A recent study by C·I·B Associate, Sjirk Geerts (based at Cape Peninsula University of Technology), together
with researchers from the C·I·B, SANBI’s Invasive Species Programme
and the University of Cape Town, stressed the importance of human activities in the spread of some of the most notorious plant invaders.
The study, published in the scientific journal Biological
Invasions, was the first detailed study of Kudzu vine (Pueraria montana var. lobata) in South Africa.
Geerts and his colleagues conducted a national wide survey and found seven populations of Kudzu vine in South Africa, covering an area of
74 hectares. By using models that predict where Kudzu vine is likely to thrive, the researchers found that the climate is suitable for Kudzu vine across the
eastern escarpment and parts of KwaZulu-Natal, while the models suggested that the rest of the country is climatically unsuitable.
In the United States of America (USA) Kudzu vine has taken over many areas and removing it costs the country millions of US dollars each
year. Geerts and collogues found that South African populations of Kudzu vine have a similar ecology to populations in the USA, with high growth rates, low
seed germination rates, no natural long-distance dispersal, little herbivory and the ability to resprout vigorously after a fire. Unlike the USA populations,
however, most South African populations produce flowers, and the flowers can produce seed without the need for insect pollinators. So Kudzu vine should be at
least as invasive in South Africa as it is in the USA?
The authors argue that the reason Kudzu vine is not (yet!) a major problem in South Africa is down to its introduction history. Kudzu
vine was introduced to South Africa in the 1930s as fodder for horses. However, it was never widely planted, and the species was for many years only
present at a single site.
By contrast, in the USA there was a concerted effort to plant Kudzu vine for fodder and erosion control, with, in some cases,
governmental funding provided to encourage Kudzu vine plantings. In South Africa, many of the plants are found on roadsides where mowing is an
important cause of spread.
The lesson is simple. If an invasive species is planted more often, the future invasions will likely be larger and any negative
impacts much greater. “The comparison between the invasions of Kudzu vine in the USA and South Africa highlights the often over-riding
importance of human-assisted dispersal and cultivation in causing widespread invasions. This should serve as a warning to people who have proposed to
use this species elsewhere in Africa,” says Dr Sjirk Geerts.
(a) Kudzu vine (Pueraria Montana var. lobata) invasion of a eucalyptus plantation close to the
initial introduction site in Mpumalanga Province of South Africa; (b) Kudzu vine smothering native and alien riparian vegetation at the
site of initial introduction (Photo credit: Sjirk Geerts)
Click here to read the article in Biological Invasions
For more information, contact Sjirk Geerts at email@example.com or
SANBI’s Invasive Species Programme at firstname.lastname@example.org