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The New Zealand Dryland Forests Initiative (NZDFI) is a collaborative tree breeding and forestry research project. It was established in 2008 and aims to select and improve drought-tolerant eucalypt tree species that produce high-quality ground-durable hardwood products. The NZDFI’s vision is for New Zealand to be a world leader in breeding ground-durable eucalypts, and to be home to a valuable sustainable hardwood industry based on 100,000 ha of eucalypt forests by 2050. See www.nzdfi.org.nz for more details.
Durable eucalypts are a group of eucalypt species (‘gum trees’, native to Australia). They produce heartwood (timber in the middle of their stem) which takes a long time to decompose because of biochemical resistance to wood rot. Naturally durable timber can last for twenty years or more in contact with the ground with minimal rot. It does not need chemical treatment to prevent rot, unlike radiata pine.
Durable eucalypts are fast-growing and tolerant of dry environments (rainfall less than 600 mm/yr). Their timber is hard, strong and durable, and has many potential uses, both on-farm and in various high-value markets. Eucalypts store carbon, and support bees and native birds at times of year when other nectar and pollen supplies are scarce. They also coppice (regrow from a cut stump) so are good for soil conservation as their roots hold the soil in place even after harvest. Some durable species are highly adapted to NZ’s dry climates where they can produce very durable timber even at a young age as well as grow in higher rainfall areas where they can maximise production of durable timber.
There are a number of durable eucalypt species, and their site requirements vary. In general eucalypts will grow best on low altitude, fertile, relatively sheltered sites with good drainage and regular rainfall. However, NZDFI trials have confirmed that some species can tolerate very hot, dry, infertile and moderately exposed conditions. Suitable sites include low-productivity hill-country and ex-radiata pine cut-over sites. Fenced-off riparian sites are another option. Flat areas with frost exceeding minus 5 degrees can kill young trees. Also areas with poor drainage should be avoided. The NZDFI’s key target regions for durable eucalypts are NZ’s warmer eastern dryland regions: Gisborne/East Coast, Hawke’s Bay, Wairarapa, Nelson/Marlborough, and North Canterbury. However, research is also demonstrating that there are some durable species which are well adapted to growing in New Zealand region’s with higher rainfall including the Central North Island region
Costs of establishment vary with site and grower objectives. The main cost elements can include:
We recommend you consult a local regional council land management adviser to discuss any ideas for new planting on your own property.
Form-pruning at age 1 or 2 years after planting is advised. This ensures the trees have one ‘leader’ (leading stem), giving them the potential to grow a single straight stem. Form-pruning can be done by with secateurs or loppers and is quick and easy. Clear-wood pruning (i.e. removing side-branches from stems to create a knot-free log) is likely to be needed only on edge trees or other trees receiving a lot of light. Trees within plantations generally self-prune.
Thinning is essential if crop trees are to grow to a marketable diameter. A minimum of two thinning operations is likely to be needed. The first, around age 4-6, should reduce tree numbers by about 50%. This operation gives the opportunity to select the best stems for the final crop. Second and any further thinnings will be needed as tree crowns begin to compete with each other. These operations may produce material which, on easily accessible sites, has potential e.g. for fencing material or firewood.
This depends on the potential end use of the timber. By around age 15-18, the trees should be big enough, and have enough durable heartwood, for various smaller product/on-farm end uses such as for fencing material and on-farm joinery. If the target market is larger saw-logs, growers should anticipate a rotation of 25-30 years.
Radiata pine is a versatile species which grows well on a wide range of site types. Durable eucalypts have greater drought tolerance, produce harder timber, and provide better biodiversity values. Durable eucalypts tend to be more site-specific however, and it is important to get good advice about which species is best adapted to your site.
A key target NZ market for durable timber is posts for vineyards, kiwifruit orchards and other horticultural crops with organic/sustainable production systems. The durable timber is a replacement to chemically treated radiata pine posts. Decking, flooring, joinery and electricity cross-arms are other potential end uses. Work is also underway to test the potential of durable eucalypts as a component of laminated veneer lumber (LVL). Export markets include those where the richly-coloured eucalypt timber could replace very high-value markets for (often illegally harvested) tropical hardwoods such as teak and rosewood.
It’s a ‘chicken and egg’ situation at the moment. The amount of durable eucalypt timber available in NZ is very limited, so we can’t put a lot of effort into developing markets until the resource is there to supply them. However, we are very confident that market potential exists and have demonstrated to the wine industry that durable hardwood posts are a viable alternative to treated pine posts. So while the NZDFI’s main efforts are currently focussed on getting a high-quality forest resource established, we know there are domestic markets for vineyard posts and want to develop others, particularly high strength engineered timber products, like Laminated Veneer Lumber and Cross Laminated Timber.
The NZDFI research team is currently working on growth models for selected durable eucalypt species. Once these are complete, we will provide forecasts of yields of different species on a range of site types and for various growing regimes.
Once we have completed our growth models, we will extend our work to evaluate the financial implications – the costs and eventual returns – of growing durable eucalypts, based on our best possible estimates of future markets and timber values. This will include economic case studies of the potential economic return based on various growing regimes. This will demonstrate that durable eucalypts can be a profitable complementary component of land-use on farms and in forests. The NZDFI has received significant financial and in-kind support from government, landowners, industry and others, all of whom have confidence in the vision of a sustainable hardwood forest industry in the future.
There are a number of unknowns and risks associated with growing durable eucalypts, which are still an emerging species group in New Zealand. These include:
The NZDFI’s research team is working hard on many of these aspects, and collaborating with international partners to fill important knowledge gaps and mitigate the main risks to NZ growers and the environment.
There is a wide range of information about the work of the NZDFI, and durable eucalypts in general, on the NZDFI website: www.nzdfi.org.nz You are also welcome to contact Paul Millen, NZDFI’s project manager, with any specific queries: firstname.lastname@example.org