ecosystems in South Africa would deliver biodiversity-based ecosystem services
valued at ZAR 22.1 billion per annum if no invasions were present. The estimated
value of the annual flow of these services was reduced by 2% (ZAR 428 million) each
year due to alien plant invasions at current levels; under a scenario where alien plants
are allowed to invade all available habitat, these losses were estimated to increase to
more than 50% (ZAR 12.9 billion) annually. Other studies have also estimated the total
value of ecosystem services in South Africa (Anderson et al. 2017; Turpie et al. 2017).
Anderson et al. (2017) estimated this value to be about ZAR 8 trillion per year—this is
nearly double that of South Africa’s gross domestic product of ZAR 4.7 trillion for the
same period. Turpie et al. (2017) estimated the value of ecosystem services provided by
terrestrial, freshwater and estuarine ecosystems to be at ZAR 245 billion annually. The
differences in the estimates between these assessments reflect methodological differences and the general challenges associated with attempts to monetise the values of
biodiversity. Nevertheless, they highlight that ecosystem services make a substantial
contribution to the economy.
17.3 Synthesis
The issue of quantifying the impacts of alien species on biodiversity remains a
major challenge, both globally and in South Africa. For the majority of species
found in South Africa, there are no studies documenting impacts, and there has
been no formal assessment of impacts at a national scale. Evidence-based impact
assessments are needed to support calls for management interventions. For example, in South Africa 556 taxa are listed as invasive, and landowners have an
obligation to manage them (van Wilgen et al. 2020a, Chap. 1, Box 1.2). However,
the regulations should arguably focus on priority species because not all of the
listed species are necessarily harmful to the extent that would justify management
especially when the current capacity to manage and to regulate them is limited
(Zengeya et al. 2017). The use of expert opinion and or formal assessments such as
EICAT could help to identify and priotise those species that should be targeted for
management.
Acknowledgements BvW, TAZ, OLFW thank the DSI-NRF Centre for Invasion Biology and
the South African National Research Foundation (Grants 109467, 103602, 109015, 110507) for
support. SK acknowledges support from the South African National Department of Environmental Affairs through its funding of the South African National Biodiversity, and the DSI-NRF
Centre of Excellence for Invasion Biology. John Measey and John Wilson provided useful
comments on an earlier draft of this chapter. The South African Department of Environment,
Forestry, and Fisheries (DEFF) are thanked for funding the South African National Biodiversity
Institute noting that this publication does not necessarily represent the views or opinions of DEFF
or its employees.
17 An Evaluation of the Impacts of Alien Species on Biodiversity
505
valued at ZAR 22.1 billion per annum if no invasions were present. The estimated
value of the annual flow of these services was reduced by 2% (ZAR 428 million) each
year due to alien plant invasions at current levels; under a scenario where alien plants
are allowed to invade all available habitat, these losses were estimated to increase to
more than 50% (ZAR 12.9 billion) annually. Other studies have also estimated the total
value of ecosystem services in South Africa (Anderson et al. 2017; Turpie et al. 2017).
Anderson et al. (2017) estimated this value to be about ZAR 8 trillion per year—this is
nearly double that of South Africa’s gross domestic product of ZAR 4.7 trillion for the
same period. Turpie et al. (2017) estimated the value of ecosystem services provided by
terrestrial, freshwater and estuarine ecosystems to be at ZAR 245 billion annually. The
differences in the estimates between these assessments reflect methodological differences and the general challenges associated with attempts to monetise the values of
biodiversity. Nevertheless, they highlight that ecosystem services make a substantial
contribution to the economy.
17.3 Synthesis
The issue of quantifying the impacts of alien species on biodiversity remains a
major challenge, both globally and in South Africa. For the majority of species
found in South Africa, there are no studies documenting impacts, and there has
been no formal assessment of impacts at a national scale. Evidence-based impact
assessments are needed to support calls for management interventions. For example, in South Africa 556 taxa are listed as invasive, and landowners have an
obligation to manage them (van Wilgen et al. 2020a, Chap. 1, Box 1.2). However,
the regulations should arguably focus on priority species because not all of the
listed species are necessarily harmful to the extent that would justify management
especially when the current capacity to manage and to regulate them is limited
(Zengeya et al. 2017). The use of expert opinion and or formal assessments such as
EICAT could help to identify and priotise those species that should be targeted for
management.
Acknowledgements BvW, TAZ, OLFW thank the DSI-NRF Centre for Invasion Biology and
the South African National Research Foundation (Grants 109467, 103602, 109015, 110507) for
support. SK acknowledges support from the South African National Department of Environmental Affairs through its funding of the South African National Biodiversity, and the DSI-NRF
Centre of Excellence for Invasion Biology. John Measey and John Wilson provided useful
comments on an earlier draft of this chapter. The South African Department of Environment,
Forestry, and Fisheries (DEFF) are thanked for funding the South African National Biodiversity
Institute noting that this publication does not necessarily represent the views or opinions of DEFF
or its employees.
17 An Evaluation of the Impacts of Alien Species on Biodiversity
505