The secondary forests on northern slope of Mt. Changbai were sampled to investigate the effect of human disturbance on their tree species diversity and community structure. Compared with broad-leaved Korean Pine (Pinus koraiensis) forests, secondary forests were much lower in tree species diversity, community structure indices and stand volume. Secondary forests were dominated by pioneer species, and nearly no natural regeneration of Korean Pine was observed in most of our plots. Stepwise regression revealed that, stand volume was the most powerful predictor for tree species diversity. Tree species diversity decreased with the decrease of volume in secondary forests, while increased in broad_leaved Korean Pine forests. Community structure indexes also dropped significantly with decreasing stand volume in secondary forests under different human disturbances. However, broad_leaved Korean Pine forests did not show significant change in community structure under natural disturbance. These results indicated that, broad_leaved Korean Pine forests were strongly resistant to natural disturbance, while secondary forests were sensitive to human disturbance. The analysis of variance showed that the tree species diversity declined significantly under intensive disturbance (volume was below 100 m3·hm -2),the community structure was influenced significantly under moderate disturbance (volume was below 150 m3·hm -2). Our results suggested that the secondary forests were poor in stand quality, and the tree species diversity and community structure index were sensitive to human disturbance. More effort should be make to protect secondary forests, together with human regeneration of Korean Pine under canopy, in order to promote the recovery of the secondary forests to the broad_leaved Korean Pine forests.
