Objective   In order to clarify the changing trend of heartwood and sapwood amount during the development of Eucalyptus cloeziana heartwood, and to provide scientific basis for the cultivation of large-diameter E. cloeziana and efficient use of wood, the variation of heartwood and sapwood, stem cross-sectional peeling diameter and height of E. cloeziana at different-aged was investigated.

  Method   5-, 17-, 29- and 35-year-old E. cloeziana were used to determine the stem cross-sectional peeling diameter, peeling radius, heartwood radius and sapwood width in four directions of east, west, south, north. Besides, the regression equation of heartwood and sapwood amount and tree age, stem cross-sectional peeling diameter, tree height was established to analyze the axial and radial variation patterns of heartwood and sapwood E. cloeziana.

  Result   The heartwood radius and heartwood area increased with the tree age, while the width of sapwood varied greatly between 5 and 29 years, but the sapwood area didn^,t change significantly with tree age. There was no significant difference in the area of sapwood between different tree ages (P > 0.05), and there were differences in the radius of heartwood, the area of heartwood and the width of sapwood (P < 0.05). The amount of stem cross-sectional heartwood increased with the increase of stem cross-sectional peeling diameter, but the amount of stem cross-sectional sapwood was weakly correlated with stem cross-sectional peeling diameter. When the stem cross-sectional peeling diameter was about 4.66 cm, E. cloeziana began to form heartwood, and then the diameter of trunk stem cross section grew by 1 cm, the heartwood radius increased by about 0.52 cm. The heartwood radius, heartwood area and sapwood area of E. cloeziana of each tree age decreased with the increase of tree height, the largest at the base of the tree, and the sapwood width decreased when the tree height was 1.0−5.3 m. There was a certain fluctuation, which was relatively constant above the height of 5.3 m.

  Conclusion   The amount of heartwood is significantly positively correlated with tree age and stem cross-sectional peeling diameter, and negatively correlated with tree height. The study suggests that the 35-year-old E. cloeziana still has great growth potential and can be further cultivated for the large-diameter E. cloeziana.