Abstract: We studied the different effects of extensive forest management regime and target tree management regime on plant community structure and biodiversity of natural secondary coniferous forest, broad-leaved forest and mixed forest in Danqinghe Forestry Farm which locates in Harbin, Heilongjiang Province, no disturbance forest stand was selected as reference. The results showed that: 1) Compared with extensive forest management regime and no disturbance, the basal area of the first canopy layer under target tree management regime was the highest, proportion of basal area was 95.00%, 90.00%, 87.00% in coniferous forest, broad-leaved forest and mixed forest respectively. The basal area of the second and third canopy layer under target tree management regime was the lowest. All of these implied that stand under target tree management regime have the best canopy structure. 2) The average stand density under target tree management regime(408-858 tree ·hm^-2)was significantly lower than that under extensive forest management regime(992-1 917 tree ·hm^-2)(P<0.05), there was no difference in average basal area. Average tree height(11.8-14.9 m)and DBH (15.94-27.34 cm)under target tree management regime were significantly higher than that under extensive forest management regime(tree height is 7.1-11.0 m and DBH is 10.18-19.00 cm)(P<0.05). 3) Above 60% of trees under extensive forest management regime and no disturbance regime were small-diameter tree(DBH smaller than 12 cm), but above 60% of trees under target tree management regime were middle-diameter tree(DBH 14-18 cm)and large-diameter tree(DBH above 20 cm).4) Diversity in tree layer under extensive forest management regime was higher than that under target tree management regime; exception of broad-leaved forest, diversity in shrub layer under extensive forest management regime was higher than that under target tree management regime; while diversity in herb layer under target tree management regime was the highest. 5) These findings confirm extensive forest management regime purse more timber production and neglect ecology requirements, while no disturbance regime just focus on ecology and neglect the requirement in using forest resources, neither of them can meet the human's needs. Target tree management regime can improve community structure, get more economic benefit and balance ecological functions simultaneously which comply with objective of sustainable forest management.

Key words: natural secondary forest, forest management regimes, community structure, plant biodiversity