of these invasions; (4) examines the broad-scale distribution patterns of naturalised
and invasive plants with reference to “alien plant species assemblage zones” defined
on the basis of the turnover of alien species; and (5) provides recommendations to
improve our understanding of the composition, distribution, and dynamics of the
South African naturalised flora.
Other chapters in this book provide complementary details related to the invasion
process of plants, including introduction pathways (Faulkner et al. 2020, Chap. 12),
environmental (Wilson et al. 2020, Chap. 13) and biotic (Le Roux et al. 2020,
Chap. 14) drivers of invasions, impacts of invaders on water resources (Le Maitre
et al. 2020, Chap. 15), rangelands (O’Connor and van Wilgen 2020, Chap. 17) and
biodiversity (Zengeya et al. 2020, Chap. 18). Issues pertaining to human dimensions
(Shackleton et al. 2020, Chap. 24) and management of plant invasions (Foxcroft
et al. 2020, Chap. 28; Hill et al. 2020b, Chap. 19; Holmes et al. 2020, Chap. 23; van
Wilgen et al. 2020b, Chap. 21) are also covered elsewhere in the book, as is the
status of alien plants in other specific ecosystems: freshwater (Hill et al. 2020a,
Chap. 4), urban ecosystems (Potgieter et al. 2020, Chap. 11), and off-shore islands
(Greve et al. 2020, Chap. 8). The focus of this chapter is on the history and current
state of plant invasions in natural and semi-natural ecosystems. Terminology
pertaining to alien, naturalised, and invasive plant taxa follows the definitions
proposed by Richardson et al. (2000, 2011a): alien taxa are those that do not occur
naturally in South Africa and owe their presence here to human actions; naturalised
taxa are alien taxa that reproduce regularly, and invasive taxa are naturalised taxa
that have spread over considerable distances from sites of introduction.
3.2 A Brief History of Plant Invasions in South Africa
Of the alien plant taxa that are currently widespread in South Africa’s terrestrial
ecosystems few (if any) were present in the region before European colonisation
began in the seventeenth century (Deacon 1986; Richardson et al. 1997; see Faulkner et al. 2020, Chap. 12 for an evaluation of evidence for post-1652 plant introductions). There is no evidence that any introduced species became invasive before
European colonisation, and no species introduced prior to 1652 is currently a major
invader of natural and semi-natural ecosystems. South Africa’s large flora of
naturalised and invasive alien plants thus comprises almost exclusively taxa that
have arrived and been disseminated in the last three and a half centuries.
Plant taxa from many parts of the world have been introduced to South Africa for
many purposes (Faulkner et al. 2020, Chap. 12). Some were accidental introductions, but thousands of taxa were intentionally introduced - as agricultural crops, for
timber and firewood, as garden ornamentals, to stabilise sand dunes, as barrier and
hedge plants, as animal fodder and for other purposes. Wells et al. (1986) reviewed
plant introductions associated with several broad phases, from the initial period of
European settlement through to “the modern phase” (up to 1985). Two key phases
3 The Biogeography of South African Terrestrial Plant Invasions
69
and invasive plants with reference to “alien plant species assemblage zones” defined
on the basis of the turnover of alien species; and (5) provides recommendations to
improve our understanding of the composition, distribution, and dynamics of the
South African naturalised flora.
Other chapters in this book provide complementary details related to the invasion
process of plants, including introduction pathways (Faulkner et al. 2020, Chap. 12),
environmental (Wilson et al. 2020, Chap. 13) and biotic (Le Roux et al. 2020,
Chap. 14) drivers of invasions, impacts of invaders on water resources (Le Maitre
et al. 2020, Chap. 15), rangelands (O’Connor and van Wilgen 2020, Chap. 17) and
biodiversity (Zengeya et al. 2020, Chap. 18). Issues pertaining to human dimensions
(Shackleton et al. 2020, Chap. 24) and management of plant invasions (Foxcroft
et al. 2020, Chap. 28; Hill et al. 2020b, Chap. 19; Holmes et al. 2020, Chap. 23; van
Wilgen et al. 2020b, Chap. 21) are also covered elsewhere in the book, as is the
status of alien plants in other specific ecosystems: freshwater (Hill et al. 2020a,
Chap. 4), urban ecosystems (Potgieter et al. 2020, Chap. 11), and off-shore islands
(Greve et al. 2020, Chap. 8). The focus of this chapter is on the history and current
state of plant invasions in natural and semi-natural ecosystems. Terminology
pertaining to alien, naturalised, and invasive plant taxa follows the definitions
proposed by Richardson et al. (2000, 2011a): alien taxa are those that do not occur
naturally in South Africa and owe their presence here to human actions; naturalised
taxa are alien taxa that reproduce regularly, and invasive taxa are naturalised taxa
that have spread over considerable distances from sites of introduction.
3.2 A Brief History of Plant Invasions in South Africa
Of the alien plant taxa that are currently widespread in South Africa’s terrestrial
ecosystems few (if any) were present in the region before European colonisation
began in the seventeenth century (Deacon 1986; Richardson et al. 1997; see Faulkner et al. 2020, Chap. 12 for an evaluation of evidence for post-1652 plant introductions). There is no evidence that any introduced species became invasive before
European colonisation, and no species introduced prior to 1652 is currently a major
invader of natural and semi-natural ecosystems. South Africa’s large flora of
naturalised and invasive alien plants thus comprises almost exclusively taxa that
have arrived and been disseminated in the last three and a half centuries.
Plant taxa from many parts of the world have been introduced to South Africa for
many purposes (Faulkner et al. 2020, Chap. 12). Some were accidental introductions, but thousands of taxa were intentionally introduced - as agricultural crops, for
timber and firewood, as garden ornamentals, to stabilise sand dunes, as barrier and
hedge plants, as animal fodder and for other purposes. Wells et al. (1986) reviewed
plant introductions associated with several broad phases, from the initial period of
European settlement through to “the modern phase” (up to 1985). Two key phases
3 The Biogeography of South African Terrestrial Plant Invasions
69