Taxonomic name: Acacia saligna (Labill.) Wendl. F.
Synonyms: Acacia cyanophylla Lindl., Mimosa saligna Labill., Racosperma salignum Labill.
Common names: blue-leaf wattle (English), golden-wreath wattle (English), orange wattle (English), Port Jackson (English-South Africa), Port Jackson wattle (English), Port Jackson willow (English), weeping wattle (English)
Organism type: tree
Due it its many uses Acacia saligna, or the Port Jackson willow, has been globally distributed with up to 300 000 ha planted worldwide and was identified as one of three priority multipurpose species for arid and semi-arid zones by FAO’s Silvae Mediterranea Network in 1996. Native to Western Australia and suited to a wide range of enviromental conditions, it is a fast growing tree utilised for soil stabilisation, animal fodder, tannin production, windbreaks, ornamental use and as a source of fuel wood. In areas where it has become invasive A. saligna can have a wide range of negative effects on native biodiversity and ecosystems and is difficult to control due to its coppicing ability and the creation of large soil seed-banks.
Acacia saligna is a bushy shrub dividing near the base into several stems, resulting in a dense bush that may be wider than high. The shrub form is usually 2 - 5 m tall but it can form a small tree 5 -9 m high, with a short but well-defined main stem (Midgely & Turnbull, 2003). Its natural occurence on the coastal plain of south-western Western Australia is mainly from sea-level up to 300 m and it occurs on many soil types, especially on poor and calcareous sands (Midgely & Turnbull, 2003). A. saligna coppices well and fodder biomass production is optimised by regular, annual harvesting, benefitting from fertilisation on infertile soils (Midgely & Turnbull, 2003). In common with many other acacias, A. saligna forms associations with VA mycorrhizal fungi (Midgely & Turnbull, 2003). It has an average lifespan of 30 - 40 years (Milton & Hall, 1981; in Wood & Morris, 2007).
Acacia cyclops, Acacia longifolia, Acacia mearnsii, Acacia melanoxylon, Acacia pycnantha
coastland, desert, planted forests, range/grasslands, ruderal/disturbed, scrub/shrublands
Acacia saligna is capable of thriving on many soil types, including high pH sands and soils in subhumid, semi-arid and arid temperate areas (Midgely & Turnbull, 2003).
In areas where it has become invasive, Acacia saligna is known to form dense monospecific stands, excluding native species and preventing their regeneration (Holmes & Cowling, 1997; Hadjikyriakou & Hadjisterkotis, 2002). It also alters vital ecosystem proceses; changing the soil processes like decomposition and nutrient cycling through incresed nitrogen levels (Witkowski, 1991a; Jovonovic et al 2009); altering the fire-regime with large soil seed-banks and more abundant biomass (Holmes, 2002); and impacting on streamflow reduction through incremental water use (Le Maitre et al 2000; in Jovonovic et al 2009). A. saligna is also known as an agricultural pest in some cultivated areas, taking up valuable agricultural space (Hadjikyriakou & Hadjisterkotis, 2002).
Plantations of Acacia saligna in warm-temperate and semi-arid areas provide stock fodder, soil stabilisation, fuelwood and charcoal (Midgley & Turnbull, 2003). In Australia, A. saligna has been used as an ornamental plant, for low windbreaks and shade, and is increasingly planted in agroforestry systems for fodder production and soil conservation (Crompton, 1992; in Midgely & Turnbull, 2003). Its fast growing, coppicing ability and capacity to thrive on sands and soils of high pH in subhumid, semi-arid and arid temperaure areas has led to it being planted widely around the world with an estimated 300 000 ha planted globally, being identified as one of three priority multipurpose species for arid and semi-arid zones by FAO’s Silvae Mediterranea Network (Midgely & Turnbull, 2003). In Tunisia, it has been successfully processed into particle board, while in the Mediterranean, it is used for vine stakes and small agricultural implements (Michaelides, 1997; in Midgely & Turnbull, 2003). It is also used extensively for sand dune fixation and gully erosion control; planted in Australia to rehabilitate areas mined for coal and minerals (Langkamp, 1987; in Midgely & Turnbull, 2003).
Native range: Australia, Western Australia (USDA-ARS, 2010).
Known introduced range: Acacia saligna has been planted extensively in Africa and the Mediterranean region: including Libya, Tunisia, Morocco, Egypt, Algeria, Ethiopia, South Africa, Israel, Jordan, Palestine, Iran, Iraq, Syria, Greece and Cyprus (Midgely & Turnbull, 2003). A. saligna is also present in the United States, in California (USDA-NRCS, 2010); and South America in Uruguay, Chile, Mexico (Midgely & Turnbull, 2003).
Introduction pathways to new locations
For ornamental purposes: Acacis saligna has been distributed on a global level due to its many uses and ability to thrive in harsh environments (Midgely & Turnbull, 2003).
Local dispersal methods
Consumption/excretion: While most of the seed produced by Acacia saligna fall straight onto the ground, seeds are also dispersed by birds (Henderson et al 1998).
Physical/Chemical: Physical and chemical control methods are possible but is very labour and cost intensive due to persistent seed banks and the coppicing capability of A. saligna (MacDonald & Wissel, 1992). These include cutting at ground level, mattocking, ringbarking and Glyphosate or Triclopyr based herbicides foliarly applied or painted onto cut stems (MacDonald & Wissel, 1992).
The reduction of the seed-bank is an important component of controlling A. saligna (Holmes, 1990; in Cohen et al., 2008). This is most often achieved with burning, with a slow intense fire more effective than a rapid one (Richardson & Kluge, 2008). Soil solarisation has also been shown to be effective in reducing A. saligna seed viability in moist soils and increasing germination rates in dry soils (Cohen et al 2008).
Biological: Biological control has been effective in South Africa, with the gall-forming rust fungus Uromycladium tepperianum being effective in reducing population density, tree longevity and reproductive output wherever A. saligna is found (Morris, 1997; Wood & Morris, 2007). An addtional biological control agent, Melanterius compactus, was released in 2001 to target the large seed-banks created before the release of U. tepperianum with preliminary monitoring showing success (Impson et al., 2009).
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Annual seed production of Acacia saligna is about 10 000 seeds per 1 square metre of canopy cover (Milton & Hall, 1981; in Henderson et al 1998). While most of these fall straight onto the ground; seeds are dispersed by birds (Henderson et al 1998). A large portion of these seeds remain dormant due to a water-impermeable testa (Rolston, 1978; in Henderson et al 1998), resulting in a large seed bank build up of about 46 000 seeds per square metre of canopy cover (Holmes et al 1987). Dormancy is broken following a fire, allowing for mass regeneration of A. saligna; resulting in dense thickets in some parts of its introduced range such as South Africa (Henderson et al 1998).
Reviewed by: Under expert review
Compiled by: IUCN SSC Invasive Species Specialist Group (ISSG) with support from the Overseas Territories Environmental Programme (OTEP) project XOT603, a joint project with the Cayman Islands Government - Department of Environment
Last Modified: Tuesday, 8 June 2010