Acacia saligna
(Port Jackson wattle)

A. saligna, a fast-growing, drought-tolerant nitrogen-fixing tree from southwestern Western Australia has been widely planted through the world’s drylands, especially around the Mediterranean basin, for fodder, fuelwood, sand stabilization, as a windbreak and as an ornamental garden or street tree. Referring to invasion of threatened Cape Floristic vegetation in South Africa, it was called “one of the worst woody invaders, a plant that has run amuck in a threatened biome, rich in endemic plant species” (Cronk and Fuller, 1995), however, a successful biocontrol programme has since largely contained the problem there. It has more recently escaped and spread invasively in parts of Cyprus, Portugal and Spain, and has naturalised and spread in southern and eastern Australia and elsewhere where introduced. It continues to be planted, especially in North Africa and West Asia, but caution is now advised as prolific seed production, ready coppicing and suckering ability, and rapid growth on even the poorest of sites make it a high risk species.

A. saligna is native to southwestern Western Australia, where it is very common on the poor sandy soils of the Swan Coastal Plain from Gingin southwards to Busselton and the coast (35°S), and on heavier clay soils as far north as the Murchison River (27°S). It is found from the coast (115°E) inland to about 200 km east of Esperance (122°E).

Being a valuable and hardy species with ornamental value, it is likely that further intentional introduction may occur. Areas particularly at risk are those where it as yet does not occur, notably potentially sensitive areas such as Caribbean, Pacific and Indian Ocean islands. It is a Declared Invader (category 2) species in South Africa (Henderson, 2001), and a weed risk assessment for South Australia produced a high risk score for A. saligna (Melland and Virtue, 2002), and thus it may be assumed that this species may also be high risk for other similar areas. Steps should then be taken to highlight the risks posed by invasion of A. saligna, also using its old but still commonly used synonym, A. cyanophylla.

In it native Western Australia, it grows best on deep sands and loams associated with watercourses, and in coastal dunes, more commonly in the hollows between dunes (Cronk and Fuller, 1995). It is also found on disturbed roadsides, and further inland in the wheatbelt, populations occur at the base of many of the large, granitic rock outcrops. It has spread on a variety of habitat types in South Africa including the fynbos, forest, karro and grassveld, where it has also spread to waterways and irrigation channels Africa. Its hardiness and ability to coppice rapidly after fires or from trunks has also led to widespread establishment (Stirton, 1980).

The mean annual rainfall for the native range humid zone is 750-1000 mm, with an abrupt drop for the sub-humid zone to 450-500 mm, and as low as 280 mm in the semi-arid zone (Doran et al., 1997), but where it normally receives additional run-on water (Crompton, 1992). A. saligna occurs on many soil types, especially poor and calcareous sands, but also moderately heavy clays and on a range of podzolics. Trees are common on alkaline, infertile sandy soils (Simmons, 1981). It mainly grows on gentle undulating topography and coastal sand plains, but extends to a wide variety of situations from swampy sites and river banks to small, rocky hills (often granitic) and the slopes of the coastal ranges (Doran et al., 1997). It can tolerate waterlogging and salt winds, and altitudes from sea level to about 325 m elevation in its native range, but much higher where introduced.

Other pests noted as attacking A. saligna elsewhere in the world are Scirothrips dorsalis producing 'bunchy-top' symptoms in a glasshouse in Queensland, Australia (Ashwath and Houston, 1990), Odontothrips confusus in Israel (Strassen and Halperin, 1990), the oleander scale, Aspidiotus nerii, and its predators in Turkey (Karaca et al., 1999), Lindingaspis rossi and a parasite (Habrolepis sp.) in Egypt (Swailem et al., 1980) and Icerya purchasi in Ethiopia (Getu, 1996). Termites may also cause serious problems in tropical countries (Michaelides, 1979) and rodents sometimes gnaw and damage the roots.

Animal feed, fodder, forage

• Fodder/animal feed
• Forage

Environmental

• Agroforestry
• Amenity
• Boundary, barrier or support
• Erosion control or dune stabilization
• Land reclamation
• Ornamental
• Revegetation
• Shade and shelter
• Soil conservation
• Soil improvement
• Windbreak

Fuels

• Charcoal
• Fuelwood

General

• Ornamental

Human food and beverage

• Emergency (famine) food

Materials

• Dye/tanning
• Gum/resin
• Wood/timber

Charcoal

Roundwood

• Stakes

Wood-based materials

• Particleboard

A. saligna is sometimes confused with A. pycnantha, but it can be generally and easily distinguished from all other commonly introduced Australian acacias from the size, shape and colour of the phyllodes, and any confusion can be resolved with the use of a simple field guide.

Further research may be illuminating, in understanding why A. saligna has become an invasive species in the European Mediterranean (Cyprus, Portugal and Spain) but not in North Africa or the Middle East.

10/01/2008 Updated by:

Nick Pasiecznik, Consultant, France