Abstract: According to the distance from forest stands to residential area and the first and second grade roads, as well as the canopy density and the percentage of damaged trees, this paper defined the disturbances, anthropogenic and natural, as low, medium and high levels. On the basis of this, the effects of different level disturbances on the plant species diversity of secondary forest in montane regions of eastern Liaoning Province were analyzed, and the differences between the effects of anthropogenic and natural disturbances were discussed. The results showed that without considering forest types, the overall plant species diversity of secondary forest under medium level anthropogenic disturbance was higher than that under low and high level anthropogenic disturbances, with the Simpson indexes being 096, 095 and 092, and ShannonWiener indexes being 377, 360 and 336, respectively. The diversities of shrub and herb layers were also the highest under medium level anthropogenic disturbance, while the highest diversity of arbor layer was appeared under the high level one. Among different forest types, there existed differences in the plant species diversity under anthropogenic disturbances, e.g., the diversity under medium level anthropogenic disturbance was the lowest in hard broadleaved forests, but the highest in other forest types. In all test forest types, no consistent tendency was observed in the changes of three layers’ diversities with anthropogenic disturbance levels, but the diversities of shrub and herb layers were greatly affected by the disturbances. After 3 years of snow/wind damage, there was no distinct difference in the diversities among the birch forests under low, medium and high level natural disturbances, with the Simpson indexes being 0.91, 0.91 and 0.92, and the Shannon-Wiener indexes being 2.30, 2.93 and 2.89, respectively. The diversities of arbor and shrub layers were both increased with the enhancement of natural disturbances, but there was no great difference in the diversity of herb layer among the three levels of natural disturbances. At present, anthropogenic disturbance mostly occurred in understory, while snow/wind damage occurred in canopy. Such dissimilarity could make the effects of environmental factors on plant species diversity differed greatly.

Key words: Evergreen broad-leaved forest, Gap characteristics, Gap formation, Dead wood, Tree regeneration