We investigated the age structure, life table, and dynamics of Fraxinus mandshurica populations on Changbai Mountain by using spatial series rather than time series and substituting trunk size structure for age structure. In broadleaved Korean pine forests, maintenance of F. mandshurica populations was largely dependent on mature trees because of low numbers of seedlings. In Betula platyphylla secondary forests, F. mandshurica populations were relatively young, but lacked seedlings. The survival curves for the F. mandshurica populations were classified as Deevey type and showed declining trends. Time-series prediction revealed that these populations will eventually decline because of an increase in the proportion of mature trees. We suggest appropriate artificial measures for ensuring continuous and steady growth of F. mandshurica populations on Changbai Mountain.