Although government efforts to control desertification have been effective, China still faces a grave challenge, a senior forestry official said Tuesday.

A survey at the end of 2009 showed that 2.62 million square kilometers of Chinese land was degraded, Zhu Lieke, deputy head of the State Forestry Administration (SFA), said at a press conference.

Sand encroachment has affected 1.73 million square kilometers of land, Zhu added.

The survey was conducted between 2005 and 2009. It was China's fourth nationwide survey of land degradation and sand encroachment.

Compared with results of the third national survey, the area of land degradation decreased 0.47 percent while that of sand encroachment fell 0.49 percent, Zhu said.

Still, in regions such as the northwest of Sichuan Province and the lower reaches of the Tarim River, China's longest inland waterway, the situation had deteriorated, he said.

As a result of climate change, poor farming practice, overgrazing, drought and abuse of water resources, desertification has become a major threat to China's ecological security, he noted.

"The task of fighting desertification is quite challenging," said Liu Tuo, the SFA official in charge of desertification control.

Of the 1.73-million-square-kilometers of land affected by sand encroachment, only 530,000 square kilometers will be able to be returned to an arable or inhabitable state again, Liu said.

To combat desertification and climate change, China has vowed to increase forest coverage by 40 million hectares and forest stock volume by 1.3 billion cubic meters by 2020 from 2005 levels.