Posted by Julia Kaplick @julekap

New Zealand kauri is one of the country’s most iconic species and of great natural and cultural importance, but this forest giant is under threat by a deadly pathogen. Kauri dieback is caused by the seemingly invisible organism Phytophthora agathidicida. The first symptoms are wilting leaves and lesions at the base of trees. Underground the fine feeding roots as well as the anchoring tap roots are rotting. Over time the infection kills the trees leaving only ghostly wooden skeletons standing.

Dead kauri tree at Waipoua forest

A recent report published by Auckland Council found that a fifth of kauri in the Waitākere Ranges Regional Park show symptoms of dieback and the picture looks especially grim along the many walking tracks. The spread of the deadly pathogen more than doubled in the last five years showing that whatever measures were taken in the past had unfortunately little effect.

Phythosanitary stations have been in place since 2008. They mostly consist of Trigene or Sterigene solution filled spray bottles and brushes to clean soil from footwear. The disinfectant kills the active zoospores of Phytopthora agathadicida, but not the dormant spores which is why it is so important to remove all soil from shoes. The Council report does however show, that the stations are not effective enough, mainly due to people ignoring them or not using them properly.

As people are the main reason why the disease spreads so quickly through the forest local iwi Te Kawerau a Maki placed a rāhui over the Waitakere Ranges. Their hope is to stop any further spread and to give the forest time to heal and recover. Auckland Council on the other hand decided to not officially close regional park. To some this might be surprising, but track closures in the past have shown, that many people just ignore them. The regional park is simply too big to enforce a complete closure. This way the cleaning station will be maintained for people deciding to go for a walk despite the rāhui. The Council does support the rāhui and several individual tracks throughout the Waitakere Ranges are closed due to dieback.

Personally, I will respect the rāhui and stay away from kauri in the Waitākere ranges and I hope many will do the same. It is for now the only way to protect kauri and preserve this iconic tree for future generations.

Julia Kaplick is a PhD student in the Centre of Biodiversity and Biosecurity, School of Biological Sciences, University of Auckland. She is researching the response of native trees to seasonal variation in climatic conditions using measurements of sap flow, water relations and carbon allocation. Julia is supervised by Cate Macinnis-Ng (University of Auckland) and Mike Clearwater (Waikato University). Julia is supported by funding from the Marsden Fund.