Genetic variation and gains for two generations of Eucalyptus dunnii in China

One hundred and forty-two Eucalyptus dunnii seedlots including 66 families and 1 bulk seedlot from natural stands, 52 families and 4 bulk seedlots from genetically-improved (first-generation) sources and 1 local plus-tree seedlot were established in trials in Yunnan, China, in 2007 and 2008. These were assessed for growth up at ages 61/2years and 51/2years, respectively. Significant differences (PP<0.01) among seed sources existed in both trials at most ages. The seedlot of local E. dunnii plus-trees proved to be markedly superior for volume over other sources, all of Australian origin, in both trials. On average, exotic improved seedlots outperformed unimproved natural stand seedlots, although in the 2008 trial, tree volume at an age of 51/2years of two natural stand seedlots exceeded that of some improved seedlots. Estimates of heritabilities for individual tree volume ranged from 0.09 +/- 0.07 up to 0.29 +/- 0.16 and genetic correlations between early age (11/2 to 21/2years) individual tree volume and that at final assessment (51/2 to 61/2years) ranged from 0.29 +/- 0.12 to 0.89 +/- 0.22. Heritabilities and correlations generally increased with age, but progressive within-plot thinning may have biased estimates of genetic parameters beyond the early assessments. The best seed orchard seedlot in each trial offered modest stem volume gains over natural stand seeds ranging from 11% to 13%. Markedly higher gain, an additional 25%, could be obtained by using seedlots of only the best seed orchard families. Genetic gains in tree volume estimated for future seed orchards developed from the trials ranged from around 8% up to 27%.