Early regeneration of Fraxinus rhynchophylla in the understorey of Larix kaempferi stands in response to thinning

The effects of thinning were investigated on naturally regenerated Fraxinus rhynchophylla Hance (Korean ash) grown in the understorey of a Larix kaempferi (Lamb.) Carr. plantation, established on a site that previously supported old growth hardwood forests. The regeneration characteristics were evaluated after thinning of the plantation (about 60 per cent of relative density was removed). In the naturally regenerated and mixed stands, Quercus mongolica Fisch. was the most abundant tree species in the overstorey, but the understorey of the thinned plantations was dominated by F. rhynchophylla with six other minor tree species. Fraxinus rhynchophylla was regenerated by four propagation types including natural seedling, stump sprout, root sprout and layering. Before thinning, the difference of average height growth for each regeneration type was insignificant. One year after thinning, the stump sprouts showed the fastest growth among the regeneration types. Height growth of advance regeneration was slow in the year following thinning but then increased rapidly surpassing the other regeneration types 5 years after thinning. Thinning had an effect on the composition of regenerated trees also by seedling, stump sprout, root sprout and layering in the understorey. Advance regenerations occupied the upper understorey at 5 years after thinning. A large number of stump sprouts emerged in the plots 1 year after thinning, while at 5 years after thinning the occupation of stump sprouts decreased. Root sprouts and layers faded away. Considering the early growth and the composition of understorey F. rhynchophylla, its advance regeneration has a high potential to develop into overstorey trees at this site.