Macrocarpa – keeping faith with the old faithful
Denis Hocking
New Zealand Tree
Grower February 2006
In the first part of this issue of Tree Grower we are featuring
articles covering some of the varying species and clones of cypress.
The main generic name is Cupressus,
and if we were to be accurate, the
full species name should be used such as Cupressus macrocarpa or C.
lusitanica. However most of us generally refer to the different
commonly known cypress just by their species name such as macrocarpa
and lusitanica. To make reading the articles easier, and to avoid
excessive use of Latin and italics, this is the style that is used
throughout the feature. However Latin names are used where it seems
necessary to do so.
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| Macrocarpa woodlot age 40 on
Lee’s property, Reporoa. |
Has good old macrocarpa been unjustifiably maligned in recent
discussions? An old faithful sent off to the knackers ahead of its
time? I am inclined to think so. After all macrocarpa – the name is
usually shortened to this one word – was the species that introduced
and educated New Zealanders to the virtues of cypress timbers, only to
be condemned by cypress canker in recent years. But are the problems
with cypress canker perhaps due as much to our misplacement and
mismanagement of the species as to its terminal failings?
Relic of an earlier era
Macrocarpa is a relic of an earlier era and colder ice age climate it
hung on by its root hairs on just 70 hectares on the foreshore of the
Monterey peninsula. Obviously the climate and conditions of modern day
Monterey do not really suit the species. If they did it would be much
more widely distributed. It is more likely that it has survived down on
the beach because of one notable attribute, tolerance of high levels of
salt wind and spray.
Despite its tiny natural range, it has been found to be genetically
quite diverse. This, along with the fact that there are a number of
closely related cypress species dotted throughout California on very
small natural ranges, suggest that Cupressus
was once a much more
dominant genus in present day California, perhaps during the colder
climate of the last ice age. Of course lusitanica and C. arizonica are
still widely distributed in higher country to the east and south along
with Chamaecyparis spp. to
the north.
So is it just possible that with appropriate selection from within this
genetic diversity and planting on cooler sites, macrocarpa might
continue to be a desirable plantation species for farm foresters, and
even foresters. What are the strengths and weaknesses of this species?
|
| Macrocarpa 10 years old grown as
understorey for slower growth and better form. |
Strengths
- Very good quality timber, stable, with attractive appearance,
good
working properties and significant natural durability. Even if
technically other cypress species may match it, macrocarpa remains the
local industry standard and market preference.
- It has relatively low and consistent sapwood content, typically
five
growth rings compared to 7 to 14 with lusitanica.
- Fast growth and the potential to grow to very large diameters.
There
are plenty of trees that have shown average annual diameter increments
of three centimetres for periods of 15 or 20 years.
- Macrocarpa responds well to silvicultural treatment with good
diameter responses to thinning, even if these are a little less
dramatic than with radiata pine.
- Responds well to pruning, including very hard pruning, and it is
easy
to produce clearwood.
- Reasonably site tolerant, with excellent tolerance to extreme
salt
wind, even salt spray, and good tolerance to shade.
- Surprisingly genetically diverse.
Weaknesses
- Susceptible to cypress canker.
- Tends to produce larger numbers of branches and larger branches
than
other cypresses which makes for more expensive pruning.
- Often produces heavily fluted logs, especially lower logs. Both
genetic and environmental influences appear to contribute to fluting.
- Needs more fertile soils than radiata pine and some of the
eucalypts,
therefore macrocarpa grows very poorly on steeper sand dunes, but
acceptably on the flats.
So the question is – how do we maximise the strengths and minimise the
weaknesses of macrocarpa? As in all forestry, we have three tricks in
the tool box – environment or site preference, genetics and
silviculture.
Site preferences
|
The same macrocarpa as above at 25
years.
|
So let us start with site preference. It seems to have been common
knowledge for many years that the healthiest and best formed macrocarpa
are almost always on cooler, shadier and sheltered sites, be it trees
on a southern slopes or understorey specimens, although there are
exceptions. Mark Self made exactly these points in a very good article
on cypress canker in the May 2003 Tree Grower,
‘Warm sites favour
canker development … wind damage facilitates infection by canker
fungi’. Apparently the canker fungi Seridium
cardinale and S. unicorne
have comparatively high optimal temperatures around 27°C. The worst
canker is normally reserved for exposed, north facing slopes.
So put your macrocarpa on reasonably good soils, on cool sites,
especially southern slopes. But bear in mind that sometimes things work
better than expected on less than ideal sites.
Genetics
Select a good canker resistant clone or seedlot. I do not think that
any commercially available seed lots offer any gains in canker
resistance. There definitely seems to be marked differences in canker
susceptibility between different clones and certain seed lots.
Kukupa was the first commercial clone released by Forest Research in
1992 and proved to be such perfect fungus fodder, it perhaps did much
to educate people on the limiting influences of cypress canker, but
probably did not do a great deal for the reputation of macrocarpa. In
my limited experience, seedlots from Rodney Faulkner’s trees have
probably performed best, but all I am really prepared to say is that
there are marked differences in canker susceptibility. Getting
hold of seedlings that can be confidently described as canker
resistant may be quite a challenge. I think it would be worth putting
more effort into wider surveys of macrocarpa plantations, looking for
improved canker resistance, and even more important, trees producing
canker resistant progeny. Progeny testing is of course, a much bigger
task than just a simple survey, but Forest Research did develop lab
tests to identify canker susceptibility in seedlings some years ago.
|
| A line of 13-year-old Rangitoto clone
with dead kukupa on each side. |
To date, all that has really been surveyed is the incidence of canker.
I would also like to see a bit more survey work done on fluting to see
whether we can tease out the significance of some of the factors here.
But I would regard this as a lower priority than canker resistance.
Silviculture
Finally there is silviculture, which in my opinion is probably less
significance for health and form, although there is some debate about
this. I had always believed that pruning, even severe pruning, does not
seem to be a major factor in canker susceptibility. Certainly there is
no evidence that pruning aids infection and the direct spread of
canker, but Patrick Milne is quite adamant that pruning does increase
susceptibility to canker when the disease is already present in a
stand. There is agreement that severely affected trees should be
thinned out
of a plantation to reduce the innoculum load.
A simple plea
So my plea is really quite simple. Faithful old macrocarpa has many
virtues, along with a few quite serious problems. With care and
attention I think we can reduce these problems to acceptable levels and
continue to benefit from the virtues. Let us not give up on macrocarpa
just yet.
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