Forest cover dynamics from Landsat time-series data over Yan’an city on the Loess Plateau during the Grain for Green Project

In order to arrest environmental degradation, China initiated the Grain for Green Project (GGP) in 1999, an ecological restoration project that aims to convert cropland to wetland, grassland, or forestland. In most parts of China, where croplands have been part of the project, most have been converted into forestlands. In this project affected farmers receive compensation from the central government and this is administered by local governments. To monitor the achievements of this project, the actual acreage of croplands that were converted to forest or other natural ecosystems needs to be known. However, local governments usually rely on field visits and on-site surveys to determine this amount. This is not only time-consuming, but also subjective. In this research we study the potential of Landsat time-series images in monitoring cropland and wasteland to forest conversion as a result of the GGP ecological restoration project in the Loess Plateau region. We developed a method to reconstruct the change history of land conversion, particularly cropland and wasteland to forest plantation from 1999 to 2009. The prefecture level city, Yan'an, on the Loess Plateau, with a total area of 37,037 km2, was chosen for the experiment. Our results indicate that an overall accuracy of 86% can be obtained for afforestation during the entire period of GGP. The GGP in Yan'an has made remarkable achievements since 1999. Between 1999 and 2009, the forested area in this region has increased by nearly 340 ± 30 thousand ha, approximately 10% of the total area of Yan'an. We also found that 5% of the GGP afforested areas were converted to urban built-up area or reverted to cropland.