Subclasses Classification Of Chinese Grassland Based On Comprehensive Sequential Classification System

China is a big country with abundant and diverse grassland resources,and the distribution of grassland area is among the top in the world.Grassland ecosystem is considered to be one of the most widely distributed ecosystem types in the world.It is not only an ecological barrier to maintain national ecological security,but also plays an important role in the development of the national economy.For a long time,due to the rapid growth of China’s market economy and the improvement of people’s daily life quality,on the basis of grassland resources products market development efforts to continuously strengthen,thus resulting in the degradation grassland productivity,growth quality degeneration phenomenon,gradually influences and restricts the grassland resources and the sustainable development of grassland ecosystem.Grassland is an important part of the terrestrial ecosystem,and the precise definition of grassland types is of great significance to the study of grassland resources.The rational allocation of grassland resources is essential for achieving the balance of grass and livestock,improving the ecological environment and achieving the sustainable development of animal husbandry.On the basis of Digital Elevation Model（DEM）and Moderate Resolution Imaging Spectrometer（MODIS）data,in this study,the comprehensive and sequential classification system of grasslands（CSCS）is used to quantitatively classify Chinese grassland subclasses,and the spatial distribution characteristics of grassland subclasses in China are analyzed.The research results can provide a scientific basis for grassland development and utilization,cultivation,protection and management,as well as the development of animal husbandry.The main conclusions of this study are as follows:（1）The division principle of grassland subclasses was first put forward.Based on the land characteristics,the subclasses of grassland in mountain area and flat area were divided respectively.In mountainous areas with complex topography,geomorphic indexes are adopted.The soil index was selected in the flat area.（2）According to the geomorphological classification standards,mountain subclasses were divided into 20 types.Mainly low relief mountain,the area of 2.54×10⁶ km²,accounting for 46.53%of the total area.The area of hills and intermediate relief mountain was 1.37×10⁶ km² and 1.35×10⁶km²,accounting for 25.14%and 24.81%,respectively.The area of high relief mountain and extremely high relief mountain is small,accounting for 3.52%in total.（3）According to China’s 1:1 million soil database,using MODIS data and DEM data,the soil types in China’s flat areas are divided into 37 types,with an overall classification accuracy of63.98%and kappa coefficient is 0.62.Among them,brown pedocals is the most distributed,with an area of 6.07×10⁵ km²,accounting for 15.20%of the total area.The area of paddy soils ranks second,accounting for 3.97×10⁵ km²,accounting for 9.92%.The distribution area of fluvo-aquic soils is3.94×10⁵ km²,ranking third,accounting for 9.86%.The types with smaller distribution area mainly include dark felty soils,dark loessial soils,red clay soils and grey-cinnamon soils,with the areas of4.19×10³ km²,1.62×10³ km²,9.54×10²km²,5.74×10²km² respectively.（4）In principle,each grassland type can be divided into 20 mountain grassland subclasses and37 flat grassland subclasses.Due to differences in spatial hydrothermal conditions,some subclasses do not exist in specific environments.For example,there is no mountain grassland subclasses in the frigid-extrarid frigid desert and alpine desert（ⅠA1）below the low altitude hills.Subtropical-extrarid subtropical desert（ⅥA6）does not exist in the flat grassland subclasses.（5）The grassland subclasses of frigid perhumid rain tundra,alpine meadow（?F36）is the most widely distributed,with an area of 1.11×10⁶ km²,accounting for 12.14%.The second is the grassland subclasses of warm temperate-extrarid warm temperate zonal desert（IVA4）,with an area of 8.47×10⁵km²,accounting for 9.27%.The area of grassland subclasses of cool temperate-arid temperate zonal semidesert（ⅢB10）was 6.07×10⁵ km²,accounting for 6.64%.The distribution area of subtropical-extrarid subtropical desert（VIA6）was the smallest,which was 7.47×10^-2 km².（6）The naming principle of grassland subclasses were"grassland name+mountain subclasses name"and"grassland name+soil type name".The mountain was named as"M",the flat land as"F",and the classification results of the mountain subclasses were"31···74,75".Then the naming methods of the mountain grassland subclasses were as follow:"ⅡD23-M-31,cold temperate subhumid montane meadow steppe low altitude hill subclasses".The classification result of flat land soil type is"albic soils,felty soils···paddy soils",then the naming method of flat land grassland subclasses is,for example"ⅢC17-F-aeolian sandy soils,cool temperate semiarid temperate typical steppe aeolian sandy soils subclasses".