Abstract: Based on the 2000-2008 MODIS-NDVI images and using dimidiate pixel model, a dynamic evaluation was made on the vegetation coverage in northern Shaanxi Province, one of the ecologically fragile area in China, under the backgrounds of returning farmland to forestland and grassland and of the integrated management of soil and water loss. In 2000-2008, the vegetation coverage in the study area fluctuated within a year, being the highest in August and the lowest in March, and showed an increasing trend from the northwest to the southeast. The annual maximum vegetation coverage had a pronounced increase, but the area of medium and high coverage increased while that of low coverage decreased. The increased area of vegetation coverage occupied more than half of the study area, especially in the northeast. Climate features and human activities were the main causes inducing the pronounced increase of vegetation coverage, reflecting to a certain extent the effectiveness of ecological restoration efforts. The dimidiate pixel model based on the MODISNDVI images could well and truly simulate the spatiotemporal variation trend of the vegetation cover in northern Shaanxi, and be applicable to quantitatively estimate and evaluate the effectiveness of vegetation restoration at regional scale.

Key words: vegetation coverage, dimidiate pixel model, spatiotemporal variation, remote sensing, ecological restoration, northern Shaanxi Province, root characteristics, available potassium releasing from mineral, mechanism of potassiumenriched.