Young trees grow on the hillside. The dirt tracks are routes made by workers driving their tractors to tree planting sites on the hill sides. Desertification poses major environmental and ecological threats to about one-third of the Earth, according to a 2004 United Nations study. China has had some success curbing the spread of its own deserts, though they are still getting bigger. The efforts of slowing the advance of deserts has been made by, The Green Great Wall, a government tree planting program. It is estimated that by 2050, the artificial forest is to stretch 400 million hectares, covering more than 42 percent of China’s landmass. However continued doubts remain about the impact of this green campaign. While the government stresses the forests' importance in combating decades of environmental damage, some critics say the type of forests planted, and their location, limit their effectiveness, arguing the Great Green Wall has contributed to a significant decline in China's forest quality, and in some places, accelerated ecological degeneration by putting pressure on precious water resources in arid and semi-arid regions.