A car drives on the mountain road at Zoumatai Village of Wuqi County in Yan'an City, northwest China's Shaanxi Province, June 5, 2019. Wuqi County has carried out a development policy since 1998 that returned farmland to forest for ecological protection and sustainable development purposes. (Photo: Xinhua)

Aerial photo taken on June 8, 2019 shows the scenery of hills covered with green at Guopan Village of Wuqi County in Yan'an City, northwest China's Shaanxi Province. Wuqi County has carried out a development policy since 1998 that returned farmland to forest for ecological protection and sustainable development purposes. (Photo: Xinhua)

Photo taken on June 6, 2019 shows the flowing clouds over hills at Yangqing area of Wuqi County in Yan'an City, northwest China's Shaanxi Province. Wuqi County has carried out a development policy since 1998 that returned farmland to forest for ecological protection and sustainable development purposes. (Photo: Xinhua)

Ma Youen picks a melon at a greenhouse in Mawan Village of Wuqi County in Yan'an City, northwest China's Shaanxi Province, June 6, 2019. Wuqi County has carried out a development policy since 1998 that returned farmland to forest for ecological protection and sustainable development purposes. (Photo: Xinhua)

Aerial photo taken on June 5, 2019 shows hills covered with green at Wuqi County in Yan'an City, northwest China's Shaanxi Province. Wuqi County has carried out a development policy since 1998 that returned farmland to forest for ecological protection and sustainable development purposes. (Photo: Xinhua)

Flowers are seen at Mawan Village of Wuqi County in Yan'an City, northwest China's Shaanxi Province, June 7, 2019. Wuqi County has carried out a development policy since 1998 that returned farmland to forest for ecological protection and sustainable development purposes. (Photo: Xinhua)

File photo taken in 1997 shows the farming condition before returning farmland to forest at Wuqi County in Yan'an City, northwest China's Shaanxi Province. Wuqi County has carried out a development policy since 1998 that returned farmland to forest for ecological protection and sustainable development purposes. (Photo: Xinhua)

Aerial photo taken on June 5, 2019 shows hills and fields after returning farmland to forest at Xigouta Village of Wuqi County in Yan'an City, northwest China's Shaanxi Province. Wuqi County has carried out a development policy since 1998 that returned farmland to forest for ecological protection and sustainable development purposes. (Photo: Xinhua)