Study on Seedling Regeneration of Arbor and Shrub in Logging Gaps in Populus davidiana-Betula platyphylla Secondary Forests in Changbai Mountain

Regeneration in relation to logging gaps sizes and ages was investigated in Populus davidiana-Betula platyphylla secondary forests in Changbai Mountain.The research result showed that there were 7%(canopy gaps area50 m2),21%(50-100 m2),36%(100-150 m2),29%(150-200 m2),7%(200 m2) in the proportion of gap sizes.28.6% of gaps shape were rotundity and 71.4% were oval.55% of the oval gaps lay in N-S direction,30% lay in N-E to S-W direction and 15% lay in S-E to N-W direction.Gaps were usually formed after 7-10 trees logged which were mainly composed of Populus davidiana,Betula platyphylla and Maackia amurensis.The seedlings was absolutely dominated by the shrub at the initial stage of logging gaps,but the dominance of the shrub seedlings would weaken step by step.At the same time,the advantage of arbor seedlings would raise correspondingly with the increasing gaps age.The density,mean high and mean basilar diameter of seedlings growing in the logging gaps were higher than those in non-gap.The growth of seedlings was the best in 100-200 m2 gaps and arbor seedlings surpassed shrub seedlings in gaps except 50-100 m2 gaps.The dominance species mainly composed of intolerant species were different in gaps of different sizes.