Growth Rates And Bole Growth
Modest growth rates are reported for teak plantations. Under favorable conditions in early life, a plantation may exhibit growth rates of between 10 and 20 m3 per hectare per year. However, growth falls to the general reported level of 4 to 8 m3 per hectare per year as the plantation ages (Htwe, 1999; Cao, 1999). On the best sites in Myanmar and India, 50-year-old plantations exhibit heights of 30 m and diameter at breast height (DBH) of 60 cm. Some growth parameters for teak grown in Malaysia are shown in Table 2.
|TABLE 2. Performance of teak at Mata Air Station, Perlis, Malaysia|
Long rotations in teak plantations appear essential if the high potential value of the heartwood is to be realized. Studies in India found that the heartwood content of 51- to 52-year-old trees was 77 percent, whereas for eight-year-old trees it was only 30 percent (Bhat, 1997). The same studies also showed a positive correlation of heartwood percentage with ring width (0.73) and with DBH (0.46), indicating that faster growth rates were associated with higher heartwood content and, by implication, higher-value timber. These results suggest that longer rotations are necessary for producing high-value logs but that faster growth rates may be benafical to the value of the timber. As plantation wood has become more common the acceptance and demand for sapwood has been increasing. The rate of growth of wood can slow considerably after 30 to 35 years so optimum harvest time for maximum economical yield is between 25 and 35 years.
The phenomenon of fluting (irregular involutions and swellings) in the teak stem has been observed in a number of plantations. In an international provenance trial the mean heritability value of stem straightness was found to be 0.83, indicating that the character for stem straightness is strongly controlled by provenance and is thus genetically inherited (Kaosa-ard, 1999). Hence, fluting can be minimized if the appropriate provenance is used in breeding trials to produce plants that exhibit straight stems.
The most important form characteristic determining the value of teak logs is the length of the clear bole, which is determined by the timing of flowering. Flowering - representing the transition from production of vegetative structures only to the production of reproductive structures - occurs in response to certain environmental signals. Flowering by the terminal shoot is then immediately followed by the initiation of the whorl of branches. Selection for late flowering seed stock has been suggested as a means of maximizing the duration of the vegetative period, also the management strategies as discussed below are generally employed to maximize the length of the clear bole.