Pines and kauri may be unhealthy mix because of dieback

Pine trees stand next to Herekino Forest in Diggers Valley, an area which could be permanently closed to the public to prevent the spread of kauri dieback. New research now shows pine plantations could be reservoirs for the disease.

A kauri dieback expert has warned the government to be cautious about planting pine trees near kauri forests, research suggesting that they may act as "reservoirs" for the disease kauri dieback.

Dr Amanda Black, from the Bio-Protection Research Centre, said radiata pine plantations and agricultural pasture may have a role in incubating and spreading the disease, as revealed by research for a Master's thesis by Lincoln University student Kai Lewis.

"We urgently need further research to clarify the role pine forests, pasture and other plants play in incubating and spreading Phytophthora agathidicida," said Dr Black, who supervised Mr Lewis' study and thesis.

"Until we are sure of what role they play, we should be very careful about planting any further pine plantations anywhere near kauri forest."

Mr Lewis studied how well P. agathidicida reproduced in kauri forest, pasture and pine forest, the results showing that in its early stages of development P. agathidicida reproduced much more rapidly in pine forest and pasture soil than it did in kauri forest soil. In pine forest soil it also produced more long-lived spores (oospores).

Other research reported earlier this year showed P. agathidicida also infected other native plants, including tanekaha, suggesting more potential hosts needed to be examined.

Mr Lewis' research also showed that P. agathidicida could infect Pinus radiata and several common pasture plants, even those that showed no symptoms, suggesting that some plants and soils may act as a reservoir.

"This raises the possibility that kauri dieback may be moving from pine plantations and pasture into kauri forests, carried by people, animals, and even on machinery," Dr Black said.

"We urgently need further research to find out if this is happening and how. Until we know the answer, we need to be very careful."

In his thesis Mr Lewis said investigating the role of unfenced pasture next to kauri forests was a high priority for further research.

He also found two other species of Phytophthora (P. pini and P. gregata), that can infect several plant species, were present in kauri forest and pasture soils. Their possible role in infecting native trees was another high priority for further research.

One paper has been submitted to an academic journal as a result of this research and is currently under review. Another is about to be submitted. One outlines the discovery of the two new species of Phytophthora in New Zealand, the other looks at the effects of fragmented landscapes on the growth and survival of P. agathidicida.