Forgotten Kohekohe - A Most Spectacular Tree

EMMA WATERHOUSE with JUNE BROOKS

In 1915, the member of Parliament for Otaki, a Mr W. H. Field, described kohekohe (Dysoxylum spectabile) as “…a very beautiful tree and easily our most valuable native tree.” (1) He was speaking in the parliamentary debate on the Scenery Protection Amendment Bill and went on to pronounce not only its value as a scenic and forest tree but also for its use in carpentry and furniture-making.

In the same debate, Mr Field, also noted that seeds of the tree had been sent to India and elsewhere “…for the purpose of planting in places where it is thought that it will grow quickly enough to be of value for timber in the course of a comparatively few years.”

New Zealand Mahogany

The only New Zealand representative of a mainly tropical/subtropical plant family, the endemic kohekohe is also known as the New Zealand mahogany. A clue perhaps to the value kohekohe was initially thought to have as a timber tree. It wasn’t long before the bold statements of Mr Field were proved wrong. Large trees are rare (kohekohe becomes hollow as it grows) and its timber potential was never fully exploited.

Māori used kohekohe for constructing river canoes, for which it was highly regarded. The lack of large trees and its rapid decay in water, meant the wood was not used for many other purposes (2).

Medicinally, the leaves and bark of kohekohe were used by Maori for a variety of complaints, as a tonic or infusion, to treat coughs and stomach aliments, skin problems and for fever (3). The leaves were described as being very bitter.

A most spectacular tree

Described as one of New Zealand’s most spectacular trees (4), kohekohe grows to about 15 m in height and is found naturally in the north to central North Island and in Marlborough.

They prefer dampish, fertile, shaded coastal lowland sites, where puriri and taraire are often also found, and do not tolerate frost.

Kohekohe has large, glossy compound green leaves which gives it a tropical appearance. Fruit are produced from the previous years’ flowering (fruiting and flowering do not occur in the same year) and three to four-celled fruit capsules open about 15 months after flowering.

Kohekohe flowers are an important and favoured source of nectar for many of New Zealand’s bush birds including tūī (Prosthemadera novaeseelandiae) and bellbird (Anthornis melanura).

Try Growing Kohekohe

Kohekohe (Dysoxylum spectabile) is a handsome forest tree that deserves to be more appreciated and widely used in revegetation programmes. 

Flowers and seeds 

The tree produces flowers in late autumn to early winter, and capsules (fruit) from the previous years’ open from mid-autumn, providing welcome early-winter food sources for birds and bats. 

Fruits are produced in green ovoid pods and the three to four brown to black seeds inside the pods are covered in a fleshy orange outer covering. The seed has a high viability and does not have a dormant period. Seeds collected from pods in mid-May can be propagated in seed trays immediately and the first seedling leaves appear two to three weeks later. 

Propagating kohekohe 

We asked Alan Phelps for advice on propagation and he advised that rats love eating kohekohe fruit to the point that none will survive to germinate if left unprotected while maturing on the tree. He advised protecting fruiting trees with rat traps and bait stations until we were ready to collect the pods/fruits to propagate. 

As our tree is next to the driveway, we were able to see when the fruit pods were forming and installed rat traps and bait dispensers around the tree until the pods were mature and started falling off naturally. We collected about 60 seeds, put them in moist folded paper towels for about one week and then into seed trays with growing medium (leaf litter compost and some well-rotted garden compost of our own). We kept them moist but not wet and saw the first show of green leaf buds in about two to three weeks. 

We contacted Okiwi Green Nursery to ask if they could help us out as we had to return to Auckland and didn’t want to take them back and risk introducing Argentine ants or plague skink eggs to another site on Aotea│Great Barrier. We will give the majority of the plants for sale, taking a few for our place. They need to be protected from rabbits when young and from cattle grazing. 

Kohekohe are very rewarding to propagate and are fast growing. I am eyeing up a tree at our gate which flowered this past May for seed collection next year. 

Aotea│Great Barrier needs more kohekohe! 

Cauliflory

One of kohekohe’s distinguishing features is its habit of ‘cauliflory’ or stem flowering. Drooping greenish-white waxy flowers and fruit panicles sprout directly from the trunk and branches during late autumn to early winter.

Few other New Zealand plants exhibit this unusual habit—flowers of the tree fuchsia (Fuchsia excorticata) sometimes appear directly on the trunk; and two rare plants species on the Three Kings Islands, Tecomanthe speciose and Pennantia baylisiana are also cauliflorus (5).  Cauliflory is thought to be evidence of a tropical origin, where pollination and seed dispersal is by bat or bird that fly beneath the forest canopy.

Kohekohe on Aotea

On Aotea│Great Barrier, kohekohe occurs in broadleaf forest and in damp gullies and lower slopes. The tree is commonly found with tawa (Beilschmeidia tawa) and taraire (B. tarairi). Nikau (Rhopalostylis sapida) are often prevalent in the sub-canopy. Kohekohe occurs up to altitudes of around 400 m although is more dominant below 200 m.

On the mainland, kohekohe is a favourite food of brushtail possums (Trichosurus vulpecula) which heavily browse the leaves, flowers and fruit (6) and also affect seedling survival (7). Although possums are not an issue for kohekohe on Aotea | Great Barrier, rats significantly inhibit regeneration by eating the fruits and seeds (8). A study on Hauturu | Little Barrier showed that kohekohe seedling numbers increased significantly following the eradication of rats (9).

Giving kohekohe a helping hand

Once common in coastal and lowland forests, kohekohe is likely to continue to decline in unmanaged area and disappear from large parts of its natural range9. Kohekohe was one of the first tree species collected by Joseph Banks and Daniel Solander in 1768. This first specimen is in the Te Papa collection (10). 

As June Brooks reports (see box previous page), protecting fruiting trees from rats can help seeds mature which in turn become available for seed raising and eventually planting out as small trees.  Kohekohe can tolerate a range of conditions, including shade. Trapping rats and using the species in replanting projects are practical ways of helping to ensure the ongoing survival of kohekohe as one of our most unusual trees.

References:

1. Parliamentary Debates, Volume 174. 20 September to 12 October, 1915. By New Zealand Parliament

2. https://www.tanestrees.org.nz/species-profiles/kohekohe. Accessed 8 February 2020

3. https://maoriplantuse.landcareresearch.co.nz/WebForms/PeoplePlantsDetails.aspx?firstcome=firstcome&PKey=2F50FE1A-D3FF-40D7-AC65-693B0C946607. Accessed 2 December 2019

4. Medway, D. 2008. Kohekohe - a spectacular New Zealand tree. http://kete.pukekura.org.nz. May 2008

5. Dawson, J.W. 1998. Forest vines to snow tussocks: The story of New Zealand plants. Victoria University Press, Wellington

6. Nugent, G., Sweetapple, P., Coleman, J., Suisted, P. 2000. Possum feeding patterns; dietary tactics of a reluctant folivore. In: Montague, T.L. (Editor), The brushtail possum. Biology, impact, and management of an introduced marsupial, pp.10-23. Manaaki Whenua Press, Lincoln, N.Z.

7. Buddenhagen, C. E., & Ogden, J. 2010. Growth and survival of Dysoxylum spectabile (Meliaceae) seedlings in canopy gaps, , 41:1, 179-183, DOI: 10.1080/0028825X.2003.9512838

8. Campbell, D.J. 2011. Seedling recovery on Hauturu/Little Barrier Island, after eradication of Pacific rats Rattus exulans. DOC Research & Development Series 325. Department of Conservation, Wellington. 53p.

9. New Zealand Plant Conservation Network. 2020. http://www.nzpcn.org.nz/flora_details.aspx?ID=1825. Accessed 9 February 2020.

10. Lebneback, c. 2010. Kohekohe, one of the funkiest trees in town! https://blog.tepapa.govt.nz /2010/04/08/kohekohe-one-of-the-funkiest-trees-in-town. Accessed 9 February 2020