Recovery process of a mountain forest after shifting cultivation in Northwestern Vietnam
2010
Van Do, Tran | Osawa, Akira | Thang, Nguyen Toan
The recovery process of fallow stands in the mountainous region of Northwestern Vietnam was studied, based on a chronosequence of 1-26-year-old secondary forests after intensive shifting cultivation. The number of species present in a 26-year-old secondary forest attained 49% of the 72 species present in an old-growth forest. Total stem density decreased gradually from 172,500ha⁻¹ in a 3-year-old forest to 24,600ha⁻¹ in the 26-year-old stand, but stem density of larger trees (diameter at breast height (D)≥5cm) increased from 60ha⁻¹ in a 7-year-old to 960ha⁻¹ in the 26-year-old forests, which was similar to that of an old-growth forest. Annual biomass increment of the 26-year-old stand was 4.2Mgha⁻¹ year⁻¹. A saturation curve was fitted to biomass accumulation in secondary forests. After an estimated time of 60 years, a secondary forest can achieve 80% of the biomass of old-growth forests (240Mgha⁻¹). Species diversity expressed by Shannon Index shows that it takes 60 years for a secondary forest in fallow to achieve a plant species diversity similar to that of old-growth forests.
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