Abstract
Eucalyptus pellita F. Muell. is currently the predominant tree species deployed for tree plantation establishment in some parts of Borneo, particularly Sabah state, Malaysia. Its low disease susceptibility, good growth and form, and desirable wood properties make E. pellita particularly suitable for plantation development in the wet tropical regions of south-east Asia. In spite the many positive traits, practical field observations indicate that the species is susceptible to end-splitting. There is some anecdotal evidence to suggest a genetic relationship with the incidence of end-split, although these observations were not statistically tested. This study evaluates the occurrence of end-splitting in five-year old plantation E. pellita in Sabah as affected by family and growth attributes. An existing progeny tree breeding trial, involving seeds that originated from Papua New Guinea, China, Vietnam, Australia, Sabah, and Sarawak with 106 families, was used to carry out the split assessment. Logs from the second thinning were cut into 2.2-m-long sections. The end splits were measured three days later; the incidence and severity of splitting were assessed at both the large and small ends of each log by using a designated split scoring system. The study shows that 99% of all log cross sections (per cut surface) experienced signs of splitting, with an average of 2.7 splits per cut surface. Overall, 54% of all splits were classed as ‘Three-Quarter Radial Splits’ while the occurrence of internal splits was negligible. Split severity showed a heritable and significant difference (h2 = 0.24 at p ≤ 0.05) among the family levels. Splitting was also significantly related to growth factors such as tree height and diameter at breast height (DBH). The findings suggest that end-splitting is caused by family–environment interactions. This offers the opportunity to improve the wood resource of E. pellita via breeding strategies.
Highlights
Three-Quarter Radial Splits sectional with an average of 2.7 splits perwith cut surface
This study has proven that, apart from the family component, growth characteristics such as tree height and diameter at breast height (DBH) play an important role in influencing the end-splitting of E. pellita
Both family and growth characteristics were the main factors associated with endsplitting
Summary
Muell., known as red mahogany, occurs naturally in the tropical regions of north-eastern Queensland, Australia, and the island of New Guinea [1]. It grows in gentle to moderate sloping terrain mixed with other eucalypt species in tall open forests and at the fringes of tropical rainforests. It prefers sand to loam soil types with good drainage at altitudes from sea level to 800 m above sea level with moderate to high rainfall of 900 to 4000 mm annually. It is one of the few Eucalyptus species that is adapted to the wet tropical climate and less susceptible to fungal leaf
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