Study On Eucalypt Clones For Plywood Superior Variate Selection

Nowadays, there is a severe shortage of timber sources in our country, and the contradiction of supply and demand has become apparent. The industry of plywood has been growing rapidly over the past five years, the production increased at an average of 63 percent a year, however, it was hard to keep up with market demand. In addition, the sale of plywood timber was according to average small end diameter of log, this method lacked examination and standard, so it was not adequately show the suitable use of wood. As for planter, they were paying attention to unit area value of plywood, however, the veneer recovery ratio and value of unit volume were cared by enterprise. The price depends on the quality, and wood value depends on veneer recovery ratio and quality. At present, several studies showed that knot and sweep were major factor of influencing veneer recovery ratio and timber quality, but all have not did systematic and in-depth study. As strategic tree species of souther fast-growing and high-yield forest, eucalyptus timbers have much more differences in wood properties between clones. Therefore, it is aim to silviculture plywood timbers with high veneer recovery ratio and excellent veneer quality, a burning question is enhancing veneer recovery ratio and quality through selecting clone possessing superior genetic material.This paper took eleven 5-yr-old, ten 6-yr-old, one 11-yr-old and one 9-yr-old eucalypt clones for materials, making study on growth characters and wood properties of stand tree, log external features, veneer recovery ratio and quality grades, finally getting results as following:(1) There were very significant differences on DBH, HT, bark thickness and individual volume among eucalypt clones of eleven 5-yr-old and ten 6-yr-old, this proved these four traits indexes possessed large selective potential, and the difference of bark thickness is larger than others. The individual volume orders of eleven 5-yr-old eucalypt clones from high to low is DH201-2, GL9, EC33, LM1, EC48, DH32-22, LH1, EC40, U6, EC42, TM3. The individual volume orders of ten 6-yr-old eucalypt clones from high to low is GL4, GL9, DH32-22, LH5, EC34, M1, UC184-1, DH201-2, LH1, SH7, and the E.urophylla×E.grandis ranked at the top of all clones.(2) There were very significant differences on wood density and MOE among eucalypt clones of eleven 5-yr-old and ten 6-yr-old, but growth strain had no significant differences among them. As for 5-yr-old eucalypt clone, there was much more difference on MOE, which showed that wood density and MOE had great selective potential, so according to silviculture aim, it was probable to elect clone with certain wood density and MOE. Oppositely, the differences of MOE between 6-yr-old eucalypt clones was less than wood density, this was not similar with 5-yr-old eucalypt clones, and this phenomenon maybe result from different species of clones. There was no significant difference on growth strain between clones, in addition, the variable coefficients were great among clones, so it was concluded that great differences of growth strain existed between each tree within clone.(3) Sweep was the most important factor of reducing veneer recovery ratio and value, and sweep increased 1 per cent would result in 3.9 to 10.5 per cent of veneer recovery ratio declining, in the next place, taper was also playing a quite important role in reducing veneer recovery ratio, it was one of the factors influencing veneer recovery ratio. Through analysis on log external features, results showed that sweep and taper had no significant differences among eucalypt clones of eleven 5-yr-old and ten 6-yr-old, so when selecting or improving sweep and taper, it was necessary to pay attention to the fine difference. At the same time, there were no significant differences on knot number and large end circularity among eleven 5-yr-old eucalypt clones and on small end diameter, knot number and large end circularity among ten 6-yr-old eucalypt clones. But the other log external features of 5-yr-old and 6-yr-old eucalypt clones showed significant differences, but they mad little sense to select veneer wood.(4) As for four ages of eleven 5-yr-old, ten 6-yr-old, one 9-yr-old and one 11-yr-old eucalypt clones, dead knots within all veneer external defects were the most essential factor of debasing veneer quality grade, and then splitting and holes also had significant effect on veneer quality grade.(5) Among main factors deciding veneer recovery ratio and value, as for 5 or 6-yr-old eucalypt wood, individual volume plaied a leading role and accounted for 58.9 percent, in the next place, sweep and taper also had an effect on veneer recovery ratio and value and accounted for 41.1 percent. Contrarily, as for 9 and 11-yr-old eucalypt wood, individual volume was still at the top place of deciding veneer recovery ratio and value, and seconder were sweep and taper. However, the importance of individual volume of 9 and 11-yr-old eucalypt clones was inferior to that of 5 and 6-yr-old.(6) The clones of EC33, DH32-22, LM1, GL9 possessed higher value of developing plywood than other 5-yr-old eucalypt clones, and also the clones of GL4, DH32-22, EC34, GL9 had greater potential as plywood lumber than other 6-yr-old eucalypt clones.(7) The non-destructive evaluation techniques including Pilodyn, Fakopp and CIRAD-Forest Method were disable to predict veneer recovery ratio and value of 5 or 6-yr-old and 9 or 11-yr-old eucalypt clones indirectly, but they could make evaluation to a certain degree by prediction to individual volume.