challenges for management. South African towns and cities share invasive species
from all taxonomic groups with many cities around the world, showing that general
features common to urban environments are key drivers of these invasions. There
are, however, several unique biological invasions in some South African urban
settings. The pattern of urbanisation in South Africa is also unique in that the imprint
of Apartheid-era spatial planning is striking in almost all towns and cities and is
aligned with stark disparities in wealth. This has resulted in a unique relationship
between humans and the physical environment (e.g. very different assemblages of
alien species in affluent compared to low-income areas). New ways of approaching
invasive alien species management are emerging in South African towns and cities,
but better facilitating mechanisms and protocols are needed for dealing with conflicts
of interest.
11.1 Introduction
Urbanisation is increasing rapidly worldwide, altering ecosystem functioning and
affecting the capacity of ecosystems to provide services for people (Elmqvist et al.
2015; Luederitz et al. 2015). In the face of this trend, many countries are struggling
to balance the demands of economic development with the obligations to conserve
biodiversity and ensure the delivery of ecosystem services (ES) to urban populations
(Elmqvist et al. 2015). Perceptions regarding nature in urban areas are changing
rapidly (Marris 2011; du Toit et al. 2018)—the notion of conserving nature in a
pristine state (excluding humans) is shifting to the view that people are part of
ecosystems and benefit from ES, and that ecosystems should be managed to ensure
resilience and the sustainable delivery of ES (Mace 2014).
Urban areas are susceptible to biological invasions for several reasons. First, they
are foci for the introduction (intentional and accidental) of alien species. Second, the
availability of large numbers of propagules due to intensive cultivation and repeated
introductions of many alien species (especially species used for ornamental horticulture, aquaculture and the pet trade) increases the likelihood of their establishment
and persistence (Williamson and Fitter 1996; Pyšek 1998; Kowarik et al. 2013).
Third, the complex networks of dispersal pathways and vectors in cities facilitate the
rapid dissemination of propagules, both within urban settings and outwards into
surrounding natural and semi-natural ecosystems (Alston and Richardson 2006; von
der Lippe and Kowarik 2008; McLean et al. 2017; Padayachee et al. 2017). Fourth,
altered disturbance regimes, complex physical structures, and increased resource
availability associated with concentrated human activities create opportunities for
the establishment, reproduction and proliferation of many alien species (Cadotte
et al. 2017). Fifth, the alteration of biotic conditions, microclimatic conditions,
hydrology, and soils are important mediators of the patterns and processes of
biological invasions in urban ecosystems (Klotz and Kühn 2010).
Knowledge of the interplay between social and ecological systems in urban
landscapes is becoming increasingly important as a growing proportion of human
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L. J. Potgieter et al.
from all taxonomic groups with many cities around the world, showing that general
features common to urban environments are key drivers of these invasions. There
are, however, several unique biological invasions in some South African urban
settings. The pattern of urbanisation in South Africa is also unique in that the imprint
of Apartheid-era spatial planning is striking in almost all towns and cities and is
aligned with stark disparities in wealth. This has resulted in a unique relationship
between humans and the physical environment (e.g. very different assemblages of
alien species in affluent compared to low-income areas). New ways of approaching
invasive alien species management are emerging in South African towns and cities,
but better facilitating mechanisms and protocols are needed for dealing with conflicts
of interest.
11.1 Introduction
Urbanisation is increasing rapidly worldwide, altering ecosystem functioning and
affecting the capacity of ecosystems to provide services for people (Elmqvist et al.
2015; Luederitz et al. 2015). In the face of this trend, many countries are struggling
to balance the demands of economic development with the obligations to conserve
biodiversity and ensure the delivery of ecosystem services (ES) to urban populations
(Elmqvist et al. 2015). Perceptions regarding nature in urban areas are changing
rapidly (Marris 2011; du Toit et al. 2018)—the notion of conserving nature in a
pristine state (excluding humans) is shifting to the view that people are part of
ecosystems and benefit from ES, and that ecosystems should be managed to ensure
resilience and the sustainable delivery of ES (Mace 2014).
Urban areas are susceptible to biological invasions for several reasons. First, they
are foci for the introduction (intentional and accidental) of alien species. Second, the
availability of large numbers of propagules due to intensive cultivation and repeated
introductions of many alien species (especially species used for ornamental horticulture, aquaculture and the pet trade) increases the likelihood of their establishment
and persistence (Williamson and Fitter 1996; Pyšek 1998; Kowarik et al. 2013).
Third, the complex networks of dispersal pathways and vectors in cities facilitate the
rapid dissemination of propagules, both within urban settings and outwards into
surrounding natural and semi-natural ecosystems (Alston and Richardson 2006; von
der Lippe and Kowarik 2008; McLean et al. 2017; Padayachee et al. 2017). Fourth,
altered disturbance regimes, complex physical structures, and increased resource
availability associated with concentrated human activities create opportunities for
the establishment, reproduction and proliferation of many alien species (Cadotte
et al. 2017). Fifth, the alteration of biotic conditions, microclimatic conditions,
hydrology, and soils are important mediators of the patterns and processes of
biological invasions in urban ecosystems (Klotz and Kühn 2010).
Knowledge of the interplay between social and ecological systems in urban
landscapes is becoming increasingly important as a growing proportion of human
276
L. J. Potgieter et al.