Beijing orchard farmers are boosting the city's economy and job market by finding valuable uses for land under their trees, authorities say.

More than 23,526 hectares, which had been left empty, is now used to grow mushrooms, traditional Chinese medicine ingredients and for keeping poultry, according to the Beijing Landscape and Forestry Bureau.

Authorities say that by the end of last year this industry - known in Chinese as the industry under the green - was worth 1.9 billion yuan ($306.5 million) and provided more than 300,000 jobs.

"The industry under the green has achieved great progress in the past few years," Hu Jun, deputy director of the bureau's desertification control office, said at an agricultural exhibition in Beijing.

The show attracted 57 companies from the capital's 12 districts and counties.

As well as keeping chickens, some farmers are increasing their incomes by cultivating flowers or using the land to develop eco-tourism.

"Each household is expected to see an income increase of 8,000 yuan a year," Hu said.

Zhang Tao, who works for a rural cooperative growing fungus in Changping district, said that although the industry has developed rapidly, there is still much potential.

He collects 10,000 kg a year of fungus grown under fruit trees from fewer than 600 farmers, and says many areas of land are still undeveloped.

Hu said the industry is also producing a greater range of products, from fungus, chickens and honey to ingredients for traditional Chinese medicine, cosmetics and essential oils.

He said Beijing has about 200,000 hectares suitable for the industry, adding that using the land helps to prevent desertification.