BEIJING, July 9 (Xinhua) -- China had seen its forest increase by 502 million mu (about 33.5 million hectares) since the project of returning farmland to forest and grassland was launched in 1999, a forestry official said Tuesday.

The increased area accounted for 42.5 percent of the country's artificial forests, Zhou Hongsheng, an official with the National Forestry and Grassland Administration, told a press conference.

About 5.03 million mu of farmland has been returned to grassland, accounting for 2.2 percent of the total artifical grassland area, Zhou said.

China has had two rounds of returning farmland to forest and grassland, with the total investment exceeding 500 billion yuan (about 72.63 billion U.S. dollars).

"The project has accelerated the process of national afforestation, and the forest coverage rates in the project areas have increased by an average of more than 4 percentage points," Zhou said, adding that 32 million farming households were able to benefit directly from policy subsidies of more than 9,800 yuan per household.

The project also helps adjust the rural industrial structure, fostering eco-economic industries and opening up new avenues for promoting the sustainable development of agriculture, Zhou said.

In the future, efforts will be made to include farmland in state-owned forest areas and those in the core areas of nature reserves into the project, Zhou added.