| Summary: | 碩士 === 國立嘉義大學 === 林業研究所 === 90 === Two different types of the Taiwania trees were compared. One was grown without the cultural and thinning treatments (tree A) and the other was grown with both treatments (tree B). It is intended from this study to provide critical information for future improvement in the forest management and in the wood processing technology by measuring the basic properties e.g. the ring width, the autumn wood percentage, the heartwood percentage, the tracheid length, the shrinkage rate, the fiber saturation point and the dielectric property of the trees.
The two Taiwania sample trees (tree A and B) were selected from 34-year artificial stands in the Shitou Working Station of the National Taiwan University. The wooden material specimens, each two meters in length as sections, were cut from base to top. Fourteen and thirteen sections were obtained from tree A and B, respectively. Each section of the wooden material was then used to measure the above-mentioned properties. The result is shown as follows
1)The fiber saturation point (F.S.P) increases gradually from pith to bark.
2)The tangential and radial shrinking percentages are smallest near pith and increase gradually in other parts of the trees.
3)Based on the method of intercept, the average F.S.P. value for tree A and tree B is 27.9% and 28.7%, respectively. However, based on the extrapolation method, the average F.S.P. value for tree A and tree B is 29.8% and 30.4%, respectively. The F.S.P. value from the method of intercept is 2-3% lower than that from the extrapolation method.
4)The dielectric constant, e’, along the three specific cut surfaces (cross cut (C), radial cut (R) and tangential cut surfaces (T)) varies with frequency. Usually, e’ is larger near pith and gets smaller close to bark. The dielectric power factor is larger near base and decreases toward top.
5)The dielectric property along the three specific cut surfaces (C, R and T) is shown as follows:
(1) For dielectric constant, C>R>T.
(2) For dielectric power factor, C<R<T
(3) For resistivity, C<R<T.
(4) For loss modulus, C<R<T.
6)The dielectric constant, e’, increases with the moisture content in wood. Therefore, in the high frequency heating, the electric energy can be converted more efficiently to heat for wood of higher moisture content.
7)The tracheid length (T) along the transverse direction can be expressed mathematically as follows
T = b+a (log x)
where x is the number of growth ring from pith as soon as the tree is mature. For tree A, x is 25 years. For tree B, x is 27 years.
8)Experimentally, tree A and tree B mature roughly around 24-26 years based on the transverse growth. Based on the longitudinal growth, the tree below 48-54% of its height is mature.
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