Abstract
The influence of two forest declines caused by forest fire and pine wilt disease on the discharge duration curve was estimated with a paired catchments experiment in Tatsunokuchi-yama Experi-mental Forest (34° 42' N, 133° 58' E). The regression lines between the discharge duration curves from Kitatani and Minamitani catchments were calculated during the control period (36 years). The observed discharge and calculated discharge with this regression line during the treatment period (19 years) were compared. Except for a few dozen days, the daily discharge was judged to be increased by disturbance on almost all days. The increased ratio on the observed discharge was around 15, 35 and 43% on the 140th, 140320th, and 320thday, respectively, in the discharge duration curve.
