Wood Properties of Pinus caribaea hybrids in Queensland

Paul G Toon

doi:10.25907/00330

This thesis has been presented in two parts. In part one (Chapter 2), several wood properties, considered to be important to utilisation, of new Pinus caribaea hybrids are compared to the current plantation taxon; and in part two (Chapter 3), the intra-clonal variation for extracted basic density, growth traits and stem straightness, of a commercially deployed P. elliottii var. elliottii x P. caribaea var. hondurensis hybrid clone is investigated. Resin-extracted basic density and grain angle are two wood properties that influence structural timber quality. These properties and percentage heartwood, percentage latewood and bark thickness were measured in current plantation species and new hybrids using 10 and 13-year-old trees at four distinct sites. The hybrids have shown superior growth and form and their future deployment depends on their wood properties. The main objective was to compare the hybrid P. caribaea var. caribaea x P. caribaea var. hondurensis with P. caribaea var. hondurensis. For grain angle, there were no significant differences at the 5% level between the hybrids and the plantation species at any of the test sties. At the three sites where P. caribaea var. hondurensis is the plantation taxon, the densities of all the taxa were similar except for P. caribaea var. caribaea that was significantly higher at the 5% level, possibly due to development of reaction wood resulting from generally poor stem straightness. The heartwood percentage of P. caribaea var. hondurensis was less than 2% at all sites, with the P. caribaea var. caribaea x P. caribaea var. hondurensis hybrid significantly lower, at the 5% level, at two sites. Due to difficulties in clearly determining the latewood zone of the annual growth ring, only 3 selected trees/taxon/site were measured and no tests of significance were performed due to the small sample size. Generally the P. caribaea var. caribaea x P. caribaea var. hondurensis hybrid had a higher percentage of latewood than P. caribaea var. hondurensis, but was more similar to P. caribaea var. hondurensis parent than the P. caribaea var. caribaea parent. The P. caribaea var. caribaea x P. caribaea var. hondurensis hybrid and P. caribaea var. hondurensis bark thickness was not significantly different at the 5% level. The wood properties of the P. caribaea var. caribaea x P. caribaea var. hondurensis hybrid recorded in this study are of no practical difference to those of pure P. caribaea var. hondurensis and should therefore produce similar timer products. The P. elliotti var. elliotti x P. caribaea var. hondurensis hybrid had the highest density where it is the currently deployed plantation taxon. A commercially deployed P. elliotti var. elliotti x P. caribaea var. hondurensis hybrid clone was sampled in a routine planting. The difference between blocks representing site differences across a 2.5 ha planting was significant at the 5% level for extracted basic density, growth traits and stem straightness. Therefore, matching clones to the site types through extensive testing for expression of low variation in wood properties, growth and stem straightness appears a potentially important strategy to maximise uniformity in clonal plantations of sub-tropical pines.

Wood Properties of Pinus caribaea hybrids in Queensland

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