THE NEGATIVE IMPACTS OF CHROMOLAENA ODORATA ON THE ENVIRONMENT

I would like to share with you the little information I gathered on C.odorata species. The C. odorata species originates from South and Central America has different common name; Siam weed, or Ortriffid. In its native environment it occurs as a dense “thicket forming” shrub which prevent the establishment of other species. C. odorata is a perennial shrub that can grow up to the height of 3m. However, if growing as climber, it can reach the height of 10 m owing to its fast growing behaviour of 20mm per day.

The C. odorata consist of a single stem with branches growing in pairs to form auxiliary buds. It produces white flowers that contain small seeds of about 3 to 5mm long every year. As it forms a dense thicket, it reduces the level of biodiversity thereby suppressing the growth of young trees. The seeds of C. odorata species can disperse for long distances with its transport media being wind, water, humans, machinery and vehicles. It has relatively large seeds bank longetivity.

The C. odorata is easily propagated from root fragment, stem and from seeds (King and Robinson, 2006) and it preferably grow in open freely-drained ground area with annual rainfall of more than 1200 mm (King and Robinson, 1997). C. odorata can grow in many different types of soils. It prefers to grow in well-drained soils and can not survive on moist and saline soils. The C. odorata has short juvenile period. The C. odorata may also occur in disturbed areas, agricultural areas, planted forest, and also in riparian zones but can not tolerate shade.

This species was introduced in Africa and in tropical regions of Asia where it became a problem, as it is considered a very invasive weed in subtropics and in humid tropics of the world. The species is non-indigenous in India, Africa, Indonesia, Sri Lanka, Malaysia and Indochina (Leslie, 2001).

In South Africa, this species was first observed in the province of Kwazulu Natal. The transport media of this plant is likely water and machinery as it resulted from the materials of packaging that were contaminated when offloaded from the ships at Durban harbour. The date in which the species was first introduced is still unknown. In 1986, C. odorata invaded other parts of provinces and countries such as Limpopo, Eastern Cape, Mpumalanga, Botswana, Mozambique, Zimbabwe and Swaziland (Leslie, 2001).

The C. odorata became a serious invader in South Africa. It possesses a major threat to agriculture, Conservation and forestry. C. odorata can easily invade the riverbanks, as a result destroying habitats of other species. For example, In South Africa, C. odorata destroyed the nests of crocodiles in St. Lucia Lake.

It is taken as a serious invader in South Africa as it is perennial and fast growing plants. The C. odorata is a major threat in South Africa because its seeds are spread rapidly over a long distance. The problem with this species is,it destroy South Africa vegetation.

The handpulling method can be used to mitigate the spread of this species, more especially in young plants. Herbicides can also be used in order to kill the mature C. odorata species. Annual burning regimes can effectively controls the invasion of C. odorata. This is because fire would kill the mature plants and prevent new seedling from establishing. Biological control may also be used.

References

King R.M and Robinson H. 1997. Chromolaena odorata [Online]. [Cited, 22 January 2007]. Available from: http://www.bangor.ac.uk/~afs101/iwpt/web-sp4.htm

King. R.M. and Robinson. H.2006. Chromolaena odorata [Online].[Cited, 23 January 2007]. Available from: http://www.hear.org/Pier/species/chromolaena_odorata.htm

Leslie, J.A. 2001. Chromolaena story, [Online]. University of Stellenbosch, South Africa. [Cited, 21 January 2007]. Available from:http://www.issg.org/database/species/ecology.asp?si=47&fr=1&sts

Linette Netshiheni
CSIR Pretoria
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