Promoting ecological progress and protecting the environment. The PLA, militia and reserve organic troops are organized to help afforest barren hills, control desertification and preserve wetlands. Specifically, they have supported the construction of key national reserves and ecological engineering projects such as controlling the sources of sandstorms affecting Beijing and Tianjin, afforesting the periphery of the Taklimakan Desert, protecting the ecological environment of the upper and middle reaches of the Yangtse and Yellow rivers, and harnessing the Yarlung Zangbo, Lhasa and Nyangqu rivers in Tibet. Over the past two years, the PLA and PAPF have planted over 14 million trees, and afforested above three million mu of barren hills and beaches by large-scale planting and aerial seeding. Besides, technical units specializing in cartography, meteorology, and water supply provide such services as cartographic surveying, weather and hydrological forecasting, and water source exploration for local people.