Growth of eight-year-old Eucalyptus regnans families on three sites.  L. A. Pederick and S. J. A. Burke.  December 1985.  23 pp. (unpubl.)

SUMMARY

Variation in diameter, straightness and branch thickness of 21 eight-year-old families of Eucalyptus regnans was examined in replicated progeny trials at sites near Toolangi, Narbethong and Powelltown in the Central Highlands. Variation among the families was greatest at Toolangi and least at Powelltown. The Powelltown trial had been burned on Ash Wednesday 1983 and over two of the six replications lost, which probably reduced the precision of that trial and also reduced differences in the overall results a little.

A majority of the families were stable, i.e. their relative growth rate was similar on the three sites. However, the relative diameter growth of five families did vary from site to site, as determined by statistical tests. Though the five families appeared to interact with site, the general conclusion reached is that genotypes can be used in different sites and localities in the Central Highlands without substantial loss in growth, i.e. with gains of about 7% in volume growth (based on a one in four family selection) as compared to 11% if selection and breeding were localised to one site.

Eleven of the 21 families had been derived from plus trees selected from stands near Noojee in the Warragul Region. Their mean diameter, straightness and branch thickness were no different from those of seven other families from seed sources not selected for superiority. Therefore, a program of species improvement based on using seeds from the eleven Neerim plus trees, i.e. the simple breeding method of mass selection, would have yielded no gains. However, three other families derived from plus trees on APM Forests land in South Gippsland were superior in growth rate to both groups of families mentioned above. This is attributed partly to a provenance effect and partly to prior selection, as the three families had been previously tested in an APM Forests progeny trial in which at four years of age they were among the most vigorous families. It is mainly due to these three families that the above-mentioned gains of 7% and 11% would be possible.

Estimates of heritability for diameter growth, stem straightness and branch thickness were calculated, being 0.06, 0.16 and 0.04 respectively. The value for diameter growth (0.06) is fairly low, and a response to selection and breeding for this characteristic would only be achieved if combined with progeny testing. Straightness appears to be a little more strongly inherited, but branch thickness very weakly inherited. Also, on account of a negative relationship between diameter and branch thickness score, such that faster growing trees tend to produce thicker branches, branch thickness does not appear to be a trait that can be readily improved.

Some estimates of gains achievable from breeding, with progeny testing, were made, based on the data from the trials.