Acacia mearnsii Totally Explained

Everything about Acacia Mearnsii totally explained

Acacia mearnsii is a fast-growing leguminous tree native to Australia. Common names for it include Black Wattle, Acácia-negra (Portuguese), Australian Acacia, Australische Akazie (German), Swartwattel (Afrikaans), Uwatela (Zulu). A. mearnsii has been introduced to numerous parts of the world, and in those areas is often used as a commercial source of tannin or a source of fire wood for local communities. In areas where it has been introduced it's often a weed, and is seen as threatening native habitats by competing with indigenous vegetation, replacing grass communities, reducing native biodiversity and increasing water loss from riparian zones. The species is named after E. A. Mearns, who collected the type from a cultivated specimen in East Africa.

Taxonomy

The trees are unarmed, evergreen and grow six to 20 meters high. The branchlets are shallowly ridged; all parts finely hairy; growth tips golden-hairy. Leaves dark olive-green, finely hairy, bipinnate; leaflets short (1.5 - 4 mm) and crowded; raised glands occur at and between the junctions of pinnae pairs. Flowers pale yellow or cream, globular flower heads in large, fragrant sprays. Fruits dark brown pods, finely hairy, usually markedly constricted.

Habitat description

In its native range A. mearnsii is a tree of tall woodland and forests in subtropical and warm temperate regions. In Africa the species grows in disturbed areas, range/grasslands, riparian zones, urban areas, water courses, and mesic habitats at an altitude of between 600-1700m. In Africa it grows in a range of climates including warm temperate dry climates and moist tropical climates. A. mearnsii is reported to tolerate an annual precipitation of between 6.6 – 22.8 dm (mean of 6 cases = 12.6), an annual mean temperature of 14.7 – 27.8°C (mean of 6 cases = 2.6°C), and a pH of 5.0 – 7.2 (mean of 5 cases = 0.5). A. mearnsii doesn't grow well on very dry and poor soils.

Weed impacts outside of native range

The invasiveness of this species is partly due to its ability to produce large numbers of long-lived seeds (which may be triggered to germinate en masse following bush fires), and the development of a large crown which shades other vegetation. Its leaves and branches may have allelopathic properties. A. mearnsii competes with and replaces indigenous vegetation. It may replace grass communities to the detriment of the grazing industry and grazing wildlife. By causing an increase in the height and biomass of vegetation A. mearnsii infestations increase rainfall interception and transpiration, which causes a decrease in streamflow. Soil under A. mearnsii becomes desiccated more quickly (than it does under grass). A. mearnsii stands also destabilise stream banks and support a lower diversity of species
Commercial plantations and invasive stands of A . mearnsii in South Africa reduce surface runoff and decrease water ability, causing an estimated annual economic loss of $US 2.8 million. According to KwaZulu-Natal Wildlife (the governmental agency responsible for managing protected areas in KwaZulu-Natal Province, South Africa) the advance of alien plants (particularly Chromolaena odorata, Lantana camara, Acacia dealbata, and Acacia mearnsii) is the most significant past and future threat to conservation in these areas.

Uses

The species is grown commercially in many areas of the world for a variety of uses. Commercial stands have been established in Africa, South America and Europe. The tannin compounds extracted from the bark of A. mearnsii are commonly used in the production of soft leather. A range of other products, such as resins, thinners and adhesives, can also be made from bark extracts. The timber is used for building materials, the charcoal is used for fuel and the pulp and wood chips are used to produce paper. In rural communities in South Africa the trees are important as a source of building material and fuel. A. mearnsii has some known medical applications, such as its use as a styptic or astringent. The planting of wattles has also been used as a soil stabiliser to decrease erosion (preferably far from river courses to minimise the water loss caused by the tree's high rate of transpiration). The agroforestry industry promotes the use of the species (among other similar species) as a potential "soil improver". Acacia mearnsii has been shown to contain less than 0.02% alkaloids.

Geographical range

Native Range: Australia. Known introduced range: North America, South America, Asia, Europe, Pacific, Africa and Europe.

For ornamental purposes (local)

By animals: The dispersal of the seeds of A . mearnsii is believed to be aided by cattle and birds.

By people: Local people collecting branches and logs for firewood may spread seeds. It also generates numerous suckers that result in thickets consisting of clones.

Gallery

Image:Acacia mearnsii blossoms.jpg Image:Acacia mearnsii pods.jpg Image:Starr 060429 9474 acacia mearnsii.jpg Image:Acacia mearnsii flowering.jpg Image:Acacia mearnsii.jpg Image:Acacia mearnsii habit.jpg Further Information

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