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Herberton, Qld (citriodora)

Duraki SF, Qld (variegata)

fruit (citriodora)

bark (citriodora)

Natural populations

Corymbia citriodora has two subspecies [1,2]:

Mixed stands occur where the two come into contact, such as near Monto. This species is usually about 25–35 m tall but sometimes taller. Trees from northernmost stands of subsp. citriodora have narrower, pendulous leaves and more often commonly cultivated because of their attractive appearance. The preferred habitat of subsp. citriodora is on ridges and steep hills on well-drained, light-textued soils derived from granite, shale or sandstone, while subsp. variegata favours clay loams derived from basalt or metasedimentary rocks [1].

Flowering and seeds

This species flowers during June to November [1,3,4]. Seed capsules are held on the tree in an indehiscent state for most of the year. There are about 140 viable seeds per gram [4]. Pretreating the seeds to induce germination is not required, however, inhibitors in the seed coat that delay germination are suspected [4]. Leaching or soaking the seeds in large volumes of water will improve germination response. The seeds start to germinate in about 5 days if grown at 25-30°C [4].

Cultivation and uses

Subsp. citriodora from northern parts of its range have narrow, pendulous leaves, pinkish bark and is commonly cultivated throughout much of southern Australia because of its attractive appearance (eg, the trees along Fraser Avenue at Kings Park in Perth, Western Australia). This form shows a remarkable tolerance of climates and soil types that differ markedly from those across its natural distribution. The subspecies is also notable for its lemon-scented (mainly citronellal) leaf oils, but these are absent in subsp. variegata. Wood harvested from natural stands of this species has been used for fuelwood, construction, joinery, flooring, tool handles and charcoal [1]. Recently in Australia, subsp. variegata has shown potential as a farm-forestry species in the 500-800 mm annual rainfall zone [6,7]. This species is widely cultivated as a plantation or ornamental species overseas (China, Brazil) [8].

Key descriptors:
Subsp. citriodora:
Climate parameters
Mean annual rainfall: 600-2000 mm
Rainfall distribution pattern: summer, uniform or winter
Mean annual temperature: 15-24 °C
Mean max. temperature of the hottest month: 29-30 °C
Mean min. temperature of the coldest month: 4-9 °C
Frosts (approx. no. per year): frost free or more or less frost free, up to 20 or greater than 20
Frost intensity: light to moderate (0 to -5°C)
Altitude: 30-1100 metres
Tolerance of climate extremes
Drought: known to be moderately drought tolerant
Fire: regenerates foliage after damaging fire
Frost: tolerates frosts in the 0° to -5°C range
Wind: tolerates salt-laden coastal winds
Soil factors
Texture: clay loam, duplex texture contrast soils, light to medium clay (35-50% clay), loam, sandy loam, sandy clay loam or sand
Soil pH reaction:  acidic (less than 6.5), neutral (6.5-7.5) or alkaline (greater than 7.5)
Soil depth: skeletal to shallow (less than 30 cm) or moderate to deep (30-100 cm or greater)
Drainage:  well-drained
Salinity: slightly to moderately saline or non-saline
Tolerance of adverse soils
Extremes in pH: acidity or alkalinity
Extremes in texture: sand
Salinity: moderate (-8 dS m-1), nil - sensitive to saline soils or slight (2-4 dS m-1)
Soil waterlogging tolerance: nil - sensitive to waterlogged soils
Biological traits under cultivation
Habit: evergreen tree 10-35 m tall, usually produces a clear trunk
Longevity: moderate to long lived (>15 years)
Coppicing ability: vigorous, responds to pruning, pollarding; lignotuberous
Root system: moderate to deep or shallow and spreading
Erosion control potential: excellent for clayey sites or excellent for sandy sites
Windbreak potential: tolerates salty coastal winds
Wood density: mod. to high (greater than 600 kg/cubic metre)
Carbon sequestration potential: high
Uses
Potential farm use: good for fence posts, good ornamental attributes
Specialty products: flowers produce nectar for honey production, pollen has value for apiculture, leaves are a source of citonellal
Urban use: good as an ornamental or amenity plant
Wildlife value: flowers are especially attractive to birds
Wood products: flooring (including parquetry), heavy construction, high quality fuelwood, industrial charcoal, panelling, poles (building, transmission, piling), posts (including fencing), speciality timber for quality furniture
Potentially undesirable attributes
Growth habit: shallow roots may outcompete adjacent plants

Subsp. variegata:
Climate parameters
Mean annual rainfall: 600-1600 mm
Rainfall distribution pattern: summer
Mean annual temperature: 11-21 °C
Mean max. temperature of the hottest month: 22-34 °C
Mean min. temperature of the coldest month: 0-10 °C
Frosts (approx. no. per year): frost free or more or less frost free or up to 20
Frost intensity: light to moderate (0 to -5°C)
Altitude: 30-1100 metres
Tolerance of climate extremes
Drought: known to be moderately drought tolerant
Fire: regenerates foliage after damaging fire
Frost: tolerates frosts in the 0° to -5°C range or tolerates heavy frosts colder than -5°C
Soil factors
Texture: clay loam, heavy clay (greater than 50% clay), light to medium clay (35-50% clay) or loam, sandy loam, sandy clay loam
Soil pH reaction: acidic (less than 6.5) or neutral (6.5-7.5)
Soil depth: moderate to deep (30-100 cm or greater)
Drainage:  well-drained
Salinity: non-saline
Tolerance of adverse soils
Extremes in pH: acidity
Extremes in texture: clayey
Salinity: nil - sensitive to saline soils or slight (2-4 dS m-1)
Soil waterlogging tolerance: nil - sensitive to waterlogged soils
Biological traits under cultivation
Habit: evergreen tree 10-35 m tall, usually produces a clear trunk
Longevity: moderate to long lived (>15 years)
Coppicing ability:  strong, responds well to pruning, pollarding; lignotuberous
Root system: moderate to deep
Erosion control potential: excellent for clayey sites
Wood density: mod. to high (greater than 600 kg/cubic metre)
Carbon sequestration potential: high
Uses
Potential farm use: good for fence posts
Specialty products: flowers produce nectar for honey production, pollen has value for apiculture
Wildlife value: flowers are especially attractive to birds
Wood products: flooring (including parquetry), heavy construction, high quality fuelwood, industrial charcoal, panelling, poles (building, transmission, piling), posts (including fencing), speciality timber for quality furniture
Potentially undesirable attributes
Susceptibility to disease or predation: foliage highly susceptible to insect predation or pathogenic leaf diseases

References

 [1] Boland DJ, Brooker MIH, Chippendale GM, Hall N, Hyland BPM, Johnson RD, Kleinig DA, McDonald MW, Turner JD (2006) Forest Trees of Australia. CSIRO Publishing, Collingwood.

[2] Slee AV, Connors J, Brooker MIH, Duffy SM, West JG (2006) EUCLID Eucalypts of Australia. Third Edition CD ROM Centre for Plant Biodiversity Research. CSIRO Publishing, Melbourne.

[3] Clemson A (1985) Honey and Pollen Flora. Inkata Press, Melbourne.

[4] Gunn BV (2001) Australian Tree Seed Centre Operations Manual. Internal Publication, CSIRO Australian Tree Seed Centre, ACT. [Online at http://www.ensisjv.com/Portals/0/atsc-opmanualcomplete.pdf  Accessed March 2008]

[5] Marcar NE, Crawford DF (2004) Trees for Saline Landscapes. RIRDC Publication Number 03/108, Canberra.

[6] Jovanovic T, Booth TH (2002) Improved species climatic profiles A report for the RIRDC/L&W Australia/FWPRDC/ MDBC Joint Venture Agroforestry Program. RIRDC Publication No 02/095, Canberra.

[7] Harwood CE, Bird R, Butcher T, Bush D, Jackson T, Johnson I, Stackpole D and Underdown M (2005) Australian Low Rainfall Tree Improvement Group (ALRTIG) Update of hardwood breeding strategies, A report for the RIRDC/Land & Water Australia/FWPRDC/MDBC Joint Venture Agroforestry Program RIRDC Publication No 05/023 RIRDC Project No. CSF-62A. [Available from the RIRDIC website at http://www.rirdc.gov.au/reports/AFT/05-023.pdf Accessed 25/02/2008]

[8] Eldridge K, Davidson J, Harwood C, Wyk Gv (1993) Eucalypt Domestication and Breeding. Clarendon, Oxford.

Internet links

Alice Spings Town Council: http://www.alicesprings.nt.gov.au/community/environment/recommended_native_plants

PlantNET National Herbarium of New South Wales:http://plantnet.rbgsyd.nsw.gov.au/cgi-bin/NSWfl.pl?page=nswfl&lvl=sp&name=Corymbia~variegata

Victorian Department of Primary Industry: http://www.dpi.vic.gov.au/ [Search site as several documents may relate to this species.]

Wikipedia: http://en.wikipedia.org/wiki/Corymbia_citriodora

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