Abstract: The qualitative vegetation-habitat classification system (VHCS) and the quantitative comprehensive and sequential classification system (CSCS) are the two major grassland classification systems in China. However, the use in practice of the classification results from these two systems has been difficult due to the different approaches (qualitative vs quantitative) and grassland definitions adopted by the two systems, causing difficulties in comparing the grassland types classified from these two systems. Through overlaying the CSCS classification map and the digitized VHCS map in ArcGIS for the grasslands in Inner Mongolia Autonomous Region and Gansu Province, this study compared the criterion and characteristics of the two systems at the first classification level (class), analyzed their compatibility and developed the corresponding relationships to translate the types between two systems. The results show: 1) CSCS is generally compatible with VHCS when comparing the broad grassland types (class); 2) at the class level, the VHCS and CSCS system are generally in agreement when comparing the class names, characteristics and parameters used; 3) if not considering forest and non-zoning classes, the results of the spatial overly indicated that the compatibility of two systems can be as high as 61.4% and 61.1% for Inner Mongolia and Gansu, respectively. The areas where the grassland classes from the two systems were different were mainly degraded from the potential natural vegetation (as classified by CSCS) and were observed as classes in the VHCS system as low-level grassland under more severe climate conditions. This indicates that the human disturbance has surpassed the survival thresholds of these potential natural grassland vegetation categories, resulting in retrogressive succession of the grasslands; 4) the results from the comparative analyses of the CSCS and VHCS systems provided insight into the succession mechanisms of grassland ecosystems under human disturbance, and are helpful in grassland management with regard to system restoration and reestablishment.

Key words: grassland, classification, comprehensive and sequence classification system, vegetation-habitat classification system, compatibility