Kauri Comparisons: Pōhutukawa

The pōhutukawa tree (Metrosideros excelsa), known as New Zealand’s Christmas tree, is another one of our iconic trees. Often seen clinging on to cliff faces by the ocean, spreading its roots and branches widely in old growth forests, or even in school yards. The symbol of the pōhutukawa is popular in the wider Aotearoa New Zealand culture, with artwork, Christmas cards and several children’s songs, all featuring the tree’s iconic red flowers. In te Ao Māori, the pōhutukawa tree and the whetū Pōhutukawa, one of the stars within the Matariki cluster, remind those observing Matariki to remember and acknowledge those who have passed in the last year. Additionally, the tree was used for rongoā Māori to treat a variety of ailments. Early settlers to Aotearoa called the tree ‘Iron wood’ for pōhutukawa’s strength, and the timber was used to make ships. 

Pōhutukawa’s original range was the coasts of most of the northern North Island. But the tree’s ornamental characteristics and hardy nature means that it can now be found throughout the country. Pōhutukawa is mainly known by its bright red flowers, but they are also known for their twisting trunks and branches, and hanging aerial roots. 

Read more about pōhutukawa in our previous ‘native plant of the month’ post. 

Same or Different? 

Print of a Pōhutukawa branch with blossoming flowers by Sarah Featon. Source: Te Papa Museum.

Kauri and pōhutukawa are both iconic rākau, so in this aspect they are the same. They are also the same in the fact that they are both threatened by plant pathogens.  

Kauri are threatened by kauri dieback (Phytophthora agathidicida), which lives in soil and therefore is spread by the movement of soil and water. Kauri dieback affects the roots, reducing their ability to absorb water and nutrients, leading to the decline and eventual death in tree health. Rāhui (cultural closure of areas or restrictions of activities), track up grades, cleaning behaviour (scrub, spray and stay on tracks), cleaning stations and animal control have all been implemented to help reduce the spread of kauri dieback.  Research has found that phosphite treatment can help decrease the effects of kauri dieback in infected kauri, but re-infection can still occur. This is promising news for all those involved in protecting kauri and kauri forests. 

Compared to kauri dieback, the pathogen affecting pōhutukawa trees arrived more recently to Aotearoa New Zealand. Pōhutukawa, like other myrtles (rātā, ramarama and maire tawake), are threatened by myrtle rust. Myrtle rust is an airborne pathogen that creates legions on the new growth (leaves, flowers, fruit) of infected hosts. This causes dieback (death of those parts) and inhibits the plants from growing and regenerating. Eventually the plant won’t be able to photosynthesise efficiently and after multiple infections, the whole plant can die.  

Myrtle rust arrived in Aotearoa New Zealand in 2017 and has since been found around the North Island and in the north of the South Island. Because the rust is airborne, controlling its spread is more difficult than with kauri dieback. Additionally, since the range of hosts (plants that can be infected) is wide, there is the potential for multiple unique native species to become extinct. In Australia the same strain of myrtle rust has already led to the loss of native myrtle in some areas. 

The key way to reduce the spread of myrtle rust is by reducing the number of host plants. The pathogen needs hosts to reproduce, spread and continue its life cycle. Different myrtle host plants will have different rates of infection, with some plants regularly being infected and others rarely. Plants that have a high rate of infection and are known as ‘super spreaders.’ One such plant is the lilly pilly, a common hedge plant that grows rapidly. This rapid growing rate means that all of the new shoots are easily infected by myrtle rust and become inoculum factories, releasing spores to infect more myrtles.  These spores are bright yellow, and are the key way to identify myrtle rust. If you suspect that you have found myrtle rust, you can take a photo of it and upload it to iNaturalist. For more information on identifying myrtle rust you can visit the Myrtle Rust in New Zealand website. 

Understanding plant pathogens and the ways we can mitigate their spread is one way we can contribute to protecting the unique biodiversity within Kaipātiki and Aotearoa New Zealand. Follow these links to go PFK's kauri protection and myrtle rust webpages.