Farm Forestry New Zealand

NZFFA guide sheet No. 1: An Introduction to Growing Radiata Pine

NZFFA, June 2007.

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:

1. Wet feet and fluctuating water tables can lead to toppling and root rot. This is the most common limitation for radiata pine.
2. On high fertility sites, especially high N (nitrogen) sites, trees will have poorer form,larger branches, and lower density wood.
3. Humid sheltered inland sites can have problems with fungal disease, particularly dothistroma and cyclaneusma. 
4. Consolidated and impervious subsoils, eg papa can cause rooting problems on some skeletal hill country soils. 
5. 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:

1. Knot-free clearwood, the highest value timber, used for finishing, mouldings, furniture, plywood, etc. 
2. Structural grade timber, with small knots and preferably higher density wood.
3. Roundwood (posts & poles) 
4. Lower value boxing and packaging timber, for logs with large knots. 
5. 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.

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:

1. Growth rate.
2. Straightness.
3. Branch habit
4. Dothistroma resistance.
5. Wood density.
6. 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.

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.

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:

1. The genetic quality of planting stock. High GF or high straightness (GF Plus) stock, and cuttings will retain better form at lower stocking rates.
2. High fertility and more exposed sites (exposed to both wind and sun) need more trees per hectare to ensure good form. 
3. Intensive pruning can remedy some faults. 
4. 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 3.16 x 3.16 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:

• Physical smothering
• Competition for moisture and nutrients.
• Chemical interactions between plants.

Control of surrounding vegetation can be achieved by:

• Physical removal or clearing.
• Mulching.
• Blanket spraying.
• 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.

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:

1. Age 2-3 years. Do sail pruning if toppling is a treat. Removal of double leaders is optional. 
2. 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. 
3. 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. 
4. 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.
5. 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.

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.

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 branch of the Farm Forestry Association, or a reputable consultant for more local information.