Promoting reforestation through supplementing native forest tree species in northwestern Vietnam

Forest enrichment and/or supplement planting is a silvicultural technique to improve number of valuable trees in natural poor forests. In this study, two native species including Canarium album(Lour.) Raeusch and Cinnamomum obtusifolium(Roxb.) Nees were planted in fallow stands by two experiments as planting in clear band of 6 m wide (band planting) and in canopy gaps of >200 m2(cluster planting). The results indicated that planted trees of both species in both planting experiments had high survival rates (>89%) after planting three years, and more than 75% survival trees had good quality as straight boles without diseases. The difference of stump diameter and stem height between experiments and species was statistically significant. C. obtusifoliumin band planting had biggest stump diameter (2.86 cm), while C. albumin band planting had tallest stem height (2.69 m) after planting three years. C. obtusifoliumhad significantly larger crown diameter in band planting (1.09 m) than that in cluster planting (0.92 m). While it was conversely found in C. albumas significantly larger crown diameter was found in cluster planting (1.12 m) compared to smaller one in band planting (0.96 m). It is concluded that silvicultural techniques are required to promote growthof planted trees after planting three years, especially for C. albumas it requires more sunlight at this age. The techniques must focus on opening forest canopy for sunlight reaching crown of planted trees and on removing bad-growth trees surrounding planted trees to minimize competitions.