SILVICULTURAL TECHNIQUES FOR RESTORING HEADWATER PROTECTION FORESTS IN DA NANG CITY, VIETNAM

Abstract

This study evaluated the effectiveness of selected silvicultural techniques for restoring watershed protection forests in Da Nang city, Vietnam, based on planted-tree growth and changes in vegetation structure over a four-year period. Four groups of treatments were examined: reforestation with native tree species (TRG), assisted natural regeneration with supplementary planting (TBS), forest enrichment planting (LGR), and under-canopy planting of non-timber forest product species (NTFPs). Survival rates of planted species ranged from 65.9% to 93.4%, with most surviving individuals classified as being of medium to good quality. Among the native tree species, Michelia tonkinensis had the highest or among the highest diameter and height growth across the TRG, TBS, and LGR experiments, while several NTFP species maintained relatively high survival rates and plant quality under the forest canopy. On non-forested land, TRG established a mixed-species tree layer, with 545 - 574 surviving trees ha⁻¹ and canopy closure of 0.51 - 0.56 after four years. In existing forest stands, TBS and LGR increased tree-layer species composition and density, basal area, stand volume, canopy closure, and natural regeneration; basal area and stand volume increased by approximately 26 - 33%, regeneration density by 35 - 49%, and canopy closure by 0.09 - 0.12. Under NTFP treatments, canopy closure increased by 0.06 - 0.07, whereas shrub and herbaceous cover increased by 11.0 - 15.5 percentage points, indicating that structural changes occurred primarily in the understory vegetation. The results demonstrate that the effectiveness and pattern of forest structural recovery depend on initial stand conditions and provide a basis for selecting appropriate species and silvicultural techniques for the restoration of watershed protection forests.