Pinus pinaster and Pinus radiata survival, growth and form on 500–800 mm rainfall sites in southern NSW

Summary

Pinus radiata (GF27- and Guadalupe-based intraspecific hybrids) and Pinus pinaster were trialled to examine the potential for commercial deployment on three lower-rainfall sites within the 500–800 mm rainfall zone of New South Wales. All three ex-pasture sites were considered to be dry for P. radiata; two lower-elevation sites to the west of Gundagai being more challenging than a high-elevation site near Bombala. Cuttings and seedlings of genetically improved P. pinaster and P. radiata and a Guadalupe × routine cross seedlot of P. radiata were planted at three stockings (625, 1250 and 1850 stems per hectare (sph)) and were assessed for survival, growth (diameter at breast height, height, volume), form (straightness, malformations, branch size, branch angle) and number of commercially acceptable trees per hectare up to age 8 years.

Survival in P. pinaster didn’t decline after minor post-establishment mortality and was not affected by stocking or plant type. In contrast, survival in P. radiata continued to decline over time at 1250 and 1850 sph stockings at the two low-rainfall, low-elevation sites. Guadalupe-based seedlings had better survival than GF27 cuttings, but both present a high risk under dryland or drought conditions.

Site and stocking affected growth of the two species differently. P. radiata grew larger than P. pinaster at all sites. The combination of survival and growth resulted in site volume production that increased with stocking and site quality for P. pinaster. P. radiata exhibited a similar pattern but with reduced volume production at higher stockings on the high-quality Bombala site due to poor survival.

The form and branching of P. pinaster was better than that of P. radiata on all sites except the high-rainfall Oak Range. Form of P. pinaster cuttings was better than of seedlings. Form and branch size were improved by higher stockings and were worse on higher quality sites for both species. However, branch angle was better for P. radiata than for P. pinaster.

P. pinaster was reasonably productive on the best performing of the low-rainfall, lower-elevation sites. Given periods of very low rainfall since the establishment of these trials, the productivity of 6–7 m³ ha^–1 y^–1 at age 8 years at stocking of 1250–1875 suggests that 12–15 m^–3 ha^–1 y^–1 may be possible when mean annual increment (MAI) peaks at a later age. Although P. radiata growth rate was high, the poor survival and form of GF27, and to a lesser extent the Guadalupe cross, suggest it presents a high risk on these sites. Continued monitoring of the sites is therefore suggested. Further work could look at more drought-resistant taxa of P. radiata.

Keywords:

• plantations
• species trials
• growth
• drought
• spacing
• water use efficiency
• silviculture

Acknowledgements

We would like to thank David Spencer and an anonymous reviewer for useful comments and suggestions on a draft of the manuscript.