Wood production and economic gains from the use of seed orchard stock in radiata pine plantations in New South Wales

Summary

Basal area (BA) and projected volume growth were compared for trees from routine genetically unimproved seedlots and a first—generation seed orchard (Green Hills) seedlot of radiata pine, planted in progeny tests on two sites in New South Wales. Trees were assessed at ages 12 and 15 years, and BA increments calculated for each seedlot. BA increment between theoretical commercial thinnings, and hence BA yield at each thinning and clearfelling, were predicted using growth models. Predicted volume yields, of sawlog and pulp, were derived from BA yields for each test site, using a taper model and a stand height model.

At the two test sites, the Green Hills Seed Orchard (GHSO) stock achieved gains over the routines for mean BA of 7% and 15% at age 12 years, increasing to 14% and 20%, respectively, at age 15 years. Gains over the routines for mean volume at 15 years were 15% and 40%, respectively. The greater BA increment of the GHSO stock placed it between two and three site classes above the routine seedlots at both test sites. The advantage by the GHSO stock over the mean of the routines, in predicted total BA production over a whole rotation, was 21% to 22%, based on data from the two test sites. The orchard stock was also predicted to yield about 20% to 25% more total sawlog volume over a rotation than the mean of the routines, while corresponding gains in mean annual volume increment were 17% to 18%.

Discounted cash flow analyses were carried out, incorporating royalties from projected volume yields from the different seedlots, and full plantation establishment and marketing costs over a rotation on two different planting site types. Almost all Net Present Values (NPVs) were positive, with substantial gains per hectare, of the order of $1300, estimated from the use of stock with growth rates equivalent to the GHSO stock rather than stock equivalent to the mean of the routines. Internal Rate of Return (IRR) for most seedlots exceeded 4%, with IRR for the GHSO stock about 0.9 percentage points higher than that for the mean of the routine stock. These results indicate that production and use of seed orchard stock equivalent to the GHSO stock, rather than routine stock, would significantly improve the return on investment in plantation projects.