The economic consequences of alien plant invasions: examples of impacts and approaches to sustainable management

Abstract. The invasion of natural ecosystems by alien plants is a serious environmental problem that threatens the sustainable use of benefits derived from such ecosytems. Most past studies in this field have focussed on the history, ecology and management of invasive alien species, and little work has been done on the economic aspects and consequences of invasions. This paper reviews what is known of the economic consequences of alien plant invasions in South Africa. These economic arguments have been used to successfully launch the largest environmental management programme in Africa. Ten million hectares of South Africa has been invaded by 180 alien species, but their impacts are not fully understood, although they are undoubtedly significant. The indications are that the total costs of these impacts are substantial. Selected studies show that invasions have reduced the value of fynbos ecosystems by over US $ 11.75 billion; that the total cost of invasion would be about US $ 3.2 billion on the Agulhas Plain alone; that the net present cost of invasion by black wattles amounts to US $ 1.4 billion; that invasions by red water fern have cost US $ 58 million; and that the cost to clear the alien plant invasions in South Africa is around US $ 1.2 billion. These few examples indicate that the economic consequences of invasions are huge. One of the unique aspects of invasive plant control programmes in South Africa has been the abilit