Spatial patterns of oak (Quercus crispula) regeneration on scarification site around a conspecific overstory tree

•Scarification treatment was a successful aiding practice for oak regeneration.•Spatial pattern of oak regeneration changed among stages of early establishment.•In the initial stage, a location beneath the crown provided favorable conditions.•In contrast, at sapling stage, a location outside the crown became more favorable.•The distance dependencies should be considered to develop oak regeneration practices.

Spatial patterns have been a major topic regarding natural regeneration of oak species, but the effects may differ considerably in sites subjected to intense forestry practices, which greatly alter many aspects of site conditions. We examined the hypothesis that the regeneration of oak (Quercus crispula Blume) following scarification (displacement of inhibiting vegetation and surface soil using machinery) is enhanced at a certain distance from a conspecific overstory tree, depending on the stage of development. We conducted both field surveys in scarification sites with different stand ages (1-16 year-old) and a laboratory seeding experiment to clarify factors contributing to its early establishment. The results demonstrate that the spatial relationship between the regeneration of oak and the conspecific overstory tree at scarification sites changes considerably among stages of the establishment. In the initial stage (0-1 years after the scarification), a location beneath the crown provided favorable conditions, whereas at subsequent stages (2-4 years), the distance-dependent effects were unclear, until eventually (8-16 years) a location outside the crown became more favorable. The condition produced by the scarification was basically competition-free and resource-rich, but it can also be harsh for acorns and small seedlings, imposing a requirement for shading to moderate the environment in the initial stage. Such an effect of facilitation was found also in the later (sapling) stage via the existence of neighbors of the other regenerated fast-growing species. The current findings supported the effectivity of a shelter-wood system, in which the regeneration starts from shaded condition followed by a gap status created by a successive felling. The area away from the conspecific crown would have a potential if acorns are plentifully supplied (e.g. by direct seeding) and they withstand the initial negative factors at the initial stage of development.