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stated that the highest peak development on the tree stem was found at the middle part of the crown.
Diameter increments at all sections of the dominant trees were greater than those of the co-dominant trees (Table 2). In similar studies, it was determined that dominant trees displayed more diameter increase than co-dominant trees (Boncina et al., 2007; Medhurst et al., 2001; Smith et al., 1997). This can be explained by the fact that the dominant trees had developed better crowns and therefore, had received more benefit from light and also because they had developed a better root system to reach more water and nutrients. Assmann (1970) indicated that the dominant trees in a plot secured more solar energy and had higher levels of photosynthesis and growth (Nyland, 1996).
According to this study, when each stem class was compared to its own control treatments, the relative response of the co-dominant trees to heavy thinning was higher than that of the dominant trees (Table 3). Since the co-dominant trees exhibited smaller diameter increments in the control plots than did the dominant trees, the increments of the co-dominant trees in the heavily thinned plots appeared to be relatively higher. In the control treatment, the diameter increments in the dominant trees were greater than those of the co-dominant trees because the dominant trees were less affected by light competition. It can be said that in dominant trees, the diameter increments are more prominent due to the competition for water and plant nutrients rather than for light. In the soil moisture measurements made at this site it was determined that in the summer, the amount of water in the soil was higher in the thinned plots than in the control plots (Çiçek et al. 2010).
The fact that the thinning intensity × cross-section height interaction did not significantly affect the diameter increment demonstrated that the diameter increments at different cross-sectional heights were parallel in all treatments. Therefore, the influence of thinning on the diameter increment at each section height was similar to the effect on the d1.30 increment. The fact that the stem diameter increments at 1.30-11.30 m, which are more important in commercial terms, were similar suggests that, according to the seven-year results, heavy thinning did not cause tapering in the stem. Consequently, subject to further research, heavy thinning can be recommended in NLA plantations.
The seven-year results achieved with this study may not provide sufficient information on how thinning in the NLA plantations affects the diameter increments along the stem. The results of thinning may vary from species to species and depending on growth environment and stand characteristics. The results obtained in this study can be assessed by comparison with longer duration thinning treatments performed in NLA plantations having different ages and characteristics.
Adegbeihn, J., 1982: Preliminary results of the effects of spacings on the growth and yield of Tectona grandis Linn. F., Ind For, 108(6): 423-430.