A very merry Metrosideros excelsa. Our chiefly Pōhutukawa.

Summer has well and truly arrived here in the Eastern Bay, with our beautiful sandy beaches attracting visitors from near and wide. Our beaches are even more special for their backdrop of large stately pōhutukawa trees (Metrosideros excelsa) bursting into a profusion of crimson flowers. This tree holds an important part in our culture, with Māori regarding it as a chiefly tree (rākau rangatira) and the blossom refered to as kahika.

A profusion of crimson flowers against the deep green 
of a tree fern at Ōhope Scenic Reserve. Source: Author (2018).

While we may take these beautiful trees somewhat for granted as part of our natural environment, it is in fact not as common as it once was in coastal areas of the upper North Island. Once pōhutukawa, and several species of rātā, could be found in a continuous coastal strip as far south as Poverty Bay on the east coast, and Northern Taranaki on the west coast. These populations have been reduced to a few isolated stands and relict individuals, with our local Eastern Bay population an important environmental taonga and significant population. 

Mature pōhutukawa have a distinctive rounded and spreading canopy,
seen here adjacent to dunes at Waiotahe Beach, Eastern Bay of
Plenty. This would have once been a common sight
all along the east and west coasts of the top half of the 
North Island. Source: Author (2018).

Pōhutukawa is adapted to coastal conditions, where the largest and healthiest specimens are usually found, with deep and tenacious roots allowing it to colonise rocky outcrops and coastal cliffs. It is also commonly seen colonising bare ground such as landslips and lava fields where it can use its roots to extract hard-to-reach nutrients and water.  The sturdy and massive roots and trunks of these trees are reflected in the name of the genera Metrosideros, meaning “iron-hearted”. Other species in the genus are rātā, and together these species belong to the Myrtaceae (myrtle) family, which includes manuka, kanuka, eucalyptus, and Callistemon (Bottlebrush) species. The species name of pōhutukawa, excelsa, refers to its outstanding or sublime, appearance when in flower.  

The bright and showy flowers of the pōhutukawa smother the canopy at this
time of the year, providing a signal to pollinators that nectar is available. Tokitoki
Historic Reserve, Ōhiwa Harbour. Source: Author (2018).

The especially hard wood was highly valued for boat building, as its nature made it particularly suitable for curved pieces required for the structural frame of boats. Where older wooden boats have used pōhutukawa for the structure, and kauri for planking, the pōhutukawa have often been found to be more durable and longer surviving than the kauri.

However, it is undoubtably the spectacular flowers of these trees that now hold such a special place in our hearts, both for their distinctive crimson colour, and the fact that the pōhutukawa flowering heralds our summer and a time of festivities and relaxation. It is the smothering of bright crimson flowers reaching their peak in mid-December that have seen the pōhutukawa affectionately referred to as the New Zealand Christmas Tree. 

Bright red flowers are highly visible, and their placement at the top of the
canopy of trees mean they can be seen from afar by potential
pollinators. Source: Author (2018).

Flowers are also highly valued by our native and non-native nectar-feeding birds, attracted by the nectar at the base of the flowers, thereby pollinating the flowers, and ensuring seed becomes fertile. A more modern pollinator taking full advantage of the offerings of the pōhutukawa flower is the introduced honey-bee.

Flowers are a type known as “brush blossoms”, formed by a mass of bright red stamen with a shallow bowl of nectar at their base. Masses of flowers displayed at the canopy of the trees attract birds from a distance, and seeking nectar, they pollinate the flowers by transferring pollen from the male stamen to the female stigma. While our most well known species of pōhutukawa is the crimson flowered variety, there is a yellow flowered sub-species 'Aurea'. All yellow pōhutukawa have their provenance in a pair discovered on Motiti Island in the Bay of Plenty. While Māori were aware of these yellow blossomed trees, they were botanically described by Norman Potts, the renowned amateur botanist from Ōpōtiki. Regional variations in flower colour and growth habit have been taken advantage of in the development of many cultivars such as a pink variety 'Pink Lady', and white variety 'White Caps'.

Detail of flowers, formed by a mass of crimson stamen tipped with pollen.
Clearly visible at the base of stamen are the circular nectar cups, attracting
pollinators who do the job of transferring pollen from the male stamen to the 
female stigma. Mahy Reserve, Ōhope. Source: Author (2018).

Detail of yellow flowered pōhutukawa. Nectar cups are also clearly 
visible in this flower at the base of the clusters of male stamen forming
the most visible part of the flower. Māngere Bridge, South Auckland.
Source: Author (2018).

Fertilised seeds develop in an ovary at the base of the stigma, in time forming a seed capsule that spreads its numerous wind-borne seeds in winter. Tiny wind-borne seeds are ideally suited to gaining a hold in rocky cracks and crevices where enough nutrients have accumulated to nurture the growing seedling. 

Where nothing else will grow a pōhutukawa seed lodges in a crevice and 
takes advantage of dust and soil collecting in the cracks of this sheared and
weathered greywacke,  providing nutrients for the tenacious seedling. 
Whakatāne Heads. Source: Author (2018).

Over time a pōhutukawa is able to send its roots exploring 
cracks and joints in weathering rock, driving it apart and 
finding nutrients and freshwater to support the tree making 
the most of this inhospitable environment. Otarawiarere,
Whakatāne. Source: Author (2018).

It is due to the wind-borne nature of these seeds that the trees are often be found colonising rocky off-shore islands, such as Rangitoto in the Hauraki Gulf, and Whakaari/White Island in the Bay of Plenty. Some of the best examples of relatively undisturbed pōhutukawa forest can be found on these offshore islands, with Rangitoto the largest Pōhutukawa forest in the country. Pōhutukawa is able to establish relatively quickly on bare lava-fields, meaning it is easily able to pass the threshold from colonising species to dominant canopy species.

Twisted and gnarled pōhutukawa trees with an understory
of ferns form a scene typical of a small fragment of pōhutukawa forest
surviving on Whakaari/White Island, despite the toxic atmosphere
and frequent eruptions. Source: Ralph Ward, date unknown. Retrieved 
from: tauranga.kete.net.nz (2018).

Here in the Eastern Bay, at Ōhōpe Scenic Reserve, one can experience one of the last remaining mainland stands of mature pōhutukawa and rewarewa dominated bush, still intact largely thanks to the tireless work of volunteers undertaking pest control. Possums heavily browse on spring vegetation, as well as mature vegetation, and if left unchecked they can lead to a premature death of trees that should be able to live to a thousand years at least. Pōhutukawa dominated forest is distinctive for criss-crossing and branching trunks of the trees. 

Vertical branches and trunks criss-cross with near-horizontal branches,
forming a pattern typical of mature pohutukawa forest, or stands of mature regenerated 
or planted pōhutukawa trees. These trees give the stretch of State Highway 2
between Ōhiwa and Ōpōtiki it's name of Pōhutukawa Drive. Source: Author (2018).

In open spaces such as reserves and parks, where pōhutukawa is a popular amenity species, trunks can grow thick, twisted and convoluted. A prime example of this is Mahy reserve in Ōhope, where trees can also be seen festooned with thick mats of distinctive aerial roots typical of mature trees.

Above and Below: Gnarled and twisted trunks of pōhutukawa
at Mahy Reserve, Ōhope. Over time aerial roots may reach
the ground and form parts of the trunk. Source: Author (2018).

Detail from above showing dense thicket of
interwoven aerial roots, typically found on mature trees.
Source: Author (2018).

The East Cape is also famous for what is reputed to be the largest pōhutukawa in the country. Te Araroa is home to a tree known as Te Waha O Rerekohu “The mouth of Rerekohu”. This is certainly the largest pōhutukawa in the country and may well be the oldest at over 400 years. 

Above and Below: Te Waha o Rerekohu, said to be the largest and the oldest pōhutukawa in the world. 
Te Araroa, Gisborne District. Source: Murray Dawson (2106). Retrieved from inaturalist.nz

So, as you enjoy the coming summer days against a backdrop of crimson flowers, clear blue skies, and glistening white sands, take a moment to appreciate this special taonga we are blessed to have amongst us. If you would like to find out more about the ecology, culture, and history of the Metrosideros species, check your local library for “Pōhutukawa and Rātā. New Zealand’s Iron-Hearted Trees” by Philip Simpson.

Reference for this post has also been made to the journal article "Biological flora of New Zealand 14: Metrosideros excelsa,pōhutukawa, New Zealand Christmas tree", by RJ Bylsma, BD Clarkson, and JT Efford. To read the full journal article link here.

Finally, I would like to thank the Whakatāne Beacon and Eastern Bay Life for supporting this column over the last year, and supporters and followers of this blog. I look forward to more exploration of our unique and dynamic Eastern Bay of Plenty and hope you will join me in 2019.  Merri Kirihemiti!