manuka are the stuff of controversy. Are they farmland weeds, or
valuable resources? Is that hillside covered with scrub, or forest? Is
it a precious example of native biodiversity and natural character, or
simply a wasteland? For that matter, some layfolk will argue there’s no
such thing as kanuka, only manuka.
look-alikes, and often confused with each other, there are major
differences between kanuka and manuka. (Details in box on page 4). Both
trees can adapt their forms according to the growing conditions. Kanuka
and manuka may look much the same, but often the differences are
obvious, even from a distance.
Looking into kanuka canopy.©
Until about 30 years ago, kanuka and manuka were both identified as
closely related species in the genus Leptospermum. Then, fundamental
differences, especially in the flowers and seed capsules, led Australian
botanists to reclassify them in different genera. Kunzea ericoides is
the ‘new’ scientific name for kanuka while Leptospermum scoparium
remains the name for manuka. (Recent PhD research by Peter de Lange has
recognised several new species of Kunzea previously included with kanuka
– watch this space!)
Kanuka leaves and seed
capsules (left) are smaller than manuka’s distinctive larger seed
capsules and prickly leaves (right). Copper-coloured manuka seed is
pictured here spilling out of split seed capsules.
© Dean Baigent-Mercer
We might feel aggrieved at the Aussies fiddling with the names of New
Zealand species in this way, but kanuka and manuka are part of a large
complex of similar species shared with Australia.
Manuka seed capsule.
Photo: Miranda Woodward
Could this be the origin of the widespread misunderstanding that kanuka
and manuka aren’t New Zealand natives? How often have I heard something
like ‘Oh, we’re only cutting scrub, we wouldn’t touch the native!’ –
implying the ‘scrub’ (kanuka-manuka) isn’t native. Far from it; both
were present well back in New Zealand’s geological past.
That word ‘scrub’ – it can be used with the emphasis of a four-letter
word to suggest the ‘weed’ status of a vegetation, its illegitimacy and
lack of value, indeed its negative value. For that reason, many
conservation-focused people avoid using the word. But ‘scrub’ is also a
straightforward technical term for closed-canopy woody vegetation
dominated by stems less than 10 centimetres diameter, a purely
descriptive term without any judgmental implications.
‘Shrubland’ is an alternative word sometimes used instead of ‘scrub’ by
people concerned with its negative connotations. But technically,
shrubland is another form of vegetation – essentially scrub with an open
canopy, where shrub cover is less than 80%. On this basis, there is
plenty of both scrub and shrubland dominated by kanuka and manuka in
many parts of New Zealand and notably Great Barrier.
Close up of manuka flowers.
Photo by Miranda Woodward
Much of the vegetation that is commonly referred to as scrub is,
however, technically forest. Scrub becomes forest when the dominant
stems forming the canopy are more than 10cms diameter at breast height.
For kanuka this normally occurs when the stand is about 30 years old, at
which time it is typically 8-12 metres tall. These are small trees,
agreed, but kanuka will keep on growing to a large size if not felled or
Many of us will know a corner with some large ‘old man’ kanuka. My
favourite is on the high marine terrace surface of Whetumatarau, a
dramatic plateau immediately behind Te Araroa on the East Cape. Large
kanuka trees are a component of a mixed forest there. I measured a
single stemmed specimen to be 94 centimetres diameter, and estimated its
height at 25 metres – a great forest tree laden with perching lilies,
orchids and other epiphytes. By comparison with nearby kanuka, known to
post-date 1857, I estimate these larger kanuka trees to be 300-400 years
So while some people see all kanuka vegetation as scrub, I cannot accept
this. Kanuka and manuka are ‘seral’ or successional species, which
dominate key parts in the series or succession of vegetation types which
follow the colonizing of a new site. Here size really does matter.
Kanuka grows en masse to form dense scrub; then, as the dominant stems
grow and the others are suppressed and die, it matures to form a kanuka
forest. This will generally diversify to a mixed forest and ultimately
be replaced in a natural succession – if we wait long enough.
Hill country farmers are very familiar with the most basic ecological
feature of kanuka and manuka – their ability to colonize the smallest of
bare patches in sparse pasture. Those tiny airborne seeds get around,
and the essentially unpalatable seedlings do well in full-light
conditions. They may also colonize extensive bare sites after fires or
Kanuka grows well on soils of middling-to-good natural fertility and
drainage. Manuka by contrast favours wetter soils and low-fertility
leached soils. It is not so much an active preference for poor
conditions; rather, that with competition between the two, kanuka fails
in such circumstances. In contrast, manuka often establishes with kanuka
on the average or better sites but is suppressed by the faster-growing
kanuka and dies out within 10-20 years, after being overtopped.
The net result is that kanuka dominates in some areas, such as most of
the Gisborne District. Manuka persistently dominates on wetland margins,
and on some particularly hard, ‘bony’ or burnt sites. It also flourishes
in areas with consistently high annual rainfall, and at higher
The different lifespans of manuka and kanuka is the basis of another
important distinction between them. Manuka is comparatively short-lived
– generally to about 60 years. As a stand approaches this age, there is
a progressive breakdown of the canopy as individual manuka die or fall.
This allows seedlings or saplings of other species to come through. Now
there is an early succession to forests dominated by broadleaved species
such as rewarewa or kamahi. In some cases, where browsing by stock or
wild animals is excessive, this natural succession may fail – then the
manuka may be replaced by mingimingi and bracken, in patches, or a
second generation of manuka establishes itself.
Kanuka by contrast is long-lived. Stands dating from the abandonment of
land during the economic depression of the 1930s, or before, are
widespread. Whether the plants beneath them are heavily browsed by
animals or not is to some extent immaterial as far as survival of kanuka
forest is concerned. The kanuka will still be there at the end of
another century. Removing browsing animals from the understorey would,
however, allow a diverse forest to establish and eventually succeed the
Manuka and kanuka have other values, too. While some iwi leaders have
declared that manuka (including kanuka) have no worth, others consider
that its former use for prized tools and weapons represents a cultural
value of high importance.
On the utilitarian front, perhaps the best known value, for kanuka
especially, is as a source of firewood. Alas, in the absence of
sustainable management systems, this use tends to be an opportunistic
‘mining’ of the resource.
The quality of kanuka timber also suits it to machining for tool
handles, with far higher value-added potential. While there have been
encouraging thoughts of harvesting kanuka for such purposes, using
sustainable management practices on quite modest areas, no one has yet
got that off the ground on a commercial basis.
kanuka near Wharariki Beach, Puponga Farm Park shows kanuka‘s
contortionist abilities in extreme conditions; its groundholding ability
is a major stabilizing influence on steep slopes. © Dean Baigent-Mercer.
There has been a tendency in the past to regard kanuka and manuka as
significant only as a ‘nursery crop’ allowing a ‘real’ forest to
develop, but there is far more that makes kanuka-manuka vegetation
valuable. High density kanuka-manuka scrub/forest is very effective at
holding the land in severe rainstorms – in maintaining slope stability
on the steep hill slopes so prone to soil-slips when in pasture. Landcare
Research has shown that the combination of canopy interception of the
rain, and the strong interlocking roots, means kanuka stands 16-20 years
old or more are as effective at erosion control as close-planted pines
of eight or more years old. With kanuka there is the added opportunity
for that stability to be maintained for centuries. Kanuka-manuka
scrub/forest won’t stop an existing gully eroding out, but it will stop
a gully initiating on a slope that in pasture would be vulnerable.
Both kanuka and manuka yield honey in large volumes. This is generally
sold as manuka honey with a significant price premium over clover honey.
Spectacularly effective antibiotic activity has been tested in some
manuka honey (but not from kanuka).
The oil extracted by steam distillation from manuka leaves from the East
Coast also has striking anti-bacterial and fungicidal properties. Manuka
oil is being used in a variety of medicinal and cosmetic products,
commercially produced and marketed from a number of sites including
Barrier Gold’s operation at Port FitzRoy.
A remarkable recent discovery is that manuka oil varies dramatically in
chemical composition and properties from district to district. This
illustrates firstly that manuka goes a long way back into the geological
past and has evolved locally, and secondly how much we have still to
learn about New Zealand’s plants and biodiversity generally.
Kanuka and manuka-dominant vegetation also provide habitat for a
remarkable variety of other plants and animals – they are major
repositories of New Zealand’s indigenous biodiversity. Many native
orchid species, for example, particularly favour older kanuka or
Measured by species numbers and ecological complexity the most important
elements of biodiversity are the invertebrates – moths, beetles,
millipedes, spiders, snails and the rest. Research work in the Gisborne
district shows that the significance and diversity of the invertebrate
fauna in 60-year-old kanuka forest is as great as that in primary
forest. Extensive kanuka-manuka areas support large numbers of the
forest birds including threatened species such as whitehead/popokatea
To some, kanuka-manuka areas are but signs of recent farming gone wrong;
an essentially unnatural phenomenon of the past century. But there is a
long history of forest modification, extending back to the first Maori
occupation and long before, due to fires and other disturbances. So
kanuka and manuka scrub forests are an important part of the natural
character of most districts.
The character of kanuka and manuka vegetation ranges as a continuum,
from nuisance weeds invading pasture at one end, to a treasure trove of
indigenous biodiversity and natural character at the other. The
challenge is deciding at what point in the continuum do the positive
values become dominant.
There is no simple answer, and to a great extent it must depend on the
specific context of an area. Landowners will commonly argue that their
own views on the subject must be paramount. I would like to think it
possible to stimulate increasing respect among landowners for kanuka and
Adapted (with permission) from an article published in Forest and Bird
by Christopher Ward.
|Telling differences between kanuka and manuka
manuka are distinctly different species, though they can look
very similar. Kanuka grows faster and bigger than manuka, but
you can’t simply call it manuka for the small stuff and kanuka
when it’s bigger! The following features help define the
• Kanuka has narrow parallel-sided leaves several
times longer than wide and notably soft to the touch
• Manuka leaves are more ovoid but sharp-pointed (‘lanceolate’)
with the prickly apex giving the foliage a harsh feel.
• Kanuka foliage is generally a rather bright olive-green.
Specific colour features of kanuka and manuka vary with the
seasons, and regionally.
• Manuka is duller, generally darker (not so obvious when very
In overview manuka often has a grey-brown look, from a
combination of the leaf colour and the branches/stems which
typically have a covering of sooty mould (which thrives on the
sugary excretion of an introduced scale insect). This mould is
much more prevalent on manuka than kanuka.
• Kanuka bark is a light tawny brown. Narrow vertical strips of
bark are characteristic of kanuka.
• Manuka bark is darker with a reddish tinge. It comes off in
very thin flakes, wider and less regular than kanuka bark.
• Kanuka flowers are notably smaller, 4-5mm across, creamy
• Manuka flowers are 10-12 millimetres across and generally pure
• Kanuka flowers are carried in dense elongated clusters (or
‘cymes’) towards the end of the branchlets
• Manuka flowers are more evenly scattered over the plants as
• Kanuka generally flowers once a year only, in midsummer.
• Manuka flowers strongly a little earlier than kanuka, and
additionally in irregular bursts at other times.
• The kanuka seed capsule is less woody, only 2-3 millimetres
across and generally disappears after a month or two. Generally
kanuka does not carry seed capsules, except briefly in late
• Manuka has a hard woody seed capsule 5-6 millimetres across
which persists on the plant for a year or more after flowering.
At any time of the year you will see seed capsules of various
• Kanuka generally has faster growth rates and reaches a larger
size so it is commonly seen as trees, 10-15 m tall and more, and
15-40 cm diameter.
• Manuka generally stops at about 6-8 m height and 7-10 cm
diameter, or less on the poorest soils (e.g. 1–2 m on the Te
The growth forms of kanuka and manuka are slightly different –
the somewhat droopy branchlets of kanuka often contrast with
more erect manuka – but there is much variation caused by the
character of the site, the density of the stand, and tree age.