Thesis (MScConEcol )--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: Over 70% of South Africa is too arid for crop farming and is used for commercial livestock ranching,
communal livestock ranching, or game ranching. These management systems differ from each other
in a number of aspects, e.g. herbivore species, stocking rate, grazing regime, and management
structure. The main question addressed in this study is: to what extent do the three management
systems affect rangeland condition? Following the equilibrium paradigm of vegetation dynamics,
communal livestock ranches are expected to have a greater detrimental effect on rangeland condition
than other management systems because stocking densities and, consequently, herbivore impacts,
are usually far higher than under the other two management systems. However, recent nonequilibrium
theories argue that vegetation dynamics in arid systems are mainly driven by rare and
stochastic rainfall events. Biotic factors, such as grazing and herbivore diversity, are predicted to have
little effect on rangeland condition. This leads to the prediction that herbivore impacts on arid
ecosystems are not density-dependent and, consequently, the high stocking densities commonly
recorded on communal livestock ranches will not cause more rangeland degradation than other
management systems.
Arid and semi-arid rangelands are characterised by high inherent spatial and temporal variation in
vegetation and soil parameters. Hence, differentiating between the effects of grazing management
systems and natural variability caused by abiotic factors, such as rainfall, is difficult. This problem can
be circumvented by examining gradients of grazing intensity radiating from water-points (=
piospheres). I examined changes in vegetation and soil parameters along 500 m-Iong grazing
gradients on ranches in the semi-arid Northem Cape province, South Africa, with the three abovementioned
management systems. Analysis of the vegetation on these ranches demonstrated the
existence of grazing gradients around the water-points. Two characteristic zones described in other
studies were identified, namely the sacrifice zone (almost complete denudation of the vegetation close
to the water-point) and the dense shrub zone (distal to the sacrifice zone). Communal livestock
ranching had a greater negative effect on rangeland vegetation than the two other ranching systems,
particularly with regard to annual grass species diversity, percentage of bare soil, and shrub density.
Within 100 m of the water-points, soil quality was negatively affected by commercial cattle ranching.
Contrastingly, there were no significant effects of the other two management systems on soil quality in
the piosphere. The feeding of supplemental forage and nutrients may explain the greater impact of commercial cattle farming on soil quality. The results of this study are consistent with the predictions
of the equilibrium theory of vegetation dynamics because grazing impacts were density-dependent in
these semi-arid rangelands. However, the results presented here also indicate that forage
supplementation alters the spatial and temporal distribution of livestock in a manner that may have
greater negative impacts on soil quality than density of livestock per se. / AFRIKAANSE OPSOMMING: Meer as 70% van Suid-Afrika is te droog vir gewasverbouing en word gebruik vir kommersiële
veeboerdery, gemeenskaplike veeboerdery of wildboerdery. Die bestuur van dié verskillende
boerderytipes verskil wesentlik van mekaar in verskeie opsigte, ondermeer herbivoorspesies, veeaanskaffingstempo,
weidingstipe en bestuurstruktuur. Die belangrikste vraag wat aangespreek word
in die studie is die volgende: Tot watter mate affekteer die drie verskillende boerderybestuurstipes die
toestand van weivelde? Gesien teen die agtergrond van die ekwilibriumparadigma van plantedinamika,
word verwag dat gemeenskaplike veeboerdery 'n groter impak op die toestand van weiveld
sal hê as ander boerderytipes, omdat veedigtheid en gevolglik herbivoor-impak gewoonlik veel hoër is
as met die ander twee boerderytipes. Onlangse nie-ekwilibria-teorië voer egter aan dat plantedinamika
in ariede gebiede gedryf word deur seldsame en buitengewone reënvalgebeure. Biotiese
faktore, soos weiding en herbivoor diversiteit sal na verwagting min effek hê op die toestand van
weiveld. Hieruit volg die voorspelling dat herbivoorimpak op ariede ekosisteme nie afhanklik is van
digtheid nie, en dat hoë veedigtheid algemeen aangeteken vir gemeenskaplike boerderye, nie rede sal
wees vir groter ver1iese in weiveld nie.
Ariede en semi-ariede weivelde word gekenmerk deur 'n hoë ruimtelike en tydelike veranderinge in
plant- en grondparameters. Gevolglik is dit moeilik om te onderskei tussen die effekte van
weidingsbestuur en natuur1ike veranderings wat veroorsaak word deur nie-biotiese faktore, soos
reënval. Dié probleem kan oorbrug word deur gradiënte van weidingsintensiteit, wat vanaf waterpunte
uitstraal, te ondersoek. Vervolgens het ek binne al drie bg. boerderybestuursisteme veranderinge in
plant- en grondparameters langs SOOm-lange weidingsgradiënte ondersoek op plase in die semiariede
Noord-Kaap provinsie van Suid-Afrika. Plantegroei-analise het getoon dat 'n weidingsgradiënt
rondom waterpunte voorkom. Twee kenmerkende sones is in ander studies geïdentifiseer, nl., 'n
opofferingsone (waar amper alle plantegroei naby waterpunte uitgetrap is) en die digte, struik-sone
(distaal to die opofferingsone). Gemeenskapsveeboerdery het 'n groter negatiewe effek op
plaasgewasse as die ander twee boerderytipes, veral waar dit betrekking het op grasspesie-diversiteit,
persentasie grond sonder plantbedekking en struikdigtheid. Binne 100m vanaf waterpunte, is
grondkwaliteit merkbaar negatief geaffekteer deur kommersiële veeboerdery. Daarteenoor, was daar
geen merkbare effek op die grondkwaliteit naby waterpunte van die ander twee boerderytipes nie.
Aanvullingsvoer kan moontlik die rede wees vir die waargenome, groter impak van kommersiële veeboerdery op grondkwaliteit. Die resultate van die studie strook met voorspellings van die
ekwilibria-teorie van plante-dinamika, daarin dat weidingsimpak digtheidsafhanklik is in hierdie semiariede
plaasgebiede. Die resultate toon ook egter, dat voedingsaanvullings die ruimtelike en tydelike
verspreiding van vee in so 'n wyse verander, dat dit moontlik 'n veel groter negatiewe uitwerking op
grondkwaliteit het as veedighteid per se.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/50074 |
| Date | 03 1900 |
| Creators | Smet, Michiel |
| Contributors | Ward, David, Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 134 p. : ill. |
| Rights | Stellenbosch University |
Page generated in 0.0026 seconds