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Lake Logue, WA

sprig with female flowers

male flower spike

mature cone

Natural populations

Casuarina obesa has an unusual distribution and is endemic to the south west of Western Australia and to far northwest of Victoria in the Wimmera and Mallee regions [1]. Its main occurrence is in Western Australia where it extends south from the Murchison Region to the Swan Coastal Plain around Perth. It has a discontinuous distribution to the east of these areas extending as far east as the Gibson and Queen Victoria Deserts. This species is a medium-sized tree rarely greater than 15 m tall. It is usually found fringing depositional sites along drainage systems. These range from river banks, margins of salt lakes, estuaries and swamps and they encompass a wide range of saline and alkaline substrates [1].

Flowering and seeds

This species dioecious with male and female flowers on separate plants. Flowering occurs during December to January [2]. Female plants bear woody cones in an indehiscent state throughout the year, with crops from two seasons may often be present. There are about 370 viable seeds per gram; seeds start to germinate in about 5 days if grown at 25°C with no pretreatment required [2].

Cultivation and uses

Casuarina obesa is a nitrogen-fixing tree with excellent potential to remediate saline sites as it is one of Australia's most salt tolerant trees [1]. Like many casuarinas, protection from grazing animals during the establishment phase is essential. Potential uses of C. obesa  include fuelwood, poles and posts, sawn timber and charcoal. Environmental benefits include shelter and windbreaks for stock, catchment protection and assisting to lower saline ground water. The wood of this species has been used for fence posts and has excellent fuelwood properties. Casuarina obesa has recently been assessed as having potential to produce commercial grade sawn timber in medium to high rainfall zones [3,4].

Key descriptors:

Climate parameters
Mean annual rainfall: 200-850 mm
Rainfall distribution pattern: uniform or winter
Mean annual temperature: 13-23 °C
Mean max. temperature of the hottest month: 27-39 °C
Mean min. temperature of the coldest month: 3-9 °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: 0-300 metres
Tolerance of climate extremes
Drought: known to be moderately drought tolerant or known to be tolerant of protracted droughts
Fire: regenerates foliage after damaging fire
Frost: tolerates frosts in the 0° to -5°C range
Wind: known or has attributes to make an excellent windbreak or tolerates salt-laden coastal winds
Soil factors
Texture: clay loam, cracking clays, heavy clay (greater than 50% clay), light to medium clay (35-50% clay), loam, sandy loam, sandy clay loam or sand
Soil pH reaction: neutral (6.5-7.5) or alkaline (greater than 7.5)
Soil depth: moderate to deep (30-100 cm or greater)
Drainage: well-drained, poorly to imperfectly drained or seasonally waterlogged
Salinity: highly saline, slightly to moderately saline or non-saline
Tolerance of adverse soils
Extremes in pH: alkalinity
Extremes in texture: cracking clay, clayey or sand
Salinity: extremely high (> 16 dS m-1), high (9-16 dS m-1), moderate (-8 dS m-1) or slight (2-4 dS m-1)
Soil waterlogging tolerance: drainage may be sluggish at times
Biological traits under cultivation
Habit: evergreen tree 10-15 m tall, usually produces a clear trunk
Longevity: moderate to long lived (>15 years)
Growth rate: fast or moderate
Coppicing ability: responds to pruning, pollarding
Root system: moderate to deep, shallow and spreading, fixes nitrogen via root symbiot, forms root suckers
Erosion control potential: excellent for clayey sites or excellent for sandy sites
Windbreak potential: excellent (known or has good attributes),r tolerates salty coastal winds
Wood density: mod. to high (greater than 600 kg/cubic metre)
Carbon sequestration potential: moderate
Uses
Potential farm use: excellent windbreak, good for fence posts, shelterbelt or shade for stock
Urban use: ideal maintenance free street tree
Wood products: liquid fuels (?), craftwood (for turnery etc.), flooring (including parquetry), high quality fuelwood, industrial charcoal, light construction, posts (including fencing) or speciality timber for quality furniture, wood composites
Potentially undesirable attributes
Growth habit: mod. to strong propensity to root sucker, shallow roots may outcompete adjacent plants
Susceptibility to disease or predation: susceptible to stem girdling by parrots
Foliage: highly susceptible to browsing by animals
Weediness: high based on its biology

References

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

[2] 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]

[3] Emmott T (no date) Swamp Sheoak (Casuarina obesa) use in Farm Forestry. Greening Australia (WA). Online at: http://www.avongro.com.au/Webpages/documents/GAWASwampSheoak.pdf

[4] Agroforestry News (2005) No. 53: http://www.mtg.unimelb.edu.au/AgroNews/AgroforestryNews53.pdf

Internet links

Emmott T (200? no date). Swamp Sheoak (Casuarina obesa) use in Farm Forestry. Greening Australia (WA):http://www.avongro.com.au/Webpages/documents/GAWASwampSheoak.pdf

FloraBase Western Australian Herbarium: http://florabase.calm.wa.gov.au/browse/flora?f=070&level=s&id=1742

Plantations 2020 Casuarina obesa Working group: http://www.plantations2020.com.au/infocus/august08_05.html

Western Australian Department of Food and Agriculture: http://www.agric.wa.gov.au/ [Search site as several documents may relate to this species.]

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