Abstract: The Three-North Shelter Forest Program (TNSFP) covers 13 provinces of China, which brings great influence to the eco-environment of North, Northeast and Northwest China (Three-North Regions). In this paper, the vegetation  cover in the Three-North Regions was estimated by using a dimidiate pixel method based on the MODISNDVI data in August 2001 and 2007, with its spatiotemporal changes analyzed. In 2001-2007, the vegetation  cover in the Three North Regions had an obvious change. The mean coverage increased by 2.07%, and the increment in Jilin, Shanxi, Shaanxi, and Ningxia provinces reached to 27.37%, 14.12%, 9.29%, and 9.22%,
 respectively. The increase of the vegetation  cover was mainly caused by the increasing of precipitation and the enhancement of peoples’ environmental awareness, as well as the implementation of closing hillsides to facilitate afforestation, returning farmland to forest/grassland, and especially, the TNSFP.

Key words: Nitrogen stress, Nutrient uptake, Biomass distribution, Fraxinus mandshurica