Managing invasive species in cities means understanding how they affect the environment and people

Species not naturally found in South Africa’s urban areas can have both negative and positive impacts on people and the environment. In some cases, this can also lead to conflicts of interest over how these species should be used or controlled. 

For example many people keep garden plants purely because they are beautiful, but those plants spread and may have negative effects like causing allergies or using a lot of water. 

Researchers say that understanding how these invasive species impact cities and the people who live there, is the key to controlling them. 

We still know very little about how invasive plants and animals spread in cities, and the role people play in that process. 

Other negative effects these species can have include trees that spread new diseases to local plants, or animals like rats that can spread diseases to humans.

At the same time, people also value some of these invasive species because they provide useful resources, like wood for fire. These positive effects are called ecosystem services, while the negative outcomes are called ecosystem disservices.

In this study, researchers reviewed the existing knowledge of invasive species in South Africa’s urban areas, to understand how they spread and the impact they have. They also identified some of the challenges that occur when managing invasive species, and suggested strategies for overcoming these problems.

The researchers found that, while South Africa’s urban areas had many of the same invasive species as others around the world, there were also some unique ones. They noted that the invasive species found in high- and low-income areas were often different.

For example, Guttural Toads, which are originally from Durban, are now also found in Cape Town, usually in high-income areas where there are larger gardens with ponds for them to breed in.

They also found that many of the invasive species provided ecosystem services and disservices in different areas. For example, in low-income areas, invasive trees like Eucalyptus are an important source of firewood and money. This means that removing them to protect the ecosystem would also have a negative impact on people’s livelihoods. 

In some cases a single species, like Jacaranda, has both negative and positive impacts. These trees are highly valued in urban gardens, but cause problems in local ecosystems when their seeds spread to natural areas around the city.

Overall, the researchers say that arguments for how invasive species should be managed are often made based on the ecosystem services and disservices they provide. This makes understanding these services, and any potential conflicts of interest, especially relevant.

They added that it is important to develop proper protocols for dealing with conflicts of interest when they do happen. They also said that future research should objectively assess both the positive and negative impacts a particular species has, and that better guidelines are needed for planning management strategies.

The study was a collaboration between scientists from South Africa and Germany and forms a chapter in a book about biological invasions in South Africa.

Abstract

As in other parts of the world, urban ecosystems in South Africa have large numbers of alien species, many of which are invasive. Whereas invasions in South Africa’s natural systems are strongly structured by biotic and abiotic features of the region’s biomes, the imprint of these features is much less marked in urban ecosystems that exist as islands of human-dominated and highly modified habitat. Surprisingly little work has been done to document how invasive species spread in South African urban ecosystems, affect biodiversity, ecosystem services and human well-being, or to document the human perceptions of alien and invasive species, and the challenges associated with managing invasions in cities. This chapter reviews the current knowledge of patterns, processes, impacts and management of invasions in South African urban ecosystems. It highlights unique aspects of invasion dynamics in South African urban ecosystems, and identifies priorities for research, and key 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.

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