21 December 2017

Sacred trees under threat

As Christmas approaches, crimson flowers of Pōhutukawa trees line the streets of Aotearoa (the Māori name for New Zealand). Widely regarded as the national Christmas tree and deeply associated with Māori culture, this species and its relatives are under threat.

By Ruth Bone , Karioi Taiapa , Poutu Taiapa , Waitangi Wood and Melanie Mark-Shadbolt

Pohutukawa (Metrosideros excelsa) in flower in Auckland Botanic Gardens

Sacred trees

On the east coast of Aotearoa, in a settlement in Te Araroa, stands a large, spreading Pōhutukawa tree (Metrosideros excelsa). As Christmas approaches, the tree is covered in crimson flowers bristling with stamens. To a botanist, it might be regarded as a specimen, and suitable for collection.

But a visitor might also notice a decorative wooden sign nearby bearing the tree’s name: “Te Waha O Rerekohu.” Like all plants in Aotearoa, this tree is under the traditional lore and protection of mana whenua of the region (locals with authority/power/influence over resources). In the case of Te Waha O Rerekohu, its guardians are the subtribe Te Whānau a Hinerupe (of the Ngāti Porou tribe), who live in the area.

Thought to be 600 years old, Te Waha O Rerekohu is sacred and removal of any part of the tree is highly restricted. Local knowledge of tikanga (customary practices) associated with this majestic tree include the suspending of the kōiwi (corpse) of a deceased person from its branches until the flesh was completely removed, after which the bones were gathered, washed, and placed on a special mound where the funeral would take place. 

Food, medicine and Mānuka honey

There are thought to be around 30 species of indigenous myrtles in Aotearoa, and many of these traditionally provided Māori with food, medicine and building materials. A sweet gum-like substance collected from the branches of the Mānuka (Leptospermum scoparium) was a favourite food. The nectar of the Pōhutukawa was eaten after drawing it out of the flower with a reed, and is also good for sore throats. As a building material, young saplings of Mānuka and Kānuka (Kunzea species) were used to make crayfish pots and the body of eel baskets. 

Medicine is still gathered from these trees, including anti-bacterial oil extracted from leaves of Mānuka, and the anti-fungal properties of oil extracted from Kānuka. Today it is Mānuka honey that is most widely known, and sought after internationally for its unique properties.

Seeing red

Myrtle rust (Austropuccinia psidii) is a virulent wind borne fungal pathogen. Since its detection on indigenous Myrtaceae of Hawai'i in 2009, it has spread across the Pacific to Australia (detected in 2010), hampering flower and fruit production and killing adult plants of the country’s diverse and unique myrtles. Within three years, two formerly prevalent species Rhodamnia rubescens and Rhodomyrtus psidioides have declined to such an extent that they have now been listed as Critically Endangered in New South Wales.

In 2013, the pathogen was found in the nearby islands of New Caledonia, and has so far has affected 67 species, comprising approximately 25 per cent of the rich myrtle flora that is unique to the country. Myrtle Rust was confirmed on mainland Aotearoa in May this year on plants in the nursery trade. Indigenous myrtles previously considered at low risk of extinction, are being reassessed in light of this threat.

Seed banking as a conservation tool

Seed banks are used to conserve high quality seeds in advance of plant health threats. In addition to their potential use for restoring habitats, stored seeds can be used for pathology research, screening seedlings for disease susceptibility and resilience.

In response to the myrtle rust incursion, the Pacific regional programme of Kew’s Millennium Seed Bank Partnership (MSBP) is collaborating with Te Tira Whakamātaki (the Māori Biosecurity Network) to support Māori who seek long-term seed conservation techniques to protect and conserve this taonga (treasured) plant group that is of great economic, cultural and ecological significance.

This December, Kew and Te Tira Whakamātaki delivered two five-day courses covering the theory and practice of wild species seed conservation, with contributions from the Australian Seed Bank Partnership that focused on their first-hand experiences with myrtle rust. The courses were hosted by Auckland Botanic Gardens and Ōtari-Wilton’s Bush Reserve (Wellington), and were complemented by Myrtaceae identification tips from colleagues at the gardens and the Department of Conservation (DoC). In addition to botanical gardens and DoC staff, representatives from eleven Iwi (tribes), Hapū (sub-tribes) and Māori organisations attended and participated in the courses. 

Equipped with techniques for long-term seed storage methods, members of the training groups have already begun to share their experiences among their wider networks, mobilising new initiatives to counter the risk of myrtle rust by conserving seeds of indigenous Myrtles. Among them are brothers Karioi and Poutu Taiapa, co-authors of this blog and custodians of the sacred Pōhutukawa tree Te Waha O Rerekohu.

Further reading

  • Mavric, E., Wittmann, S., Barth, G. & Henle, T. (2008). Identification and quantification of methylglyoxal as the dominant antibacterial constituent of Manuka (Leptospermum scoparium) honeys from New Zealand. Molecular Nutrition and Food Research. 52(4): 483-489.
  • Pegg, G., Taylor, T., Entwistle, P., Guymer, G., Giblin, F. & Carnegie, A. (2017). Impact of Austropuccinia psidii (myrtle rust) on Myrtaceae-rich wet sclerophyll forests in south east Queensland. PLoS ONE 12(11): e0188058. Available online
  • Shearer, B. L., Crane, C. E. & Cochrane, A. (2004). Quantification of the susceptibility of the native flora of the South-West Botanical Province, Western Australia, to Phytopthora cinnamomi. Australian Journal of Botany. 52: 435-443.
  • Soewarta, J., Carriconde, F., Hugot, N., Bocs, S., Hamelin, C. & Maggia, L. (2017). Impact of Austropuccinia psidii in New Caledonia, a biodiversity hotspot. Forest PathologyAvailable online