led to the facilitated movement of Guttural Toads outside of their invaded range in
Cape Town (Measey et al. 2017). Many people still value these animals for the
original ornamental attributes for which they were introduced, and this has led to
several conflict situations with control.
11.3.2 Ecosystem Disservices (EDS)
Plants Since alien plant species make up a large proportion of urban floras
(e.g. Pyšek 1998; Kühn and Klotz 2006), it is important to weigh the detrimental
effects of alien plant species against the ways they enhance local diversity and
maintain important functions (Elmqvist et al. 2008). Arguments for and against
managing invasive species in urban areas increasingly hinge on their contributions
to the delivery of ES and EDS (Potgieter et al. 2017, 2018; Vaz et al. 2017). Many
alien species that were introduced specifically to supply, augment or restore ES have
spread beyond sites of original containment, captivity or plantings to become
invasive. Some of these invasive alien plant species can alter ecosystem functions,
reduce native biodiversity, and have a negative impact on ES (Box 11.2; Pejchar and
Mooney 2009; Shackleton et al. 2016). Negative impacts include financial costs
(e.g. costs of pruning, repairing damage to urban infrastructure), social nuisances
(e.g. allergenic pollen, safety hazards from falling trees) and environmental costs
(e.g. alteration of nutrient cycles, displacement of native species), which impact
negatively on human well-being (Escobedo et al. 2011; Roy et al. 2012; Potgieter
et al. 2017; Vaz et al. 2017).
Box 11.2 Key Ecosystem Disservices Provided by Invasive Plants
in Urban South Africa
Biodiversity: The effects of urbanisation on biodiversity are particularly serious in South Africa because many urban centres occur in or around areas with
high levels of species richness and endemism. For example, in Cape Town the
impact of invasive species on the rich biodiversity is of major concern
(Holmes et al. 2012). The city is located within the Cape Floristic Region
(CFR), a global centre of plant endemism (Cowling et al. 1996). The city
(2445 km
2 in extent) surrounds the Table Mountain National Park (221 km
2 ),
17 smaller nature reserves, and 500 biodiversity network sites that together
cover 270 km
2 . Invasive tree species such as pines (Pinus species) grown in
plantations, and Australian wattles (e.g. Acacia saligna) planted mainly along
the coast for dune stabilisation, have spread widely into natural vegetation
(figure below) where these species outcompete and replace natural vegetation
leading to homogenisation and a decrease in native biodiversity (Rebelo et al.
2011). For example, P. radiata that occurs in commercial plantations in and
around Cape Town is highly invasive (Richardson and Brown 1986) and poses
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L. J. Potgieter et al.
Cape Town (Measey et al. 2017). Many people still value these animals for the
original ornamental attributes for which they were introduced, and this has led to
several conflict situations with control.
11.3.2 Ecosystem Disservices (EDS)
Plants Since alien plant species make up a large proportion of urban floras
(e.g. Pyšek 1998; Kühn and Klotz 2006), it is important to weigh the detrimental
effects of alien plant species against the ways they enhance local diversity and
maintain important functions (Elmqvist et al. 2008). Arguments for and against
managing invasive species in urban areas increasingly hinge on their contributions
to the delivery of ES and EDS (Potgieter et al. 2017, 2018; Vaz et al. 2017). Many
alien species that were introduced specifically to supply, augment or restore ES have
spread beyond sites of original containment, captivity or plantings to become
invasive. Some of these invasive alien plant species can alter ecosystem functions,
reduce native biodiversity, and have a negative impact on ES (Box 11.2; Pejchar and
Mooney 2009; Shackleton et al. 2016). Negative impacts include financial costs
(e.g. costs of pruning, repairing damage to urban infrastructure), social nuisances
(e.g. allergenic pollen, safety hazards from falling trees) and environmental costs
(e.g. alteration of nutrient cycles, displacement of native species), which impact
negatively on human well-being (Escobedo et al. 2011; Roy et al. 2012; Potgieter
et al. 2017; Vaz et al. 2017).
Box 11.2 Key Ecosystem Disservices Provided by Invasive Plants
in Urban South Africa
Biodiversity: The effects of urbanisation on biodiversity are particularly serious in South Africa because many urban centres occur in or around areas with
high levels of species richness and endemism. For example, in Cape Town the
impact of invasive species on the rich biodiversity is of major concern
(Holmes et al. 2012). The city is located within the Cape Floristic Region
(CFR), a global centre of plant endemism (Cowling et al. 1996). The city
(2445 km
2 in extent) surrounds the Table Mountain National Park (221 km
2 ),
17 smaller nature reserves, and 500 biodiversity network sites that together
cover 270 km
2 . Invasive tree species such as pines (Pinus species) grown in
plantations, and Australian wattles (e.g. Acacia saligna) planted mainly along
the coast for dune stabilisation, have spread widely into natural vegetation
(figure below) where these species outcompete and replace natural vegetation
leading to homogenisation and a decrease in native biodiversity (Rebelo et al.
2011). For example, P. radiata that occurs in commercial plantations in and
around Cape Town is highly invasive (Richardson and Brown 1986) and poses
(continued)
290
L. J. Potgieter et al.