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Acacia saligna

Evergreen shrub or small tree, of greenish-blue leaves and golden yellow spherical flower heads.

Scientific name: Acacia saligna (Labill.) H. L. Wendl.

Common names: Port Jackson wattle, blue-leaved wattle

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 bracteata Maiden & Blakely, Acacia cyanophylla Lindl., Acacia lindleyi Meissner, Mimosa saligna Labill., Racosperma salignum (Labill.) Pedley

Last update: 01/07/2014

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How to recognise it

Shrub or small tree up to 8 m; with a dark grey rhytidome smooth or finely fissured.

Leaves: evergreen, reduced to phyllodes with 8-25 x 0,5-5 cm (reaching 8 cm width on the sprouts that form on the stumps of cut trees), frequently glaucous-green, laminar, linear or lanceolate, symmetrical on the base and with a longitudinal vein and a mucronate apex .

Flowers: golden yellow arranged in globular flower heads of 6-15 mm diameter, which in turn are arranged (2-10) into racemes.

Fruits: compressed pods, straight or curved, constricted  between the seeds; seeds with a short, whitish funicle.

Flowering: February to March.

 

Similar species

Acacia retinodes (water wattle) is similar but has narrower phyllodes (> 1,5 cm), the clusters have pale yellow flowers and an inferior diameter (< 0,8 cm), and the funicle is rosy and it encircles the seed. Acacia pycnantha (golden wattle) is also similar but it has phyllodes with an asymmetric base, they are falcate present 10-20 flower heads per raceme.

Characteristics that aid invasion

It reproduces by seed; it produces many seeds that remain viable in the ground for many years. Germination is enhanced by fire.

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

 

Native distribution area

Western Australia and Tasmania.

 

Distribution in Portugal

Mainland Portugal (Beira Litoral, Estremadura, Ribatejo, Alto Alentejo, Baixo Alentejo, Algarve), Azores archipelago (island of São Miguel), Madeira archipelago (island of Madeira).

Geographic areas where there are records of Acacia saligna

Other places where the species is invasive

Europe (Spain, Cyprus, France, Italy, Greece), Asia (Israel), South Africa, Australia (Victoria), South America (Chile), New Zealand, western USA (California.

 

Introduction reasons

For ornamental purposes and for controlling coastal dunes erosion.

 

Preferential invasion environments

Arid regions, resisting very well to dryness, so it is very frequent on coastal dunes and on roadsides in the south of the country.

It is a robust species, but it bears frost poorly.

 

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

It has potential expensive control measures.

 

Natura 2000 Network habitats more subject to impacts

– Atlantic decalcified fixed dunes (Calluno-Ulicetea) (2150);
– Coastal dunes with Juniperus spp. (2250);
Cisto-Lavenduletalia dune sclerophyllous scrubs (2260);
Cistus palhinhae formations on maritime wet heaths (5140);
– West Mediterranean clifftop phryganas (Astragalo-Plantaginetum subulatae) (5410).

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 saligna include:

Physical control

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

 

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. For shoots of larger dimensions (from 2-3 cm diameter) repeat 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.

 

Biological control

The fungus Uromycladium tepperianum (Sacc.) McAlp (Pucciniales: Uredinales), forms galls on the young tissue, having been used in South Africa with success in the control of A. saligna.

The weevil Melanterius compactus (Coleoptera: Corculionidae), feeds off the seeds, and is also used with success in South Africa since 2001 to control A. saligna.

These agents have 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].

Dana ED, Sanz-Elorza M, Vivas S, Sobrino E (2005) Especies vegetales invasoras en Andalucía. Consejería de Medio Ambiente, Junta de Andalucía, Sevilla, 233pp.

Dufour-Dror J-M (2012) Alien invasive plants in Israel. The Middle East Nature Conservation Promotion Association, Ahva, Jerusalem,213pp.

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.

Morris MJ (1999) The contribution of the gall-forming rust fungus Uromycladium tepperianum (Sacc.) McAlp. to the biological control of Acacia saligna (Labill.) Wendl. (Fabaceae) in South Africa. African Entomology: Memoir n°1: 125-128.

Osorio VEM, de la Torre WW, Silva L, Jardim R (2008) Acacia saligna (Labill.) H. L. Wendl. 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. 451-453.

Whibley DJE (1980) Acacias of South Australia. Pretoria, South Australia.

 

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