山火事が森林生態系における水・主要塩類の収支に及ぼす影響 : I.水収支

抄録

Precipitation (P) and stream flow rate (Q) were measured simultaneously in three watersheds : strongly burnt, moderately burnt and undamaged natural forests through the year from December of 1979 till November of 1980 at Etajima Island, Hiroshima Prefecture, west Japan, where a fire occurred in June of 1978. Rain fall (2077-2156 mm) in the year studied was 500 mm more than that in usual years (1575 mm), and threre was little difference of precipitation among the watersheds. On the other hand, discharge from each watershed increased at the burnt forest ; therefore, annual evapotranspiration, calculated as the difference between precipitation and discharge, decreased after the forest fire due to the loss of interception by the forest canopy and transpiration by plants. Annual ratio of discharge to precipitation (Q/P) was estimated at 0.657,0.604 and 0.519 in the strongly burnt, moderately burnt and natural forests respectively. This finding suggests that the discharge increased or the evapotranspiration decreased in proportion to the ratio of burnt area to its watershed area. Loss of the discharge per burnt ratio was calculated at 2.7mm/%, which was comparable to the value estimated from the data obtained in the deforested watersheds.