ACACIA MEARNSII IS A THREAT TO SOUTH AFRICA
Acacia mearnsii is a threat to South Africa. This alien invasive species is native in Australia and were introduced in South Africa 154 year ago [De Bakker 2003]. Acacia mearnsii is known as the Black Wattle Tree. This species can grow between five to ten meters in height [Anon 1999].The seeds of Acacia mearnsii are dispersed by cattle, birds and water. Birds and water can disperse seeds faster for long distance compared to the cows. This species reproduce through coppice of the seeds because they are small enough to be dispersed.
Acacia mearnsii outcompete native plants for water, nitrogen and organic materials. Acacia mearnsii has a potential of reducing the catchment water yields. Dye and Jarmain (2004) conducted a study in 2004 at Western Cape (Wellington and Groot Drankennstein) and KwaZulu- Natal (Seven Oaks) about water use by Acacia mearnsii. They discovered that Acacia mearnsii use 7mm of rainfall per day and they estimated additional loss of 185 mm of rainfall used annually by Acacia mearnsii. Therefore, each species use the total amount 2740 mm of rainfall annually. I can imagine if ten species are found in one area. South Africa as a water scarce country is faced with the challenge of the spread of Acacia mearnsii, especially the planners, manager and the policy makers that have to come up with the strategies of how to control the Acacia mearnsii species [Dye and Jarmain 2004].
This species provides wood for fuel especially, in the rural areas. Acacia mearnsii prevent erosion because it consists of the long roots that hold the soil particles together. Rouget et al (2002) indicated that Acacia mearnsii and Pinus species “occupy 60% area under commercial plantation and 54% of the area invaded by the alien trees and shrubs”.
However, Acacia mearnsii is a threat; it also provides a good commercial product, Soft – leather, building houses, fencing, electric poles, as woods, etc. The cutting of this species is of importance for commercial use and to save the little water that we have in South Africa.
Anonymous. 1999. Acacia Mearnsii. Available from: http://www.hear.org/Pier/species/acacia_mearnsii.htm.
De Bakker L. 2003. Combating the aliens. Radio Netherlands, Science Unit. Available from: http://www.radionetherlands.nl/features/science/030825alien.html
De Wit M.P, Crookes D.J and van Wilgen B.W. 2001. Conflicts of interest in the environmental management: estimating the costs and benefits of a tree invasion. CSIR Division of water, Environment and Forestry Technology. P167-169.
Dye P. and Jarmain C. 2004. Water use by black wattle (Acacia mearnsii): implications for the link between removal of invading trees and catchment streamflow response. CSIR Division of water, Environment and Forestry Technology. P 40-43.
ISAC (Invasive Species Advisory Committee). 2006. Invasive Species Definition Clarification and Guidance White Paper. Available from: http://www.invasivespeciesinfo.gov/docs/council/isacdef.pdf
Rouget M, Richardson D.M, Nel J.L and Van Wilgen B.W. 2002. Commercially important trees as invasive aliens – towards spatially explicit risk assessment at a national scale. Institute for Plant Conservation, Botany Department, University of Cape Town. P 397 – 398.
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