Justification
Metrosideros kermadecensis is a large tree endemic to Aotearoa / New Zealand and found on six of the Kermadec Islands and Islets. It was assessed as 'At Risk – Naturally Uncommon’ in 2023, using the New Zealand Threat Classification System. The species is considered dominant in parts of its range and still occurs in large numbers. However, it is suspected that the impact of the rust Austropuccinia psidii, which causes myrtle rust disease, will cause severe decline in the species. In cultivation this species is readily infected by Austropuccinia psidii and soon dies. It is projected that over the next 100 years this rust will have caused at least a 30% decline in M. kermadecensis. It is therefore assessed as Vulnerable.
Geographic Range Information
This species is endemic to Aotearoa / New Zealand and found on the Kermadec Islands of Raoul, North and South Meyer Islands, as well as the Herald Isltes (Napier, Nugent and Dayrell). Distribution map is generalised.
Population Information
No accurate population estimate for the Metrosideros kermadecensis is available. However, the species is the dominant tree of Raoul Island (2,943 ha), North (0.86 ha) and South Meyer (7.2 ha) and only the summits of Napier 2.44 ha), Nugent (0.47 ha) and Dayrell (1 ha) Islands (de Lange 2023).
It is suspected that the impact of the rust Austropuccinia psidii, which causes myrtle rust disease, will cause severe decline in the species. In cultivation this species is readily infected by Austropuccinia psidii and soon dies. It is projected that over the next 100 years this rust will have caused at least a 30% decline in M. kermadecensis in the wild.
Habitat and Ecology Information
Metrosideros kermadecensis is the dominant tree species of the larger northern Kermadec Islands. On Raoul Island it is encountered from almost sea level to Moumoukai, the summit of that island. The canopy is almost continuous, rarely broken by other trees – though when so these are usually Alsophila kermadecensis, A. milnei or Rhopalostylis baueri, and in a few places near the summit and along the crater tops Coprosma acutifolia, Melicytus ramiflorus subsp. ramiflorus, Pouzolzia australis and Homalanthus polyandrus. Near to the coast in the dry forest (Oliver 1910) it co-associates with Myrsine kermadecensis and at the coast itself Coprosma petiolata and Myoporum rapense subsp. kermadecense. This is a large canopy tree up to 20 m in height. It is the main tree of both dry and wet forest types (de Lange 2023).
Threats Information
Metrosideros kermadecensis does not appear to have been as seriously impacted by browsing animals as other Kermadec Island endemics (Sykes 1969, 1977). Some weedy vine species that had established on the island from failed settler gardens pose a minor threat to the establishment of saplings and potentially trees growing in more exposed sites. Until the sars-cov-2 pandemic reached Aotearoa / New Zealand Raoul Island had a team of resident rangers who were mostly involved in weed eradication. As a response to the pandemic, they were evacuated back to Aotearoa / New Zealand (2020) and since that time there has not been a continuous human presence on the island. This is a risk as the island is frequently visited by boats / ships and illegal landings could be a source of new diseases / pest incursions.
During April 2017 the exotic rust Austropuccinia psidii which causes myrtle rust disease was first detected on Raoul Island on Metrosideros kermadecensis. The impact of this rust on Myrtaceae worldwide is serious, and as it was known to kill inoculated Metrosideros species in cultivation susceptibility trials it was regarded as a serious threat to all of the indigenous Myrtaceae in Aotearoa / New Zealand (de Lange et al. 2018). The New Zealand Department of Conservation undertook a range of surveys to determine the extent of the rust on the island but so far it would seem that its impact on Metrosideros kermadecensis is still minor. Indications, based on the spread and impact of the rust in Aotearoa / New Zealand on Myrtaceae there are more concerning (Prasad et al. 2022), with the observation that planted specimens of Metrosideros kermadecensis are starting to die from this fungus. Due to the sars-cov-2 pandemic response from the Department of Conservation, at the time of writing the impact of Austropuccinia psidii on Metrosideros kermadecensis, six years after it was first detected on Raoul Island is still unknown.
Use and Trade Information
This species is commonly cultivated in Aotearoa / New Zealand and in many parts of the world for example Australia, Norfolk Island, Sardinia, and Spain where it has sometimes naturalised.
Conservation Actions Information
The only serious threat to Metrosideros kermadecensis is Austropuccinia. At this stage the impact on the natural population of Metrosideros kermadecensis is still unknown but it is likely to be severe resulting over time in the death of not only seedlings and saplings but mature adults. As the rust infections increase in severity the loss of host plants is anticipated to increase. Currently there is no known cure for Austropuccinia, all that can be hoped for is that some lineages of host plants have or develop resistance.
As the rust is wind dispersed, quarantine measures are ineffective. The seed of Metrosideros has short-term viability so seed storage is of limited value. Current measures to secure the species should consider holding tissue-cultures. Consideration should be given to those locations where this species is cultivated outside the global distribution of Austropuccinia, to see if at those sites the species can be secured in Botanic Gardens and other threatened plant collections.
Research into finding a cure for Austropuccinia is a global issue and many organisations are working in this area. Like all research however, those investigations are subject to funding issues and political whim. Austropuccinia is a global problem, a global response is needed – only time will tell if humanity understands the consequences of the loss of the Myrtaceae on world ecosystems and make the right steps to find solutions to help manage this rust.
It was classified as ‘Threatened / Nationally Critical’ Qualified ‘DP’ [Data Poor], ‘IE’ [Island Endemic], ‘OL’ [One Location] (de Lange et al. 2018), but de Lange et al. (2024) changed the status to 'At Risk – Naturally Uncommon’ in 2023. It is vital to monitor the situation with the myrtle rust disease and how this invasive fungus effects M. kermadecensis.
