Thesis (MScConEcol (Conservation Ecology and Entomology))--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: 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.
My results suggest that in heavily grazed Nama Karoo rangeland Prosopis invasion (~15
percent canopy cover) and clearing can significantly change rangeland vegetation composition,
with invasion leading to greater alien species cover and lower indigenous species richness, while
clearing leads to lower alien species richness and cover and greater indigenous species richness
and cover. However invasion seems to have no effect on alien species richness and overall
indigenous species cover. Clearing appears to facilitate the spontaneous restoration of alien
species cover and indigenous species richness within four to six years but not species
composition, alien species richness and indigenous species cover. In addition my results also
indicate that Prosopis invasion can lower rangeland plant canopy and basal cover and grazing
capacity while clearing, even under heavy grazing, can substantially raise them. Clearing
however does not seem to facilitate the restoration of rangeland plant canopy and basal cover
and grazing capacity to pre-invasion levels within four to six years after clearing. / AFRIKAANSE OPSOMMING: Ek het die impak van Prosopis indringing en verwydering van indringers op ekologiese
struktuur, funksie en landbou produktiwiteit in ‘n swaar beweide Nama Karoo gebied op twee
skaapplase naby Beaufort-Wes in die Wes-Kaap provinsie van Suid-Afrika geëvalueer. My
doelwitte was om (1) te bepaal wat die gevolge van die indringing en verwydering van
indringers op die natuurlike plantegroei samestelling, diversiteit (uitheemse en inheemse
spesiesrykheid) en struktuur (uitheemse en inheemse spesies bedekking) sal wees, sowel as die
effek op plantegroei bedekking (kroon en basalebedekking) en landbou produktiwiteit
(weidingkapasiteit), (2) die plantegroei prosesse te beskryf wat onderliggend deur die impakte
van indringing en verwydering van indringers veroorsaak word, en (3) die sukses van die
verwydering van indringers te evalueer deur die fasilitering van blote restorasie van ekologiese
struktuur en funksie en landbou produktiwiteit in voorheen ingedringde gebiede. My hipotese is
dat indringing ‘n aansienlike verandering in natuurlike plantegroeisamestelling en struktuur sal
veroorsaak, wat sal lei tot groter uitheemse spesiesrykheid en bedekking met minder inheemse
spesiesrykheid en bedekking, terwyl die verwydering van indringers sou lei tot minder
uitheemse spesie diversiteit en bedekking met 'n groter inheemse spesiesrykheid en bedekking.
Verder vermoed ek dat indringing die natuurlike kroon- en basalebedekking en
weidingkapasiteit sal verminder, terwyl die verwydering van indringers dit aansienlik sal
verhoog. Ten slotte voorspel ek dat plantegroei samestelling, uitheemse en inheemse
spesiesbedekking en -rykheid, kroon- en basalebedekking en weidingkapasiteit sou terugkeer na
voor-indringing status en vlakke binne vier tot ses jaar na die verwydering van indringers.
My resultate daarop dat die indringing van Prosopis (~ 15 persent kroonbedekking) en die
verwydering van indringers in swaar beweide Nama Karoo gebiede ‘n aansienlike verandering
in die gebied se natuurlike plantegroei samestelling toon, waar indringing gelei het tot groter
uitheemse spesiesbedekking en minder inheemse spesiesrykheid, terwyl die verwydering van
indringers lei tot minder uitheemse spesiesrykheid en groter inheemse spesiesrykheid en -
bedekking. Dit lyk egter of indringing geen effek op uitheemse spesiesrykheid en algehele
inheemse spesiesbedekking het nie. Die verwydering van indringers blyk om die spontane
herstel van indringerbedekking en inheemse spesiesrykheid binne vier tot ses jaar te fasiliteer,
maar nie spesiesamestelling, uitheemse spesiesrykheid of inheemse spesiesbedekking nie.
Benewens dui my resultate ook aan dat Prosopis indringing die natuurlike kroon- en
basalebedekking sowel as weidingskapasiteit verlaag, terwyl die verwydering van indringers,
selfs onder swaar beweiding, die bedekking aansienlik kan verhoog. Verwydering van
indringers lyk egter nie asof dit die herstel van die gebied se natuurlike kroon- en
basalebedekking en weidingkapasiteit na voor-indringing vlakke toe kan fasiliteer binne vier tot
ses jaar na die verwydering van indringers nie.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/6751 |
| Date | 03 1900 |
| Creators | Ndhlovu, Thabisisani |
| Contributors | Esler, Karen J., Milton, Suzanne J., University of Stellenbosch. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 122 p. : ill., maps |
| Rights | University of Stellenbosch |
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