Eucalypts for vineyards
Allan Levett, New Zealand Tree Grower February 2008.
An important workshop for eucalyptus growers in vineyard regions was held on in July last year, significantly in Blenheim, New Zealand’s largest wine-producing centre.
Growing ground durable hardwood for vineyard posts was organised by farm foresters Paul and Ash Millen, who have created the commercial research and development company Vineyard Timbers Ltd to lead the local establishment of suitable eucalyptus species. The meeting attracted over 50 people representing a wide cross-section of the relevant components of the industry – vineyard owners and wine-makers, eucalyptus growers, researchers and consultants, regional council staff, nurserymen and seed producers mostly from the South Island.
The potential benefits
Richard Hunter, a Marlborough consultant, outlined the potential benefits from ground durable hardwood timbers for viticulture locally, but his comments apply to all grape growing areas in New Zealand. Richard identified the climate, soils and land use in Marlborough and indicated their suitability for both grapes and certain eucalyptus species. He further suggested broad management issues and showed the opportunity that exists for tree growers. Vineyards in Marlborough – and presumably throughout the country – have to replace over 5 per cent of their treated pine vine posts each year because of breakage. In Marlborough this is about 450,000 posts annually.
Richard Hunter argued that the eucalypt species in general can add capital value in a variety of other ways. For example, the timber of their various species has wide uses and does not require chemical treatment, they have aesthetic value, and there is a range of pollinating seasons among eucalypts so they can provide year round feed for birds and bees. Finally, eucalyptus species can be established rapidly, adapt to different site conditions and have the ability to survive extreme conditions.
The right species, site and uses
Ruth McConnochie of Ensis said that success with eucalypts could be obtained by choosing the right species, having the right site and being clear about the appropriate end uses. As to species she indicated some that have been discarded because research has shown that they have unsuitable wood properties and are susceptible to diseases in New Zealand. On the other hand E. nitens and E. fastigata have established improved seed sources, produce good growth and yield, and have good wood properties and established markets. Lately the stringybarks have been favoured and are being trialled.
Regarding site, the stringybarks are suited to lower elevations under 400 metres like some of the ash species, whereas E. fastigata and E. nitens are capable of growing at heights up to 800 metres. All do best in a mid-range of soil quality. The soil for eucalypts should be well drained, cultivated and responsive to fertilisers and sheltered from extreme exposure. Weed growth should be controlled and the site protected from extreme out of season frosts.
Ruth listed a variety of end uses for the range of eucalyptus species and reported on a sawn timber study that measured mean DBH, heartwood percentage and whole tree density for 15 trees each of E. pilularis, E. muelleriana, E. globoidea and E. fastigata at 25 years.
Mean DBH ranges for 398 mm for E. pilularis to 522 mm for E. fastigata, the others falling between. Heartwood percentage is greatest for E. pilularis at 85% and the least for E. fastigata at 82%. E. muelleriana has the highest tree density at 640 kg per cubic metre, E. fastigata the least at 490. Several other traits were measured in this study again showing diversity among species that will affect choice of end uses and young eucalyptus posts are stronger that pine posts.
Ian Nicholas of Ensis outlined the classes of durability and showed the service life of each class, both in ground and above ground using Australian and New Zealand evaluation results.
Class 1 Very durable eucalypt species include E. bosistoana, E. melliodora, E. microcorys, E. paniculata, E. sideroxylon and E. wandoo
Class 2 Durable species include E. agglomerata, E. camuldulensis, E. eugenoides, E. globoidea, E. leucoxylon, E. longifolia, E. maculata, E. muelleriana, E. pilularis and E. quadrangulata.
Class 3 Moderately durable species include E. baxterii, E. blaxlandii, E botryoides, E. cameronii, E. globulus sub-species maidenii, E. jacksonii, E. laevopinea, E. macrorhyncha, E. obliqua and E. saligna.
Three species are being examined in different forms, including as stakes, fence battens, split posts and sawn cross arms. E. globoidea is showing the best durability after 14 years followed by E. pilularis and E. muelleriana, but there is considerable variability within species.
Viticulture industry concern
Paul Millen began his illustrated presentation by identifying current viticulture industry concern about the treated radiata pine posts:
- Low strength with post breakage of 5%-10% annually
- The high cost of replacement
- Difficulty of disposal – vineyards are stock-piling them
- Toxic leachates consumer concern and – a market threat.
The ground durable eucalypt vine post offers a hardwood solution to the viticulturist’s concerns. It has high strength, natural residues, zero waste and no treatment costs. The competing alternatives to timber vine posts are steel and recycled plastic and perhaps improved chemical treatment of radiata pine.
Paul saw the need for a resource development strategy to guide the establishment of new forest plantations of ground durable eucalypts to meet the challenge posed by viticultural industry concerns about radiata pine posts and the possible other alternatives.
The strategy requires co-ordinated joint venture research and development projects to improve seed selection, identify optimal sites and growers, establish trials and breed improved species.
A variety of eucalyptus species have been located throughout Marlborough including recent stringybark trial species and several hardwoods including E. bosistoana. E. cladocalyx, and E. quadrangulata. Some old growth trees suggest that E. bosistoana has good potential even in the drier parts of South Marlborough.
Ash Millen gave a demonstration of hardwood eucalypt sawn timber with samples of different species cut in different ways for a variety of possible uses including vineyard posts. E. bosistoana is an attractive timber that will coppice, offering the options of sawlog posts from trees 20 to 30 years old or roundwood posts from coppiced plantations with a possible rotation age of 8 to 12 years. Paul provided an estimate of costs and returns for both options.
Other presentations indicated interest from both Southernwoods Nursery and Proseed in many of the research and development proposals and willingness to work co-operatively with Vineyard Timbers Ltd.
Allan Levett is the Chairman of the Eucalypt Action Group