砂礫州における生物多様度と相関性の高い洪水撹乱指標について

抄録

For elucidating the relationship between flood disturbance and biodiversity of vegetation in gravel bed bars, Breakage or Overturning Index (BOI) and Wash-Out Index (WOI) were derived considering the difference of vegetation breaking phenomena due to floods, i.e. trunk breakage or overturning, and wash-out of trees or grass, respectively. Coupling the two indices, the method for classifying the river habitat into five, not tree breaking and not washout (Region A), tree breaking and not washout (Region B), not tree breaking and washout (annual grass) (Region C), tree breaking and washout (annual grass) (Region D), and washout of all vegetation (Region E), is proposed. The condition at which WOI is larger than 0.5, and WOI is less than one, is correlated with the Shannon-Wiener index at three gravel-bed bars in the Arakawa River, Japan. Especially, when BOI is larger than one, the biodiversity is increased. For Region A and E, the trend is assumed to be affected by the duration after flood. The proposed index for Region D has possibilities to express middle class disturbance that is closely related to the biodiversity at the habitat.