Abstract:

The regeneration and plant diversity in different sized gaps and understorey were investigated in a 34-year-old Larix olgensis plantation in 8 years after thinning operated respectively only in gaps and uniformly in a stand. The results showed that saplings of shade tolerant tree species (Juglans mandshurica, Populus davidiana, Ulmus japonica) with height more than 1.5 m were found in gaps rather than understorey in the uniformly thinned stand. Even higher saplings more than 2 m of J. mandshurica was found in relatively large gaps. Simpson diversity index and coverage of woody species in gaps were greater than understorey of the uniformly thinned stand(P<0.05), and the coverage in large gaps was greater than that in small gaps (P<0.05). There was significant difference in the composition of under canopy functional groups. The ranking of importance values of woody competitor species was: large gaps small gaps, and understorey of the uniformly thinned stand, and the ranking of importance values of stress tolerant species was opposite (P<0.05). In large gaps, annual herby species had greater importance value and perennial herby species had lower importance value than those in small gaps and understorey of the uniformly thinning stand (P<0.05). The importance values of weeds in Grime' strategy groups in large gaps were greater than that in small gaps and understorey of the uniformly thinned stand (P<0.05). Our results suggested that gap thinning, combined with uniformly thinning of forests were able to transform the pure L. olgensis into a mixed forest with the larix, and promote natural regeneration and improve plant diversity, and the performances were better in relatively larger gaps (120-150 m²).

Key words: Larix olgensis, plantation forest, close-to-nature transformation, gap thinning, uniform thinning, regeneration, plant diversity