The study results of 73 gaps in the broad leaf evergreen forest states of Xuan Son National Park detennined that mean gap area fluctuated from 112.4 m2 to 168.3 m2. Gaps derived from naturally dead trees and those with the area under 100 m2 were dominant. The tree regeneration composition in gaps was diverse, ranged from 43 to 85 species; however, there were only from 2 to 5 species appearing in the tree species composition formula. Regeneration density ranged from 8,800 stems/ha to 12,533 stems/ha. The rate of good quality regenerating trees was from 77.3 percent to 86,7 percent and they were mostly originated from seed. The rate of advanced regeneration (height or = 2.0 m) in gaps accounted for from 25.28 percent to 38.07 percent of overall regeneration density, with from 29 to 54 in species richness and from 4 to 6 species appearing in the tree species composition formula. The regenerating tree species richness in gaps was from 36.2 to 67.1 percent similar to the canopy tree species richness in surroundings, and the similarity index fluctua.ted from 0.45 to 0.61. For the species richness of the advanced regenerating tree layer in gaps, this similarity was from 25.7 percent to 52.9 percent, and the similarity index ranged from 0.35 to 0.60.
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