Abstract:

Objective: The growth and variation characteristics of heartwood and sapwood,ring number of heartwood,and height of heartwood in different-aged teak (Tectona grandis) plantations in Daqing mountain of Guangxi were investigated,so as to provide scientific basis and basic data for understanding the developmental characteristics of heartwood,predicting heartwood quantity and efficiently cultivating high-quality and large-diameter teak target trees in this region. Method: Average trees from 10,18,31 and 41-year-old teak plantations in Daqing mountain of Guangxi province were selected to analyze variation of heartwood and sapwood among orientations and among individual trees using variance analysis,and the regression model between amount of heartwood and sapwood,cross-sectional diameter,and total number of annual rings were fitted by curve estimation method to study the growth variation of teak heartwood and sapwood. Result: The heartwood radius of teak trees was the largest in the north direction,while the sapwood width was the largest in the north and the east directions,and there were no significant differences in the heartwood radius and sapwood width among four stem orientations at the same age (P>0.05). The heartwood radius,heartwood area and sapwood area decreased with tree height regardless of ages. The sapwood width was relatively larger at the base of the trunk (0-1 m) and remained constant in a certain area. With the increase of forest age,the amounts of sapwood and heartwood increased in the four forests,and there was no significant difference in sapwood width (P>0.05),however there were significant differences in heartwood radius,heartwood area and sapwood area among forest ages (P < 0.01). The cross-sectional heartwood and sapwood increased with the increase of the cross-sectional diameter and the total number of annual rings,among which the influence of stem cross-sectional diameter was higher than that of the total number of rings,and the total number of annual rings had a great influence on the early development of heartwood. There was relatively large tree-to-tree difference in the amounts of sapwood and heartwood,as well as the maximum heartwood height of teak trees for the same forest age,in which the degree of variation in the areas of heartwood and sapwood was similar,and the degree of variation in the heartwood radius,the sapwood width,and the disappeared maximum height of the heartwood were also similar to each other. Teak began to form heartwood at the age of four years. The number of heartwood rings of different ages increased with the increase of the total number of annual rings. The total number of annual rings accounted for more than 80% of the variation in the number of heartwood rings. The annual growth rates of 10-,18-,31-and 41-year-old teak trees were 0.9 ring,0.7 ring,1.0 ring,and 1.0 ring,respectively. The maximum height and relative height of heartwood were positively correlated with forest age,with the increase of forest age,the heartwood disappeared at a higher position of the trunk. Conclusion: The initial age of heartwood formation of teak trees was 4 years,which was a tree species with early heartwood formation. Within each forest age,the orientation had little effect on the heartwood and sapwood of teak trees. The heartwood radius,heartwood area,sapwood area and maximum heartwood height increased significantly with the age of teak trees,while the heartwood width did not change significantly. The cross-sectional diameter could better explain the variation in the amounts of sapwood and heartwood,and the total number of rings only explain the variation in the amount of heartwood prior to 31-year-old teak trees. According to the study,41-year-old teak heartwood still has great growth potential,and longer cultivation is needed to reach the goal of high-quality and larger-diameter teak trees.

Key words: Tectona grandis, forest age, growth, heartwood, sapwood