Growth Performances of Three Indigenous Tree Species Planted in a Mature Acacia mangium Plantation with Different Canopy Openness under a Tropical Monsoon Climate

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With the aim of establishing silvicultural techniques for tree species indigenous to monsoon tropical areas, we examined the survivorship and growth performance of three tree species under different light conditions. A 23-year-old Acacia mangium plantation was thinned in different ways: group selection thinning (gap creation, 50 m by 60 m in size), 2/3 random selection thinning based on basal area, 1/3 random selection thinning, and no thinning (control). The seedlings of Hopea odorata, H. ferrea, and Xylia xylocarpa var. kerrii were planted in each treatment area with three replications. At 30 months after planting, all species achieved a high survival rate (>90%) in all treatments, perhaps owing to intensive tending in the experimental plots. Both stem thickening and height growth were promoted as light conditions improved: most in the gap plot and least in the control plot for all species. H. ferrea grew to a large height even in dark conditions, suggesting that this species is considerably shade-tolerant. In contrast, X. xylocarpa var. kerrii was light-demanding owing to vigorous growth in the gap plot. The growth of the seedlings seemed to be associated with regeneration patterns in their natural habitats. The group selection thinning seemed to be most suitable for the growth of indigenous tree species.