Abstract
Since rural reforms in the 1980s, both the state and local governments of China have devoted great efforts to combating desertification through a number of eco-environmental restoration campaigns, resulting in burgeoning contention at all levels of government and sparking public concern. Monitoring and accurately assessing the statuses and trends of grassland desertification are important for developing effective restoration strategies. The Horqin Sandy Land (HSL), a very typical desertified grassland (DG) with better hydrothermal conditions among sandy lands in north China, was recently selected (1985–2013) to assess the spatiotemporal dynamic performances of grassland desertification before and after implementing restoration projects. Landsat images (TM/ETM+/OLI), field investigations and expert review were integrated to form a classification scheme for the HSL. Then, spectral mixture analysis and the decision-tree method were used to extract bare-sand ratios and vegetation cover fraction dynamics. A favourable phenomenon of DG was seen to be reversed in an accelerated pace during 2001–2013, despite challenge from both climatic and anthropogenic factors. However, overexploitation of grassland (especially for farming) and ground water for irrigation has led to remarkable decreases in the ground water level in recent decades, which should be highly concerning regarding the formulation of restoration campaigns in the sandy land.
Highlights
Desertification is a type of land degradation that occurs in arid, semi-arid, and sub-humid regions due to the synthetic action of climatic variations and human activities[1]
Desertified grassland (MDG) and severely desertified grassland (SeDG) are mainly distributed southwest of Horqin Sandy Land (HSL), where Ongniud, Naiman, Hure, and Aohan are involved in the administrative division
SeDGs are mainly located in the triangle region that is formed by Wufendi-Wudan-Wuduntaohai in Ongniud and the Xar Moron and Jiaolai Rivers
Summary
Desertification is a type of land degradation that occurs in arid, semi-arid, and sub-humid regions due to the synthetic action of climatic variations and human activities[1]. Desertification monitoring and assessment (M & A) must be conducted if the Parties to the UNCCD are to have reliable information that supports monitoring the effectiveness of their activities[5]. Given that pixels in remote sensing images are usually mixed, especially in arid and semiarid environments, extracting information at the sub-pixel scale is important. It is very helpful to study the dynamic changes in grassland desertification under the interactions between climate change and anthropogenic factors for understanding the man-earth relationship and for developing effective solutions. The specific objectives of this study were (1) to design a grassland desertification grading system applicable to HSL; (2) to investigate the suitability of Landsat images and SMA methods for grassland desertification monitoring; and (3) to monitor and analyse the dynamics of grassland desertification during the previous 30 years in the sandy land
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