Factors limiting the distribution of deciduous broadleaved trees in warm-temperate mountainous riparian forests

We examined differences in the responses of deciduousand evergreenbroadleaved treesto fluvial disturbance and light environment near a river-facing forest edge in order to identify the factors limiting the distribution of deciduous trees, which are important components of warm-temperate mountainous riparian forests. Deciduous treestended to be distributed on lower terraces of less than 2-m relative elevation from the water level, which corresponded with sites suffering from strong bank erosiondue to high flood frequency. On the other hand, evergreen treesshowed an opposite trend of distribution, indicating that high flood frequency associated with strong erosion-dominated soil disturbances might be a constraint for their establishment and/or survival. Furthermore, crowns of deciduous treestended to be in the canopylayer at the forest edge, with fewer individuals observed beneath the canopyof evergreen trees, even at the forest edge. In contrast, evergreen treeswere concentrated in the understoryof the forest interior. These observations suggested that the light environment is the predominant factor affecting the establishment and survival of deciduous treesin warm-temperate mountainous riparian forests; however, the river-facing forest edge beneath the evergreen canopyis not a suitable habitat for deciduous trees. We concluded that erosion-dominated soil disturbance on lower terraces provides suitable habitats for deciduous treesby facilitating their reaching the canopylayer by limiting the establishment and/or survival of evergreen trees.