Density and microfibril angle (MFA) of tension wood and normal wood were assessed in the sapwood and heartwood, from three provenanaces of 10-year-old Eucalyptus globulus Labill. Density was measured using a modified saturation method that also enabled the calculation of the extractives lost during saturation. Microdensity and MFA were determined by SilviScan 2, a rapid X-ray densitometry and X-ray diffraction system developed at CSIRO. Significant differences were found in density and extractives between provenances and also density between the sapwood and adjacent heartwood from each provenance. This result may explain some of the drying differences between provenances found in an earlier study (Washusen and Ilic 2000). Sapwood samples with high percentages of tension wood fibres had high density and a significant positive correlation was found between microdensity and tension wood fibre percentage. MFA was found to be very low in normal wood in the sapwood, where most tension wood was found, so tension wood could not be identified by MFA. The positive association between tension wood and wood density suggests that caution should be taken when selecting trees for high wood density in tree improvement programs.
The termiticidal efficacy of sodium octaborate tetrahydrate,
boric acid, borester-7, and tri-methyl borate as
wood preservatives was evaluated after each was
impregnated into seasoned sapwood of Pinus radiata D.
Don and Eucalyptus regnans F. Muell in laboratory bioassay
against Coptotermes acinaciformis (Froggatt).
There was clear difference between the different borate
retentions in treated and untreated blocks, mass loss,
and mortality rate of the termite used in the bioassay
units. After 8 weeks of laboratory bioassay, the results
suggested that borate was toxic to termites even at
0.24% m/m BAE and caused significant termite mortality,
but termites were not deterred from attacking the borate-treated
timber at a higher retention of >2.0% m/m BAE.
These laboratory results indicated that the minimum
borate treatment required to protect timber against termite
attack and damage was >1.0% m/m BAE.