Hybrid Holds Up Within Forestry Trial

For the first time globally, a stand of hybrid P. radiata and P. attenuata pine trees has been milled – allowing scientists to compare its wood qualities against two purebred species.

The hybrid stand (a cross of P. radiata and P. attenuata) from the Ribbonwood Station trial was milled recently by Radiata Pine Breeding Company Limited (RPBC)¹. RPBC contracted the project’s co-authors Marco Lausberg (Wood Quality Consulting) and Jonathan Harrington to complete the study.

The hybrid conversation has been in the production equation because of the trees’ potential tolerance of high-country climates – including their ability to handle snow loading – which is where P. radiata has historically faltered.

The trials were originally planted in 1998 by the former Forest Research Institute (FRI) in collaboration with Proseed. When the trial was harvested in 2025, it afforded the RPBC the opportunity to undertake direct measurements of wood properties and to verify earlier analysis.

In all, 92 butt logs, including examples of the three species – the hybrid, P. radiata, and P. attenuata trees – were processed at Niagara sawmill in Winton, Southland. The focus of the milling study was to compare the wood quality across all three species.

Volume and quality

Marco said the stand was well-sited – 485m (591 feet) above sea level – to definitively test the hybrid. When the farm manager wanted to clear the stand, RPBC moved quickly, taking the opportunity to validate its results in a sawmill for the first time.

“I think we had double the volume of logs in terms of acceptable sawlogs in the trial,” Marco said. “The hybrid tree was much, much better in terms of growth and form.

“We had trouble really getting nice, pure P. radiata and pure P. attenuata sawlogs from that site just because they had been so badly hammered by snow. I had to warn the sawmill that the logs coming from those trees were ugly, and for them not to expect normal log quality.”

The results revealed higher than average log velocity and board stiffness from the hybrid logs.

“The results give us confidence. If they are sited well, no-one is going to go backwards on the wood properties when they use the hybrids,” Marco said.

He also took the time to ask the mill staff what they thought of the logs.

“They couldn't tell any difference between the hybrid and the pure P. radiata or P. attenuata in their appearance because visually it blended in with the normal radiata in-feed resource,” Marco said. “The only comment they had – and, this is more interesting than useful, they said the hybrid smelled different.”

“I didn’t notice it, but they said the logs smelled a bit more like Douglas-fir than Radiata logs. But, because that’s the only difference they noticed in the mill, you can blend this timber in with Radiata in terms of your production without having your customers worry that it looks different.

“The major application from this is to plant it in an area where you know your P. radiata is going to suffer from snow damage.”

Hybrid excels at high altitude

Milling of the Ribbonwood Station trial supports the findings of another 2022 study². This study compared the predicted log grade recovery and financial performance of P. radiata x P. attenuata hybrids in two South Island high country sites in the Tekapo region including Ribbonwood Station.

At the Ribbonwood site, tellingly and in-line with the “Wood Quality Of The Attenuata Hybrid” report, the hybrid had almost double the basal area of P. radiata x P. attenuata primarily because of poor survival rates and ongoing losses through weather damage in the P. radiata. It translated directly to volume growth with the hybrid predicted to produce 150-300m3 more per ha log volume recovery at harvest.

The financial impact was assessed under the set of standard assumptions modelled on an “on-skid” (harvest through to loading) basis. The Internal Rate of Return (IRR – key financial metric calculating the annualised, percentage return on investment) forecast to be delivered by the hybrid at age 23, was 13.5%. Under the same assumptions the P. radiata and P. attenuata delivered 6.3%.

Mill measurements supports field tests

The take-home message was clear.

Marco said, “The hybrid has not lost out on wood properties. It's as good as, or slightly better, on this site than the two pure species that it came from.

“The big question for our report was whether we lose anything in terms of stiffness of the timber by planting the hybrid.

“The results show we didn’t, and what makes that so impactful is that for the first time we had actual timber properties to validate it.”

RPBC final word

RPBC’s Tree Improvement Manager Mark Paget said because tree breeding and research was a long-game, it was always gratifying to bring meaningful trials to fruition.

One warning is that the Attenuata species hybrid is a “magnet” for Dothistroma Needle Blight (DNB), a fungus that kills pine needles, affecting pine tree growth and wood quality.

Because of that, it is recommended that current deployment of the Attenuata hybrid is contained to the South Island’s high country and the Snowy Valleys of New South Wales** where DNB isn’t as common.

Mark said, “While there is that Dothistroma caution, the trials have confirmed what RPBC’s analysis found on the standing trees, that the Attenuata-Radiata hybrid is a valuable and viable species for specific sites.”

To that end, RPBC has completed significant work crossbreeding P. radiata and P. attenuata parents that exhibit the highest levels of resistance to DNB. RBPC has deployed the resulting progeny into highly susceptible DNB sites, and it is tracking and analysing their performance.

Mark said, “We’ll start to assess these progenies in two or three years, to see if there is scope to improve DNB tolerance in the hybrid.”

Download the full report of the Attenuata hybrid’s wood quality from the Ribbonwood trial at Winton below.

¹ RPBC is New Zealand’s sole radiata pine breeding company. It’s advanced breeding and research activities forms an integral part of the forestry supply chain, benefiting growers, seed producers, and processors across 16 shareholders that collectively own and manage 1.6 million hectares in New Zealand, and east and south-eastern Australia. RPBC’s primary function is to select and breed top-performing trees to produce faster-growing and more resilient plantation forestry trees. In addition to breeding elite trees RPBC also invests in collaborative research in emerging areas like disease and drought tolerance – freely sharing its work and knowledge for the benefit of the Australasian forestry sector.

² Predicted log grade recovery and financial performance of P. radiata x P. attenuata hybrids in two high country sites. T. Fowler and P. Adams, Matariki Forests.

³ RPBC and New South Wales is running separate Dothistroma needle blight trials.