Abstract:

Regeneration dynamic in logging gap of different sizes and ages was studied in Populus davidianaBetula platyphylla secondary forests in Changbai Mountain by using line transects method. The results showed: The gaps occupied 7％(canopy gaps area<50 m²)，21％(50～100 m²)，36％(100～150 m²)，29％(150～200 m²)，7％(>200 m²) in the proportion of logging gap sizes respectively; Gaps were usually formed after 7～10 trees logged that were mainly composed of P. davidiana, B.platyphylla and Maackia amurensis. The composition of seedlings species was simple and the distribution of seedlings was not evenness in gaps. The species number, individual density, LAI, mean height and mean basilar diameter of seedlings were better in gaps than in non gaps. Some species, such as Acer mono, Sorbus pohuashanensis, M. amurensis adapted well to gaps, but other species, such as Fraxinus mandshurica and Malus baccata adapted well to non gaps. With the increasing of gap ages, owe to the litter and nutrition content increasing in soil, the species number and individual density of seedlings increased distinctly, and seedlings growth was improved, the advantage for regeneration in gaps was more obvious than in non gaps. The seedling trait was obvious difference at different position, within gaps result from the obvious space heterogeneity of PAR, soil nutrition content and litter. The regeneration was best at west edge of gap and most inferior at center and midnorth of gap. The seedlings of regeneration in <50 m² gaps were as equivalent as those in nongaps, the least in >200 m² gaps and excellent in 100～150 m² gaps where the individual density, LAI, height growth and basilar diameter growth were firstclass, which was due to the huge difference of PAR in gaps of different sizes. Therefore, the gap of 100～150 m² benefited the regeneration of seedlings best.

Key words: logging gap, regeneration, secondary forest, Changbai Mountain