Scientific name: Acacia karroo Hayne
Family: Fabaceae (Leguminosae)
Risk Assessment score: (in development)
Synonymy: Acacia dekindtiana A. Chev., A. eburnea sensu auct., A. horrida auct., non Willd., A. inconflagrabilis Gerstner, A. karroo Hayne, A. natalitia E. Meyer
Last update: 30/06/2014
How to recognise it
Flowering: June to September.
Characteristics that aid invasion
It reproduces by seed, producing many seeds. An adult tree produces up to 19000 seeds each year, which may be viable for 7 years in the ground. Germination is stimulated by fire.
Native distribution area
South Africa to Zambia and Angola.
Distribution in Portugal
Mainland Portugal (Beira Litoral, Estremadura, Baixo Alentejo, Algarve).
Geographic areas where there are records of Acacia karroo
Europe (Spain), South Africa, some regions of Australia.
For ornamental purposes and to form hedges.
Preferential invasion environments
It is found dispersed along roadsides, but as yet in only a few locations in this country.
It tolerates adverse conditions like frost, drought, fire, strong winds and salt spray.
In the native distribution area it grows from 0-1800 m, from sand to silt soils, and in locations where there is some available water in the soil.
Even though it’s legally considered as being an invasive in Portugal, its distribution is still limited in our country.
Impacts on ecossystems
It can potentially form dense thickets, inhibiting the development of native vegetation.
It produces a lot of nitrogen-rich litter, which promotes soil change.
It has potential expensive control measures.
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 karroo include:
Hand pulling: preferential methodology for seedlings and small plants. When in more compacted substrates, pulling must be made during the rainy season as to facilitate the removal of the root system.
Cutting: preferential methodology for adult plants. Cut the trunk as close to the ground as possible by using manual and/or mechanical equipment. It should be done before seed maturation.
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.
Department of Environment and Heritage (2003) Weed management guide – karroo thorn (Acacia karroo). Department of Environment and Heritage, Canberra, 6pp. Department of Primary Industries (2014) Karoo and giraffe thorn. Available: http://www.depi.vic.gov.au/agriculture-and-food/pests-diseases-and-weeds/weeds/state-prohibited-weeds/karoo-and-giraffe-thorn [Retrieved 03/03/2014]. 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.