The Ramsar Convention's resources on Wetland Restoration

The STRP Expert Working Group on Wetland Restoration

Restoration Approach: Weed Control

Wetland type: All types, but especially subtropical and tropical freshwater wetlands

Background: Thousands of species of plants have been transported beyond their natural ranges, both intentionally and unintentionally. Many introduced species spread prolifically in environments where predation and competition are limited.  Examples of plant species that have led to wetland degradation include Eichornia crassipes (water hyacinth), Salvinia molesta (salvinia, a water fern), and Nymphaea mexicana (yellow waterlily).  Plants can sometimes be controlled manually or mechanically (i.e., harvesters), with pesticides, with biological control agents (grazers or pathogens intentionally introduced to control nuisance species), through hydrological manipulation, or by some combination of these methods.  Examples of restoration efforts that have relied in whole or in part on weed control include 1)restoration of sites infested with Salvinia molesta in Botswana’s Okavango and 2) control of Ludwigia peruviana in the Botany Wetlands of Sydney, Australia.

Advantages: Weed control can allow re-establishment of native plant communities.

Disadvantages: Once introduced plant populations become well established, complete removal is difficult or impossible. Biological controls that are effective on dense populations become less effective as populations decrease in size and become patchy in distribution.  Manual and mechanical control is prohibitively expensive.  Control using pesticides is not appropriate in all circumstances, either because chemical pesticides may not be appropriate for the restoration site or because available pesticides may impact desirable native species. Hydrological manipulation is not always possible.  In all cases, scattered individuals or seedbanks remaining after restoration efforts can lead to renewed infestation of sites.

Further information: Forno, I.W. and P.A. Smith.1999. Management of the alien weed, Salvinia molesta, in the wetlands of the Okavango, Botswana. Pp. 159-172 In W.J. Streever (ed.) An International Perspective on Wetland Rehabilitation. Kluwer Academic Publishers, Dordrecht, The Netherlands.

Sainty, G.R. and S.W.L. Jacobs. 1994. Waterplants in Australia. Sainty and Associates, Darlinghurst, Australia.

Return to STRP Wetland Restoration index page

For further information about the Ramsar Convention on Wetlands, please contact the Ramsar Convention Bureau, Rue Mauverney 28, CH-1196 Gland, Switzerland (tel +41 22 999 0170, fax +41 22 999 0169, e-mail ). Posted 8 January 2001, updated 15 February 2002, Bill Streever and Dwight Peck.