MATURATION STATUS AND GENETIC IMPROVEMENT EFFECTS ON GROWTH , FORM , AND WOOD PROPERTIES OF PINUS RADIATA CUTTINGS UP TO AGE 12 YEARS

A field trial was initiated in 1986 to evaluate nursery methods for producing aged cuttings of varying physiological age (PA) from stool-beds. Seedlings and cuttings taken from 5-year-old Pinus radiata D.Don seedlings grown in the field were included as controls. Three seedlots of different genetic improvement levels from unimproved bulk seed (GF3) to control-pollinated seed from a seed orchard (GF21) were used to study differences in growth rate, tree form, and wood properties (density and acoustic velocity) between cuttings of five different physiological ages up to 5 years and seedlings, and any interaction between physiological age and levels of genetic improvement. Results showed no persistent long-term height growth differences, and by 4 years of age, any height differences were no longer significant. GF16 and GF21 plants had significantly larger diameters than GF3 plants at both 4 and 11 years of age. Also, seedlings (PA0), and cuttings from 1-year-old seedlings (PA1), had significantly larger diameters than PA5 cuttings from field-grown trees; the cuttings of other physiological ages were intermediate at both 4 and 11 years of age. Physiologically older cuttings had better butt log straightness and freedom from malformation than seedlings and PA1 cuttings. There was no effect of seedlot or physiological age on wood density, up to a physiological age of 5 years. However, acoustic velocity at breast height (as an indicator of stiffness) increased significantly and consistently with increasing physiological age. Previous research has shown that cuttings with a physiological age of 1 to 3 years will perform as well as or better than seedlings on both farm and forestry sites, with an optimum physiological age of about 3 years, when there will be improved stem form without any early loss of growth rate. This trial on a fertile ex-farm site has confirmed these trends and also shown improvement in breast-height acoustic velocity of around 6.4% from PA3 cuttings and more than 11% from PA5 field cuttings, compared with seedlings.