The Cultivation Technique For Knot-free Timber Production Of Chinese Fir (Cunninghamia Lanceolata)

Chinese fir [Cunninghamia lanceolata Lamb. (Hook.)], a traditional timber welcome by the people in Fujian Province, is facing the problem of selling. So, to cultivate new kind of timber is also an important measure to increase the price of Chinese fir timber. In recent years, along with the development of economic and living standard of the people, the demands for variety and quality of timbers are increasing. So far, the techniques for Chinese fir knot-free timber production have not been studied. So, trial sites were established in 2 sites: Yangkou State Forest Farm, and Weimin State Forest Farm in Fujian Province. Different pruning intensities (6 cm, 8 cm, 10 cm and 12 cm) for knot-free timber production and their control (non-pruning) on tree growth, stem shape, soil fertility and understorey plant biodiversity indices were studied and compared. The results showed that:1. The experiment was started in December 1999, and the plantation (planted in the spring of 1996) was 4 years old. There was no significant difference in tree growth before the treatments among the plots that were to be treated with different pruning intensities.2. Pruning was carried out once a year. Five years after the treatments (at 10 years of age), tree height, diameter at breast height (DBH) and single-tree volume of pruned trees decreased with increasing pruning intensities, but the height to the lowest living branch increased with increasing pruning intensities. At Yangkou site, tree height of the 12 cm-intensity pruned tree (11.31 m) was the highest, while that of the 6-cm intensity pruned tree (10.47 m) was the lowest. Differences in tree height of pruned trees among different pruning intensities were not statistically significant (P>0.05).At Yangkou site, DBH of pruned tree of the 12 cm-intensity (16.84 m) was the highest, followed by that of the 10 cm-intensity (16.20 cm), and that of the 6 cm-intensity (14.47 cm) was the lowest. DBH of pruned tree treat with 12 cm intensity was 2.37 cm (16.38%) higher than that treated with 6 cm intensity. At Yangkou site, differences in DBH of pruned trees between 6 and 10 cm intensity and 6 and 12 cm intensity were both significant. At Weimin site, except for no significant difference in DBH of pruned trees between 10 and 12 cm intensity, the differences in DBH of pruned trees among difference intensities were significant.At Yangkou site, single-tree volume of pruned tree of the 12 cm intensity (0.12973 m~3) was the highest, followed by that of the 10 cm intensity (0.12040 m~3), and that of the 6 cm intensity (0.09194 m~3) was the lowest. Single-tree volume of pruned tree treat with 12 cm intensity was 0.03719 m~3 (41.1 %) higher than thattreated with 6 cm intensity. Difference in single-tree volume of pruned trees between 6 and 10 cm intensity and 6 and 12 cm intensity were both significant.