| The death of overstory trees creates gaps in forest canopies.As a kind of frequent small-scale disturbance,these canopy gaps make a positive impact on forests regeneration and succession.Great attention have been paid on the forest gaps studies in recent years. Previous studies focused on the gaps created by natural disturbance in the native forest, whereas few studies were conducted on the logging gap in the natural secondary forests. The logging gap and regeneration in the gap has an positive effect on conservation, restoration and the sustainable management of natural secondary forests.The forest on Changbai Mountain,as the representative forest of North-East forest region, is becoming degeneration because of artificial disturbance. Based on the investigation and measurement on seedlings and microsites in logging gaps in 3 main types of forest,including populus davidiana-Betula platyphylla secondary forest,secondary broad-leaved forest and broadleaved-korean pine mixed forest,the interaction among ecological factor and the regeneration responses of seedlings to ecological factor in logging gap was studied in this dissertation in order to obtain the regeneration rule, which provides a scientific basis for further studying the regeneration and succession of forest ecosystem and scientifically managing forests. Main results are as follows:In the populus davidiana-Betula platyphylla secondary forests,the logging gaps,gap size of 100～150 m2 in general, were usually formed after 7～10 trees logged that were mainly composed of Populus davidiana,Betula platyphylla and Maackia amurensis.PAR,as the dominant factor among microclimate factors in gaps, retarded the growth of height and stem of seedling.PAR peaked in the gap size of 100～150 m2,while air temperature and ground temperature rised with the increasing of gap size. The PAR and temperature in gaps were greater than under closed canopy. PAR at the 1.5 m level over the ground was higher than at the surface of ground,but the temperature and relative humidity in the air were lower than at the surface of ground.The microclimate elements were different in different sites of gap.The maximum PAR occured at north site of gap, with tiptop of relative humidity at west site of gap,tiptop of temperature at center and south site of gap. Litter facilitated obviously the stem growth of seedlings.The elevation of soil PH made a positive effect on the survival and growth of seedlings.With the increasing of gap age,the beneficial impact of TK to seedling species density was tended to decrease but the negative effect on high growth and stem growth of seedlings began to enhance. The litter and content ofTN,TP,TK and SOM in soil had remarkable difference among gaps of different size and age, but without significant difference between gaps and non-gap stands.At the same time,the litter and SOM was obviously different in different position within gaps.The soil seed band reserves had significant difference among gaps of different size and age but decreased with the gap age.The seed band reserve was largest in the gap size of 50～100 m2 and varied evidently in different site within gaps. The seed band was mainly composed of humus layer (0～10 cm) at the initial stages of gap,but litter-fall layer seed bank contributed to total seed band more largely from year to year due to retardarce from litter-fall layer.Species diversity of seed band was greater in gaps than under canopy.The dominant species in the seed bank was made up of Fraxinus mandshurica,Tilia amurensis,Maackia amurensis and Acer mono,which account for 74.3％of all seed numbers.There was no significant correlation between seed band and seedlings within gaps.The regeneration layer was absolutely dominated by the shrub at the initial stage of logging gaps,but the shrub would lose the dominance step by step whereas the advantage of arbor would raise correspondingly with the increasing gaps age. Seedlings growing in the logging gaps had higher density,mean high and mean basilar diameter than in non-gap.The dominance species were mainly composed of intolerant tree species,such as Acer mono,Tlia amurensis,Fraxinus mandshurica and Maackia amurensis,which accorded with soil seed bank.The species and numbers of seedlings was most in gap of 100～200 m2,with best growth and largest species diversity.Therefore,the gaps of about 100～200 m2 should be established through selective cutting in course of management ofpopulus davidiana-Betula platyphylla secondary forests in order to accelerate the regeneration and succession of forest.In the secondary broad-leaved forest, predominated by Tilia amurense, Acer mono and Quercus mongolica,the logging gaps,smaller than 60 m2 mostly,were usually formed after 3～4 trees cut which were mainly composed of Tilia amurense,Quercus mongolica and Maackia amurensis.PAR, as the dominant factor among microclimate factors in gaps, damaged the species density of seedlings.The ground temperature retarded distinctly the height growth of seedling.PAR peaked in the gap size <20 m2,while air temperature and ground temperature were lower in large gaps than in small gaps.The PAR and temperature in gaps were greater than in non-gap stands. PAR at the 1.5m level over the ground was higher than at the surface of ground, but the temperature and relative humidity in the air were lower than at the surface of ground. The maximum temperature occured at south,north and center site of gap,with tiptop of relative humidity at east edge of gaps.TN content in soil decided seedling species density,while TP accelerated the stem growth and TK enhanced the high growth of seedlings.The advantageous function of soil nutrition was weaked with the gap age.The litter and content ofTN,TP,TK and SOM in soil was significant difference among gaps of different size and age,but without significant difference between gaps and non-gap stands. The litter and SOM was obviously different in different position within gaps.The seed band reserve was largest in the gap size of 20～40 m2 and decreased with the gap age.Seed bank reserves had significant difference in different site with in gaps.The variety of species density and individual density of seed was not identical in seed bank.Species diversity of seed band was lower in gaps than under canopy. The dominant species in the seed bank was made up of Tilia amurensis, Tilia mandshurica,Acer triflorum,and Acer tegmentosum,which account for 83.2％of all seed numbers.There was no significant correlation between seed band and seedlings within gaps.In the course of 10a to 14a after gap formed,the seedlings density and species diversity were obviously more in gaps than non-gap stands.The species diversity had a tendency to decline with increasing sizes and ages of gaps,but the dominant species was more standout.The dominance species were different in gaps of different sizes,but were mainly composed of intolerant species,such as Pinus koraiensis,Acer mono,Maackia amurensis,Tilia amurensis and Acer pseudo-sieboldianum,which was out accord with soil seed bank.Seedlings had best growth in gap of 20～40 m2,especially the important value of Korean pine seedlings was maximum in gap of 40～60 m2,which showed that the age size of 40"--60 m2 benefited the regeneration of seedlings.Therefore,the gaps of about 20～60 m2 should be established through selective cutting in course of management of secondary broad-leaved forest in order to accelerate the regeneration and succession of forest. In the broadleaved-korean pine mixed forest, logging gaps, gap size of 100～150 m2 mostly, were usually formed after 5～12 trees cut which were mainly composed of Picea koraiensis, Pinus koraiensis, Quercus Mongolic, Acer pseudo-sieboldianum and carpinus cordata. The interaction among microclimate factors was feebleness and the dominant factor was unobvious. With increasing gap age, The adverse influence of PAR at the surface of ground on seedlings species density and individual density especially tended to increase, however, the damagement of ground temperature to seedlings high growth bated. PAR rised with the increasing gap size, while air temperature and ground temperature were lower in large gaps than in small gaps. The PAR and temperature in gaps were greater than under canopy. PAR at the 1.5 m level over the ground was higher than at the surface of ground, but the temperature and relative humidity in the air were lower than at the surface of ground. The microclimate elements were different in different sites of gap. The tiptop of temperature occured at east site of gap with tiptop of relative humidity at west site of gap. With the increasing of gap age, the advantageous effect of litter on seedlings growth tended to enhance. Rising PH enhanced stem growth but restrained the emergence and survival of seedlings. The litter and content of TN,TP,TK and SOM in soil had remarkable difference among gaps of different size and age, but without significant difference between gaps and non-gap stands. The litter and SOM was obviously different in different position within gaps.The seed individual density in soil seed bank had advantageous effect on seedlings species density and individual density, but The seed species density had negative effect on seedlings species density and individual density, indeed on seedlings growth. The seed band reserve was largest in the gap size of 200～500 m2 and increased with the gap age. Seed bank reserves had significant difference in different site with in gaps. The variety of species density and individual density of seed was not identical in seed bank. The seed band was mainly composed of humus layer (0～10 cm) at the initial stages of gap, but litter-fall layer seed bank contributed to total seed band more largely from year to year due to obstructing from litter-fall layer. The dominant species in the seed bank was composed of Acer mono, Pinus koraiensis, Tilia amurensis and Quercus Mongolic, which account for 73.4% of all seed numbers. There was not obvious difference about species diversity in seed band between gaps and non-gap stands. The regeneration layer, mostly dominated by Pinus koraiensis, Picea koraiensis and Acer tegmentosum, was rich at the initial stage of logging gaps. However, the dominant species would be replaced by Acer pseudo-sieboldianum, Acer mono and Tilia amurensis and the species diversity tended to decrease with increasing gap age. The seedlings growth was best in gap of 300～500 m2 , with largest species diversity in gap of 300～500 m2. The predominance of was much larger under canopy than in gaps. Therefore. the gaps of about 300～500 m2 should be established through selective cutting in course of management of broadleaved-korean pine mixed forest in order to maintain the stability of this type of forest. In addition, the Pinus koraiensis seedlings under canopy should be protected.
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