Biomass accumulation of Acacia hybrid plantation across ages and site indexes in Yen Bai province, Vietnam

Abstract

The study was conducted in two districts of Luc Yen and Yen Binh, Yen Bai province to determine the biomass characteristics of Acacia hybrid (Acacia auriculiformis  Acacia mangium) plantations across ages and site indexes. A total of 56 representative plots of 500 m 2 (20  25 m), 280 subplots of 16 m 2 (4  4 m) and 280 basic plots of 1 m 2 (1  1 m) were established to measure growth of all trees, determination of biomass of understory vegetation and litter fall (including dead wood) of Acacia hybrid plantations. Accordingly, 56 sample trees were destructed to determine the biomass of each tree components of the individual tree, including stem, branches, leaves, bark, and roots. Research results show that there is a very close correlation between dry biomass of Acacia hybrid individual trees and its DBH (D1.3), in which, the Power function (Y = a  X^b) is the be form of simulation function to use for estimating dry biomass of Acacia hybrid trees. Total dry biomass of individual Acacia hybrid trees ranges from 3 to 105 kg/tree, corresponding to the age of 1 - 7 in site index I; 1.8 -67 kg/tree in soil index II; 1 - 56 kg/tree in soil index III; and 0.7 - 35.2 kg/tree in soil index IV. On average for all 4 soil indexes, the biomass of Acacia hybrid trees concentrated mainly in the stem (accounting for 46.37%), followed by the roots (accounting for 18.6%), branches (accounting for 16.4%), leaves (13.1%) and the lowest in bark (5.6%). Total dry biomass of Acacia hybrid entire stand ranged from 8.9 to 138.1 tons/ha, equivalent to age 1 - 7 in soil index I; from 9.6 to 93.3 tons/ha in soil index II; from 4.1 to 76.5 tons/ha in soil index III; and from 7.7 to 50.1 tons/ha in soil index IV. In which, biomass is concentrated mainly in the high tree layer - Acacia hybrid (average 76.5%), followed by litter fall + dead wood (14.5%) and the lowest is in understory vegetation (accounting for 9%) of the total biomass of the entire stand