Montane riparian forest is often characterized by a complex disturbance regime, including gap formation and less frequent fluvial disturbance, and high species diversity. By analyzing sapling distribution patterns in a riparian forest in northern Japan, we tested the hypothesis that canopy and debris disturbances play different roles on the establishment of sapling community in riparian forest.

The majority of saplings were found on disturbed sites compared to beneath-canopy sites. Based on sapling relative densities, some species mainly occurred to gaps (e.g. Cercidiphyllum japonicum, Fraxinus lanuginosa) and others mainly on gravel deposits (Pterocarya rhoifolia, Ulmus laciniata, Acer mono). These major species were also separated into three groups of different light requirement. Thus, regenerating species may differ in their dependence on disturbance and shade-tolerance during the sapling stage, in support of the niche segregation. Disturbance complexity of this riparian forest may be contribute to structural diversity of sapling community and ultimately to the high species richness of the forest.