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Wheel Cactus: A Plant with Prickly Personality

Words by Monash Biological Society

 

If you’ve lived in Australia for an extended period, chances are you’ve seen some pretty funky plants and animals (platypuses are weird, you can’t change my mind). In a nutshell, a combination of Australia’s early split from Gondwana (a past supercontinent), a general lack of tectonic activity, and some chaotic climate fluctuations over time have meant our flora and fauna have evolved quite differently compared to the rest of the world. However, the uniqueness of Australia’s native environment comes at a cost; it’s very vulnerable to sudden and unnatural changes, such as the introduction of an invasive plant or animal species.

Wheel Cactus, or Opuntia robusta, is a species of cactus native to central and northern Mexico. It is easily recognised thanks to its clear blue/green colour and large circular pads. The wheel cactus can grow up to 3 meters tall, covering itself with spines, and in the spring/summer producing red fruits filled with seeds. This spikey scoundrel was originally introduced to Australia as a hardy garden plant, but today it has earned its place on the Weed of National Significance (WoNS) register, the result of 3 unfortunate factors:

  1. Australia’s climate is quite similar to the wheel cactus’ native home in Mexico, so it’s already well adapted for an arid environment. 
  2. Wheel cactus can create new plants from either its seeds, which are transported by birds or mammals that feast on the fruits, or from fragments of the parent plant. This makes it easy for the cactus to spread over a large area, but hard for it to be killed effectively.
  3. Australia lacks any native plants or animals that are effective in putting enough pressure on the wheel cactus population numbers, essentially meaning it can go about relatively uncontested in the Australian environment. 

The highly invasive capabilities of this plant have had negative flow-on effects for multiple aspects of the Australian environment, culture, and economy.

Environment

First and foremost, the introduction of an invasive species such as the wheel cactus to a vulnerable ecosystem such as the Australian environment can be devastating for the fine-tuned balance between plants and animals. Wheel cactus have been shown to out-compete native Australian plants and provide refuge for other invasive species such as rabbits. As a result, not only do we have a direct loss in the biodiversity of native Australian plants, but any other plants or animals that relied on THOSE plants for their survival will now also struggle to survive. In the end, the introduction of 1 species can lead to a loss of the diversity, complexity, resilience, and beauty of an entire ecosystem.

Culture + Economic

The nature of the growth of wheel cactus (i.e. big dense patches of prickles and pain) have meant that sometimes stretches of land have been rendered inaccessible/unusable because of this pest’s presence. This can have some serious negative impacts on the human side of things, such as restricted country for Indigenous Australians, and limitations imposed on agricultural land and tourist sites. As such, wheel cactus can effectively result in a loss of both cultural ties and economic gains, devastating Australian communities on a local, regional, and national level.

Leaving these wheel cacti outcroppings to grow, spread and strengthen can only worsen its strangling hold on the land, further pushing out people, plants and animals. Luckily, there ARE ways to manage the spread of this plant. Because of the high invasive properties of wheel cactus, control of the plant should first and foremost:

  • Kill all mature, fruiting plants first.
  • Kill juvenile plants before they mature to fruit-bearing age.
  • Remove fruit and dispose of by incineration or burial. 

Chemical control is a widely used and trusted method for killing wheel cactus and involves injecting the lobes of the cactus with herbicide, poisoning the plant from the inside. The Tarrangower Cactus Control Group (TCCG) is a Victorian-based land care organisation that focuses on the eradication of wheel cactus with the help of community volunteers using this chemical control method. For years, the Monash Biological Society has collaborated with the TCCG to run Cactus Camp, a weekend away near Maryborough that is spent killing invasive wheel cactus, eating smores, and hopefully making some life-long friends. If that sounds right up your alley, the Biological Society would love to have you tag along! Cactus Camp 2022 will be held in the break after Sem 1, so keep an eye on our socials as we start the countdown for ticket sales. 

 

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