,typical features of the ecosystem and unique management way of grassland animal husbandry production.Over past several decades,Hulunbuir Grassland has the great changes because of excess reclamation,urban expansion and coal mining,etc.The trend of grassland degradation is becoming more and more serious,which has begun to threaten the agriculture production and people’s living.Thus,investigating the grassland distributions and changes in Hulunbuir Grassland over the past 30 years by using remote sensing data has important significance for protecting and managing the grassland.According to the need of the branch project of the National Key Basic Research Program on Global Change(Grant No.2011CB952001),titled "Spatial and Temporal Characteristics of the Large-Scale Land Use and Cover Change of China over the Past 30 Years",this study evaluated the grassland distributions and changes in Hulunbuir Grassland,China from 1981 to 2010,by using low-spatial resolution remote sensing data from Advanced Very High Resolution Radiometer(AVHRR)and Moderate Resolution Imaging Spectroradiometer(MODIS).Then,this study obtained the land cover maps from 1983 to 2010 in typical area of Hulunbuir Grassland by using moderate-spatial resolution remote sensing data from Landsat MSS/TM/ETM+,and evaluated the grassland distributions and changes in typical area of Hulunbuir Grassland.The main contents and results of the study are presented as follows:(1)The NDVI time series data from 1981 to 2010 in Hulunbuir Grassland was constructed.The initial NDVI time series data was obtained based on the AVH09C1 and MOD13A2 products.Then,the noises of the NDVI time series data were effectively removed by using the S-G filtering method.The data became more consistent with the phenology of the vegetation.As a result,the NDVI time series data of every sixteen days during the growing season(day 81-289)in Hulunbuir Grassland were constructed.(2)The distribution and change patterns of grassland in Hulunbuir Grassland were analysed based on the NDVI derivative indexes calculated through the NDVI time series data in Hulunbuir Grassland from 1981-2010.The results revealed that the NDVI in Hulunbuir Grassland increased gradually from the west to the east.The area of grassland degradation accounted for 59.6%of the total area,and the grassland degradation phenomenon became more and more drastic from the west to the east in Hulunbuir Grassland.(3)The annual and seasonal fluctuation degree of the grassland NDVI in each county was statistically analysed based on the administrative units.The results revealed that different county had different characteristics.In terms of the seasonal fluctuation degree of the grassland NDVI in each county,they all showed a downward trend,except Ergun County and Yakeshi County.And Evenk County has the most drastic seasonal fluctuation degree of the grassland NDVI.In terms of the annual fluctuation degree of the grassland NDVI in each county,the most severe region was distributed in the central,which included Old Barag County,Hailar District,Evenk County,and the surrounding areas.(4)The land cover maps and the change maps between grassland and the other land cover types from 1983 to 2010 in typical area of Hulunbuir Grassland were made.And the patterns of grassland and change of the internal structure of grassland were analysed.The results revealed that the grassland areas were mainly distributed in the central and western regions of the typical area,and accounted for more than 70%of the total area,but decreased gradually.The grassland type was given priority to the medium vegetation coverage grassland,and it presented a characteristic that the grassland types switched from the medium vegetation coverage grassland to the high ones.(5)The mutual conversion between grassland and the other land cover types was analysed based on the change maps in the typical area of Hulunbuir Grassland.The results revealed that they were mainly wetland,forest,and cropland that switched frequently between grassland and the other land cover types.Moreover,the intensity of the grassland changes slowed down gradually from 1983 to 2010,and the pattern of grassland changes was being stabile.In a word,the study revealed the spatial distribution characteristics of grassland in Hulunbuir,and analysised the seasonal and annual fluctuation of grassland in Hulunbuir from 1981 to 2010.The research conclusions are significantly useful for protecting the eology and managing the grassland resource in Hulunbuir.