The Government should be cautious about planting pine trees near northern kauri forests because they may be incubating kauri dieback, some scientists say.
Dr Amanda Black, of Lincoln's Bio-Protection Research Centre, said she supervised a masters' thesis that showed the pathogen that killed kauri reproduced more rapidly in pine forest and agricultural pasture than it did in a kauri forest.
In pine forest soil it produced more long-living spores.
Dr Black said care was needed when the Government promoted increasing commercial forestry as part of its one-billion trees programme.
"We urgently need further research to clarify the role pine forests, pasture, and other plants play in incubating and spreading the organism that causes kauri dieback," said Dr Black said.
"Until we are sure of what role they play, we should be very careful about planting any further pine plantations anywhere near kauri forest."
Lincoln University masters student Kai Lewis' thesis led to Dr Black's caution. Mr Lewis studied how well the pathogen phytophthora agathidicida reproduced in three types of soil: Kauri forest, pine forest and pasture.
He collected samples near Waipoua Forest in Northland and one of the original mainland sites from which kauri dieback had spread, Dr Black said.
"Mr Lewis's research showed that P. agathidicida could infect Pinus radiata and several common pasture plants, even those that show no symptoms. This suggests other plants and soil may act as a reservoir for P. agathidicida," Dr Black said.
Other research reported earlier this year showed the kauri dieback organism also infected other native plants, including tanekaha, suggesting more potential hosts need to be examined.
"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.
However, Dr Nari Williams from the crown forestry research institute Scion, who was a supervisor of the study said it did not justify stopping pine planting.
"It's important to know that the study did not try to find if the pathogen was (already) present in the soil samples.
"In the study phytophera agathadicida was artificially introduced to soil taken from pine forests, pasture and kauri forests," she said.
Many soil types and plants had the potential to harbour the pathogen, and it would be unreasonable to single out specific plants or locations as a higher risk (to kauri) than others, Dr Williams said.
Other plant scientists said the study raised biosecurity issues and pines should not be planted near kauri forest in the meantime.
Associate Professor Bruce Burns, from Auckland University's School of Biological Sciences, said the study was highly significant because it extended the potential host range for the kauri dieback and land uses that could be susceptible to it.
The research had also identified two species of phytopthera that hadn't been found in New Zealand before, and were known to cause disease on plants overseas, he said.
"At this stage the research doesn't justify a stop to the government's new pine plantations... but it does indicate that pine plantations planned near kauri forests should be avoided or delayed until the full extent of this risk is known," Dr Burns said.
Dr Nick Waipara, a senior scientist at Plant and Food Reserach, said the study showed the kauri killer organism could function outside a kauri stand, which had significant biosecurity implications.
"It is emerging that kauri is not the only plant host of agathadicida - it can survive using other plants.
"These findings... yet again show the lack of fundamental knowledge of agathadicida's impact and ecology in New Zealand... we need this type of research to continue," Dr Waipara said.
Professor Euan Mason from Canterbury University's School of Forestry said pine plantations were likely to be planted on sites outside the range of kauri so putting a stop to all pine planting was high unlikely to be justified.
The question was whether adding more pine plantations on grassland north of Hamilton would significantly add to the risk of kauri dieback.
"If the alternatives were pine or pasture then an increase in risk by planting pines would seem unlikely, based on these results," he said.