organisms (Enterobacteriaceae) such as Salmonella species, Shigella serotypes,
Proteus species, Vibrioaceae species, Pseudomonas species, Escherichia coli, Campylobacter species, and Newcastle disease (Sulochana et al. 1981; Ryall and Reid
1987; al-Sallami 1991). These diseases are likely due to the tendency of populations
to frequent areas where waste foods and faeces are dumped. It is also a known faecal
contaminator of human environments and water resources. The crows may also hold
potential for spreading bird flu viruses.
Cats have devastating effects on native biodiversity worldwide (Hagen and
Kumschick 2018), and South Africa’s feral and domestic cats appear to be no
different. Cats on the urban edge have been shown to have a significant impact on
adjoining biodiverse areas in the Table Mountain National Park (George 2010;
Morling 2014).
The negative impacts of invasive alien fish in the context of urban rivers and
water bodies in South Africa remains poorly understood. Kruger et al. (2015)
reported a negative effect of the invasive predatory Mosquitofish (Gambusia affinis)
on native amphibian community assemblages and abundance in Potchefstroom.
Pests and pathogens Internationally, trees in urban environments play an important
role in preserving biodiversity and supplying ES in urban areas, and as the world
becomes more globalised, urban forests will provide increasingly valuable benefits.
However, trees in urban environments are particularly vulnerable to pest and pathogen invasions. Most tree damaging insect pests and pathogens (hereafter referred to
as pests) arrive as accidental introductions, a by-product of increasing trade and
globalisation (Santini et al. 2013; Meurisse et al. 2018). Urban areas are hubs for
international trade and frequently serve as the first point of entry for alien forest pests
(Paap et al. 2017). Besides being subjected to high propagule pressure, urban trees
experience stressful conditions resulting from anthropogenic disturbances, increasing their susceptibility to pest attack (Paap et al. 2017). Once established in urban
environments, introduced pests can spread into natural or planted forests often
resulting in permanent damage, and efforts at controlling such invasions can become
costly.
Considering the vulnerability of urban trees to invasive pests, there have been
moves globally to focus surveillance on urban trees for early detection of new pest
invasions. Most pests are not problematic in their natural range, which means that
many damaging invasive pests were unknown to science before they arrived and
established in a new environment. Such pests were therefore not on watch lists and
could not have been regulated against. ‘Sentinel plantings’, that is, plants established
outside their natural range, are increasingly being used to identify new host-pest
associations, predict future tree health threats and fill gaps in pest risk analyses
(Eschen et al. 2018; Poland and Rassati 2018). The range of impacts caused by
damaging invasive pests on tree health in South Africa are highlighted by the
following case studies.
Some invasive alien pests in South Africa may only be problematic on alien tree
hosts with no risk to agriculture, planted forests or the natural environment. The
Sycamore Lace Bug (Corythucha ciliata), a highly invasive tingid native to eastern
parts of North America and Canada, is a recent invader in South Africa (Picker and
294
L. J. Potgieter et al.
Proteus species, Vibrioaceae species, Pseudomonas species, Escherichia coli, Campylobacter species, and Newcastle disease (Sulochana et al. 1981; Ryall and Reid
1987; al-Sallami 1991). These diseases are likely due to the tendency of populations
to frequent areas where waste foods and faeces are dumped. It is also a known faecal
contaminator of human environments and water resources. The crows may also hold
potential for spreading bird flu viruses.
Cats have devastating effects on native biodiversity worldwide (Hagen and
Kumschick 2018), and South Africa’s feral and domestic cats appear to be no
different. Cats on the urban edge have been shown to have a significant impact on
adjoining biodiverse areas in the Table Mountain National Park (George 2010;
Morling 2014).
The negative impacts of invasive alien fish in the context of urban rivers and
water bodies in South Africa remains poorly understood. Kruger et al. (2015)
reported a negative effect of the invasive predatory Mosquitofish (Gambusia affinis)
on native amphibian community assemblages and abundance in Potchefstroom.
Pests and pathogens Internationally, trees in urban environments play an important
role in preserving biodiversity and supplying ES in urban areas, and as the world
becomes more globalised, urban forests will provide increasingly valuable benefits.
However, trees in urban environments are particularly vulnerable to pest and pathogen invasions. Most tree damaging insect pests and pathogens (hereafter referred to
as pests) arrive as accidental introductions, a by-product of increasing trade and
globalisation (Santini et al. 2013; Meurisse et al. 2018). Urban areas are hubs for
international trade and frequently serve as the first point of entry for alien forest pests
(Paap et al. 2017). Besides being subjected to high propagule pressure, urban trees
experience stressful conditions resulting from anthropogenic disturbances, increasing their susceptibility to pest attack (Paap et al. 2017). Once established in urban
environments, introduced pests can spread into natural or planted forests often
resulting in permanent damage, and efforts at controlling such invasions can become
costly.
Considering the vulnerability of urban trees to invasive pests, there have been
moves globally to focus surveillance on urban trees for early detection of new pest
invasions. Most pests are not problematic in their natural range, which means that
many damaging invasive pests were unknown to science before they arrived and
established in a new environment. Such pests were therefore not on watch lists and
could not have been regulated against. ‘Sentinel plantings’, that is, plants established
outside their natural range, are increasingly being used to identify new host-pest
associations, predict future tree health threats and fill gaps in pest risk analyses
(Eschen et al. 2018; Poland and Rassati 2018). The range of impacts caused by
damaging invasive pests on tree health in South Africa are highlighted by the
following case studies.
Some invasive alien pests in South Africa may only be problematic on alien tree
hosts with no risk to agriculture, planted forests or the natural environment. The
Sycamore Lace Bug (Corythucha ciliata), a highly invasive tingid native to eastern
parts of North America and Canada, is a recent invader in South Africa (Picker and
294
L. J. Potgieter et al.