Seedling survival within forest gaps: the effects of gap size, within-gap position and forest type on species of contrasting shade-tolerance in Northeast China

Previous studies on gap regeneration have seldom addressed potential differences due to within-gap position, condition of forest type and within-gap vegetation competition. We excluded understorey vegetation competition, and tested the effects of gap size, within-gap position and forest type on the survival of three species with contrasting shade tolerance by planting seedlings in twelve gaps (four each of small, medium and Large size) created in secondary forests and four small gaps created in Larch (Larix spp.) plantations. In the absence of vegetation competition, the survival of planted seedlings was generally higher in gaps than in forest understoreys despite there being significant differences among species. Light-demanding Juglans mandshurica survived better in Large and medium gaps than in small gaps, and in the gap centre, transition, north edge and east edge than in other within-gap positions. Moreover, seedlings in Larch plantation gaps had higher survival rates than in secondary forest gaps of the same size. Shade-tolerant Picea koraiensis had high survival rates that were not affected by gap size, within-gap position and forest type. Shade-tolerant Acer mono had extremely Low survival rates in all treatments. Our findings suggest that, in addition to gap size, within-gap position and forest type condition should be considered to promote seedling establishment of Light-demanding species during enrichment planting within gaps.