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Effects of Prosopis invasions and clearing on Nama karoo rangelands

Nama karoo rangelands are vulnerable to overgrazing and consequently soil erosion, but what of the impact of invasive plants? With most research focussing on the impact of alien plants on South Africa’s water resources, the costs of plant invasions on other ecosystem services, such as soil retention, remain understudied. This was a gap targeted by student Thabisisani Ndhlovu. The effects of Prosopis invasions and clearing on vegetation cover of Nama Karoo rangelands was the topic of his recent paper published in African Journal of Range and Forage Science. Vegetation cover plays an important role in rainfall infiltration, runoff and soil erosion.

Ndhlovu and his C·I·B affiliated co-supervisor Karen Esler, and Suzanne Milton, found that below a critical threshold cover level of 6.4%, Prosopis did not affect indigenous vegetation, but rather added to it. Beyond this threshold, the impact of Prosopis on the indigenous vegetation is significant by reducing the cover of plants, especially grasses. After the clearing of Prosopis stands, vegetation cover can return to pre-invasion levels.

“These findings have the potential to direct clearing efforts in identifying priority areas for clearing,” says Thabisisani Ndhlovu, lead author of the paper and currently a PhD student in the Department of Conservation Ecology and Entomology.

Vegetation surveys at a study site in the Nama Karoo

Thabisisani Ndhlovua conducting vegetation surveys at a study site near Beaufort West in the Nama Karoo, Western Cape, South Africa. (Photo credit: Karen Esler)




Read the papers:

Ndhlovu, T., Milton, S., Esler, K.J. (2015) Effect of Prosopis (mesquite) invasion and clearing on vegetation cover in semi-arid Nama-Karoo rangeland, South Africa. African Journal of Range and Forage Science, DOI: 10.2989/10220119.2015.1036460

Ndhlovu, T., Milton, S.J. Esler, K.J. (2011) Impact of Prosopis (mesquite) invasion and clearing on the grazing capacity of degraded semi-arid Nama Karoo rangeland, South Africa. African Journal of Range and Forage Management, 28(3):129-137

For more information, contact Thabisisani Ndhlovu at thabisisani.ndhlovu@gmail.com