Farm Forestry New ZealandPlantation forestry species for Northland
| Species | Density, dry (kg/m3) | Bending strength, MoR (MPa) | Stiffness, MoE (GPa) | Hardness, Janka (kN) |
|---|---|---|---|---|
| Pinus radiata | 500 | 85.8 | 8.2 | 3.6 |
| Cupressus macrocarpa | 475 | 74.3 | 6.9 | 2.6 |
| Cryptomeria japonica | 384 | 66.1 | 7.2 | 1.8 |
| Sequoia sempervirens | 380 | 24.4 | 6.6 | 1.9 |
| Poplar, Kawa | 440 | 56.9 | 5.4 | 2.3 |
| Totara | 480 | 55.0 | 7.39 | 2.4 |
| Rata x Pohutukawa hybrid | 880 | 114 | 11.4 | NA |
| Cupressus lusitanica | 460 | 69.6 | 6.5 | 2.5 |
| Kahikatea | 450 | 75 | 10.7 | 4.2 |
| Cupressus 'Ovensii' | 495 | 85.6 | 7.9 | NA |
| Eucalyptus botryoides | 675 | 100 | 13.5 | 6.75 |
| Eucalyptus globoidea | 675 | 100 | 13.5 | 6.75 |
| Eucalyptus microcorys | 750 | 100 | 13.5 | 6.75 |
| Eucalyptus muelleriana | 675 | 100 | 13.5 | 6.75 |
| Eucalyptus pilularis | 675 | 100 | 13.5 | 6.75 |
| Eucalyptus saligna, Sydney blue gum | 675 | 100 | 13.5 | 6.75 |
| Eucalyptus sphaerocarpa | 750 | 100 | 13.5 | 6.75 |
Pine
A range of pine species are grown in Northland but the only commercial species is Pinus radiata.
Pinus radiata, radiata pine
Radiata pine is the primary plantation forest species grown in Northland and throughout New Zealand. Northland has a reputation for growing some of the strongest and densest radiata timber in New Zealand. The well-established industry provides a ready market for logs, high-quality genetically improved planting stock and well established management regimes with good data on productivity and expected yields. Radiata pine is a versatile timber used for a wide range of products, with reasonable strength and stiffness properties suitable for most structural applications. The key to its historical success as a timber in New Zealand is that it is easy to treat with preservatives, especially Chrome Copper Arsenic (CCA) formulations. Being very permeable, radiata is the only species authorised for treatment to hazard classes H3.2 and above in the building code, with proven durability performance in a range of exterior applications. However, because radiata heartwood is so permeable this can be seen as a double-edged sword because this property makes radiata both treatable but also perishable. It holds very low natural durability so industry depends on being able to treat it with preservatives. Radiata pine also has reasonably low stiffness values so applications are limited by this, in particular longer structural spans.
Health: Subject to foliar diseases, including cyclaneusma needle cast and red needle cast. Red needle cast is worse in high-elevation Northland sites. Dothistroma doesn't appear to be prevalent in Northland. Incidences of flagging seem to be on the increase. Subject to root disease where drainage is poor.
Timber: Low durability, fairly soft, moderately strong and stiff. Radiata timber processes well into a range of structural products because it is easy to machine and glues well. Perhaps its greatest claim to fame is the ease with which radiata and other pines take chemical treatment, the heartwood can be easily pressure-treated with water-borne preservatives such as CCA.
Mechanical properties (dry wood) Species Density, dry (kg/m3) Bending strength, MoR (MPa) Stiffness, MoE (GPa) Hardness, Janka (kN) Pinus radiata 500 85.8 8.2 3.6 Siting: Radiata pine is hardy to strong wind and poor fertility soils, but has some siting limitations. Trees are prone to toppling and root disease where soil drainage is poor so the species is best planted on free draining soils. Radiata will grow on slip faces, skeletal soils devoid of topsoil and soils with a low nutrient status, but growth rates will be reduced on these sites. It is recommended that phosphate be applied if the soil is especially poor. Radiata will grow reasonably well on exposed ridgetops but poorer form and slower growth will result compared with less-exposed sites.
Steep slopes: Because radiata roots decay rapidly after harvest, clearfell radiata regimes pose concerns regarding risk of post-harvest erosion. The higher costs involved with harvesting under a continuous canopy regime limit economic viability because of higher harvesting costs. The log price threshold that justifies greater harvesting costs is the subject of research.
Species characteristics: Hardy and "bulletproof", with fast growth rates and a short rotation length.
Recommended regime: Plant at 600-1200 stems per hectare. For clearwood production prune to 6-8m in 3-4 lifts and thin down to 200-400 stems per hectare. For unpruned framing regimes final crop stocking can be as high as 600 stems per hectare.
Key message: The conservative option, tried and true.
Cypress
Cypress timber is generally identified as "macrocarpa" in New Zealand. Cypress species require free draining soils with moderate fertility.
Regimes for growing cypress include shorter rotations with higher stockings targetting higher grades of knotty timber that include sapwood, clearwood regimes where clear heart/sapwood is targeted and regimes for clear heartwood production.
If cypress are to be pruned for clear heartwood production it must be understood that diameter over stubs (DOS) should be kept to a minimum, final crop stocking should be low (200-400 stems per hectare) and rotation length should be a minimum of 35 years to maximise tree diameters and therefore clear heartwood production. The grower must understand if clear heartwood is the goal, pruned log diameters must be large.
Cupressus macrocarpa, Macrocarpa
Macrocarpa has a history of being widely planted in Northland, with considerable volumes of timber grown and sold from the region. What we know as "macrocarpa", the old shelter rows and farm woodlots throughout the region, were more likely to be macrocarpa hybrids grown by nurseries that collected seed from healthy locally-grown trees.
Most of the resource is gone now and attempts to replant have mostly failed because of cypress canker disease. Although this failure is often presented in a negative light, research in Northland has shown that there are genotypes available that offer canker resistance. Indeed the current prevalence of canker actually resulted from nurseries growing a single Southland-sourced seedline from the 1980's onwards that proved to be highly susceptible to the disease. For over twenty years growers who planted the species were disappointed with the results, without being aware of the reason for crop failure. Although this tarnished reputation now appears to be unjustified and merely the result of one poor seedlot being so widely grown, rebuilding a lost reputation is a long and slow process. However, the lesson provides a clear message to growers to be sure that the seedline they use must be of proven canker-resistant origin.
Health: Macrocarpa as a species is susceptible to canker disease. Only carefully selected seedlines and cultivars should be planted in Northland, which because of its warmth and humidity, is considered to be a marginal region for the species.
Cattle and deer will strip the bark from this species at all ages if given access.
Timber: Macrocarpa has earned a reputation for being a high-quality timber and substitute for kauri. Much of the locally produced macrocarpa originated from large old trees, which produce the best quality timber in terms of durability, colour and strength. A plantation industry would need to build on the good reputation for macrocarpa but also make sure that consumers are aware that plantation timber from younger trees is not as richly coloured as the historical resource. Rotation length can be as short as 20 years provided sapwood is accepted in the product.
Macrocarpa heartwood is highly scented, has a rich golden colour and decorative appearance, with good natural durability. Sapwood is paler but still holds decorative appeal and is resistant to anobium borer. Tests have shown that even the sapwood holds reasonable durability, greater than Douglas fir. This property offers an opportunity for utilising untreated macrocarpa in structural applications, specifically for buildings of simple design under clause B2 of the building code.
Mechanical properties (dry wood) Species Density, dry (kg/m3) Bending strength, MoR (MPa) Stiffness, MoE (GPa) Hardness, Janka (kN) Cupressus macrocarpa 475 74.3 6.9 2.6 Siting: Requires free-draining soils. All cypress species require very free draining soils that are moderately fertile.
Macrocarpa is very hardy to wind exposure, including salt-laden winds. However, it becomes heavily-branched in highly-exposed sites and such sites are not very well suited for timber production. Macrocarpa prefers cooler south-facing slopes.
Steep slopes: Macrocarpa roots are slow to decay and if crop trees are not pruned can be held at a fairly high stocking to maturity. A species suitable for controlling erosion in steeper slopes and provided log values were high enough could be grown as a continuous cover forest to further reduce erosion risk.
Species characteristics: Requires high initial stockings to limit size and number of branches. Macrocarpa is notoriously branchy and slower to prune than radiata pine using traditional loppers.
Recommended regime: Plant at 1600-2000 stems per hectare. Thin in 3-4 stages down to 400-600 stems per hectare for a 25 year rotation. This gives a 4:1 thinning ratio. A higher thinning ratio provides better growth rates, health and form in residual trees. For clearwood production prune to 6-8m in 3-4 lifts and thin down to 200-300 stems per hectare for a 35 year rotation.
Key message: If you are wanting to grow macrocarpa, ensure you collect or purchase seed from canker-resistant Northland-grown trees, or grow cultivars with a proven track record in the region.
Cupressus lusitanica, Mexican cypress
Lusitanica cypress is closely related to macrocarpa and has a very similar timber. Lusitanica is a common plantation forest species in Northland and provided it is well sited, is a reliable species producing good volumes of timber in rotations of 25-40 years. Like all the cypress species, growth is slower than radiata pine but because shade tolerance is greater stocking can be higher. This means productivity can be high provided the market accepts smaller diameter logs. New regimes are being considered for specialised small diameter log processing that involve no pruning but produce decorative timber with live ("green") knots.
Health: Lusitanica cypress is generally a healthy tree in Northland and with a low incidence of cypress canker disease. Possums and Kaka can cause damage to the tops of trees. Cattle and deer will strip the bark from this species at all ages if given access to trees.
Timber: The timber is scented, decorative, has reasonable structural properties and is naturally durable. Suitable for interior trim, furniture, sarking, framing, exterior cladding (heartwood only)
Mechanical properties (dry wood) Species Density, dry (kg/m3) Bending strength, MoR (MPa) Stiffness, MoE (GPa) Hardness, Janka (kN) Cupressus lusitanica 460 69.6 6.5 2.5 Siting: Lusitanica cypress needs careful siting. It requires shelter from strong winds and has low tolerance of salt-laden winds. Lusitanica requires moderate soil fertility and free draining soil.
Steep slopes: Lusitanica roots are slow to decay and if the trees are not pruned they can be held at a fairly high stocking. A species suitable for steeper slopes and provided log values were high enough could be grown as a continuous cover forest to further reduce erosion risk.
Species characteristics: A reliable, well proven species for Northland provided it is appropriately sited.
Recommended regime: Plant at 1600-2000 stems per hectare. Thin in 3-4 stages down to 400-600 stems per hectare for a 20-30 year rotation. This gives a 4:1 thinning ratio. A higher thinning ratio provides better growth rates and form in residual trees. For clearwood production prune to 6-8m in 3-4 lifts, targeting a maximum diameter over stubs of 10cm and thin down to 200-300 stems per hectare for a 35 year rotation length.
Key message: Prune for clearwood production on a longer rotation or grow as an unpruned stand on a shorter rotation.
Cupressus 'Ovensii', Oven's cypress
Ovensii is a clonal cypress hybrid, meaning that trees are cutting-grown and genetically identical, originating from one parent tree. Ovensii is a cross between lusitanica cypress and Nootka cypress and has inherited desirable traits from both parent species. Although only planted for 25 years or so in Northland, Ovensii cypress is gaining a good reputation among growers for resilience and reliability.
Although slightly slower growing than macrocarpa and lusitanica, Ovensii timber may hold slightly higher durability than those species. Furthermore, wood properties are consistent between trees, unlike the variability inherent in seedling-grown trees. However, because Ovensii is cutting-grown, trees can be expensive unless sourced from a nursery specialising in producing them.
Health: Good resistance to canker and healthy in Northland. Cattle and deer will strip the bark from this species at all ages if given access.
Timber: Ovensii produces a decorative, lighter-coloured wood than macrocarpa and lusitanica, with less "lustre". It has fairly good mechanical properties and durability, lending itself well to structural applications where natural durability is specified. The wood is stable and suitable for a range of joinery applications such as windows, doors and fittings and heartwood can be used for cladding.
Mechanical properties (dry wood) Species Density, dry (kg/m3) Bending strength, MoR (MPa) Stiffness, MoE (GPa) Hardness, Janka (kN) Cupressus 'Ovensii' 495 85.6 7.9 NA Siting: Ovensii is fairly resilient to wind exposure but is not well adapted to coastal conditions and salt-laden winds. Like other cypresses, Ovensii requires free draining soil and moderate fertility.
Steep slopes: Suitable for exposed eroding slopes but may require the addition of phosphate where eroded soils have become skeletal. Ovensii roots are slow to decay and if the trees are not pruned they can be held at a fairly high stocking. Provided that log values were high enough Ovensii cypress could be grown as a continuous cover forest to further reduce erosion risk.
Species characteristics: Well formed, healthy and moderately fast growing. Prone to some ramicorn-type (large, upward growing) branches.
Recommended regime: For clearwood production interplant 600 stems per hectare with 800-1000 seedling macrocarpa or lusitanica. Prune all Ovensii to 6-8m in 3-4 lifts and progressively thin the seedlings. Thin Ovensii down to 300 stems per hectare for a 35-40 year rotation. For 25-30 year rotation plant 600 stems per hectare and prune any double leaders and large ramicorns.
Key message: A reliable choice for Northland but planting stock can be expensive. An increased scale of planting would lower the price.
Cedar
Cedar timber is light, stable and durable, suitable for cladding and exterior joinery but not suitable for structural applications. The only cedar species well suited to Northland's subtropical climate is the Japanese cedar, Cryptomeria japonica.
Cryptomeria japonica, Japanese cedar
Japanese cedar is highly productive on the right site and very adaptable to windy sites. Japanese cedar grows well in Northland's climate and is relatively untroubled by pests and diseases.
Health: Very healthy. Cattle and deer will strip the bark from this species at all ages if given access.
Timber: Japanese cedar timber is reddish-brown, light and stable and the heartwood is durable, suitable for cladding and exterior joinery but not suitable for structural applications. A similar timber to redwood but strongly scented.
Mechanical properties (dry wood) Species Density, dry (kg/m3) Bending strength, MoR (MPa) Stiffness, MoE (GPa) Hardness, Janka (kN) Cryptomeria japonica 384 66.1 7.2 1.8 Siting: Requires good soil drainage and moderate fertility. Adaptable to strong winds but not coastal conditions
Steep slopes: Tolerates high wind exposure and fairly thin topsoil provided fertility is reasonable. On exposed ridgetop slopes devoid of topsoil may require the addition of fertiliser (in particular phosphate).
Species characteristics: Tall narrow-conical tree that tends to be lightly branched. For this reason initial stocking does not need to high to control branch size. Management should avoid overstocking and formation of black (dead, bark-encased) knots.
Recommended regime: Plant at 600 stems per hectare.
Key message: Reliable species for steep slopes, provided stock are excluded from the stand.
Redwood
Redwood timber, like cedar, is light, stable and durable, suitable for cladding and exterior joinery but not suitable for structural applications. There are two species of redwood from North America grown in New Zealand, the giant sequoia and the coast redwood. Giant sequoia is a cold-climate species whereas coast redwood, from the fog belt of California, suits Northlands humid subtropical climate.
Sequoia sempervirens, coast redwood
Some of the largest Coast redwood trees in the country are found in Northland. Coast redwood grows well in Northlands humid climate and is relatively untroubled by pests and diseases.
Good growth rates and form are achieved by improved clonal stock. Research is still underway for improved heartwood content and durability.
Health: Relatively untroubled by pests and diseases.
Timber: Redwood timber is red, light and stable. The heartwood is durable above ground and is suitable for cladding and exterior joinery but not very suitable for structural applications because of issues with fixings. A similar timber to Japanese cedar but not strongly scented.
Mechanical properties (dry wood) Species Density, dry (kg/m3) Bending strength, MoR (MPa) Stiffness, MoE (GPa) Hardness, Janka (kN) Sequoia sempervirens 380 24.4 6.6 1.9 Siting: Requires moderately fertile soils and sufficient soil moisture and depth. Not suitable for exposed slopes deficient in topsoil.
Steep slopes: A coppicing species, i.e. the roots do not die but the stump stays alive after felling and re-sprouts. Coppicing species hold the soil from slipping even after harvest. However, redwood requires adequate soil depth and shelter so not suitable for upper slopes.
Species characteristics: Coppices. Not suitable for exposed and skeletal sites. Pruning requires careful management because of epicormic shoots that emerge from pruning scars. Tall narrow-conical tree that tends to be lightly branched. For this reason stocking does not need to be as high as for other species. Management should avoid overstocking and formation of black (dead, bark-encased) knots, while limiting knot size.
Recommended regime: Plant clonal stock at 600 stems per hectare.
Key message: A reliable choice for lower slopes with a potential market for sawn timber to California.
Eucalypt
Northland experience has identified eucalypt species that have grown well in our region, are relatively untroubled by insects, and offer high potential for quality timber production. The high quality attractive timber certainly has appeal.
Eucalypt species produce hardwood of varying densities, durability and strength. Timber colour also varies with species, from pale brown to rich red.
For simplicity, species can be grouped according to timber properties. The species identified as having the greatest potential for premium applications are the "medium density" eucalypts.
| Timber properties | Growth rate | Density | Species |
|---|---|---|---|
| Group 1: Red timber, wide sapwood, moderately durable to durable, strong | Fast to very fast | Medium | E. botryoides |
| E. saligna | |||
| Group 2: Pale brown timber, narrow sapwood, moderately durable to durable, strong | Fast | Medium | E. globoidea |
| E. muelleriana | |||
| E. pilularis | |||
| Group 3: Pale brown timber, durable to very durable, very strong | Medium | Medium to high | E. microcorys |
| E. sphaerocarpa |
The "rule of thumb" is that for greater durability the species will be slower growing, have higher density and be less easily worked.
Species also vary in their siting requirements, in particular soil drainage requirements and wind exposure:
| Species | Tolerance to wind exposure | Tolerance of Salt-laden wind | Soil requirements |
|---|---|---|---|
| Eucalyptus botryoides | high | good | poor - free draining |
| Eucalyptus globoidea | good | moderate | free draining |
| Eucalyptus microcorys | low | low | average - free draining |
| Eucalyptus muelleriana | medium | moderate | free draining |
| Eucalyptus pilularis | medium | moderate | free draining |
| Eucalyptus saligna | low | good | poor - free draining |
| Eucalyptus sphaerocarpa | high | moderate | free draining |
Species selection can also be based on economic factors that influence risk, log value and species productivity:
| Species | Growth rate | Sapwood width1 | Compression core2 | Biological risk3 | Timber value |
|---|---|---|---|---|---|
| Eucalyptus botryoides | fast | wide | large | high | high |
| Eucalyptus globoidea | fast | narrow | small | low | high |
| Eucalyptus microcorys | medium | medium | negligible | low | very high |
| Eucalyptus muelleriana | fast | narrow | small | low | high |
| Eucalyptus pilularis | fast | narrow | small | low | high |
| Eucalyptus saligna | fast | wide | large | high | high |
| Eucalyptus sphaerocarpa | medium | narrow | negligible | low | very high |
- Sapwood width affects recovery of heartwood products from the log, which tend to hold significantly higher value than those containing sapwood.
- Compression core is the wood in the centre of a eucalypt tree that has very low strength and durability resulting from compressive forces that cause micro-fractures in the wood and make it brittle. This can affect sawn recoveries from a log.
- Biological risk is the assumed risk of a new incursion occurring that impacts on the health of the species, evaluated based on historical incursions of insect pests and fungal pathogens.
Nursery stock and planting
Eucalypts should be container grown and planted out when 15-25 cm tall, well hardened and with 6-8 pairs of leaves. The root system should not be constricted and excessively deformed in the container. The bottom quarter of the plug should be cut off in roottrainer stock to encourage new roots and reduce deformation in regenerating roots. Side-slot containers are the best for reducing root deformation, which can strangle the growing plant and increase the risk of windthrow in the first few years after planting. A sample of trees should be removed from the containers and the soil removed to expose the taproot. This should be checked for deformation resulting from poor pricking out procedures. Generally eucalypts are planted in early spring when the risk of hard frosts is over but soil moisture is still good. Winter planting is acceptable on slopes above where frost drains to.
Weeds are usually desiccated prior to planting by spot spraying with glyphosate. Eucalypts are sensitive to weed competition, particularly grasses. Containerised trees should not be "slit & stuff" planted. The soil should be sufficiently cultivated and clods of soil well broken up so that the plug does not get squashed and deformed when the soil is firmed back into place. Air cavities must not be present in the planting hole after the soil is tramped back in place. Trees should not be planted deep in winter-wet soils to avoid collar rot. Trees respond well to fertiliser tablets placed in the planting hole underneath the tree. If weed control is good 50g DAP can be spread immediately above the tree on sloping ground or around the tree on flat ground. Fertile soils should not be fertilised at all.
Eucalypt silviculture
Silviculture of eucalypts can be very different from radiata pine. If planted at a high stocking, eucalypts self prune (shed their lower branches), negating the need to prune for clearwood, which can offset the high costs of planting at a high stocking rate. Efficient methods are available for thinning high stockings of eucalypts, such as chemical injection, which kills the tree to the roots. Chainsaw thinning is useful for thinning eucalypts where it is desired for them to coppice from the stump and remain as an understory tree, for example within a continuous cover forest. Most eucalypt species coppice (re-grow) from the stump when felled. The roots stay alive and a new stem grows, providing a second tier of understory trees and an opportunity to regrow a poorly formed tree. Because their roots do not die when cut down, eucalypts are a desirable species for retaining soil in erodible hill country.
Eucalypts also require different processing methods than softwoods such as pine to overcome tension in the logs. The grower must determine what the optimum log diameter is for processing in order to design a regime that maximises profit. Key variables influencing tree diameters are rotation length and stocking. Traditionally larger diameter logs were favoured because of inherently lower tension stresses, but modern sawmills offer solutions to overcome the higher levels of stresses inherent in smaller diameter logs and produce straight boards cost-efficiently. Large logs take longer to grow and require a low final crop stocking, so the grower should be well informed on processing options when thinning eucalypts, because extending rotation length and reducing tree stockings to achieve large diameters carries with it risk of windthrow. Suggested regime is a final crop stocking of 300-400 stems per hectare and a 25-30 year rotation.
Eucalyptus botryoides, Southern mahogany
Closely related to E. saligna, producing a rich red-brown durable heartwood. Form not as good as E. saligna but E. botryoides is fairly resistant to wind, including salt-laden wind. Fast growing, comparable with radiata pine.
Health: Susceptible to a range of insect pests. There are provenances available in Northland that offer good resistance to these. Susceptible to browsing by possums at all ages.
Timber: Medium density. Heartwood rich red with interlocked grain, very decorative and hard. Sometimes the interlocked grain can cause processing problems. Large logs are preferred by processors because of low sawn recoveries due to large core of compression wood and wide sapwood band. The heartwood is moderately durable and suitable for decking, flooring and structural applications. Because the sapwood is white, this is usually excluded for appearance applications. However, the sapwood is resistant to lyctus borer so can be used for internal applications such as flooring.
Mechanical properties (dry wood) Species Density (dry) Bending strength, MoR (MPa) Stiffness, MoE (GPa) Hardness, Janka (kN) Eucalyptus botryoides 675 100 13.5 6.75 Siting: E. botryoides grows best in moist sites and can tolerate fairly poor soil drainage. It also grows well in soils with low fertility, provided the soil has some depth. However, fairly adaptable to a wide range of soil conditions, including drier clays. Best form is in sheltered sites but E. botryoides is tolerant of wind.
Steep slopes: Suitable for steep slopes, a coppicing species with fast growth rates. Well-suited to continuous cover forestry because of high timber value, adaptability to a range of sites and fast growth rates.
Species characteristics: Fast growing, yielding a high quality rich red heartwood but with low sawn recoveries. Prefers sites with good soil moisture and can grow in poorly drained (but not swampy) soils.
Recommended regime: Plant at 1600-2000 stems per hectare. Thin in 3-4 stages down to 400-600 stems per hectare. This gives a 4:1 thinning ratio. Because available seedlines are unimproved, a high initial stocking is recommended for a sufficiently high thinning ratio and greater selection for growth and form. Lower tree stockings require costly form pruning for sufficient quality in residual crop trees.
For clearwood production prune potential crop trees to 6-8m in 3-4 lifts and thin down to 300 pruned stems per hectare. However, although pruning improves grade recoveries from those logs, this is not necessary to produce clearwood because trees self-prune provided tree stocking is sufficiently high to induce this. The tradeoff is therefore between the cost of pruning and higher establishment costs. A higher thinning ratio also provides greater selection for growth and form so a high initial tree stocking is recommended.
Key message: Best planted on moderately fertile sites with good soil depth and moisture, but adaptable to a range of conditions and sites. Because of variable form a high initial stocking is required for selection of well formed, fast growing trees.
Eucalyptus globoidea, white stringybark
A true "stringybark" eucalypt, this species has been widely grown throughout Northland with good success. Originating from coastal New South Wales, E. globoidea is well suited to Northland's climate, with some very large trees grown and harvested in Northland. Fairly good growth rates and a very narrow sapwood band offer good productivity and a quality hardwood with moderate durability and good strength properties. Durability and mechanical properties improve with tree age. Slightly slower growing than E. muelleriana and E. pilularis but might handle more exposed conditions.
Health: Resistant to insect pests and with no health problems in Northland.
Timber: Medium density. Similar to E. muelleriana and E. pilularis, a moderately durable light brown heartwood with good strength properties. Sapwood band is narrow and sapwood is resistant to lyctus borer attack. Compression core is negligible and sawn recoveries are high. Suitable for flooring, decking, appearance joinery and structural applications.
Mechanical properties (dry wood) Species Density (dry) Bending strength, MoR (MPa) Stiffness, MoE (GPa) Hardness, Janka (kN) Eucalyptus globoidea 675 100 13.5 6.75 Siting: Requires free draining soils of moderate fertility. Quite good wind tolerance but stem breakages and loss of form can occur in sites with high wind exposure.
Steep slopes: Well suited to steep erodible slopes provided soil drainage is good and fertility reasonable. A coppicing species, i.e. the roots do not die but the stump stays alive after felling and re-sprouts. Coppicing species hold the soil from slipping even after harvest.
Species characteristics: The stem can be significantly tapered and double/multiple leaders can occur. Usually a straight tree with little sweep. Because available seedlines are unimproved, a high initial stocking is recommended, or alternatively form pruning practiced to remove multiple leaders and retain a single leader in crop trees.
Recommended regimes: Plant at 1600-2000 stems per hectare. Thin in 3-4 stages down to 400-600 stems per hectare. This gives a 4:1 thinning ratio. Because available seedlines are unimproved, a high initial stocking is recommended for a sufficiently high thinning ratio and greater selection for growth and form. Lower tree stockings require costly form pruning for sufficient quality in residual crop trees.
For clearwood production prune potential crop trees to 6-8m in 3-4 lifts and thin down to 300 pruned stems per hectare. However, although pruning improves grade recoveries from those logs, this is not necessary to produce clearwood because eucalypt trees self-prune provided tree stocking is sufficiently high to induce this. The tradeoff is between the cost of pruning and higher establishment costs. A higher thinning ratio also provides greater selection for growth and form.
Key message: A well-proven performer in Northland producing valuable hardwood timber.
Eucalyptus microcorys, tallowwood
Eucalyptus microcorys is a subtropical eucalypt from Northern New South Wales. It is considered one of the finest hardwoods in Australia. Because of its reputation tallowwood has been widely planted in Northland, one of the few regions in New Zealand where it can be grown, being frost tender.
Health: Susceptible to possum browsing as a young tree. Few insect or disease problems.
Timber: Medium to high density. The timber is pale brown, hard and very durable with exceptional stiffness and strength properties. Produces high density, durable and strong wood from an early age. Applications include high-quality timber decking, timber flooring, external structural applications (above ground), posts and poles. Sapwood band is fairly wide and sapwood is susceptible to lyctus borer. Sapwood can be treated with boron for internal applications.
Mechanical properties (dry wood) Species Density (dry) Bending strength, MoR (MPa) Stiffness, MoE (GPa) Hardness, Janka (kN) Eucalyptus microcorys 750 100 13.5 6.75 Siting: Requires shelter from strong winds. Susceptible to frost damage in the first winter following planting, best planted in spring after winter frosts have finished.
Steep slopes: A coppicing species, i.e. the roots do not die but the stump stays alive after felling and re-sprouts. Coppicing species hold the soil from slipping even after harvest. However, E. microcorys requires adequate soil depth and shelter so not suitable for upper slopes.
Species characteristics: Slower-growing at first than other eucalypts, but capable of very high volume productions because the crown is dense and shade-tolerant.
Recommended regime: Plant at 1600-2000 stems per hectare. Thin in 3-4 stages down to 400-600 stems per hectare. This gives a 4:1 thinning ratio. Because available seedlines are unimproved, a high initial stocking is recommended for a sufficiently high thinning ratio and greater selection for growth and form. Lower tree stockings require costly form pruning for sufficient quality in residual crop trees.
For clearwood production prune potential crop trees to 6-8m in 3-4 lifts and thin down to 300 pruned stems per hectare. However, although pruning improves grade recoveries from those logs, this is not necessary to produce clearwood because eucalypt trees self-prune provided tree stocking is sufficiently high to induce this. The tradeoff is between the cost of pruning and higher establishment costs. A higher thinning ratio also provides greater selection for growth and form.
Key message: Exceptional timber and with high volume production on the right site.
Eucalyptus muelleriana, yellow stringybark
A true "stringybark" eucalypt, this species has been widely grown throughout Northland with good success. From coastal New South Wales and Victoria, E. muelleriana is well suited to Northland's climate with some very large trees grown and harvested in Northland. Fairly good growth rates and a very narrow sapwood band offer good productivity and a quality hardwood with moderate durability and good strength properties. Durability and mechanical properties improve with tree age. Slightly faster growing than E. globoidea. Suitable for flooring, decking, appearance joinery and structural applications.
Health: Relatively resistant to insect pests and with no health problems in Northland.
Timber: Medium density. Similar to E. globoidea and E. pilularis, a moderately durable light brown heartwood with good strength properties. The sapwood band is narrow and sapwood is resistant to lyctus borer attack. Compression core is negligible and sawn recoveries are high.
Mechanical properties (dry wood) Species Density (dry) Bending strength, MoR (MPa) Stiffness, MoE (GPa) Hardness, Janka (kN) Eucalyptus muelleriana 675 100 13.5 6.75 Siting: Requires free draining soils of moderate fertility. Reasonable wind tolerance but stem breakages can occur in sites with high wind exposure.
Steep slopes: Well suited to steep erodible slopes provided soil drainage is good and fertility reasonable. A coppicing species, i.e. the roots do not die but the stump stays alive after felling and re-sprouts. Coppicing species hold the soil from slipping even after harvest.
Species characteristics: Some sinuosity and sweep can occur in the stem. Because the available seedlines are unimproved, a high initial stocking is recommended, or alternatively form pruning practiced to remove multiple leaders and retain a single leader in crop trees.
Recommended regimes: Plant at 1600-2000 stems per hectare. Thin in 3-4 stages down to 400-600 stems per hectare. This gives a 4:1 thinning ratio. Because available seedlines are unimproved, a high initial stocking is recommended for a sufficiently high thinning ratio and greater selection for growth and form. Lower tree stockings require costly form pruning for sufficient quality in residual crop trees.
For clearwood production prune potential crop trees to 6-8m in 3-4 lifts and thin down to 300 pruned stems per hectare. However, although pruning improves grade recoveries from those logs, this is not necessary to produce clearwood because eucalypt trees self-prune provided tree stocking is sufficiently high to induce this. The tradeoff is between the cost of pruning and higher establishment costs. A higher thinning ratio also provides greater selection for growth and form.
Key message: A well-proven performer in Northland producing valuable hardwood timber.
Eucalyptus pilularis, blackbutt
Not a true "stringybark" eucalypt but very closely related, E. pilularis has been widely grown throughout Northland with good success. From coastal New South Wales, E. pilularis is well suited to Northland's warm humid climate with good volumes of trees grown and harvested in Northland. Fairly good growth rates and a very narrow sapwood band offer good productivity and a quality hardwood with moderate durability and good strength properties. Durability and mechanical properties improve with age. Slightly faster growing than E. globoidea and similar growth rates to E. muelleriana. Suitable for flooring, decking, appearance joinery and structural applications.
Health: Resistant to insect pests and with no health problems in Northland.
Timber: Medium density. Similar to E. muelleriana and E. globoidea, a moderately durable light brown heartwood with good mechanical properties. Sapwood band is narrow and sapwood is resistant to lyctus borer attack. Compression core is negligible and sawn recoveries are high.
Mechanical properties (dry wood) Species Density (dry) Bending strength, MoR (MPa) Stiffness, MoE (GPa) Hardness, Janka (kN) Eucalyptus pilularis 675 100 13.5 6.75 Siting: Requires free draining soils of moderate fertility. Reasonable wind tolerance but stem breakages can occur in sites with high wind exposure.
Steep slopes: Well suited to steep erodible slopes provided soil drainage is good and fertility reasonable. A coppicing species, i.e. the roots do not die but the stump stays alive after felling and re-sprouts. Coppicing species hold the soil from slipping even after harvest.
Species characteristics: Sinuosity and sweep occurs where exposed to wind or on fertile sites, although provenances have been identified in Northland that grow straight in these situations. Usually a straight tree in sheltered sites of moderate fertility. Because the available seedlines are unimproved, a high initial stocking is recommended, or alternatively form pruning practiced to remove multiple leaders and retain a single leader in crop trees.
Recommended regimes: Plant at 1600-2000 stems per hectare. Thin in 3-4 stages down to 400-600 stems per hectare. This gives a 4:1 thinning ratio. Because available seedlines are unimproved, a high initial stocking is recommended for a sufficiently high thinning ratio and greater selection for growth and form. Lower tree stockings require costly form pruning for sufficient quality in residual crop trees.
For clearwood production prune potential crop trees to 6-8m in 3-4 lifts and thin down to 300 pruned stems per hectare. However, although pruning improves grade recoveries from those logs, this is not necessary to produce clearwood because eucalypt trees self-prune provided tree stocking is sufficiently high to induce this. The tradeoff is between the cost of pruning and higher establishment costs. A higher thinning ratio also provides greater selection for growth and form.
Key message: A well-proven performer in Northland producing valuable hardwood timber.
Eucalyptus saligna, Sydney blue gum
Closely related to E. botryoides, producing a rich red moderately durable heartwood. Excellent growth rates and form, sometimes superior to radiata pine. Not as resilient to wind as E. botryoides and prefers sheltered valleys with deep soil. Does not require good soil drainage or fertility but prefers deep soils.
Health: Susceptible to a range of insect pests. There are provenances available in Northland with some resistance to these. Susceptible to browsing by possums at all ages.
Timber: Medium density. Heartwood red with straight grain, decorative and hard. Large logs are preferred by processors because of low sawn recoveries resulting from a large core of compression wood along with a wide sapwood band. The heartwood is moderately durable and suitable for decking, flooring and structural applications. Potential for structural products such as appearance glulam, because of excellent stiffness properties. Because the sapwood is white, this is usually excluded for appearance applications. The sapwood is susceptible to lyctus borer so would require boron treatment for internal applications.
Mechanical properties (dry wood) Species Density (dry) Bending strength, MoR (MPa) Stiffness, MoE (GPa) Hardness, Janka (kN) Eucalyptus saligna, Sydney blue gum 675 100 13.5 6.75 Siting: E. saligna grows best in moist sites and can tolerate fairly poor soil drainage. It also grows well in low fertility soils, provided there is some soil depth. Fairly adaptable to a wide range of soil conditions, including heavy clays. Best form is in sheltered sites. Intolerant of wind exposure (can suffer from limb and top breakages).
Steep slopes: Suitable for the bottom of steep slopes and reasonably sheltered mid-slopes with good levels of soil moisture, a coppicing species with fast growth rates. Well-suited to continuous cover forestry because of high timber value, adaptability to a range of sites and fast growth rates.
Species characteristics: Fast growing, yielding a high quality rich red heartwood but with low sawn recoveries. Prefers sites with good soil moisture and can grow in poorly drained (but not swampy) soils.
Recommended regime: Plant at 1600-2000 stems per hectare. Thin in 3-4 stages down to 400-600 stems per hectare. This gives a 4:1 thinning ratio. Because available seedlines are unimproved, a high initial stocking is recommended for a sufficiently high thinning ratio and greater selection for growth and form. Lower tree stockings require costly form pruning for sufficient quality in residual crop trees.
For clearwood production prune potential crop trees to 6-8m in 3-4 lifts and thin down to 300 pruned stems per hectare. However, although pruning improves grade recoveries from those logs, this is not necessary to produce clearwood because eucalypt trees self-prune provided tree stocking is sufficiently high to induce this. The tradeoff is between the cost of pruning and higher establishment costs. A higher thinning ratio also provides greater selection for growth and form.
Key message: Best planted on sheltered moderately fertile sites with good soil depth and moisture, but adaptable to a range of soil conditions. A high initial stocking is recommended for selection of well formed, fast growing trees and self-pruning.
Eucalyptus sphaerocarpa, Blackdown stringybark
Eucalyptus sphaerocarpa has only been grown in New Zealand and Northland for 20 years but the species is proving to have many desirable traits suggesting potential for commercial production forestry.
This species combines the resilience to wind exposure of the ash group of eucalypts with the good timber properties of the stringybark eucalypts. Indeed the timber is superior in strength and durability to blackbutt and the stringybark eucalypts and at an earlier age. Like tallowwood, this species produces durable and strong timber from an early age, but unlike tallowwood has a very narrow width sap band.
Health: Few insect or disease problems. Some leafminer damage to young trees in exposed sites.
Timber: The timber is pale brown, very strong, hard and very durable. Produces high density, durable and strong wood from an early age.
Mechanical properties (dry wood) Species Density (dry) Bending strength, MoR (MPa) Stiffness, MoE (GPa) Hardness, Janka (kN) Eucalyptus sphaerocarpa 750 100 13.5 6.75 Siting: Requires good soil drainage. Adaptable to fairly low fertility but best growth is on moderately fertile sites. The most wind-hardy of the recommended eucalypt species for Northland.
Steep slopes: Well suited to steep erodible slopes provided soil drainage is good and fertility reasonable. A coppicing species, i.e. the roots do not die but the stump stays alive after felling and re-sprouts. Coppicing species hold the soil from slipping even after harvest.
Species characteristics: Slower-growing at first than stringybark eucalypts, similar growth rate to tallowwood. Although called a "stringybark", this species is actually an ash eucalypt. Seed is available commercially from Northland stands and although a high initial stocking is recommended to ensure selection of the fastest growing trees with the best form, the species is well enough formed to grow at radiata stockings.
Recommended regime: Plant at 1200-1800 stems per hectare. Thin in 3-4 stages down to 400-600 stems per hectare. This gives a 3:1 thinning ratio. Because available seedlines are unimproved, a high initial stocking is recommended for a sufficiently high thinning ratio and greater selection for growth and form.
For clearwood production prune potential crop trees to 6-8m in 3-4 lifts and thin down to 300 pruned stems per hectare. However, although pruning improves grade recoveries from those logs, this is not necessary to produce clearwood because eucalypt trees self-prune provided tree stocking is sufficiently high to induce this. The tradeoff is between the cost of pruning and higher establishment costs. A higher thinning ratio also provides greater selection for growth and form.
Key message: High quality durable timber, adaptable to steep slopes with thin soils and wind.
Poplar
A range of poplar varieties are grown in Northland but the best-performing of these for plantation forestry and timber production is 'Kawa', a Chinese poplar hybrid.
Poplar is not suitable for planting in exposed, drier hill country or where soils are thin.
Poplar, Kawa
The "Kawa" variety poplar was bred in New Zealand in 1986 and is a hybrid between Populus yunnanensis (Chinese poplar) and P. deltoides (black poplar). Kawa has good form for timber production and is a vigorous variety well suited to Northland's subtropical climate, holding its foliage well into winter and flushing fairly early in spring with no risk of frost damage.
Health: Very healthy, not damaged by poplar rust and fairly resistant to possum browsing. Pruning wounds are a risk factor for entry of silverleaf fungus which can kill the tree. Low susceptibility to blackheart.
Timber: Poplar has a pale whitish coloured timber with a very attractive sheen or lustre. Poplar is low density, very soft and of low natural durability. Although for its density it has good mechanical properties, it does not meet the density and strength requirements for structural applications under the building code. Air-dry density is 440 kg/m3 (lower than for radiata pine) and stiffness (modulus of elasticity) is below 6 MPa, the threshold for structural radiata. However, because density varies so little within and between trees, this suggests potential for customised structural grades and applications that take advantage of the cultivar's consistent strength and stiffness. Because the heartwood is perishable poplar would require H1.2 boron treatment for interior structural applications. For exterior structural applications CCA treatment to H3.2 would be required, along with evidence that treatment methods achieve penetration and retention requirements as per NZS 3640.
Because the wood is odourless, potential applications for poplar wood may include fruit and vegetable packaging crates. Finishing grades of timber are suitable for appearance applications such as internal joinery and panelling, but low surface hardness tends to detract from using poplar for furniture. Research into hardening technologies would open market opportunities for high-value appearance applications.
High quality pruned logs have excellent potential for sliced and peeled veneer and poplar is suitable for paper pulp.
Sawn CCA treated fence posts have proven to be a successful product in Hawkes Bay but growers would need to be confident with potential products and applications before a plantation forest industry were to become viable. The export log market is available, however, with demand for logs from Asian countries.
Mechanical properties (dry wood) Species Density, dry (kg/m3) Bending strength, MoR (MPa) Stiffness, MoE (GPa) Hardness, Janka (kN) Poplar, Kawa 440 56.9 5.4 2.3 Siting: Requires good soil fertility and moisture, but tolerates poor soil drainage. Requires adequate moisture through the summer months, therefore adequate soil depth. Adaptable to reasonably strong winds but not coastal conditions and salt spray. A good site is important for volume production.
Steep slopes: Often used for stabilising steep pastoral slopes to retain grazing. Rough bark takes some years to form and although the bark on younger trees appears rough it is thin and susceptible to stock browsing. Stumps and roots remain alive and coppice after harvesting. Wide spaced poplar would take longer to achieve high levels of soil binding than where closer planted. Where erosion potential is high, a closed canopy tree cover is recommended.
Species characteristics: A fast growing hardwood with a soft, low-density timber. Suitable for lower slopes and alluvial soils with some fertility.
Recommended regime
- Production forestry, Plant 90cm forestry wands or rooted cuttings at 600 stems per hectare. Prune to 10 m and thin to 300 stems per hectare by year 15. Harvest at 25-35 years old.
- Timberbelts (pastoral), Poles, not less than 4 m apart in single rows.
- Conservation/timber plantings (pastoral), Poles at 100-200 stems per hectare, approximately 8 m x 8 m, pruned to 10m. Log volumes of 500 m3/ha can be expected by year 30, with approximately 40% of the total log volume being pruned logs.
Planting and establishment: Forestry wands require pre-plant spot spraying with glyphosate and one release in late spring. If glyphosate is used for releasing it must not come into contact with green stem. Larger poles require plastic sleeves to protect them from stock browsing. Smaller poles and wands require exclusion of stock for 2-3 years, until the trees are sufficiently well established and the bark thick enough to overcome browsing temptation.
Silviculture: Poplar prolifically produces epicormic shoots when pruned. Pruning should be undertaken in late summer to reduce the incidence of epicormic shoots. Epicormic shoots tend to arise with lower tree stockings and those that do arise need to be removed
Key message: A good species for soil stabilisation in pastoral settings. Markets for the wood are under-developed and research is required to generate market opportunities for the timber.
Native softwoods
Native softwood species (conifers) are notoriously slow to grow. These species include rimu, matai and miro, species that all produce high quality timbers from natural old-growth forests. Kauri, although faster growing than other native conifers and a species subject to a historical research effort including establishment of plantations in Northland, in recent times has succumbed to kauri dieback disease. Because this disease appears to be spread by wild animals and kills trees it come in contact with, the risk appears to be too high for timber plantations of the species.
The growth of native species is particularly slow in the establishment phase so can benefit by good weed control for at least the first few years.
Totara, Podocarpus totara
Totara is reasonably fast growing when compared with other native conifer species and is also well positioned as a species suitable for market development, with an existing resource of regenerating trees in Northland.
Totara is a hardy pioneer conifer species suitable for planting in open and exposed sites. Although initial growth is slow, this can accelerate during the pole phase provided stand density is managed by thinning out poorer quality trees.
Health: Generally a healthy tree, however totara is the most susceptible native podocarp to defoliation by insects. Native insects such as stick insects, scale and cicadas can damage totara, with leafroller damaging terminal shoots and affecting tree form.
Timber: Totara heartwood is a dull pinkish-red to pinkish-brown colour and the sapwood a pale brownish white. Heartwood is very durable. Totara timber is relatively light, straight grained and soft and has a very even texture and excellent stability. The timber is of medium strength but with a rather low shock resistance.
Totara machines well and is easily brought to a smooth finish. Totara is renowned as an excellent joinery timber, with good screw and nail holding capacity and resistance to denting.
Totara sapwood is resistant to attack by Anobium borer. Although the sapwood can be treated with CCA preservatives for in-ground or outdoor use, it is moderately resistant to pressure treatment.
Totara is suitable for interior and exterior joinery, door frames, window sashes, boat building, furniture and carving and totara wood is in demand for cultural use by Maori.
Second growth ("farm totara") trees less than 100 years old have a high proportion of sapwood but the wood is suitable for all interior uses, particularly feature linings, joinery and furniture.
Mechanical properties (dry wood) Species Density, dry (kg/m3) Bending strength, MoR (MPa) Stiffness, MoE (GPa) Hardness, Janka (kN) Totara 480 55.0 7.39 2.4 Siting: Tolerates the presence of livestock. Can grow on boney dry soils but best growth requires some soil depth and fertility. Tolerates some wind exposure.
Steep slopes: Perhaps the best-suited of the native conifers for steep eroding slopes that are exposed to wind. Well suited to continuous cover forestry.
Species characteristics: A light-demanding coloniser. Unlike most native conifers, totara is not well adapted to shade.
Recommended regime: Requires a high stocking rate or nurse crop for good pole form. Recommended planting of 1600-2000 stems per hectare, or alternatively 800 stems per hectare interplanted with 800 stems manuka for honey production and as a nurse crop to draw the totara upwards. Requires good weed control in the establishment period. Silvicultural management requires development, but thinning of dense stands is essential for volume production and pruning is essential for stands where existing pole trees are heavily branched.
Key message: Very suitable for less productive pastoral slopes and compatible with livestock farming. An average diameter of 55cm can be expected in 75 years.
Kahikatea, Dacrycarpus dacrydioides
Kahikatea is a fairly slow growing native conifer species well suited to infertile sites, especially those with poor soil drainage. Where correctly sited, kahikatea has been fairly reliable in Northland plantings and survival good. The species has a narrow conical form and is straight.
Health: Healthy with no significant pest problems.
Timber: Heartwood is white to pale yellow-brown and sapwood is white and very wide. Sapwood is highly susceptible to borer but can be treated with boron salts. Fine and even in texture and straight-grained. Holds nails and screws well, easily worked. Kahikatea's resistance to splitting allows it to be machined and turned without difficulty into mouldings, joinery and turnery. Kahikatea's rather flat appearance and lack of colour may limit its appearance applications, but the non-tainting properties of the timber have been and can be used for applications associated with food. Potential for plywood, decorative veneers and boatbuilding.
The wood is easily dried but highly susceptible to sap stain. Kahikatea wood cannot be adequately pressure treated with CCA preservatives for in-ground use. Similar to radiata pine in structural properties with a good strength to weight ratio. Good bending and gluing properties.
Mechanical properties (dry wood) Species Density, dry (kg/m3) Bending strength, MoR (MPa) Stiffness, MoE (GPa) Hardness, Janka (kN) Kahikatea 450 75 10.7 4.2 Siting: Prone to compression wood on exposed sites. Well suited to poorly drained sites of low natural fertility. Responds well to improved fertility.
Steep slopes: Suitable for planting on sites too wet for totara.
Species characteristics: Not a particularly exciting timber for modern applications, but among the few conifer species suited to poor fertility waterlogged soils.
Recommended regime: Regular releasing from weed competition is necessary for good growth rates. Recommended planting of 1600-2000 stems per hectare, or alternatively 800 stems per hectare interplanted with 800 stems manuka per hectare for honey production and as a nurse crop to draw the kahikatea upwards.
Key message: Not a fast-growing species, heights of 4-6 m can be achieved in 20 years.
Native hardwoods
Native hardwood species to consider for timber plantations in Northland include puriri, rewarewa and pohutukawa.
Rewarewa is well adapted to phosphate-deficient soils and is a good nectar producer. Rewarewa is hardy, slow growing and if open-grown tends to have poor form with multiple leaders. The timber is very attractive but highly susceptible to borer so would require treatment for all applications.
Puriri, although fairly slow growing, produces a high quality, dense, durable and strong timber with significant market potential. However, little work has been done on managing the species in plantations. Puriri is highly susceptible to the puriri moth, which bores into and damages the wood. The level to which this insect would damage plantations is unknown. Puriri requires good quality fertile soils for reasonable growth rates.
Rata x Pohutukawa hybrid, Metrosideros spp.
Pohutukawa does not generally have a form suitable for timber production, but reasonable growth rates, adaptability to harsh conditions and excellent timber properties suggest the species is a good contender for work on selection for straight form. Pohutukawa and its hybrids can be clonally propagated (grown from cuttings) so selection and propagation of vigorous straight-formed trees should be fairly straight forward.
Anecdotal evidence suggests that straight, single-stemmed pohutukawa occur naturally in Northland as hybrids with northern rata. A range of named hybrid clones are also available and are grown as ornamental trees. However, these have not been tested for form and site requirements in a plantation forestry setting.
Annual diameter growth of up to 2 cm is possible on good sites, which is good for a native tree species. Average growth rates of 50 cm diameter in 50 years can be expected.
A range of Graham Platt's hybrid selections are available, including Mistral, Sirocco, Hauparapara, Mercer Bay and Waikakariki, which are reputed to be straighter and faster growing than the pure species. The pohutukawa clones Maori Princess and Pink Lady also have a reputation for good form.
Health: Susceptible to browsing by possums. A range of indigenous insects feed on pohutukawa but do not impact significantly on tree health.
Timber: very dense, strong, hard and durable. Cuts out red but ages to a rich reddish-brown colour.
Mechanical properties (dry wood) Species Density, dry (kg/m3) Bending strength, MoR (MPa) Stiffness, MoE (GPa) Hardness, Janka (kN) Rata x Pohutukawa hybrid 880 114 11.4 NA Siting: Resilient to both poor soil conditions and strong winds. However, growth rates would be expected to be slow in such conditions. Seedlings are frost tender and vulnerable to dessication by wind and drought. Young trees need to be free of weed competition. Does not cope with waterlogging.
Steep slopes: Perhaps the most suitable of the native species for exposed eroded slopes. A coppicing species, i.e. the roots do not die but the stump stays alive after felling and re-sprouts. Coppicing species hold the soil from slipping even after harvest.
Species characteristics: Reasonable growth rates, excellent timber properties and adaptability to harsh conditions offers potential for production forestry on exposed eroding slopes deficient in topsoil.
Recommended regime: Plant clonal selections at 800 stems per hectare, interplanted with 800 stems manuka per hectare for honey production and as a nurse crop to draw the Metrosideros upwards. Epicormic shoots are likely to result from pruning open-grown trees.
Key message: Hybrids grow straighter and faster than pohutukawa. Research is required to trial hybrid selections and develop management techniques.
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