Why are Invasive Alien Plants (IAPs) bad?

Feb 23, 2022 | Environmental Education, Goukou Resilient River, Gouritz Ecological Corridors Project

When we think of natural disasters and threats, we often tend to think of very extreme manifestations of weather and natural elements; we hardly ever turn our thoughts to plants and trees. In a world where increased deforestation is a threat to our survival, it doesn’t come naturally to consider any tree or plant as the enemy. In South Africa, however, we need to do just that. All across our incredibly beautiful natural landscape, a silent enemy grows in strength and numbers every day – a natural disaster of extreme proportions, one which most South Africans look at every single day (perhaps without knowing it): invasive alien plants. 

For some people, the problem of invasive alien plants (or IAPs) is either a problem that they are all too familiar with, the degree and scale of which has overwhelmed and or desensitised them, or, on the other hand, many people are completely unaware of the threat and the extent of the problem. Across all ends of this spectrum, we need to be reminded again of the exact nature and scale of the problem and why, as we walk, drive and move around our towns, cities and landscapes, we need to look and see the invasive alien plants for the threat that they are. Like the internal repulsion that plastic in the ocean or litter on the street causes, we should have the same gut reaction when we look up at our beautiful natural landscapes and see them increasingly overrun by the stark monoculture of one of the 383 invasive alien plant species that threaten our country. 

What many may ask, however, is why should we care? What is the big deal with IAPs that gets the environmentalists all worked up, and how does it affect the average South African? For those that are new to this topic, or for a refresher on the seriousness of the problem, we will unpack the basics of what to know and understand about IAPs in South Africa. 

Not all foreign plants are a problem in a non-native landscape. Invasive alien plants are defined as such when they are resistant to local diseases and have no natural enemies. This allows them to spread aggressively, threatening the stability of the natural biological systems. After direct habitat destruction, invasive alien plants are recognised as the second-largest global threat to biodiversity. Additionally, IAPs also pose huge threats to natural resources and the economy, health and livelihoods of people.  

IAPs and Water

In South Africa, one of the single biggest threats posed by invasive alien plants is to water security. South Africa is a water-scarce country – a fact that most South Africans don’t need to be reminded of, as many districts and towns across the country continue to face extreme droughts and water restrictions. At first, it may seem hard to make the connection between the dull grey-green mass of a black wattle forest and notably decreased water levels in your local rivers or dams. However, this is exactly what needs to happen – when we see wattles, blue gums, pines and the like, we need to see drought. Many of the invasive alien plants in South Africa are extreme water guzzlers, much more so than most of our indigenous species. This has a significant and very real effect on our water supplies. For example, research on the impact of invasive alien plants on the Western Cape Water Supply System estimates a loss of about 38 million m3 of water per year – that is equivalent to the volume of Wemmershoek Dam (Franschhoek/Paarl). And that is just the Western Cape. 

Invasive alien plants have a direct impact on all South Africans – droughts and water restrictions should make us immediately turn our attention to the alien plant invasions in our area. 

Invasive Alien Plants and Fire

Another problem that is exacerbated by IAPs is that of fire – as climate change drives hotter and drier conditions across much of the Western Cape, wildfires are expected to become a more frequent occurrence. Whilst fire is part of the natural functioning of many South African vegetation types – such as fynbos – the seasonality, duration and intensity of these fires makes all the difference in whether these systems remain healthy or not. Fires that burn too hot, too long, or too frequently or in the wrong season can have devastating effects to the natural biodiversity. In most cases, IAPs increase the fuel load significantly compared to indigenous vegetation – i.e. there is more available plant material to burn. When there is more biomass to burn, the fires generally will burn hotter and longer than with fynbos, for example (where fires tend to burn quicker and cooler). In many cases, this will result in the stored seed banks of indigenous plants being destroyed by the intense heat, as well as the health of the soils, leading potentially to increased erosion. Additionally, when wildfires burn too often, we can end up losing rare and endangered species forever. And those are only the biological impacts; most of us don’t need to be reminded of the threat that fire poses to humans and infrastructure, with the numerous devastating fires in the last decade in Knysna and Cape town still fresh in our minds. 

IAPs and Ecosystems, Livelihoods and the Economy

IAPs also threaten our biodiversity and through so doing the livelihoods and the economy of South Africa. Living in this beautiful country, we may sometimes take for granted the incredible natural diversity that surrounds us – the Cape Floral Region, one of the six floral kingdoms of the world (of which it is the smallest), has been recognised as a world heritage site by UNESCO because of its phenomenal diversity (number of different types of plants), density (number of plants) and endemicity (the number of species that occur only here and nowhere else) of plants. IAPs outcompete indigenous plants through different mechanisms, sometimes through using resources (using more water, taking up more space and shading out indigenous species), or through changing the soil chemistry, making it unfavourable to indigenous plants. When IAPs change our natural landscape, they threaten the economies that are built on them, such as tourism or agriculture. Sometimes, the impact is indirect, such as industries suffering under the burden of drought, in which scenario decreased water availability could be largely due to the presence of IAPs in the land. In other cases, the impact could be direct, such as the loss of infrastructure due to fires in IAP stands. Either way you look at it, IAPs are a threat to the economy and, therefore, the livelihoods of South African people. 

What do we do about invasive alien plants (IAPs)

The problem of IAPs in South Africa may seem insurmountable – and indeed, addressed by individuals alone, it is. To tackle such a large-scale problem one needs large scale support and buy-in. Landowners, farmers, industry leaders and individuals can all play a role in the fight against IAPs. The first step in that fight is to start to recognise the problem and help others to do so also – watch this space for more news and information about IAPs, and share and spread awareness; it’s the first step in the war against IAPs, to claim back our landscapes.

Written by Luami Zondagh


References: 

National Environmental Management: Biodiversity Act, Act 10 of 2004. No. 1003, 18 September 2020. Department of Environmental Affairs, Pretoria

Richardson, DM. and Van Wilgen, BW. (2004). Invasive alien plants in South Africa: How well do we understand the ecological impacts? South African Journal of Science, 100(1), pp.45-52.

Van Wilgen, BW. et al.  (2008). A biome-scale assessment of the impact of invasive alien plants on ecosystem services in South Africa. Journal of Environmental Management 89(4), pp. 336-349.

Kraaij, T. and Van Wilgen, BW. (2014). Drivers, ecology and management of fire in fynbos.  Fynbos: Ecology, Evolution, and Conservation of a Megadiverse Region. Edited by Nicky Allsopp,  Jonathan F. Colville and G. Anthony Verboom. © Oxford University Press 2014.  Published 2014 by Oxford University Press

Department of Environmental Affairs and Development Planning. (2019). [online] Available at: https://www.westerncape.gov.za/eadp/news/national-alien-invasive-species-week-highlights-damage-caused-our-natural-resources [Accessed 8 February 2022].

The Conversation. (2018) Invasive alien plants in South Africa pose huge risks, but they can be stopped. [Online] Available at: https://theconversation.com/invasive-alien-plants-in-south-africa-pose-huge-risks-but-they-can-be-stopped-94186 [Accessed 8 February 2022]
UNESCO | World Heritage List . (2022)Cape Floral Region Protected Areas [Online] Available at: https://whc.unesco.org/en/list/1007 [Accessed 14 February 2022]

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