Silky Oak

24.05.17

Silky oak (Grevillea robusta) or southern silky oak is a native Australian tree that grows naturally in northern New South Wales and south east Queensland. Contrary to its name, silky oak is not an oak. It is the tallest species of Grevillea, growing 20–30m high with fern-like foliage and brown fibres. The common name of silky oak comes from the feel of the freshly split wood and prominent ray cells similar to those found in English oak.

Overview

Silky oak has been grown widely throughout Australia as an ornamental tree for almost 100 years.

Observations of ornamental plantings indicate that silky oak is drought tolerant, grows on a wide range of soil types, has a tough bark (making it suitable as a shade tree in paddocks of grazing animals), produces flowers and gum that support native wildlife and can grow large enough for milling within a reasonable time. However, in some states, it is considered a minor environmental weed.

Due to its limited availability from native forests silky oak has been of minor timber commercial value but it has recently gained recognition as a potential planting species.

Silky oak has had a good reputation for quality furniture in the past, and continues to be sought for specialised woodworking, cabinetry and furniture, suggesting a market might exist for the timber in the future.

Commercial farm trees have the potential to offer a range of benefits to farmers and land managers by increasing Australia’s long-term timber supply while contributing social, economic and environmental benefits to regional areas.

Trees are often planted to provide windbreaks and shelterbelts for crops and livestock, to manage the watertable or to protect topsoil from erosion. However many landholders, using existing infrastructure and integrating tree management practices into existing farm operations, may be able to earn an alternative income from planting farm trees that earn a commercial return. The risk inherent in all commercial tree operations is the long period between establishment and harvest which can range from 30 to 50 years with no financial returns in the interim.

Facts and figures

The silky oak is the largest species of the Grevillea genus and is a fast-growing large upright tree
It grows 20–30m high and the trunk can develop a diameter up to one metre
Growth rates of silky oak are reasonable suggesting sawlogs could be grown in about 30 years on most sites
The timber is sought after for specialised woodworking, cabinetry and furniture
Silky oak is considered a minor environmental weed in some states

Production status
Silky oak is a minor commercial industry in Australia. There are a number of small plantations set up as trials and some genetic provenance trials in south east Queensland.

Map of current and potential growing regions

Uses

The timber of silky oak is pinkish brown with a typical oak grain and is used in:

cabinet work
furniture
wood turning
plywood
panelling
veneers.

Production Requirements

Growing regions

Silky oak occurs naturally on the coastal ranges in northern New South Wales and south east Queensland in subtropical to dry rainforest and wet sclerophyll forest.

Soil type

Silky oak prefers fertile basalt and alluvial soils but also grows on moderately shallow sedimentary soils.

Climate

Silky oak grows naturally in warm humid conditions of the subtropics but it will tolerate dry conditions and moderate frosts.

Varieties

Although there has been some limited provenance testing of silky oak (Grevillea robusta) there has been no varietal selection of the species for plantation purposes.

Other ‘oak’ trees, native to Australia have been milled for their timber. A closely related species to silky oak is the silver oak or beefwood (Grevillea parallela). It is a desert species and doesn’t grow as large but has a darker timber that is prized by wood turners. The northern silky oak (Cardwellia sublimis) found in far north Queensland is from the same family (Proteaceae) as the Grevillea, and was once widely milled from native forests.

Planting and crop management

When selecting a planting site for commercial tree production, it is important to take into account access to the trees for maintenance and harvesting. Being on flat, accessible land, with good access roads and room to manoeuvre heavy equipment will make management easier and keep costs down over time.

Silky oak can be easily grown from seed. Young silky oak trees will need protection from grazing stock and pests. Silky oak is also susceptible to wind damage, so if planting on exposed sites it is recommended that a fast growing nurse crop, like a wattle, be included in the plantation to provide shelter to the young trees.

Silky oak with malformed stems or with poor vigour could be removed to allow remaining high quality trees access to available land, nutrients and water. The final stocking rates in a silky oak plantation are suggested at about 150 trees per hectare, with an average spacing of 8–9m.

For timber production, the aim is to grow a straight trunk at least 50cm in diameter and free of branches. Therefore, pruning will need to be undertaken regularly (annually) to remove any branches on the stem greater than 2cm in diameter, up to the point of anticipated log length (about six metres).

Weeds, pests, and diseases

Weed control in plantations is particularly important before planting and for the first few years of growth. Competition by weeds for sunlight, nutrients and moisture can reduce growth rates in young trees.

Infrastructure Requirements

Land is the main infrastructure requirement for commercial tree growing.

If planting trees on a small scale and integrating them into the agricultural enterprise as windbreaks and shelterbelts, then manual maintenance, including pruning and thinning, can usually be managed with a chainsaw and farm equipment.

If planting a commercial plantation of high value sawlogs, then tree farm-scale, tractor-based forestry equipment may be necessary, including logging winches and chains. Unless the plantation is large and consists of high value logs, it will not be economical to purchase specialised harvesting equipment or modify existing farm equipment to undertake harvest. Contractors with specialised equipment and machinery may also be considered.

Harvesting & Processing

Silky oak can be milled by a skilled operator with very simple equipment, for example a chainsaw and mobile milling unit, and is easily air-dried.

Note that the wood contains a chemical that can cause an allergic reaction in some people, so care must be taken when handling the timber.

Initial site selection for commercial trees will have an influence on harvest method—well-spaced trees near access roads will be easier and cheaper to harvest.

The sapwood is susceptible to Lyctus borer so it will require treatment (Boron or equivalent) if the timber is to be sold in New South Wales or Queensland.

Markets & Marketing

Silky oak is considered a minor commercial species, therefore, consideration of silky oak as a business enterprise is highly speculative.

For all timbers, but especially species like silky oak, it is important to consider current and/or future markets before establishing a small or large plantation. However, with commercial trees taking around 30 years to provide a return on investment (in most cases) it is difficult to accurately predict future market opportunities at establishment.

Distance from markets will affect the profitability of a commercial timber enterprise, generally speaking, when the plantation is more than 100km from the processing centre (or road conditions are difficult), as transport costs can be high. The closer the planting is to the processing centre, the greater the return for any given product, particularly if providing a high volume of a lower value timber, such as pulpwood and woodchips.

Planting and managing for high quality sawlogs can counter some of the market uncertainty and absorb transport costs, as it is often easier to find markets for high value timber, even with longer transport distances involved. High value timber requires ongoing maintenance of trees, ensuring they are managed for the specifications particular to high value markets, essentially: good form, diameter and limited defects.

Consideration of local markets of the timber provides options should future markets change as described in the Risk/challenges section. Local markets could include the building or construction industry in the region, farm use as fence posts, or domestic use as firewood.

Risks & Regulations

Risks/challenges

Uncertainty and risk are inherent in commercial tree operations due to the long period of time between establishment and harvest (around 30 years).

Some of the risks include:

mills closing or relocating, leaving plantings at an uneconomical distance from processors
timber preferences or ‘fashions’ changing, resulting in decreased markets as certain colours or grades of timber fall out of favour with designers and builders and consumers
government policy changing, impacting on industry structure and profitability
alternative products developing, resulting in a falling demand for timber.

Alternative benefits from commercial tree plantings should be investigated to help reduce exposure to these risks. It is recommended that a short-, medium- and long-term return or benefit be identified when considering planting commercial trees. For example, a short-term benefit could relate to carbon sequestration or watertable abatement. A medium-term benefit may be derived from the trees providing a windbreak or shelterbelt for crops and livestock, and a long-term benefit might be income from harvested timber.

To further manage risk, it is recommended that tree selection take into account the potential for local use for the timber. A timber versatile enough to be processed and used locally will limit some of the uncertainty around future markets if there are alternative opportunities to earn income. For example, local markets could include the local building and construction industry, farm uses such as fence posts, and domestic uses such as firewood.

When selecting a site for silky oak it is important to take into consideration that the trees are prone to wind damage and susceptible to severe frosts. Also, care should be taken when harvesting and milling silky oak, as the leaves and wood contain chemicals that can cause allergic reactions in some people.

Silky oak is considered a minor environmental weed in some states.

Regulatory considerations

If seeking to establish a commercial plantation (the definition differs by state, but is generally defined at around 30 or 40 hectares) liaison with the relevant state government agency will be necessary. Regulatory systems vary across states, with some requiring plantations to be authorised and others requiring plantations to meet legislative requirements and/or a management Code of Practice.

Silky oak is considered a minor environmental weed in some states and the relevant state department of primary industry should be contacted for further information.