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Kauri dieback disease and protecting our natural heritage

23-Mar-2019

• In the Orakei Local Board area Dingle Dell and Waiatarua Reserve are possibly infected with kauri dieback disease. 

* New Zealand kauri (Agathis Australis) is a keynote tropical species for New Zealand. It is one of a group of conifer species which survived the breakup of Gondwanaland – 17 other species depend on the kauri ecosystem. There is 1% of unlogged kauri left. Regrowth has increased this to 3%. There is however very little genetic diversity. 

• Kauri can survive with very poor soil on the forest floor, but need their forest litter (dropped branches and leaves) to form a 10cm mulch to provide nutrients to their shallow root system which extends three times the distance beyond the dripline of the tree to 30 metres. The roots hate compaction and it’s very easy to walk on them and infect because we clear away the rotting vegetation in our gardens. 

• Kauri dieback is a new disease, about 50-70 years old. Did it come back from WW2 on the boots of soldiers returning from the Pacific? Or did it develop in the N Z Forest Service Sweetwater nursery in the Waipoua forest and get planted in existing forests? 

• The genetic work still needs to be happen. Kauri science is still relatively new. Neither DOC nor MPI have funded any scientific research into native kauri. 

• Kauri dieback disease is caused by a microscopic soil-borne pathogen Phytophthora agathidida (PA). PA also caused the potato blight and has also attacked avocado trees, tanekaha and rewarewa. PA is killing jarrah trees in Western Australia, as well as 250 other species. 

• The PA pathogen damages the tree’s roots, reducing its ability to take water and nutrients from the soil and transport it throughout the plant. PA spores can live on boots and tools for years, and come alive when contact is made with rain or water. Cleaning stations only work on dry walking tracks. 

• One million people p.a. go into the Waitakere Ranges, walking on kauri roots and mud. The Auckland Council Natural Environment Targeted Rate provides funds to revive and prevent 8-19% of kauri trees in the Waitakere Ranges. Kauri trees are now quarantined. The Hunua Ranges are also closed. 

• Avocado trees have been treated using phosphite, and this is being injected into kauri trees to see if this can delay dieback disease. 

• Auckland Council is the only council to have surveyed the parks in 2015 and 2015. Kauri dieback disease is primarily along the walking tracks, with the main infected areas being Piha and Cascades areas. 50% of trees are within 50 metres of a walking track, which have not been maintained. 

• Kauri dieback disease is a ‘root rot’ disease. There is no cure for kauri dieback disease which kills most if not all of the kauri it infects. The disease is spread through soil movement, by human activity, as well as deer, pigs and goats in rural areas. 

• A citizen science project is underway to have 50 landowners treat their own diseased trees. There is no cure for kauri dieback. They get a $700 pack which includes phosphite. 

• The signs are bleeding sticky gum near the roots of the tree which is an attempt by the tree to stop the pathogen coming in. The tree bleeds sideways and ring barks the tree, starving the canopies so that the leaves drop off. It is not known if injections of phosphite will work long-term – is a science issue. 

• Lots of volunteers are available to help in local parks and gardens. It is important to mulch the roots, stop mowing and keep people away, leaving the branches and leaves to drop on the roots. 

• Astelia trinervia (Kauri grass) http://www.terrain.net.nz/friends-of-te-henui-group/new-plant-page/astelia-trinervia-kauri-grass.html is a common constituent of kauri forest of Northern New Zealand and may help protect the tree trunks. 

• Infected areas have no seedlings – no resistant trees have been found yet, so the continued threat level is very high. 

• For more information see https://www.kauridieback.co.nz/ on how to protect our natural heritage. https://www.aucklandcouncil.govt.nz/environment/plants-animals/pests-weeds/Pages/protect-our-kauri-trees.aspx 

See also - Proposed kauri dieback mitigation in local parks in the Ōrākei Local Board area: File No.: CP2019/02436. http://infocouncil.aucklandcouncil.govt.nz/Open/2019/03/OR_20190321_AGN_7723_AT_WEB.htm

This was the content of a talk by Dr Mels Barton who works with works with many community organisations and not-for-profits including The Tree Council, Friends of Regional Parks, Revive Our Gulf and Living Wage Aotearoa New Zealand. She is Chair of both the Titirangi Residents & Ratepayers Association and the Combined Waitākere Ranges R&R Group and is a former Trustee of Ecomatters Environment Trust and the Weedfree Trust. She has been the National and Auckland Coordinator of NZAEE Seaweek since 2011 and is a leading member of the Waitākere Rāhui campaign and the Kauri Rescue project team.