Impact of Prosopis (mesquite) invasion and clearing on ecosystem structure, function and agricultural productivity in semi-arid Nama Karoo rangeland, South Africa

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Date
2014-04-24Author
Ndhlovu, Thabisisani
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I evaluated the impact of Prosopis invasion and clearing on ecological structure, function and
agricultural productivity in heavily grazed Nama Karoo rangeland on two sheep farms near the
town of Beaufort West in the Western Cape Province of South Africa. My aims were to (1)
determine the effects of invasion and clearing on rangeland vegetation composition, diversity
(alien and indigenous species richness) and structure (alien and indigenous species cover), soil
vegetation cover (plant canopy and basal cover) and agricultural productivity (grazing capacity),
(2) describe the vegetation processes that underlay the invasion and clearing impacts and (3)
evaluate the success of clearing in facilitating unaided restoration of ecological structure,
function and agricultural productivity in formerly invaded rangeland. I hypothesised that
invasion would significantly change rangeland vegetation composition and structure, leading to
greater alien species richness and cover and lower indigenous species richness and cover while
clearing would lead to lower alien species diversity and cover and greater indigenous species
richness and cover. In addition I hypothesized that invasion would reduce rangeland plant
canopy and basal cover and grazing capacity while clearing would substantially increase them.
Finally I predicted that vegetation composition, alien and indigenous species cover and richness,
plant canopy and basal cover and grazing capacity would revert to pre-invasion status and levels
within four to six years of clearing.