ECONOMIC EFFECTS OF INVASIVE ALIEN SPECIES
According to the report by global invasive species programme (GISP) 2003; invasive alien species are posing a serious threat to the world economy. From the ecological point of view, this problem is affecting the biological diversity resulting to its reduction. The most valuable agricultural systems which people depend on for food production are also affected. 
Invasive alien species are continuing to pose some negative impacts on the economy through-out the world. The invasive alien species is a problem threatening the value of biodiversity in South Africa. The proliferation of weeds has brought many problems in valuable farming lands. Weeds are opportunistic plants that take advantage of the manipulated agro ecosystem environment to grow and reproduce rapidly. While growing they exert competitive pressure on crop plant . The quantity and quality of crop yields are reduced. Example the kariba weeds (Salvinia molesta). A Kariba weed is a water floating fern and it is native to Brazil. These directly affect the production of foods. 
The kariba weeds affect the agricultural sectors in many ways such as blocking the water pipelines, irrigation schemes and other water ways. Harmful aquatic organisms including bacteria and viruses  are discharged from the ballast water. Commercial fishing industries are affected hence result to decrease in the economy. 
In South African cape floral kingdom, the establishment of weeds decreases the supply of water to the surrounding communities and threatens the native biodiversity . This resulted to the government spending millions of rands on manual and chemical control of the invaders . The invasive are said to have the indirect consequences to the environment which increase the cost for management and prevention. Invasive may cause changes in nutrients cycling, hydrological cycle etc .
In many parts of Africa, food production is affected by invasive alien insect’s pests. The white cassava (manihot esculenta) meal bugs are serious threat to agricultural sectors. The invasive weeds make it difficult to restore land for future use because they are able to grow faster. Weeds increase the risk of fire because when they dry-up, the area become prone to fire. Increase in fire result to changes in soil chemistry where it becomes uninhabitable by other by other types of plants . The water hyacinth ( Eichhornia crassipes)uses enough water resulting to competitions between the native plants and the invaders. The invasive are able to with stand and survive until they out compete the native species. 
In agricultural sectors, this is costing a lot of money for government around the continent. The current situations indicate that there is a serious threat by the alien invasive species. Much need to be done in order reduces this problem. More efforts on eradication and prevention need to be strengthened.
1. GSIP. Africa invaded: Lantana [Internet]. [Cited 2007 Jan 24]. Available from
2. Wikipedia contributors. Weed [Internet]. Wikipedia, The Free Encyclopedia; 2007 Jan 21, 09:14 UTC [cited 2007 Jan 24]. Available from: http://en.wikipedia.org/w/index.php?title=Weed&oldid=102182870.
Mr Lufuno Mukwevho
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