Abstract: An investigation was made on the biomass- and energy allocation in 1-4-year-old  Eucalyptus urophylla×Eucalyptus tereticornis plantations at Beipo Forest Farm of Suixi County in Guangdong Province. Stand age had significant effects on the retained biomass of the plantations (P＜0.01). The biomass was in the range of 10.61－147.28 t·hm^-2. Both the total biomass and the biomass of above- and belowground components increased with increasing stand age. The proportions of leaf , branch and bark biomass to total biomass decreased with year, while that of stem biomass was in reverse. The biomass allocation of the components in 1- and 2- year-old plantations decreased in  order of stem＞branch＞bark＞root＞leaf, and that in 3-  and 4-year-old plantations  was in  order of stem＞root＞branch＞bark＞leaf. The mean ash content (AC) of the five components at different stand ages ranged from 0.47% to 5.91%, being the highest in bark and the lowest in stem. The mean gross caloric value (GCV) and ash free caloric value (AFCV) of different components ranged from 17.33 to 20.60 kJ·g^-1 and from 18.42 to 21.59 kJ·g^-1 respectively. Of all the components, leaf had the highest GVC and AFCV, while bark had the lowest ones. Stand age had significant effects on the GVC   of branch, stem,and bark, and on the AFCV of leaf, stem, and bark (P＜0.05), but the effects on the GVC of leaf and root, the AFCV of branch and root, and the GVC and AFCV of individual trees were not significant (P＞0.05). The retained energy of 1-4-year-old plantations ranged from 199.98 to 2837.20 GJ·hm^-2, with significant differences among the stand ages (P＜0.01). The retained energy of various components and plantations increased with stand age, and the energy allocation of various components had the same trend as biomass allocation.

Key words: stand age, Eucalyptus urophylla×Eucalyptus tereticornis, biomass, caloric value, energy, Astragalus membranaceus var. mongholicus, chemical composition, inorganic element, climatic factor.