acacia_melanoxylon (59)

Acacia melanoxylon

Evergreen tree, with leaves slightly shaped like a scythe and pale yellow spherical flower heads.

Scientific name: Acacia melanoxylon R. Br.

Common names: Australian blackwood, blackwood, acacia blackwood

Family: Fabaceae (Leguminosae)

Status in Portugal: invasive species (listed in the annex I of Decreto-Lei n° 565/99, of 21 December)

Risk Assessment score: (in development)

Synonymy: Acacia arcuata Sprengel, Acacia melanoxylon R. Br. var. arcuata (Sprengel)Ser., Acacia melanoxylon R. Br. var. obtusifolia Ser., Acacia melanoxylum R. Br., Mimosa melanoxylon (R. Br.) Poiret, Racosperma melanoxylon (B.Br.) Mart., Racosperma melanoxylon (R. Br.) Pedley

Last update: 30/06/2014

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How to recognise it

Tree up to 15 m, with a dark brown rhytidome deeply fissured.

Leaves: evergreen, where the young leaves are of two types: the first are bipinnate and the others are reduced to phyllodes; the adult leaves are all reduced to laminar phyllodes, slightly falcate, with 3-5 longitudinal veins.

Flowers: pale yellow, arranged in globular flower heads of 10-12 mm diameter.

Fruits: brownish-red pods, compressed, contorted; seeds completely encircled by an orange funicle.

Flowering: February to June.

 

Similar species

Acacia cyclops (coastal wattle) is similar but it only reaches 4 m height, it has flower heads with bright yellow flowers and the seeds are encircled by a scarlet funicle. Acacia longifolia (Sydney golden wattle) has some similarity, but it has linear phyllodes and the flowers are arranged in bright yellow spikes.

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Characteristics that aid invasion

It reproduces by seed; it produces many seeds that remain viable in the ground for more than 50 years. The seeds are dispersed by birds, wind, water or rodents. The seeds germinate after a space opening and/or fire occurrences.

The species also propagates vegetatively, forming vigorous sprouts from the stump and roots.

 

Native distribution area

Southeast Australia and Tasmania.

 

Distribution in Portugal

Mainland Portugal (all provinces), Azores archipelago (islands of São Miguel, Santa Maria, Terceira, Graciosa, S. Jorge, Pico, Faial and Flores), Madeira archipelago (islands of Madeira and Porto Santo).

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Geographic areas where there are records of Acacia melanoxylon

Other places where the species is invasive

Europe (Spain, France, Italy, United Kingdom), South Africa, Asia (India), USA (California, Hawaii), South America (Argentina, Chile), New Zealand.


Introduction reasons

For ornamental purposes. It has also been cultivated as a shade tree for wood production and soil improvement.

 

Preferential invasion environments

Roadsides and watercourses banks, skirts or understory’s of forest areas or open spaces.

It prefers granite terrains, avoiding calcareous ones. It tolerates drought, salt winds, polluted locations and extreme temperatures very well.

 

Impacts on ecossystems

It forms very dense populations inhibiting the development of native vegetation.

It produces a lot of nitrogen-rich litter, which promotes soil change.

 

Economic impacts

Expensive control methods.

 

Natura 2000 Network habitats more subject to impacts

Alluvial forests with Alnus glutinosa and Fraxinus excelsior (Alno-Padion, Alnion incanae, Salicion albae) (91E0);
– Riparian mixed forests of Quercus robur, Ulmus laevis and Ulmus minor, Fraxinus excelsior or Fraxinus angustifolia, along the great rivers (Ulmenion minoris) (91F0);
– Salix alba and Populus alba galleries (92A0);
– Riparian formations on intermittent Mediterranean water courses with Rhododendron ponticum, Salix and others (92B0);
– Southern riparian galleries and thickets (Nerio-Tamaricetea and Securinegion tinctoriae)  (92D0 pt1, pt2);
– Rivers with muddy banks with Chenopodion rubri p. p. and Bidention p. p. vegetation (3270);
Arborescent matorral with Laurus nobilis (5230);
– Thermo-Mediterranean and pre-desert scrub (5330).

 

Controlling an invasive species demands a well-planned management, which includes the determination of the invaded area, identifying the causes of invasion, assessing the impacts, defining the intervention priorities, selecting the adequate control methodologies and their application. Afterwards it is fundamental to monitor the efficiency of the methodologies and recuperation of the intervened area as to perform, whenever necessary, the follow-up control.

The control methodologies used for Acacia melanoxylon include:

 

Physical control

Hand pulling: preferential methodology for seedlings and small plants. When in more compacted substrates, hand pulling must be made during the rainy season as to facilitate the removal of the root system. It should be guaranteed that no stumps and main roots are left in the ground.

Cutting with brushcutter: preferential methodology for plants resulting from the germination that are still very small. It should just be applied on warm days as long as the security conditions are respected.

Ring-barking: preferential methodology for adult plants with a smooth, unwounded bark. Make a continuous ring incision around the trunk, at the height most comfortable for the operator, and remove all the bark and vascular cambium until the ground surface, if possible, until the root. It should be applied only when the vascular cambium is active, which may vary from place to place; the best seasons for this technique coincide with warm temperatures and some humidity. Ring-barking for this species becomes more difficult in large individuals that have very thick bark; in these situations, one may use a chainsaw to perform the incisions/cuts.

 

Physical + chemical control

Cut stump method: Apply to adult plants. Cut the trunk as close to the ground as possible and immediately (in the following seconds) apply herbicide (active substance: glyphosate) to the cut stump. If shoots should latter on appear, these should be immediately eliminated through cutting, pulling or foliar application of herbicide (active substance: glyphosate); up to 25 to 50 cm high. Shoots of larger dimensions (from 2-3 cm diameter) may be peeled off or else should be repeated the initial methodology (cut stump method).

 

Chemical control

Foliar application of herbicide: over recent sprouts (25-50 cm tall) or when high germination rates occur. Spray with herbicide (active substance: glyphosate) limiting as much as possible its application to the target species. Due to the existence of phyllodes with thick cuticles, this method may prove to be inefficient; in some situations, the application of herbicide with an atomizer improves the results.

 

Biological control

The weevil Melanterius acaciae Lea (Coleoptera: Curculionidae), that feeds off the A. melanoxylon seeds (and sporadically of nearby A. cyclops and A. saligna), was introduced in South Africa in 1986, currently verifying extensive damage in the target species.

This agent has not yet been tested in Portugal as to verify its safety relatively to native species, so its use has not yet constituted an alternative in our country.

 

Prescribed fire

It may be strategically used to favour germination of the seed bank, e.g., after the control of adult individuals (with the adequate management of the resulting biomass) and the subsequent elimination of seedlings. This method provides an advantageous reduction of the seed bank, both by destroying part of the seeds or by stimulating the germination of the remainders.

 

Visit the webpage How to Control for additional and more detailed information about the correct application of these methodologies.

Agricultural Research Council – Plant Protection Research Institute – Weed Research Division (2014) Management of invasive alien plants: A list of biocontrol agents released against invasive alien plants in South Africa. Available: http://www.arc.agric.za/arc-ppri/Documents/WebAgentsreleased.pdf [Retrieved 03/03/2014].

Campbell P (1993) Wattle Control. Plant Protection Research Institute. Handbook n° 3. Pretoria, South Africa, 43pp.

Dennill GB, Donnelly D, Stewart K, Impson FAC (1999) Insect agents used for the biological control of Australian Acacia species and Paraserianthes lophanta (Willd.) Nielsen (Fabaceae) in South Africa. African Entomology: Memoir no.1: 45-54.

Fernandes FM, Silva L, Land EO (2008) Acacia melanoxylon R. Br. In: Silva L, Land EO, Luengo JLR (eds) Flora e fauna terrestre invasora na Macaronésia. Top 100 nos Açores, Madeira e Canárias. Arena, Ponta Delgada, pp. 342-345.

Global Invasive Species Database (2012) Acacia melanoxylon. Available: http://www.issg.org/database/species/ecology.asp?si=197&fr=1&sts=sss&lang=EN [Retrieved 06/11/2012].

Marchante E, Freitas H, Marchante H (2008) Guia prático para a identificação de plantas invasoras de Portugal Continental. Imprensa da Universidade de Coimbra, Coimbra, 183pp.

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