From bare to blooming – the story of the world’s largest pōhutukawa forest

At this time of the year, references to the snow, warm fires and sleigh bells in ubiquitous Christmas carols can either conjure up festive feelings, or a desire to reach for noise-cancelling headphones. Thankfully, a more natural signal that summer (and therefore Christmas) is upon us is, is the blooming of our ‘down under’ Christmas tree – the mighty pōhutukawa.

For most, summer means Christmas, which means time spent with family, BBQ’s, the sound of cicadas, sea swims, sandcastles and lazy days. For Māori, whose relationship with pōhutukawa is centuries-old, this special tree is a symbol of chiefdom, tenacity and wisdom, as well as a source of rongoā Māori (Māori medicine) and many other practical uses.

From the low-hanging branches we clamber on, to the generous shade provided by its canopy, and the brief but beautiful red carpet left after it flowers, the pōhutukawa (Metrosideros excelsa) is the tree that has earned a special place in our hearts and minds. What you may not know is that across the water in Auckland/Tāmaki Makaurau, in the Hauraki Gulf Marine Park/Ko te Pātaka kai o Tīkapa Moana, the world’s largest pōhutukawa forest resides on Rangitoto Island. A visit to New Zealand’s youngest volcano gives you an insight into the evolutionary features and behaviour of this iconic tree, which thrives on… well, bare rock.

From barren beginnings

Those who first step foot on Rangitoto are often surprised to learn that it isn’t the lush green island seen from the other side of the water, but rather, a harsh hunk of lava rock. From such barren beginnings rises a mighty forest of pōhutukawa, whose sprawling exposed roots attach themselves to rock crevices, drawing nutrients from pockets of soil and moisture.

This is because pōhutukawa is a colonising species, capable of colonising bare lava rock in Aotearoa, creating in its wake a gentler environment for a broader range of species. On Rangitoto, pōhutukawa are slowly changing the hellishly hot and dry lava fields into gradually expanding islands of shelter for other plant species such as mingimingi, koromiko and puka to grow.

The ability of pōhutukawa to grow aerial roots, including from its branches, is one of the characteristics it shares with others of its genus, Metrosideros. In New Zealand, the Metrosideros genus is represented by two types of pōhutukawa (mainland and Kermadec), three types of tree rātā (Northern, Southern and Bartlett’s), and six species of rātā vine. The genus belongs to the large family Myrtaceae, a group of tropical and warm temperate trees including feijoa and eucalyptus, and closer to home, mānuka, kānuka and swamp maire.

Iron-hearted symbols of cheifdon, wisdom and tenacity

Metrosideros translates to ‘iron-hearted myrtles’, a reference to another of this species characteristics: their hard and heavy heartwood. The strength of its slow-growing wood is what gives pōhutukawa the ability to grow on unstable habitats (such as rocky clifftops) by spreading the weight of the crown via its winding, sprawling branches, whilst also protecting its aerial roots from sun damage. This slow-growing nature enables pōhutukawa to grow as old as 1,000 years.

The strong, hard wood provided early Māori with a material perfect for tools such as paddles, digging sticks, hammers and weapons. Likewise, its strength, age and perseverance made pōhutukawa a symbol of chiefdom, wisdom and tenacity for Māori, and is deeply connected to the spiritual world.

Splashed by the spray

Pōhutukawa naturally grow along the northern New Zealand coastline and have some unique adaptations to cope with strong, salt-laden winds. One of these is its distinctive leaves, glossy on the top and furry underneath. The tough, shiny coat of wax on the upper side protects it against drought, salt, and glare, while the tiny hairs underneath help to reduce moisture loss. This resilience to the sea’s tempestuous weather is possibly the source of one translation of pōhutukawa – ‘splashed by the spray’.

A home for many and a source of medicine

As a stalwart of the coast, it’s not surprising that the pōhutukawa provides for a large number of species associated with the coastal forest ecosystem. Looking up into the branches of pōhutukawa, you may notice a number of epiphytes such as perching lilies and astelia that have attached to the rough and stringy bark, storing water for themselves and the host tree. Unusually on Rangitoto, epiphytes such as pekapeka (an orchid with pretty small white flowers), kakakaha (a perching lily), and kohurangi (a perching daisy), have ventured down off the pōhutukawa and into the vegetation islands the tree create. The stringy bark of pōhutukawa is also an excellent home for spiders and insects, while the inner bark was used as a cure for dysentery by Māori.

The iconic bright red flowers attract and provide an excellent nectar source for not only nectar-loving birds such as tūī, but also bats, geckos (Common, Pacific and Duvaucel’s), and even some stick insects. On Rangitoto, endangered native birds including tīeke/saddlebacks and pōpokotea/whiteheads enjoy pōhutukawa nectar, as well as kākā, kākāriki and korimako/bellbirds, which have returned to the island since rats and stoats were eradicated in the 2000’s. The nectar was also used in the treatment for sore throats by Māori. Birds such as shags and white-faced herons often nest or roost in pōhutukawa because of their proximity to the birds’ feeding grounds (the sea and estuaries), while down below, hardy snails can live in the trees’ leaf litter.

Hybrid swarm – the art of living together in harmony

But shock, horror… is Rangitoto’s forest truly a pōhutukawa forest? Take a closer look and you will notice that some trees that otherwise appear to be pōhutukawa, have the flat, smooth oval leaves characteristic of rātā.

That is because pōhutukawa and Northern rātā (Metrosideros robusta), which usually don’t grow closely to one another, have cross-pollinated on Rangitoto. Their hybrids, in turn, have cross-pollinated back with the parent trees, resulting in a continuum of plant forms. As such, biologists describe Rangitoto’s pōhutukawa forest with the slightly menacing term “hybrid swarm.”

Pōhutukawa and back-crossed hybrids dominate, with some great specimens found near the summit, while Northern rātā are more common on the eastern edge of the island where the original ancestor was likely to have originated.

Under threat

Pōhutukawa forests were once widespread on the coasts of northern New Zealand (north of New Plymouth and Gisborne), but it is estimated that more than 95% have been destroyed by farming, roading, urban development, and possums.

Last century, a major threat to pōhutukawa on Rangitoto were possums and wallabies which were eating the leaf shoots, buds and newly expanding flowers. This browsing opened the trees’ canopy, weakening and eventually killing them. Possums and wallabies were eradicated on Rangitoto and Motutapu in 1992, enabling the forest to regenerate successfully. Today, a major weed eradication programme continues to support the health of the island’s forest.

Another potential threat to pōhutukawa, and rātā is the fungal disease myrtle rust, which attacks members of the Myrtle family. In some cases, this disease severely attacks pōhutukawa leaves and stems. Myrtle rust has not yet been found on Rangitoto – if you see any sign of the yellowish fluffy spots, please photograph it, note the location, and report it to DOC on 0800 HOT DOC. This disease is being researched and monitored to determine what impact it will have on our native tree species.
To restore pōhutukawa and rātā habitat, DOC works closely with agencies such as Project Crimson through revegetation and education programmes.

Wishing you a Meri Kirihimete

After the year that was 2020, this summer we hope you get to enjoy what our much-loved Kiwi Christmas tree has to offer. Kick back under its shady reach and snatch a 10-minute snooze while the kids play beach cricket, and the birds enjoy the rich nectar of its flowers.

And if you’ve never been, we suggest you get over to Rangitoto Island to marvel at the world’s largest pōhutukawa forest – just remember to wear good walking shoes, sunscreen and a hat, and bring plenty of food and water. Walk slowly – you might hear the “skrack” of kākā and get to observe cheeky tīeke/saddlebacks and chatty pōpokotea/whiteheads which are thriving on Rangitoto. All the information about visiting Rangitoto can be found here, while the Fullers360 ferry timetable to the island can be found here.

Love it, Restore it, Protect it.