The conservation work was started at the natural sources of watershed forests and streams, in the Northern degraded or cleared highlands especially. The deforestation done by the hilltribes was stopped and replaced by the reforestation of mixed types of water-retaining trees, useful also for fruit, firewood, and timber. Another very effective method devised was small weirs or check dams constructed across waterways throughout the country, which help restore and maintain moisture in streams and create small “wet forests” or fire breaks. The work in the South, however, is more about the conservation and development of the swamp forests, or pa phru, and the mangroves. These places, rehabilitated and dredged, can be made use of to retain excessive water for the dry season.