Abstract: Eucalyptus U6 and Acacia crassicarpa were mixed planted with different ratios and modes to investigate the growth parameters of the two tree speci
es. In the 2-3 years old mixed plantation, the windthrow of A. crassicarpa decreased markedly with increasing ratio of Eucalyptus U6, the decrement being 26.14% when the Eucalyptus U6/A. crassicarpa ratio was 3∶1, but the survival rates of Eucalyptus U6 and A. crassicarpa had no significant difference under different planting modes. Mixed planting retarded the A. crassicarpa growth to some extent, with the DBH being 90% of that in pure A. crassicarpa stand. The mixed planting had little effects on the height growth of Eucalyptus U6, but promoted its DBH growth markedly, and the beneficial effect increased with increasing ratio of A. crassicarpa. In the 6 years old 1∶1 Eucalyptus U6/A. crassicarpa plantation, the Eucalyptus U6 individuals with DBH>15 cm occupied 32.1%; while in pure Eucalyptus U6 stand, they only accounted for 5.83%. Mixed planting with 2∶1 Eucalyptus U6/A. crassicarpa could obtain a maximum total biomass of 198.8 m³·hm^-2, which was 118.8% of the total biomass in pure Eucalyptus U6 stand, or 169.9% of that in pure A. crassicarpa stand.  Mixture of  Eucalyptus with Acacia would be a good choice to produce Eucalyptus trees with larger DBH.

Key words: Eucalyptus, Acacia, mixed plantation, growth effect, forest region of Northeast China, soil carbon pool, forest type, forest age, spatial variability.