内蒙古温性草原草地类型近20年时空动态变化研究

Spatiotemporal dynamic variation of temperate grassland classes in Inner Mongolia in the last 20 years

草地类型是人类科学开发、合理利用和有效保护草地资源的重要依据,同时还是维持草地生态系统可持续发展的重要依据。目前,国内外有关土地利用类型时空变化的研究已有丰硕成果,但区域尺度草地类型时空动态变化的研究鲜有报道。因此,以内蒙古温性草原为研究对象,基于遥感植被指数、气象、土壤、地形和无人机航拍资料,结合机器学习算法构建了内蒙古草地类型分类算法,并以此为依据,分析草地类型时空动态变化特征。结果表明:1)所有遥感分类特征指标中,降水、归一化植被指数(NDVI)对研究区草地类型分类的重要性值高于其他指标,前18个分类指标(按重要性值排)的累计贡献率达85%以上;2)随机森林(RF)模型对内蒙古温性草原草地类型的分类精度最高,总体分类精度(OA)为82.16%,卡帕系数(Kappa)为0.76;3)过去20年来内蒙古地区草地类型之间的转换比较剧烈,多发生在典型草原、荒漠化草原和荒漠之间。相较于20世纪80年代草地类型,2000-2009年草地类型多由湿润类型向干旱类型转变,然而2010-2019年的草地类型则由干旱类型向湿润类型转变。本研究结果可为全球气候变化和人类活动下内蒙古草地类型的变化研究提供科学依据,同时也可为内蒙古地区草地可持续发展提供理论依据和技术支撑。

Grassland classification is essential for rational utilization and effective protection of grassland resources and also crucial for maintaining sustainable development of grassland ecosystems.There has been considerable achievement in documenting spatio-temporal changes in land use types,but few reports on the spatio-temporal dynamic variation of grassland classes at the regional scale.Hence,this study explored the spatio-temporal variation of temperate grassland classes in Inner Mongolia.Several grassland class identification methods were constructed based on remote sensing vegetation index,meteorology,soil,topography,unmanned aerial vehicle(UAV)data and machine learning algorithms.Then the spatio-temporal variation was analyzed based on the optimal classification method.It was found that:1)Among all the remote sensing classification characteristics and indexes evaluated,the importance values of precipitation and normalized difference vegetation index(NDVI)for grassland classification were higher than those of other indexes in the study area,and the cumulative contribution of the importance values of first 18 classification characteristics and indexes was more than 85%;2)The random forest(RF)model gave the highest classification accuracy and was superior to other methods in grassland class identification in Inner Mongolia,with an overall accuracy of 82.16%and Kappa coefficient of 0.76;3)In the past 20 years,the transition between grassland classes in Inner Mongolia has been intense,and has mainly occurred through transition among the classes typical steppe,desert steppe and desert.Compared with the grassland types in the 1980s,the grassland types in 2000-2009 changed from wet to dry,while the grassland types in 2010-2019 changed from dry to wet.The results of this study provide a scientific evaluation of the changes in grassland type in Inner Mongolia under global climate change and as a result of human activities,and provide a theoretical basis and technical support for planning sustainable grassland development in Inner Mongolia.