Mamaku, the giant umbrella of the forest - New Zealand's largest fern species.

Mamaku, our tallest tree fern, with immense fronds up to 6 metres long, can be referred to as the giant umbrella of the forest. It is not uncommon for this ancient plant, dating back to the time of the dinosaurs, to reach heights of 20 meters.

Spheropteris medullaris (syn. Cyathea medullaris), also known as the black tree fern, is easily recognised by its jet-black frond stalks (stipes) covered in black scales and its trunk displaying distinctive hexagonal stipe scars (where the old fronds have fallen off).

Mamaku, also known as katātā or kōrau in te reo Māori. Photo by Gabriela V.

We have only recently begun to understand the significant role it plays in forest regeneration. Mamaku is often the first to appear in areas where a forest has been cleared, aiding in landscape recovery after disruption. It is commonly found on wetter, steeper south-facing sites, where it quickly forms short-lived forests. Beneath their dark canopies, sensitive broad-leaved species such as kohekohe (Dysoxylum spectabile), pukatea (Laurelia novae-zelandiae), tawa (Beilschmiedia tawa), and miro (Prumnopitys ferruginea) can grow and eventually replace it.

Mamaku, a hydrophyte (a plant species adapted to thrive in water or wet conditions), typically favours moist environments and can often be observed growing along streams. It is predominantly found in broadleaved forests, but also grows in podocarp, beech, and kānuka forests.

Its trunk acts as an aerial nursery for seedlings of several native plant species. Often in the forest, you will see remnants of mamaku acting as a support for a newly grown tree that has taken its place.

Young seedling of native Brachyglottis repanda growing happily on the trunk of a tree fern. Photo by Gabriela V.

With time, the native tree will get more and more established, eventually replacing the tree fern at the end of its life. Photo by Gabriela V.

The decomposing fronds of mamaku enrich the soil, benefiting nearby forest plants and aiding nutrient-hungry seedlings in growing into large trees. Additionally, the fibrous trunk of the mamaku provides an ideal habitat for various insects.

One of Aotearoa's rarest bird species, the Hihi or stitchbird, uses mamaku fibres collected from the kōrau (the spiral-shaped new fern frond) to build its nests and blanket its eggs.

Hihi - male - unbanded. credit: digital trails. Creative Commons.

Mamaku's kōrau - the newly forming frond. Photo by Gabriela V.

Hihi nest with young chicks. Photo by Chris Devine @ Forest and Bird Notice the kōrau fibres lining the nest.

In addition to aiding land regeneration and supporting various plant and animal species, mamaku also offers calming medicinal benefits for humans.

In Rongoā Māori, the traditional Māori healing system, different parts of mamaku are used to treat skin conditions, rashes and ulcers, cure internal parasites, soothe sore throats and assist with the post-partum recovery.

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Source: Nature Guide to the New Zealand Forest (Dawson, J. & Lucas, R. 2000, Random House,New Zealand); The Meaning of Trees (Vennel, R. 2019 Harper Collins Publishers, New Zealand); NZ Forest and Bird authoritative website https://www.forestandbird.org.nz

The Pōhutukawa tree, an emblem of quiet resilience and generosity

Sometimes referred to as 'The Crimson Coast'. The drive up the coast from Thames on the Coromandel Peninsula offers a spectacular display of countless shades of red. Photo by Gabriela V.

Its name is derived from the term 'hutukawa,' referring to a headdress adorned with red feathers, and 'po,' which holds various meanings, including references to the night or the underworld. The Māori people traditionally planted Pōhutukawa trees to commemorate the burial sites of chiefs, battle locations where warriors perished, or the birthplace of a chief's son. They utilized the bark's juice for its anti-inflammatory properties and as a treatment for conditions such as diarrhoea, dysentery, gangrene, and thrush. Chewing the bark served as an anaesthetic for alleviating sore gums and toothaches, while sucking on its nectar was a remedy for a sore throat.

The Pōhutukawa (Metrosideros excelsa) is a member of the myrtle family (Myrtaceae), which comprises approximately 3,000 species of tropical and warm temperate trees, shrubs, and vines.

Exceptionally well-suited to its natural habitat. The tree's canopy, more horizontal than vertical, distributes weight through its root-laden branches to withstand severe storms. Minute seeds can infiltrate even the smallest crevices, while its leaves are equipped with soft hairs to reduce water loss. Remarkably adapted for colonizing barren lava, the pōhutukawa's branches develop extensive clusters of aerial roots that, upon contacting the ground, secure themselves in typically unstable rock. These trees can live for up to 1,000 years.

Rupestral habit means the root system spreads over bare rock. Photo by Gabriela V.

This coastal tree serves a significant ecological role by offering a habitat that supports the growth of other colonising plants, it provides nourishment, shelter, and support to an impressive array of animals, and insects too.

Honeyeaters such as tūi, bellbirds, and stitchbirds (which are now absent from the mainland) thrive on the tree's slightly salty nectar, as do pekapeka, our native short-tailed bats. Geckos are attracted to the newly opened flowers and contribute to pollination in a minor capacity. Shags and white-faced herons find refuge and nesting sites in the canopies, while bats inhabit split branches and crevices. Saddlebacks nest within trunk cavities, and the tree's flaky bark supports a diverse array of insects and spiders. Weevils, beetles, flies, moths, and scale insects consume the foliage, bark, fruit, and the twig and leaf litter surrounding the trunk. Just above the strand line (the extreme high water mark), resilient snails persist in the decaying litter.

The impressive aerial roots adorning the gnarled branches of the Pōhutukawa trees. Photo by: Gabriela V.

If you have ever been curious about the cause of the small holes in the leaves of a Pōhutukawa tree, the most probable culprit is the Pōhutukawa leaf miner, Neomycta rubida.

Adult pōhutukawa leaf miner weevil, Neomycta rubida, about 3mm long. Creator: Tim Holmes. ©Plant & Food Research

This endemic weevil is found in the North and South Islands of New Zealand, where its primary host plants are located. Adult weevils feed on young leaves, while the larvae create tunnels within the leaves. Female weevils begin laying eggs when new leaves emerge, depositing a single egg into the blade of a young leaf. Upon hatching, the larva tunnels into the leaf, forming a serpentine mine.

The leaves affected by the weevil's activity. Photo by: Gabriela V.

Damage to the young leaves of Pōhutukawa and northern rātā by the weevil has occasionally raised concerns; however, this does not appear to have any long-term impact on the health of the trees.

This gentle giant from the plant kingdom coexists harmoniously with the smallest creatures within its verdant protective embrace.

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Source: pohutukawa TREE OF AOTEAROA (Bercusson,L. & Torrance, J. 1998, Tandem Press, New Zealand), http://www.landcareresearch.co.nz an authoritative website of Landcare Research New Zealand

The Chemistry of Giving and Receiving - Carmichaelia

Photo by J Davis (2020). Carmichaelia australis - Common broom - Otari-Wilton’s Bush. https://www.thepaintboxgarden.com/otari-wiltons-bush/48-carmichaelia-australis-common-broom-otari-wiltons-bush/

Gracefully composed of flattened evergreen stems, native brooms confront the morphologies expected of any shrub or small tree.

Carmichaelia australis' (Common native broom, mākaka) cascading stems, leaf-like but for any true leaves that may appear, are known as cladodes and perform the role of photosynthesis in the plant. Immature or shaded specimens may bear a pinnate arrangement of leaves, but these typically do not last into adulthood. Its habit is open, upright, and spreading, stems arching as they grow up to 4m high and 3m wide. C. odorata (Scented broom) is slightly smaller, growing 3m x 2m, and has finer stems.

Carmichaelia australis flower | common native broom, mākaka, maukoro, tainoka, taunoka, taranagahape. Photo by E. Hanzel

Flowers of white, pale lilac, lavender, and mauve are individually minute (with a five-petal arrangement of banner, wings, and keel), but born in short dense spikes that trail the lines of these architectural shrubs in abundance. Following a spritely bloom beginning in September-October, seeds develop through May or longer and are dispersed via dehiscence, wind, and granivory. Orange seeds and a replum, the structure that remains as the pod walls fall away, indicate the fruit of C. australis (those of C. odorata are less showy).

C. australis seed, replum. Photo by E. Hanzel

Growing in disturbed soils, Carmichaelia species habitually weep over open landscapes and perch on vulnerable slopes.

As fabaceous plants -those of the Fabaceae or Leguminaceae (legume/pea/bean) family, Carmichaelia fix nitrogen, allowing them to occupy these tenuous interfaces between the biotic and abiotic.

Nitrogen fixation is the process wherein free, or atmospheric (N2), nitrogen, is converted to ammonia (NH3) in the soil. Atmospheric nitrogen is relatively inert and incompatible with plants until it has been chemically altered. This requires associations with soil microorganisms that possess nitrogenase, the enzyme responsible for the reduction of N2 to NH3.

Adhered to the root systems of fabaceous species are nodules containing rhizobia, symbiotic bacteria that convert nitrogen into ammonia in a mutualistic relationship with their associated plant. In return, the rhizobia recieve habitat and energy in the form of carbohydrates. As limited nitrogen compounds are accessible to species of Carmichaelia, they are able to grow in lean and otherwise prohibitive soils.

As such, Carmichaelia are present through wide ranging habitats in both New Zealand islands: Coastal to montane environments, river terraces, stream banks, colluvium, rock outcrops, talus and fan toe slopes, tussockland, scrub, frost/bush margins, and in swamps.

In response to their ecological niches, the genus demonstrates adaptive radiation, an accelerated development of morphologically diverse, but closely related species. Of 24 endemic species, most exhibit its characteristic cladodes, but Carmichaelia appressa is prostrate, sending its thread-like stems over sand dunes in the Kaitorete Spit near Christchurch. C. monroi (stout dwarf broom) and C. nana (dwarf broom) project bluntly from diminutive mounds appropriate for the rock outcrops, borderland scree, river eyots, and alpine slopes they inhabit. Carmichaelia crassicaulis subsp. crassicaulis (coral broom) stoically observes scrub and subalpine landscapes in the South Island. Rising ruggedly above tussock and rock, the craggy brown forms are evocative of shou sugi ban sculptural installation, their very morphology adapted for the exposed conditions of their isolated habitats.

Photo by R. Janes and L. Caygill (2021). Carmichaelia crassicaulis subsp. crassicaulis https://www.facebook.com/Trees4Canterbury/posts/carmichaelia-crassicaulis-subsp-crassicaulis-coral-broom-is-a-very-unique-specie/4808463145871634/

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The more readily available garden species, Carmichaelia australis, C. odorata, and C. stevensonii (a highly ornamental specimen of showering stems and showy flowers) will grow quickly and remain hardy in partial-direct sun and well-drained soils. Their flowers are attractive to bees and insects and their layered forms valuable habitat and refuge for birds and insects.

Carmichaelia odorata mingling with Libertia grandiflora in residential project. Photo by E. Hanzel