Abstract: The typical Quercus liaotungensis forest communities along 364m long sample belt along the slope of Dongling Mountain in Beijing have been divided to be the lower, middle and higher 3 parts. The 8 dominant plant population diameter(or base diameter) structures and dynamics of Quercus liaotungensis, Fraxinus rhynchopylla, Betula dahurica, Acer mono, Lespedeza biocolor, Abelia biflora, Rhododendron micranthum, Spiraea pubescens populations in the community have been studied systemically on statistics along environment grade. Except for the Betula dahurica population that are declining, the other populations all show developing or stable status which have more numbers of younger seedling. Quercus liaotungensis populations show stronger adapted ability as altitudes increase since diameter structures are reasonable. The Fraxinus rhynchopylla, Acer mono populations can replace each other on the size and density along slope. In shrub layer, except Rhododendron micranthum population, Lespedeza biocolor, Abelia biflora and Spiraea pubescens have more numbers of seedlings, and their diameters structures are reasonable. In this area, if the disturbance from human being could be stopped, the Q. liaotungensis forest system will develop to be more mature status.

Key words: Quercus liaotungensis forest, population diameter structure, stability of community