biodiversity were conservatively estimated to be US$57 million per year. All of
these were predicted to grow as invasive species continue to spread, and as more
species become invasive. This remains the only study to provide economic estimates
at a national scale.
The full amount spent by South Africa on the control of alien species is
not known, but it amounts to at least ZAR 2 billion (US$142 million) each year,
this being the amount currently spent by the national government’s Department
of Environment, Forestry, and Fisheries (i.e. the Working for Water programme).
This is about 16% of the current estimate of costs (US$875 million per year). Both
are underestimates, as not all expenditure or impacts are accounted for. Rates of
return have yet to be estimated for this investment. A number of factors would need
to be taken into account here, including the current rate of spread of invasions, the
area that would be occupied if these species were allowed to invade all available
habitat, and the effectiveness of the control measures in reversing (or at least
slowing) the ongoing rate of spread. Indications are that the returns on investment
could well be positive, but that achieving a positive return would require increases in
management efficiency, and a focus on priority areas (van Wilgen et al. 2016).
While a few studies have attempted to estimate the returns on investment from
manual and chemical clearing of alien plants, most have had to be based on
assumptions, or have looked at relatively small areas, so the level of confidence in
the estimates is often low. The returns on biological control have been summarised
by van Wilgen and De Lange (2011). Their review suggests that biological control
programmes against invasive plants have been extremely economically beneficial,
delivering benefit:cost ratios of between 8:1 and 3726:1 at a national scale. Further
details of the costs of invasions, and the returns on investment from control are to be
found in Chaps. 15, 16, 21, and 22 (Le Maitre et al. 2020; van Wilgen 2020; van
Wilgen et al. 2020a; Davies et al. 2020).
1.4 Scope and Arrangement of This Book
In planning this book, we set out to compile an encyclopaedic reference to biological
invasions and their management in South Africa, with the aim of providing information that can help current and future generations to deal more effectively with
invasions. The intended audience thus includes academics, post-graduate students,
policy makers, and conservationists.
The book is composed of 31 chapters (including this one) that are divided into
seven parts. The 104 contributing authors include academics, policy makers, conservationists, managers, and post-graduate students—representing a diverse range of
expertise on biological invasion in South Africa and beyond.
Part I (Chaps. 1 and 2) provides a broad overview of biological invasions in
South Africa, to set the scene for the material that follows (van Wilgen et al. 2020a,
this chapter), and gives a selective account of some of the South African researchers
and research initiatives in this field over the past 130 years (van Wilgen 2020,
Chap. 2). It is evident that South Africa has made a disproportionate contribution
22
B. W. van Wilgen et al.
these were predicted to grow as invasive species continue to spread, and as more
species become invasive. This remains the only study to provide economic estimates
at a national scale.
The full amount spent by South Africa on the control of alien species is
not known, but it amounts to at least ZAR 2 billion (US$142 million) each year,
this being the amount currently spent by the national government’s Department
of Environment, Forestry, and Fisheries (i.e. the Working for Water programme).
This is about 16% of the current estimate of costs (US$875 million per year). Both
are underestimates, as not all expenditure or impacts are accounted for. Rates of
return have yet to be estimated for this investment. A number of factors would need
to be taken into account here, including the current rate of spread of invasions, the
area that would be occupied if these species were allowed to invade all available
habitat, and the effectiveness of the control measures in reversing (or at least
slowing) the ongoing rate of spread. Indications are that the returns on investment
could well be positive, but that achieving a positive return would require increases in
management efficiency, and a focus on priority areas (van Wilgen et al. 2016).
While a few studies have attempted to estimate the returns on investment from
manual and chemical clearing of alien plants, most have had to be based on
assumptions, or have looked at relatively small areas, so the level of confidence in
the estimates is often low. The returns on biological control have been summarised
by van Wilgen and De Lange (2011). Their review suggests that biological control
programmes against invasive plants have been extremely economically beneficial,
delivering benefit:cost ratios of between 8:1 and 3726:1 at a national scale. Further
details of the costs of invasions, and the returns on investment from control are to be
found in Chaps. 15, 16, 21, and 22 (Le Maitre et al. 2020; van Wilgen 2020; van
Wilgen et al. 2020a; Davies et al. 2020).
1.4 Scope and Arrangement of This Book
In planning this book, we set out to compile an encyclopaedic reference to biological
invasions and their management in South Africa, with the aim of providing information that can help current and future generations to deal more effectively with
invasions. The intended audience thus includes academics, post-graduate students,
policy makers, and conservationists.
The book is composed of 31 chapters (including this one) that are divided into
seven parts. The 104 contributing authors include academics, policy makers, conservationists, managers, and post-graduate students—representing a diverse range of
expertise on biological invasion in South Africa and beyond.
Part I (Chaps. 1 and 2) provides a broad overview of biological invasions in
South Africa, to set the scene for the material that follows (van Wilgen et al. 2020a,
this chapter), and gives a selective account of some of the South African researchers
and research initiatives in this field over the past 130 years (van Wilgen 2020,
Chap. 2). It is evident that South Africa has made a disproportionate contribution
22
B. W. van Wilgen et al.