Forest management method for the water resource conservation function of forests: example for determining the location and area of trees cut down

Forests are expected to exhibit various functions in addition to the functions of supplying timber and fuel. Particularly, expectations for the water resource conservation function of forests are increasing considerably because of widespread concerns about water resource shortages caused by climate change in recent years. Forest vegetation has a greater evapotranspiration rate than either agricultural land or grassland, and therefore has the effect of reducing the runoff volume. Consequently, a forest management method that appropriately adjusts the evapotranspiration rate by trees while preserving forest soil can be considered to exploit the water resource conservation function of forests. Moreover, a forest management regional plan must include appropriate locations and amounts of trees to be cut down. Therefore, in this report, a forest management method is reviewed to exert the water resource conservation function of forests and a model is developed to predict changes in the annual amount of available water resources caused by tree cut down. As results, the percentage of the annual amount of available water resources was found to be roughly proportional to the tree cut down ratio. Based on the points raised above, the method of calculating the number of trees to be cut down to achieve the required increase in the annual amount of available water resources is discussed using an example, particularly considering the case requiring an increase of 4,200 m(3) in the annual amount of available water resources in 10 ha of forest basins of 2,229 trees ha(-1) in a region with annual precipitation of around 1,400 mm.