Are pine trees killing kauri?

The Four Sisters walk in Waipoua Forest was closed last year after the discovery of kauri dieback. Picrture / File

A new study suggests that kauri dieback disease may be connected to the lack of protective fungi in plantation pine forest soil.

Published in FEMS Microbiology Ecology, the study, by Bio-Protection Research Centre PhD candidate Alexa Byers and others, looked at the differences in the bacteria and fungi living in the soil of kauri forest and surrounding pine plantations in the Waipoua area. It found soil in the pine forest's neighbouring kauri forests lacked several species of fungi and bacteria that protect plants, promote growth, and improve their health (for example Trichoderma and Pseudomonas).

"The loss of core microbiota from native soil microbial communities… surrounding remnant kauri fragments could be altering the forest's ability to respond to pathogen invasion," Ms Byers wrote.

"Understanding the ecological impacts of these changes to the soil microbial communities surrounding remaining kauri fragments is important to protect the long-term health and functioning of these fragments."

She also found some non-native fungi were now present in kauri forest soil.

"The differences in soil microbial diversity between forest systems could potentially result in the exposure of kauri fragments to introduced microbial communities which now have kauri within their range," she added.

The introduction of invasive species into native ecosystems through non-native trees was a recognised driver of disease in forests, Ms Byers wrote, a risk that was particularly high for Phytophthora species, with the plant nursery trade being identified as a vector for introduction and dispersal into new ecosystems globally.

Kauri dieback is caused by Phytophthora agathidicida.

Dr Amanda Black, who is one of Ms Byers' supervisors, and a co-author of the study, said the results showed more research was needed into the relationship between fragmented kauri forests and the pine and pasture ecosystems surrounding them.

"We have just 7500 ha of original kauri forest left, and it exists as fragments, surrounded by 60,000ha of plantation forests and regenerating kauri forest," Dr Black said.

"We need to understand what part this plays in the spread of kauri dieback."