Aboveground Net Primary Production at Acacia mangium Plantation in Northern Vietnam

Net primary production (NPP) is an important index for understanding carbon cycling in forest ecosystems. In this study, aboveground NPP at Acacia mangium plantation was estimated basing on allometry for aboveground biomass increment (ΔM) and litter trap technique for litterfall (Lf). The experiment was conducted in two plots of 300 m2 each (15 × 20 m), established at a 21-month old plantation. Data were collected five times of 3-month intervals in a total duration of 357 days. The results indicated that Lf and ΔM were seasonal-dependent. Litterfall was highest (4.06 g m-1 day-1) during Sep-Jan (late rainy season, early winter) and lowest (1.10 g m-1 day-1) during Mar-Jun (early rainy season, early summer). While, ΔM was highest (13.51 g m-1 day-1) during Jun-Sep (rainy season, summer) and lowest (3.10 g m-1 day-1) during Jan-Mar (dry season, winter). Total Lf in a duration of 357 days was 9.69 tons ha-1 and ΔM was 27.71 tons ha-1, leading to total aboveground NPP of the present study plantation of 37.40 tons ha-1. It is concluded that aboveground NPP of acacia plantation was much higher than other forests of different types and ages around the world. Such difference indicates the importance of acacia plantation in soil nutrient cycling through litterfall decomposition and carbon sequestration through aboveground biomass increment.