Sugar Gum for Farm Forestry (DPI Vic)

September, 2000 Sugar gum for farm forestry AG0892 Melanie Waters, Rick Webb & Belinda Measki, Hamilton ISSN 1329-8062

This Agriculture Note describes the characteristics, site widths of 1.5 m. On poorer sites, heights range from 8-15 requirements and wood quality of sugar gum as a farm m with diameters to 40 cm. forestry species.

Figure 2. Natural occurrence of sugar gum Figure 1. Sugar gum woodlot near Dimboola, Victoria In their natural range, sugar gum grows on poor, often Sugar gum (Eucalyptus cladocalyx) is a medium to large shallow soils. eucalypt that has been widely planted in western Victoria since the 1870s. It is a common sight along roadsides and Provenance fence-lines, where it has been planted to provide firewood, No formal breeding work has been done on sugar gum. poles and shelter. However, after a 100+ year history of cultivation it is clear Sugar gum has a hard, durable and attractive pale timber that there is considerable variability in form between suited to a range of products. Its favourable sawing and different collection locations. Investigations have drying characteristics, combined with tolerance to adverse commenced to determine which provenances (seed- conditions, make it a suitable species for farm forestry. sources) produce the straightest, fastest growing timber This species is characterised by its colourful, smooth trees. ‘gum’ bark. Plates of old bark are periodically shed, It is known that trees from the southern Flinders Ranges leaving irregular patches of orange, yellow and gray. Its grow larger and straighter than from the Eyre Peninsula leaves are dark green and glossy on the top and pale green and Kangaroo Island. In Western Australian plantings, the below. The foliage is typically clustered at the ends of Port Lincoln provenance has proven to be the most long, upright branches. The fruit is ribbed and barrel- drought-tolerant. In South Australian trials, the Wanilla shaped with a small opening at the top. They grow on provenance is proving to be very poor for timber leafless branches inside the crown and are shed in production. Seed from western Victorian plantations has abundance. performed well in Victorian provenance trials. Seed from the Wail plantation, derived from the Wirrabara Natural occurrence and species provenance, is probably superior to most other collections, description as the trees have undergone some selection since the first Sugar gum comes from a few distinct locations in South plantations were established. Australia (Kangaroo Island, Eyre Peninsula and southern A genetic defect causing multiple stem form and low Flinders Ranges), where rainfall ranges from 380-650 mm bushy growth has been popularised in the horticultural per year(see Figure 2). In the high rainfall areas of the trade. This variety is not suited for timber production but Flinders Ranges trees may attain heights of 35 m and

© State of Victoria, Department of Primary Industries Page 1 Sugar gum for farm forestry AG0892 together with its aesthetic value, may be useful for shade Growth rates and shelter. In a 450 mm rainfall zone a saleable firewood crop can If collecting seed to grow for timber production, collect it generally be harvested after 15 years, while sawlogs may from preferred sources exhibiting the tallest, straightest be produced by age 35. growth. These traits will tend to be maintained in the new Recently, Melbourne University released a report on planting. An opportune time to collect large quantities of growth measurements of several tree species in the seed is when trees are being harvested from belts of Wimmera region. This report includes growth information woodlots. for sugar gum planted in state forest reserves, community plantings and school blocks from the 1940s. The report Site requirements 2 estimated growth per year, expressed as basal area (m /ha, Sugar gum is often selected for farm forestry on infertile measured at 1.3 m height), to be 0.27-0.63 m2/ha/yr. sites because it typically performs well, where few other These growth rates, and the measurements presented in species do. Table 1, suggest that sugar gum could be grown for sawlog It is tolerant of drought and exposed conditions. Sugar production on a 25-35 year rotation length. gum will tolerate low to moderate salinity but is intolerant Table 1 highlights the environment’s impact on growth, of waterlogging. with areas of higher rainfall showing higher MAI. The Avoid planting too early in the season if there is a above growth rates refer to growth in the main stem. likelihood of post planting frosts, as it is susceptible to Overall growth (including side branches harvested for frost damage in the first year. firewood) could perhaps double these figures. Table 1. Sugar gum growth rates from established plantations (excluding branch volume) Plantation Barrett Reserve You Yangs Thurgoona Lake Hume Hamilton Vic Warracknabeal Vic Vic NSW NSW (thinned) (thinned) Annual rainfall (mm) 420 450 625 625 700 Age (yrs) (1) 13 (2) 23 42 19 42 5.5 Current Stocking (stems/ha) (1) 800 (2) 1000 667 140 160 1100 Basal area (m2/ha) (1) 8.0 (2) 13 23.5 18.2 22.2 10.5 Height (m) (1) 9.0 (2) 14.5 20.2 20.9 23.9 7.6 Mean Annual Increment (MAI) (m3/ha/yr) (1) 1.8 (2) 2.7 3.8 6.7 4.2 4.8

In other yield information collected from firewood cutting These stands should also be thinned. Thinning would operations on the basalt plains of western Victoria, the periodically remove trees of poor form and slow-growing MAI was estimated in 11 various-aged plantations; both trees, to reduce competition for water and nutrients and coppiced and previously uncut stands. These yields concentrate growth onto the best trees in the stand. suggest a MAI of stacked merchantable firewood of 3 Sugar gum is often planted on a 3 m x 4 m grid in areas around 16 m /ha/yr. A wood density of 0.85 tonnes per receiving less than 600 mm of rain annually, or in areas cubic metre was assumed when estimating volume. This that have low soil fertility. At this spacing 833 trees are higher growth rate can be attributed to a higher stocking planted per hectare. In higher rainfall areas planting rate (averaging around 1200-1400 stems/ha), greater densities of 3 m x 3 m (1100 trees/ha) and 4 m x 2.5 m rainfall and inclusion of side branches in volume (1000 trees/ha) are possible. This spacing encourages the estimates. trees to grow straight and to develop light branches. With improved management and use of select seed it is Vehicles are able to drive between the planting lines, expected that higher growth rates will be achieved. making access for pruning and weed control works easy. For site preparation information, refer to Agriculture Note Managing for specialty timber production AG0771: Eucalypt plantation establishment – site To improve wood quality trees should be regularly pruned preparation. to produce ‘clearwood’ - timber that is free from knots Fencing off trees from stock is required, as the juvenile (see Agriculture Note AG0773: Eucalypt stem pruning). If foliage has a sweet taste due to the presence of a chemical contract pruners are not used, it is recommended that the compound called glucoside. Guarding the trees will help to landholder only commits to small annual plantings of 1 to deter browsing and should be carried out with other pest 2 hectares. This will spread the pruning requirement out control techniques such as shooting and baiting. Guarding over a number of years. also offers some protection from frost damage. Form-pruning to produce strong apical growth should be undertaken (see Agriculture Note AG0774: Guide to early age ‘form’ pruning).

Managing for firewood production conventional droppers. Sugar gum has wider uses for railway sleepers, telephone poles, house stumps, bearers Thinning operations can produce residues for sale as under tile roofs, decking, and building frames. firewood, or a stand can be solely managed for firewood. Some of these more valuable products can be produced, Firewood woodlots do not require any pruning or thinning provided that the timber is handled properly after felling works, and are usually harvested after about 15 years. See (ie. stacked, covered and dried). The wood can be milled Agriculture Note AG0814: Managing coppice in eucalypt and used as excellent high-strength appearance-grade plantations. timber for indoor and outdoor furniture and flooring. The After harvest, firewood stands may not have to be sawn timber can replace messmate for green framing replanted. This species has an excellent ability to re-sprout timber but unless used immediately after milling requires (coppice) from the stump. The new shoots can be managed drilling before nailing, because of its hardness and as new crop trees. tendency to split. To encourage strong coppice production, stumps should be When woodcutters come on to farms and harvest standing cut 5 to 10 cm from the ground (high stumps produce sugar gums for firewood, farmers currently receive $2- weak coppice which is unstable in strong winds) at a time 10/m3. Dry firewood fetches between $60-110/m3 of year when frost and moisture-stress is unlikely to affect depending on point of sale, while A-grade green sawn the new shoots. timber may sell for around $500/m3. Kiln-dried sawn When the trees are 3-5 years old, two of the strongest and timber may sell for $1800-2700/m3. Processing the timber straightest shoots should be selected and the rest knocked on the farm may increase returns to the grower. There are off. These retained shoots can be grown on until they are several portable mills available on the market, or you 10-30 years old, when they can be cut for posts, poles or might be able to employ a local miller to cut it for you. firewood. Remember to handle the timber properly after milling. If the shoots are being managed for sawlog production, the Sugar gum is popular with apiarists (bee keepers) and has best stem on each stump should eventually be selected, also been used for charcoal production. and the others removed, to maximise growth on one stem only. Trees can be coppiced in this way many times. Wood quality Sugar gum leaves should not be used for fodder while Sugar gum has a pale yellow-brown heartwood that when leaves are wilting following coppicing or in their juvenile polished becomes a light ginger-brown color. The sawn state, as cyanide is produced that is harmful to all types of timber is well featured, caused by an interlocking grain. grazing stock. Grazing stock on dead and adult leaves is The timber has a uniform texture and is extremely hard. acceptable. The wood of sugar gum is prone to termite attack and the sapwood may be susceptible to the lyctus borer, although Pests and disease risks the heartwood displays good resistance. The heartwood is Extreme environmental conditions or competition among also resistant to chemical impregnation. Sugar gum timber trees can cause trees to become weakened and therefore is difficult to work, but polishes to an elegant finish. More more susceptible to insect attack. Sugar gum is resilient to research is still required into gluing techniques of sugar most insect pests, but is susceptible to small outbreaks of gum. leaf feeders, or sap sucking insects and borers. These The green density is 1200 kg/m3 and air dried density (at outbreaks are usually not damaging enough to require 12% moisture content) is 1100 kg/m3. Sugar gum falls into chemical spraying. CSIRO’s natural durability Class 1 rating (highly durable), Insect attack needs to be carefully monitored in sugar gum and has an expected life both above and below the ground coppice, as bark beetles can ringbark new stems, causing of at least 21 years. them to die. For more information on treatment of affected CSIRO has recently completed a study on the potential of stands see Agriculture Notes: low rainfall species (including sugar gum) to be grown for AG0801: Insect Pests-Control, and high quality solid wood products. The study found that AG0799: Insect pests of young eucalypt plantations. green and dead knots were a major factor preventing boards from receiving a high appearance-grade. Regular Uses pruning to control the size of the knotty core is likely to improve product quality by producing clearwood. Sugar gum is fast becoming a recognised species for the high-quality sawn timber it produces. There are currently Drying characteristics three furniture manufacturers in Victoria purchasing logs from existing plantations, paying around $100/m3 at the Sugar gum is slow to dry and care must be taken to avoid mill door. At least a further 6 small-scale millers and significant degrade in the drying process. Drying degrade portable millers are sawing sugar gum in western Victoria such as surface checking can be avoided by sealing the log alone. ends with paint and ensuring appropriate drying facilities, (ie. timber is evenly stacked to allow free circulation Sugar gum has many on-farm uses including posts and around each piece). Air-drying will lower the moisture poles, stock yard railings and due to its low electrical content of the timber to 15-17%. For high value products conductivity, electric fence droppers as well as the more such as flooring and fine furniture, kiln drying is required

© State of Victoria, Department of Primary Industries Page 3 Sugar gum for farm forestry AG0892 to lower the moisture content to 8-12%. Slow kiln-drying schedules are required to minimise surface checking. Shrinkage caused by the loss of moisture from timber drying varies within species, but generally for sugar gum it is low, at 6% around the board and 10.5% along the board. Acknowledgments The information in this Note, was obtained from a number of sources (listed below). For further information, refer to the following references: Bird, P.R. (2000) Farm Forestry in Southern Australia, a manual with a focus on clearwood production of specialty timber. Agriculture Victoria, Hamilton, Victoria. Boland, D.J., Brooker, M.I.H., Chippendale, G.M., Hall, N., Hyland, B.P.M., Johnston, R.D., Kleinig, D.A. and Turner, J.D. (1994) Forest Trees of Australia. CSIRO Publications, East Melbourne, Victoria. Doran, J. (2000) Electronic forestry compendium full data sheet for Eucalyptus cladocalyx CSIRO Forestry and Forest Products. Hamilton, L. (2000) Commercial sugar gum plantations for firewood and sawlog production. Department of Natural Resources and Environment, Victoria. Stewart, M., Binns, R. and Hamilton, B. (1999) Report on growth measurements of several tree species in the Wimmera region. Institute of Land and Food Resources, University of Melbourne. Washusen, R., Waugh, G. and Hudsen, I. (1999) Wood products from low rainfall farm forestry- final report Forest and Wood Products Research and Development Corporation.

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