NZFFA guide sheet No. 1: An Introduction to Growing Radiata Pine
03 June 2005
Site Selection
Regimes
Radiata Pine Genetics
Seedlings & Cuttings
Planting Stock
Site Preparation
Planting
Stocking Rates
Releasing
Toppling
Pruning for Clearwood Regimes
Thinning
Rotation Length
Health, Safety & Training
Reading & Video Tapes
Site Selection
Where should you site the plantation ? Will the site suit radiata pine?
Radiata pine is a very site tolerant species, but limitations include:
- Wet feet and fluctuating water tables can lead to toppling and
root rot. This is the most common limitation for radiata pine.
- On
high fertility sites, especially high N (nitrogen) sites, trees will
have poorer form,larger branches, and lower density wood.
- Humid sheltered inland sites can have problems with fungal
disease, particularly dothistroma
and cyclaneusma.
- Consolidated and impervious subsoils, eg papa can cause rooting
problems on some skeletal hill country soils.
- The most serious trace element is Boron deficiency in the East
Coast of both islands, especially drier parts.
Tree form will be better on moderately sheltered and somewhat shady
sites, than sites exposed to full wind and sun. The best sites for
growing good quality trees are lower fertility well-drained sites,
without full exposure to wind. Generally these are not prime pasture
sites.
Note:
- Closed canopy forests are the most effective way of
stabilising erosion prone slopes. They are at least four times more
effective than well maintained spaced planting of poplars on grazed
pasture. A plantation may be a good use for unstable erosion-prone
slopes.
- Easy and cheap access for logging trucks at harvest
can dramatically lift profitability. Small inaccessible blocks can be
worthless.
- Check with both your district council and
regional council to determine whether there are any restrictions or
conditions on growing or harvesting trees in your area.
Regimes
Radiata pine timber can have a number of uses, including:
- Knot-free clearwood, the highest value timber, used for
finishing, mouldings, furniture, plywood, etc.
- Structural grade timber, with small knots and preferably higher
density wood.
- Roundwood (posts & poles)
- Lower value boxing and packaging timber, for logs with large
knots.
- Pulp wood, the lower value market for the roughest logs.
Each forestry regime produces several, and possibly all grades of logs
and timber, but in differing proportions. A clearwood regime gives the
highest returns per hectare, but requires significant investment in
pruning. A framing(structural) grade regime needs higher stocking rates
to control branch size, but avoids pruning, and can be quite
profitable. Roundwood (posts and poles) regimes are shorter, with high
stocking rates. Currently a strong market exists because of vineyard
development. Can suit 10 — 15 year old thinnings.
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Radiata Pine Genetics
Most people are familiar with the GF classification of radiata pine,
where trees were selected for growth (G) and form (F), weighted 2:1.
There was no selection for wood properties, which can be poor in even
the highest GF material. The more recently introduced GF Plus system
rates radiata pine trees on the basis of the following 6 features:
a) Growth rate.
b) Straightness.
c) Branch habit
d) Dothistroma resistance.
e) Wood density.
f) Spiral grain (relates to wood stability).
This allows selection for a range of characteristics in planting stock.
In future years, there may be a significant premium for radiata pine
with improved wood properties, eg high wood density, low spiral grain
timber. Other characteristics can be valuable on certain sites, eg
dothistroma resistance.
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Seedlings & Cuttings
Most planting stock is raised from seed. Cuttings, especially
‘physiologically aged’ cuttings taken from trees which are 3-4 years
old, offer the advantages of better form, lighter branching, less risk
of toppling, but possibly slightly reduced vigor. Generally cuttings
are planted in nursery beds for a year to develop roots. Cuttings are
3-4 times more expensive than seedlings- they are a useful option for
stabilising fast growth of high fertility sites or reducing time taken
to prune.
Planting Stock
Most radiata pine stock is open rooted, rather than container grown.
Traditionally emphasis has been placed on developing a dense fibrous
root mass, with roots trimmed to no more than 6 to 7 cm long. This will
ensure vigorous early growth, but seedlings with fewer roots are
generally more wind firm, though slower growing.
Site Preparation
The planting site should be cleared of major brush weeds (gorse,
manuka, etc) prior to planting. Establishing radiata pine in light
wells or lines cut in scrub is a less satisfactory option. Some
herbicides used to control brush weed, eg Escort, can have residual
effect, and should not be used less than 3 months prior to planting.
Tight soils, and soils with hard pans, can be ripped along planting
lines prior to planting. This makes planting easier and the fractured
soil encourages tree root development.
Hard grazing, before planting can be beneficial, but can increase
susceptibility to pests, particularly hares. Hares, rabbits, possums,
and goats may need controlling if present.
Keep sheep and cattle out for 2-3 years, especially in spring. Stock
damage can be unpredictable... bulls and dairy heifers are amongst the
worst, also stags. Fencing, animal pest and weed control should be
completed before planting to avoid disasters.
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Planting
For open rooted radiata stock use a strong planting spade with a blade
at least 30 cm long and 15cm wide. It can be helpful to mark out rows,
eg with stakes, to guide planters. Straight rows make releasing easier.
Make at least two cuts to the full depth of the spade at right angles
to each other. More cuts may be required in tight soils. Use the spade
to open out and cultivate the planting slit, taking particular care to
cultivate and open the soil at the base of the slit. Push the seedling
to the bottom of the slit, firm slightly, then pull up 5 to 10cm to
ensure that the roots are pointing down before firming further. When
firming with your boot take care not to scrape the stem of the
seedling. Never twist or screw the seedling into the slit. Dig up
occasional seedlings to ensure that the roots are well spaced and
pointing down.
Stocking Rates
The number of seedlings planted per hectare (stocking rate or SPH) will
depend on several factors:
- The genetic quality of planting stock. High GF or high
straightness (GF Plus) stock, and cuttings will retain better form at
lower stocking rates.
- High fertility and more exposed sites (exposed to both wind and
sun) need more trees per hectare to ensure good form.
- Intensive pruning can remedy some faults.
- Higher stocking rates can be used to smother weeds, such as
gorse.
Typical stocking rates are around 1000 per hectare, but depending on
some of the factors could range from 600 to 1500 seedlings per hectare.
Initial stocking needs to be between 2 and 3 times the final crop
stocking, to allow for adequate selection of final crop trees.
Note: a hectare is 10,000 square metres, so planting at spacings of 2 x
5 metres, 2.5 x 4 metres, or 3.3 x 3.3 metres will all give 1000 trees
per hectare (1 tree per 10 square metre).
Releasing
Seedling growth rates are severely reduced, and seedlings can be
killed, by competing vegetation. This may be due to:
a) Physical smothering
b) Competition for moisture and nutrients.
c) Chemical interactions between plants.
Control of surrounding vegetation can be achieved by:
a) Physical removal or clearing.
b) Mulching.
c) Blanket spraying.
d) Pre-planting or post-planting spot spraying (releasing)
Releasing is normally done a short time after planting using
long-lasting residual herbicides of the triazine group, eg. Velpar and
Gardoprim (terbuthylazine). Both can be applied over seedling pines
prior to growth flushing in spring. Velpar has a wider target range,
including blackberry, creeping buttercup and bracken, but can kill
seedlings planted in soils with low organic content, eg. Sands.
Valzine, a Gardoprim Velpar mix is now widely used over Pinus radiata
but not other species. Velpar granules are easier to apply on steep
sites. Gardoprim may be mixed with Gallant for extra control of
grasses, particularly tropical (C4) grasses.
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Toppling
On exposed sites with heavy or wet soils toppling can be a serious
problem from 2 to 5 years. The best solution is a fairly severe pruning
to reduce the sail area of the tree ie the cross-section area presented
to the wind. Small toppled trees can be stood up, re-firmed and then
pruned. In severe cases toppled tree can be cut above the first whorl
to let a branch take over as a new trunk. In extreme cases, re-plant.
Physiologically aged field cuttings are markedly more stable.
Pruning for Clearwood
Regimes
The objective of pruning is to remove the branches from the trunk when
it is 10 to 20 cm in diameter, and then grow a thick sheath of high
value knot-free clearwood around this knotty core.
The key technical terms here are DOS (diameter over stubs) and defect
core. The DOS is the largest diameter over the freshly pruned branch
stubs for each pruning lift. A resin pocket forms in the occlusion zone
outside the pruned branch stub, between 1 to 1.5 times the branch
diameter, before clearwood forms. The defect core, inside the clearwood
is larger than the DOS, and this difference is proportional to the
branch diameter. The best logs have small defect cores.
Normally pruning is carried out in 3 lifts, sometimes in 2 or 4, to a
final height of 6.5 metres. This allows for 6.1 metre pruned butt log,
the maximum length commonly traded. Logs of 4-6 metres long are all
tradable.
A typical clearwood pruning regime is as follows:
- Age 2-3 years. Do sail pruning if toppling is a treat. Removal of
double leaders is optional.
- Age
3-4 years. When trees are about 5 metres high, clear lift prune to a
trunk diameter of about 10cm, rather than a constant height. Leaving
about 2.5 to 3 metres of green crown. Note that trunk diameter
correlates strongly with the crown height above. A 10cm caliper can be
used as a guide. Prune with loppers or saw flush withthe bark collar at
the base of the branch. Remove double leaders in the crown and possibly
cut large branches back to less than half their length.
- Aged
4-6 years.(between 8 to 18 months after the first lift, depending on
growth rate). When the tree height is about 8 metres, prune to a trunk
diameter of 10 to 11cm leaving 3 to 4 metres of green growth. Use a
trunk diameter of 11cm or more on more stressed or disease-prone sites
and 10cm on less stressed sites. Remove any double leaders in the
crown. Maximum DOS should be less than 20cm preferably averaging 16 to
18cm. Average pruned height should be about 4 metres.
- Aged
6-8 years (between 8 to 18 months after second lift, depending on
growth rates). Prune to a 6.5 metre target height. Prune to 10-11cm
trunk diameter. Leaving 3-4 metres of green crown. On stressed or
disease-prone sites do not prune below a trunk diameter of 11-12cm.
- If necessary, return in about 12 months to prune smaller trees to
6.5 metres target height.
The number of trees pruned per hectare will depend on the site,
objectives and costs.
Typically 400 to 600 stems per hectare will be pruned on the first
lift, decreasing to about 200 — 400 per hectare on the final lift. To
ensure an adequate sheath of clearwood (15cm) trees must be grown to a
DBH (diameter at breast height — 1.4 metes) of at least 55cm and
preferably to 60cm. Fewer trees can be grown to such diameters on lower
fertility sites than on higher fertility sites. Typically hill country
sites will not be able to grow more then 300 trees per hectare to
adequate diameters.
A pruned stand certification
scheme, is available to provide independent proof of pruning
standards.
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Thinning
Thinning is the removal of trees not selected for the final crop. Do
not leave unpruned trees competing with pruned trees for too long
because they may suppress them. However thinning too early encourages
excessively rapid early diameter growth (of low quality juvenile wood)
and heavy branching of final crop trees.
Early thinning is normally to waste, but from about 10 production
thinning for roundwood and later for low grade sawlogs may be an option
on accessible sites. There are a number of factors to consider here,
and it is best to discuss options with local operators. For successful
production thinning there must be a market for the smaller diameter
logs, and the site must be suitable for logging without damage to final
crop trees.
Rotation Length
The desire to fell trees early for financial reasons is understandable.
Younger trees will produce a high proportion of low-quality wood. We
strongly urge farm foresters to aim for rotations of around 30 years.
Health, Safety & Training
Forestry is a high risk occupation. Guidance on health and safety is
available from the Occupational Health and Safety Service of the
Department of Labour, who are also responsible for investigating any
accidents.
Training is available from some Polytechnics and private training
providers. The program is co-ordinated by the Logging and Forest
Industry Training Board.
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Reading & Video Tapes
Maclaren, J P (1993) Radiata Pine
Growers’ Manual, FRI Bulletin No .184 New Zealand Forest Research Institute.
Logging and Forestry Training Board, Tree
Releasing, Logging & Forest Industry Training Board, Forest Research Institute, Rotorua.
Maclaren J P (1989) A Manual for
Selection of Crop Trees when Thinning and Pruning Radiata Pine,
FRI Bulletin No 133, NZ Ministry of
Forestry
OSH (1999) Approved Code of Practice
for Safety and Health in Forest Operations, Department of Labour
Occupational Safety & Health Service.
OSH (1995) ‘Guidelines for the
Provision of Facilities and General Safety and Health in Forestry Work, Department of Labour
Occupational Safety & Health Service.
Logging and Forest Industry Training Board, (1992), Quality Tree Pruning, Cardno Video
Productions, P 0 Box 2047, Rotorua
Forest Research Institute & Tasman Forestry Ltd (1992), Pruning Radiata Pine, Video
Available from the New Zealand Forest Research Institute, Private Bag
3020, Rotorua.
Caution
This is necessarily a brief and incomplete document. Consult your local Farm Forestry Association,
or a reputa-
ble consultant for more local information.
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