Farm Forestry New Zealand

Planting

Container grown stock is available from some commercial nurseries; Price per tree should range from $0.80 - $1.50 for 1 year-old contract-grown forestry stock (2020 prices).

Blackbutt requires a warm, sunny site with moderately fertile soil, good soil drainage and an annual rainfall of 1,000 – 1,500 mm spread over the year. The seedlings are frost tender so unless the site is completely frost free, plant in the spring after the last winter frost.

Blackbutt seedlings are not shade tolerant so should be planted in an open site. Use wetted water-absorbing gel in the planting holes to ensure the seedlings don’t dry out before they establish roots. Freshly planted seedlings can be desiccated by severe equinox winds.

Short planting videos are available on Establishing eucalypts on grassland and Establishing eucalypts on cut-over sites.

Spacing

As there can be a lot of variability in planting stock, use a high initial stocking to ensure a wide choice of final crop trees with a good selection of well-formed fast-growing stems. An initial stocking of 2000 stems per hectare (2m x 2.5m) will allow the trees to self-prune with a small defect core and provide a high selection ratio. Trees from genetically improved seedlines can be planted at 600 - 1000 stems per hectare and pruned.

Releasing

Control competing weeds in the first season by manual clearing or by carefully spraying with a residual herbicide. Be aware that eucalypts are very sensitive to herbicides. Spray in calm conditions a couple of months after planting, after the bulk of spring weed germination has occurred. Do not use triazine group chemicals (terbuthylazine, etc.) on light soils such as sands. Use glyphosate with a shield to protect the young trees and make sure no herbicide gets on foliage or green stems. Haloxyfop is safe to use around eucalypts for controlling grasses.

Spray-releasing can also be used during the second season to increase the rate of growth. However, this is not recommended because trees become more prone to toppling in strong winds (windthrow).

See Successful establishment of tree seedlings »

Grazing/Browsing

Eucalypts are damaged if grazed by stock, goats and deer so fence the area to keep them out. A single hotwire electric fence will deter most cattle, but it is best to construct a full post and wire fence.

During the first summer eucalypt seedlings are highly palatable to possums which should be controlled with poison, trapping or shooting. Young eucalypt seedlings are also palatable hares and rabbits. They will slice off trees near ground level at a 45 degree angle, killing them.

Pests and diseases

Blackbutt currently has few insect pests In New Zealand. On permanently or seasonally wet sites blackbutt is susceptible to root diseases. The species grows best on well drained soils where rainfall is well distributed over the year.

See Eucalypt pests and diseases »

Blackbutt is grown for timber, carbon storage or firewood. Grown for timber, aim for large logs rather than attempt to restrict branch growth. Grown for carbon, note that a reasonably high stocking of slim trees can hold more tonnes/ha than a low stocking of fat ones. Likewise, grown for firewood, slim trees (up to 30 cm diameter, age 7 - 15) will be easier to fell and handle.

Suitability for steep slopes: Blackbutt does not like strong winds, or bony thin soils with low fertility. However, provided exposure and erosion is not too severe, blackbutt is suitable for erosion control in warmer locations. Blackbutt coppices, so is suitable for permanent erosion control on steep slopes. See Report: Trees for steep slopes - Eucalyptus »

A series of short videos are available on growing eucalypts for timber.

Pruning

If planted at a high stocking, pruning is not required because trees will self-prune and any poorly formed trees will be thinned out.

Form pruning: Blackbutt tends to have good form with few double leaders. However, where double leaders emerge, these should be reduced to a single leader as soon as possible so the tree can straighten up. If planted at a low stocking, form prune dominant branches and double leaders annually to minimise branch size and encourage a single dominant leader, and clearwood prune the trees annually to minimise defect core diameter. Pruning can begin once the trees are well-established and above the height of any competing weed vegetation – e.g. from around 2 metres tall.

Form pruning guidelines are available here.

See video on Form pruning eucalypts »

See video on Pruning eucalypts for clearwood »

Thinning

For timber production, thinning is critical and should be undertaken progressively to reduce the risk of windthrow in residual trees.

For clearwood pruned trees, once pruned to full height (e.g. 6-8 m), thinning should commence once the crowns touch and before lower branches begin to die. Thinning should aim for a final crop stocking of around 200-350 stems per hectare of evenly-spaced trees, depending on the target log diameter and rotation length. Thinning can commence before pruning lifts are completed and care needs to be taken to thin before the height to diameter ratio gets too high. Trees left at a tight stocking for too long become tall and skinny.

See a short video on thinning eucalypts.

When to harvest

Every locality is different, but on a good site blackbutt should get to 50 cm diameter within 30 years. Small sawlogs can be grown on rotations as short as 16 years.

Blackbutt is readily sawn, has fewer growth stress problems than most other eucalypts, and no checking occurs with drying. The wood is a pale yellow-brown, hard, strong, tough, moderately heavy and durable. It is coarse textured; fairly straight grained and the sapwood is resistant to borer attack.

Blackbutt is naturally durable and heartwood can be used untreated for structural applications, cladding and exterior decking. Because of its decorative appearance blackbutt is used for flooring, joinery, panelling, furniture, and veneer. Blackbutt can also be used for in-ground applications such as fence posts.

When correctly sawn and seasoned, eucalypt timber can have attractive appearance, along with high strength and stiffness. Most eucalypts have a compression core and tensioned outer wood. When cut longitudinally the ends will bow out. Quartersawing gives the best results in terms of dimensional stability, and to get straight quarter sawn boards a straightening cut is required.

Markets and demand

There is good demand for blackbutt timber because it is hard, strong and suitable for applications requiring durability. Thus the species competes with high-value imported hardwoods and can achieve very good prices in the market, provided grades are good.

A handful of mills around the country have developed a small marketplace for blackbutt timber.

Blackbutt is relatively fast growing. Diameter growth is approximately 1 cm per year and height growth 1-1½ metres a year for the first 20 years. Mean tree height after 8 years is about 12 m, after 22 years is about 30 m and after 50 years is typically about 45 m.

Practical hints for measuring trees offers some advice on monitoring growth.

As blackbutt is an exotic hardwood. tables A2.2 and A2.4 apply, suggesting it stores carbon roughly three times faster than indigenous forest and about 80% as fast as radiata pine.

Timber return on investment

Analysis suggests possible internal rates of return of around 8% pa excluding land costs and carbon revenue, but the result is very dependent on end-use options and log prices. Improved log prices will significantly lift IRR. If logging of old growth tropical rainforests declines as a result of environmental concerns, demand for durable hardwoods such as blackbutt would increase, potentially increasing returns.

• The Eucalypt action group promote growing of eucalypts for the timbers natural durability, strength and hardness properties and decorative appearance.
• Eucalyptus - Information resources