Local plant communities are assembled through three major filters, i.e. dispersal limitation, environmental filterring and interspecific competition. I examined effects of these filters on community assembly of understory plants in a semi-boreal forest of Tomakomai. At first, I tested whether relative importance of dispersal limitation and environmental filterring as determinants of spatial population structure is different or not among species. Although moderate importance of both filters have been demonstrated in numerous community-scale studies, this would be a first population-level study, which detected a considerable interspecific difference in the importance of dispersal limitation. Furthermore, the interspecific differences were not predictable from the functional traits of species, including dispersal mode and seed mass. Secondly, I sought evidences of environmental filterring and interspecific competition by trait-based permutation tests. Patterns that suggest variable effects of environmental filters and interspecific competition depending on stand type were found for multiple functional traits. These results represent complicated roles of the three filters in assembly of the understory plant community.