LHASA, May 8 (Xinhua) -- In Xizang, referred to as the "roof of the world," there exists a place called Nagqu, intriguingly dubbed the "roof of the world's roof." Averaging over 4,500 meters above sea level, the prefecture-level city in Xizang has the highest average elevation of any Chinese city.

The city proper of Nagqu is known for its rarefied atmosphere, arid climate and sandy soil, and it was once the only prefecture-level city in China without trees used for urban greening. After years of efforts, the sight of trees is no longer a luxury beyond reach in Nagqu. Various kinds of trees have survived here and are growing alongside roads. The urban greening, along with many other aspects of urban development, is improving steadily in the city.