Abstract:

Experimental plots were established for thinning effects on stand and tree growth,tree species composition,species diversity and soil factors etc. in the mixed larch-spruce-fir stands which originated from planted larch pure forest by observations for 12 years after thinning. Experimental treatments included medium intensity thinning (average removal of 20% of the volume), heavy intensity thinning(removal of 30% of the volume) and control. Results showed that thinning had a significant effect on residual stand growth, but there was no significant difference between medium and heavy thinning treatments. Periodical annual increment (PAI) of diameter, basal area and volume for both whole stand and individual trees showed similar trends, stands with heavy thinning treatments had the highest PAI, stands with medium thinning second, and unthinned stands the lowest. Thinning had no significant effects on total yield in 12 years after thinning. Stand development during the 12 years following thinning was characterized by high mortality in the unthinned stands, which occurred primarily for larch and broad-leaved tree species. The number of ingrowth was very small in all stands, the ingrowth mainly occurred for shade-tolerant tree species such as Spruce, Fir, Korean Pine and broad-leaved tree species. It is recommended to reserve Korean Pine and broad-leaved tree species for current mixed Larch-Spruce-Fir stands to develop towards deciduous Korean Pine forest. No significant differences were detected in tree species composition between thinning and unthinned stands, Therefore, the species composition of Larch, other conifer and broad-leaved tree species with the proportion of 6∶3∶1 maybe stable. Thinning stands with the thinning intensity of about 20% and 30% had no significant effects on species diversity, biomass of shrub and herb, and physical properties of soil. However, species diversity, the biomass of understory shrub and herb, and total porosity and capillary porosity of thinning stands were a little higher than those of control stands.

Key words: mixed larch-spruce-fir stands, thinning, growth, species diversity, physical properties of soil