Abstract
The Inner Mongolia grassland has been facing critical degradation. To combat this issue, China has launched a series of ecological restoration programs since the early 2000s to promote the recovery of degraded grasslands (e.g., the Beijing-Tianjin Wind/Sand Source Control Program, the Grazing Withdrawal Project, and the Ecological Compensation Policy). However, the long-term effects of these measures on the recovery of the Inner Mongolia grassland still need further evaluation. To quantitatively assess the grassland degradation status and dynamics, we utilized long-term remote sensing datasets (GIMMS NDVI and MODIS NDVI) from 1982 to 2020 to calculate the fractional vegetation cover (FVC, the ratio of vegetation canopy's vertical projection area to the unit area) and grassland degradation index (GDI, the ratio of average FVC during peak growing season to historical optimum FVC). Results showed that across the study region, the average FVC was 42% over the past four decades, with degraded grassland (GDI < 0.9) accounting for 84.6% of the total area. Noteworthy spatial differences were observed. Specifically, study region to the west of 115°E had an average FVC of 20.7% with 98.2% areas exhibiting a degraded state. By contrast, study region to the east had an average FVC of 57.7% with 68.5% areas experiencing degradation. Over time, the proportion of degraded grassland generally decreased, particularly in the past two decades. However, approximately 3/4 of the grassland remained degraded in the last decade (2011-2020). Although degraded grassland is recovering, grassland degradation remains serious, especially in the west of 115°E, where 80.8% of the grassland was moderately and severely degraded (GDI < 0.6) in the last decade. Our findings suggest that while the implementation of ecological protection measures in Inner Mongolia has slowed down grassland degradation, the persisting degradation underscores the necessity of region-specific grassland protection and restoration.