Scion scientists looking to establish New Zealand’s largest mixed-species Experimental Forest have sought inspiration from overseas.

Puruki Experimental Forest, south of Rotorua, is a 35-hectare Pinus radiata forest. It was originally established in 1968 as part of a United Nations land use study. With the second rotation approaching harvest, Scion is looking to build on its legacy to create an exciting integrated research platform that underpins the development of new forest systems capable of thriving under climate change.

In March, Scion received support for four exchange projects through a Joint Linkage Call Agreement between INRAE — France’s National Research Institute for Agriculture, Food and Environment — and Science New Zealand.

Among them was an exchange between Scion’s Designing Forests – Mahi Tahi Whaihua Portfolio Lead Yvette Dickinson and INRAE Principal Scientist Hervé Jactel aimed at fostering long-term collaboration on diverse forest plantations. Jactel has been visiting Scion this month after Dickinson’s trip to France in October and his expertise will help inform the future design of trials at Puruki.

His visit is the latest in a long-lasting co-operation between Scion and INRAE which also opens the door to larger collaborative projects.

Jactel has a background in forest ecology and entomology. While working on the largest plantation forest in Europe — a 1-million-hectare pure stand — he started exploring the effect of tree species diversity on resilience to pests and diseases. This led to joining TreeDivNet – an international network of tree diversity experiments, and Jactel developed France’s first experiment comparing pure and mixed stands in planted forests.

The work expanded to include other aspects of forest function such as productivity, carbon sequestration, and biodiversity conservation. He’s also looked at how biotic and abiotic disturbances are combining to increase damage to forest ecosystems.

His visit to Scion covered many areas including field visits, and conversations around current and proposed projects related to mixed forests, pests, diseases and biosecurity.

The most significant project Scion is drawing on Jactel’s expertise for is Puruki Experimental Forest where plans for the forest’s third rotation are being discussed, including the choice of species and the design of integrated research programmes.

Dickinson’s visit to France included trips to some long-standing tree diversity experiments to gain knowledge to inform the design of Puruki. She says she was able to learn about their experiences mixing species and how to design and manage  a tree diversity experiment.

Converting Puruki to a mixed species Experimental Forest also presents the opportunity to be the first New Zealand forest join TreeDivNet, an international network of collaborative experiments. Joining the network will allow access to shared data and knowledge.

Jactel says mixed stands have many advantages.

“Mix species forests are truly more resistant to pests and diseases. They are also associated with a higher level of biodiversity and in most cases, they are also more productive. They are also sequestering more carbon, both in soil and above ground,” he says.

Managing forests for resilience, sustainability and carbon sequestration all align with the Designing Forests – Mahi Tahi Whaihua portfolio Dickinson leads.

“We're also interested in it from an overyielding perspective. While mixing species can sometimes improve productivity, it doesn't always happen. Globally we're trying to understand why it happens in some places and not others,” she says.

"To be able to demonstrate sustainability as a whole, we need to understand all of these different aspects. Puruki is an opportunity to build economics and social sciences alongside the environmental and technological systems.”

The hilly nature of the site could also allow for study into the benefits of tree diversity on erosion, Jactel says.

Tim Barnard who is leading the Puruki work, says the proposed integration of different fields of science on the one site will be novel and building on the legacy of science at Puruki.

“When Puruki was set up it was driven by the United Nations UNESCO programme which was concerned about water quality around the world at the time.

“People had the vision to create that forest 50 years ago and now we’re picking up that legacy to create new forest systems that are going to endure over the next 50 years,” he says.

“It’s not only about diversity, it’s about the need for diversity in the face of climate change.”