Development and application of a vegetation degradation classification approach for the temperate grasslands of northern China

Abstract

To establish a unified grassland degradation assessment system, this study proposed a classification approach using a statistical method based on the percent decrease in the annual maximum leaf area index from a long time series of remote sensing data. The obtained classification thresholds for vegetation degradation were temporally stable and spatially universal and were thus well-suited as a new standard. They were specific for different temperate grassland types and applicable to large and heterogeneous areas. Meadow steppes had the lowest degradation thresholds, sensitive to changes in plant growth, desert-related steppes had the highest thresholds, and typical steppes had intermediate thresholds. We then used the obtained thresholds to assess the degradation status of temperate grasslands in northern China from 1981 to 2017. Degraded grasslands accounted for 8.2 % (1.72 × 107 ha), of which moderately, severely, and extremely severely degraded grasslands accounted for 38.6, 34.9, and 4.6 %, respectively. More than half (∼67 %) of the degraded grasslands in northern China occurred in the Inner Mongolia Autonomous Region, and these were dominated by severely degraded grasslands. About 20 % of all degraded grasslands in northern China occurred in the Xinjiang Uygur Autonomous Region, and were dominated by moderate degradation. These results were highly consistent with the Chinese national standard regarding the total degraded area. However, differences occurred in specific grassland degradation levels and grassland types. Therefore, compared with traditional approaches, the new approach provided a more accurate degradation assessment, which is crucial for protecting and restoring the different temperate grasslands of China.