Farm Forestry New ZealandMacrocarpa 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.
| 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.
NZFFA on facebook