Yellow Oleander, Thevetia peruviana. Single open flower and buds growing in Phrao, Chiang Mai, Thailand. (Photo by FlowerPhotos/Universal Images Group via Getty Images)
KwaZulu-Natal’s urban spaces are filled with invasive alien species that need to be removed, according to a study by a master’s student employed by the Natural Science Collection Facility.
The study by Maxine Manickum looked at tree diversity in urban parks in eThekwini municipality.
“There is a strong presence of invasive alien plants and a decline in coastal terrestrial vegetation,” she said in a press release. “Only 26% of its land is in a natural, non-degraded state.”
In an ecosystem, everything is interconnected and having only 26% of the land in a non-degraded state means that if one part of biodiversity is removed or destroyed, “you are essentially removing a food or shelter source for the next species”, Manickum told the Mail & Guardian. “Some species can adapt, but some species are specific to an area. It’s like a ripple effect.”
All 13 parks in Manickum’s research had an invasive species, which she said was “a worrying trend”.
“There are three categories of invasive species, according to the National Environmental Management Biodiversity Act 2004. Categories 1a and 1b should be removed, while categories 2 and 3 are permitted,” she said.
The yellow oleander (Cascabela thevetia) and Brazilian peppertree (Schinus terebinthifolia), which fall in category 1b, were common ones found in the parks.
The yellow oleander, like the peppertree “competes with and has the potential to replace indigenous species”, according to Invasives South Africa. Both species are poisonous.
The problems with these invasive species is that they have rapid growth rates, high seed production and efficient seed dispersal.
“With regards to dealing with invasive species, categories 1a and 1b should be removed and replaced with indigenous species,” Manickum said.
“There also needs to be tree planting management in all parks, planting trees that are suitable to each site, and not just what is available to plant. There are a lot of considerations to managing invasive species in urban parks.”
The importance of local species cannot be understated, she said. They contribute to biodiversity conservation and ecosystem resilience, “making them valuable assets in park ecosystems”.
They have numerous other benefits to general ecosystems. These include “ecological soundness, interconnectedness, and the potential to enhance native flora and fauna while strengthening soil biological vitality”.
“Native species enhance ecological health, while non-native species diminish it by endangering the structure and operation of ecosystems and decreasing habitat possibilities,” Manickum said.
The South African National Biodiversity Institute categorises invasive plant species in the following way:
Category 1a:
Invasive species requiring compulsory control. Remove and destroy. Any specimens of category 1a listed species need, by law, to be eradicated from the environment. No permits will be issued.
Category 1b:
Invasive species requiring compulsory control as part of an invasive species control programme. Remove and destroy. These plants are deemed to have such a high invasive potential that infestations can qualify to be placed under a government sponsored invasive species management programme. No permits will be issued.
Category 2:
Invasive species regulated by area. A demarcation permit is required to import, possess, grow, breed, move, sell, buy or accept as a gift any plants listed as category 2 plants. No permits will be issued for category 2 plants to exist in riparian zones.
Category 3:
Invasive species regulated by activity. An individual plant permit is required to undertake any of the following restricted activities (import, possess, grow, breed, move, sell, buy or accept as a gift) involving a category 3 species. No permits will be issued for category 3 plants to exist in riparian zones.