Genetic variation and genetic gain for energy production, growth traits and wood properties in Eucalyptus hybrid clones in China

Eucalyptus has become an important genus for pulp wood and veneer wood grown in short rotations in China, and is also a potential resource for energy production. The aim of this study was to estimate genetic parameters, relationships and genetic gains, and to consider the implications for growth and calorific values based on clonal forestry. We assessed growth traits, wood properties, individual tree wood weight and individual tree calorific value for 23 Eucalyptus hybrid clones in China, measured at 8.5 years. There were significant differences in growth traits, basic density, individual tree wood weight and individual tree calorific values between clones, while differences in ash content, extractives content with 1% NaOH, holocellulose content, lignin content and calorific value were not significantly different between clones. Coefficients of genotypic variation ranged from 15.1% to 87.1% for growth traits, and 3.7% to 29.3% for wood properties, and were 24.3% for individual tree wood weight and 25.1% for individual tree calorific value. Repeatability ranged from 0.93 to 0.99 for growth traits, and 0.02 to 0.88 for wood properties, and was 0.90 for individual tree wood weight and 0.90 for individual tree calorific value. The correlations between growth traits and basic density were positive, ranging from 0.00 to 0.29 for genotypic correlations and 0.07 to 0.19 for phenotypic correlations. The genotypic and phenotypic correlations between growth traits and ash content, extractives content with 1% NaOH, lignin content and calorific value were all negative, indicating that the clones of higher growth rates had lower values for wood chemical properties and lower energy value. The selection gains for individual tree calorific value were 65%, 45%, 30% and 11% when the selected number of clones were 5, 10, 15 and 20, respectively. Five E. grandis and E. urophylla hybrid clones were selected based on individual tree calorific value.