Recent years, the development of national reports on greenhouse gases (GHGs) emissions is compulsory for nations that have been involving in as a member of United Nations Framework Convention on Climate Change (UNFCCC). Forest biomass, which is known as an important factor in GHGs inventory programs, can be calculated by different methods. One of the most common methods recently used are the use of biomass expansion factor (BEF) to estimate the forest biomass. Nowadays, in Vietnam, there have been few researches on BEFs, which are used to convert wood volume to forest biomass. The researches have not yet met the requirement on biomass estimation of GHGs inventory programs at national levels. The purposes of this study were to calculate BEFs and develop allometric equations which were based on the data of destructive trees between BEFs and DBHs of tree individuals of some popular plantations including Acacia hybrid, Acacia mangiwn, Pinus merkusii and Pinus massoniana. Research results showed that there was a gradually declining trend of BEFs by ages and that the higher the stand ages were, the more stable the BEFs' values became. The highest mean biomass expansion factor, which showed the lowest value (0.889 Mg/cm3) in Acacia hybrid plantations, of Pinus merkusii ones wass 1.314 Mg/cm3. Furthermore, research results also showed that there were significant differences between BEFs at different age classes of the same plantations (Sig 0.05). Results on the developed allometric equations between BEF and DBH showed that fluctuations in correlation levels of different species were true and depended on function types which were used to simulate the relationships between BEF and DBH. The established allometric equations statically existed and can be applied widely to calculate BEFs for a specific age of plantations.
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