Temporal and spatial variations of grassland desertification in Lingwu and Yanchi of Ningxia, China

摘要

In the face of increasingly serious grassland desertification, state and local governments have implemented a series of grassland protection policies. In 2003, Ningxia was the first to implement a region-wide grazing ban and the effect of the ban has become both contentious at all levels of government and a topic of public concern. Grassland desertification in the study area is the most direct indicator of the effect. We selected YanChi and Lingwu in the central part of Ningxia as the study area for the desertified grassland in Ningxia mainly distributed there, then the grassland desertification classification and grading system for the study area was designed after conducting fieldwork. Based on Landsat TM/ETM+ images, the Spectral Mixture Analysis (SMA) and decision-tree methods were selected to interpret the remote-sensing images of the study area during four periods: 1993, 2000, 2006 and 2011. Temporal and spatial variations of grassland desertification were evaluated by taking the bare-sand ratio and vegetation coverage as the main evaluation indicators. The following results were obtained: from 1993-2011, the area of desertified grassland in Ling-Yan decreased gradually to 5,661 km2 in 2011 from 6,435 km2 in 1993, a decrease of 12.03%; the degree of desertification gradually reduced from 2229 km2 of severely desertified grassland in 1993 to 748 km2 in 2011, a decrease of 66.42%; desertified grassland vegetation was restored rapidly during 2000–2006 and 2006–2011, reducing the total area of desertified grassland annually by 1.63 and 0.45%, respectively; finally, the area of severely desertified grassland decreased annually by 4.63 and 8.38% during 2000–2006 and 2006–2011, respectively. Since the climate in the study area is altering in a direction that is not conducive to the restoration of grassland vegetation and desertification reversal, the results obtained here demonstrate that grassland vegetation has continually been rest- red and that there has been a gradual decrease in the degree of desertification and in the extent of the desertified area for the implementation of region-wide grazing ban and other ecological engineering measures in the study area, indicating that human effort can effectively contribute to the reversal of desertification.