Abstract:
Eucalyptus nitens is an important forestry species
grown for pulp and paper production in the temperate,
summer-rainfall regions of South Africa. A tree improvement
programme has been ongoing at the Institute for Commercial
Forestry Research for two decades, but genetic improvement
in the species has been slow due to delayed and infrequent
flowering and seed production. Three trials were established,
firstly, to quantify the gains that have been made in the first
generation of improvement in the breeding programme and,
secondly, to establish whether a number of seed source and
orchard variables influence the performance of the progeny.
These variables were the amount of flowering trees in the seed
orchard, year of seed collection, seed orchard origin and
composition of seed orchard bulks. Diameter at breast height
and tree heights were measured in the trials at between 87 and
97 months after establishment, and timber volumes and survival
were calculated. Improved seed orchard bulks performed
significantly better (p<0.01) than unimproved controls in the
field trials. Genetic gains ranging from 23.2 to 164.8 m3ha−1
were observed over the unimproved commercial seed. There
were significant differences (p<0.01) in progeny growth between
the levels of seed orchard flowering, with higher levels
of flowering (≥40 %) producing substantially greater progeny
growth than lower flowering levels (≤20 %). The seed orchard
had no effect on progeny growth in this trial series. This
suggests that seed collected from any of the four seed
orchards tested will produce trees with significant improvement
in growth.
