Acacia saligna(Labill.) H. Wendl.

 
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Leguminosae (Mimosaceae)

Synonyms

Acacia cyanophylla Lindl.; the intraspecific variability is so great that A. cyanophylla and A. saligna were previously considered separate species. The synonym is still in agricultural use in several countries (including Tunisia).

 Author: J.M. Suttie

 

Common names

Golden wattle, acacia bleu (French).

Status

It occurs naturally in the south-western comer of Western Australia but has been introduced to other regions of Australia and to many other countries. It is used as browse in dry parts of North Africa

Non-forage uses:

The wood is sappy and light and reported not to be particularly good as fuel, although in many arid regions plantations of A. saligna have been established for firewood as it is fast growing and productive in such unfavourable sites. It is used for dune stabilisation in both North and South Africa and as a decorative tree in many dry, warm sites, including southern Europe. It coppices readily and also produces suckers which is of interest in dune control.

Description

A small, many-stemmed bushy shrub, 2 – 5 metres in height but there is a form which is a tree with a distinct trunk up to 30 cm in diameter which reaches a height of 8 metres. The bark is smooth and reddish-brown at the level of the twigs; on old trees the bark is dark grey and fissured. The phyllodes are dark green to blue-green with a marked central vein, very variable, long and straight or sickle-shaped from 8 – 25 cm long by 0.4 – 2 cm wide, often larger towards the base of the tree. Flowers are bright yellow, grouped 25 – 55 in spherical heads 7 – 8 mm in diameter, grouped in racemes. The pods are narrow, 4 – 6 mm wide and 8 – 12 cm long, sometimes slightly curved with slight constrictions between the seeds.

Environmental adaptation

It grows on a wide range of soil types but is outstanding on sandy coastal plains and sand dunes. It is used extensively for sand dune stabilization and reclamation (it prefers an annual rainfall range of 350-600 mm but will grow well in areas with rainfall as low as 250 mm and as high as 1 200 mm). It is moderately tolerant of soil salinity. It has no marked soil preferences in North Africa and grows well in deep sands; it is tolerant of salinity and alkalinity and has a reputation of resisting coastal salty winds. In North Africa the tree lives for 7 – 15 years under rainfalls of 150 – 200 mm but only 5 years on shallow soils.

Cultivation and management

Acacia saligna is usually raised in nurseries, in plastic sachets and transplanted in the cool season as soon as rainfall permits; in arid areas some watering may be necessary to get the plants established. Spacings vary greatly according to the system of management foreseen; Nefzaoui (1997) mentions very widely spaced rows intercropped with barley in dry parts of Tunisia and discusses its use along with Atriplex and fodder cactus in feeding systems. The cost of installation in Tunisia (average for several types of fodder shrub) was US $ 1 000 per hectare, including maintenance for the first three years and subsidies to farmers.

It can nodulate effectively with both fast and slow-growing Rhizobia but seems to have preferences for Brachyrhizobia (Domergues et al. 1999). Inoculation is strongly recommended since natural nodulation is very erratic and in the arid sites where it is usually planted hardly any Rhizobia are present.

Seed production

Acacia saligna is a free seeder; seed can be collected by hand from selected trees of good palatability and production.

Crop use and grazing management

It is reasonably tolerant of browsing and defoliation and some reports indicate it can be completely defoliated without harming the plant (NAS 1979) However, Gutteridge (1990) reported 50% mortality with regular defoliation over 4 years. The bushes may be browsed in a rotational system or lopped periodically. It is mainly used for small ruminants in North Africa. In Tunisia it is used as a dry season feed and lopped and browsed in alternate years.

Composition

The phyllodes of A. saligna are often used as supplementary feed for sheep and goats in countries such as Libya (El-Lakany 1986) Crude protein content of phyllodes varies from 12 to 16% and in vitro dry matter digestibility has been measured at 40% (Vercoe 1989). Le Houerou (1984) recorded daily consumption rates of 1.6 kg per head daily for sheep over prolonged periods without apparent detrimental effects.

Crop improvment

There is a great deal of natural variability within the species so improvement is likely to be possible.

Pests and diseases

.A. saligna is generally trouble-free but gall nematodes have been reported from nurseries in Morocco.

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