No. 18 High quality timber eucalypts for warmer sites
NEW ZEALAND FARM FORESTRY ASSOCIATION INFORMATION LEAFLET
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| Eucalyptus
pilularis growing on coastal sand dune country. |
While a number of eucalypts are adapted to growing in cool climates,
the best timbers are generally produced by species favouring warm sites
such as can be found in northern New Zealand and on north-facing slopes
in the northern half of the South Island. Most are somewhat sensitive
to frost,
particularly as seedlings, but note that frost susceptibility depends
on their physiological state – semi-dormant seedlings conditioned to
drought or starved of nitrogen are much hardier than actively growing
seedlings.
Timber eucalypts
favouring warm sites fall into two main groups:
1. The
stringybark eucalypts
2. The eastern blue
gums
3. Other species
Natural
durability in the ground
Establishment
Pruning and thinning
Processing
and end use properties
1. The
stringybark eucalypts
This group produce a light brown timber that is easy to saw and season,
and which is hard, strong, stable, and ground durable. Although best
suited to free draining, lower fertility soils, they will tolerate
winter-wet clays e.g. in Northland. Growth rates vary with species and
provenance, but are generally slower than the faster growing ash
eucalypts. Few suffer from serious insect problems, and four species
are currently recommended:
E.
pilularis
(blackbutt) comes from the coastal forests of NSW where it
grows to huge size. Seedlings do not tolerate frosting but trees will
stand moderate exposure to salt winds. Form is quite variable and
rather poor in some provenances, but to date the Waipoua seedlot seems
to have performed best in New Zealand.
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| Eucalyptus
muelleriana on coastal sand dune country. |
E.
muelleriana
(yellow stringybark) is a medium to large tree from
southeast NSW and eastern Victoria. Probably the best milling eucalypt
of all. Generally a vigorous tree of variable form prone to double
leaders. Rather frost tender but there has been limited provenance
selection to date.
E.
globoidea (white
stringybark) is a smaller tree, commonly regarded
as a slower growing species for harder sites, but provenances vary
considerably. Seedlots tracing back to Glenbervie (Northland) are
preferred.
E.
laevopinea
(silvertop stringybark) is a tall forest tree from the
cooler northern tablelands of NSW. Not common in NZ, but tolerates
colder sites. A good milling species of good form and vigour.
2.
The eastern
blue gums
This group produces hard, strong, durable timbers attractively coloured
pink or red. While the timber is easy to dry, the species often suffer
extreme growth stresses making them difficult to saw. Logs greater than
70cm diameter are preferred. The major problem with this group is the
succession of insect pests that have arrived in recent years, and until
these are under biological control, the species cannot really be
recommended.
E.
botryoides
(Southern Mahogany) occurs both as a poor-form coastal
species and as a tall
forest species, so provenance is very important. It is tolerant of salt
winds and wet sites (not swamps) but tends to be heavily branched and
suffer crown breakage on windy sites.
E. saligna (Sydney
blue gum) is a tall tree from the eastern strip of
NSW and southern Queensland. Generally of good form, it requires
reasonably fertile soils, but does not tolerate salt winds and can
suffer crown breakage on exposed sites. Neil Barr used to emphasise the
desirability of provenances with interlocked wavy grain. These are more
stable, but opinions on relative merits vary.
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| Eucalyptus
saligna 23 years old, Northland. |
E.
grandis (Flooded
gum) is similar to E. saligna
and often confused with it
in Northland.
E. robusta (Swamp
mahogany) is a smaller, poorer form tree, rare in NZ, but
it has the merit of growing in swamps.
3.
Other species
Amongst the myriad of other possible timber species, two are notable:
E.
maculata
(Spotted gum, also known as Corymbia
maculata)
is a good
milling species for warmer sites on a range of moderate to good soil
types. Suffers from some insect problems.
E. microcorys
(Tallow wood) is a slower growing species for warmer
frost-free sites on a variety of soils.
Has grown well on coastal sands as far south as the Manawatu. An
attractive tree with few insect or disease problems. Extremely durable
timber, regarded as the best hardwood of eastern Australia.
Natural
durability in the ground
Only mature heartwood is durable, and
even then, durability is variable between and even within trees. Note
that the most durable timbers are very heavy, and difficult to staple
when dry.
Class
I durability (lasting more than 25yrs in the
ground) E.
microcorys, E. bosistoana (frost hardy), E melliodora (frost
hardy),
E. propinqua, E.
cornuta, E. sideroxylon (frost hardy), E. paniculata,
E. leucoxylon
Class
II durability (15 to 25yrs in the ground) The stringybarks
and eastern blue gums
(top)
Establishment
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| Typical log out-turn from a 35
year-old eucalyptus. |
All these species are best established in the spring (Sept-Oct.) using
Rootrainer® seedlings 20-30cm tall. A high-nitrogen
fertiliser, applied either as a slow release tablet or as loose
fertiliser in a slit 15-20cm from the seedling assists in rapid
establishment. Eucalypts are sensitive to many
chemicals used for releasing, but Gallant, Gardoprim and Versatil have
all been used successfully. Avoid spraying the foliage as much as
possible.
Planting alternate rows with a radiata pine nurse is cheaper than
planting pure eucalypts and works well at total stockings of 1000 to
1200sph. Faster growing eucalypts (most species on favoured sites)
should be planted a year behind the pines, but severely prune and then
remove the pines before they dominate the eucalypts.
Pruning and
thinning
Most eucalypts will shed their smaller branches naturally, but annual
pruning from age 2 to 3 is recommended. Start by removing double
leaders and any branches over 4cm diameter, and prune in the driest
part of the year (mid-late summer).
Thinning is critical and should be done progressively as crowns touch
until the trees are 12 to 15m high and pruned to 6m. Thinning can then
be to a final crop stocking of no more than 100 to 200sph depending on
species and site.
A simplified structured regime is as follows:
Year 3 –
Form prune 300 potential crop trees/ha
Year 5 –
Prune the best 200/ha to 3m and thin to 300 to 400/ha
Year 8 –
Prune 150 best crop trees/ha to 6m, and thin or,
Year 12 –
Prune to 9m at crop height 25m and thin to 150/ha
On good sites, trees may get to 70cm dbh and be millable by age 30, but
it is probably better to grow them on to 40 years and to bigger
diameters.
Warmer
climate eucalypt
processing and end use properties
Every locality is
different, and there is no substitute for local experience, so make use
of the knowledge of your local farm forestry members. For more detailed
information, see Neil Barr’s book Growing
eucalypts for milling,
available from your
local branch.
(top)
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Graphic and
photo reproduced from Special Purpose Timber Species – no.1 in the
Small Forest Management series, jointly produced by the Ministry of
Forestry and the NZ Forest Research Institute. © Crown Copyright
Ministry of Forestry, May 1995.
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