RUNOFF CHARACTERISTCS OF FOREST WATERSHEDS UNDER DIFFERENT FOREST MANAGEMENTS

Abstract

Water resource management on a watershed-scale becomes crucial to cope with expected water shortage in the future. One of the key factors in water resource management is forest management, since forest cover changes have large impacts on hydrological processes on watershed scale. Afforestation, forest thinning, clear-cutting and tree species conversion are the most common techniques of forest cover managements. Though it is essential for water resource management, how the forest cover management impacts on hydrological processes has not been systematically understood. Thus, we reviewed the effects of the above four technics in forest cover management on the runoff characteristics from various watersheds in the world. Afforestation is not suitable for countries with a little precipitation because mature forests can reduce much amount of runoff. On the other hands, planting trees in the upland part of the catchment can reduce the flood risk in the downstream area. Thinning and clear cutting can increase the amount of runoff, but at the same time, can decrease the water quality of streamflow. Converting natural/secondary forests to a single plant forest strongly decreases the total amount of runoff. The broadleaf deciduous can produce higher annual runoff but control flood discharge than evergreen coniferous forest. To replace pine trees with eucalyptus for forest plantation has a positive effect on the total amount of timber that can be produced but has a huge impact in decreasing water resource, because of high water consumption of eucalyptus for its growing up fast.