Thesis (MSc)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: West Coast Renosterveld is one of the most threatened vegetation types in South
Africa. Less than 5% of the original extent of this vegetation type remains, of which
80% is on private land. In addition to fragmentation, much of the vegetation has been
ploughed for crop production and then abandoned and invaded by alien plants.
Restoration of transformed areas may improve the conservation status of this
vegetation type. Indigenous species do not return to abandoned agricultural fields for
decades even if these are adjacent to natural areas since their return is limited either
by seed dispersal or seedling establishment. The aim of this study was to examine
the recovery of indigenous vegetation on abandoned fields.
Renosterveld, as we know it today, is an asteraceous shrubland, dominated mainly
by renosterbos (Eytropappus rhinocerotis), but might have been a grassland or a
grassland-shrubland mosaic. Historical records indicate that species of large game
were common in the Western Cape when the early settlers arrived, but most of these
have since disappeared. It is thus impossible to reconstruct exactly the ecological
processes and functioning of Renosterveld.
The first part of the study was designed to examine the effects of grass competition,
grazing by indigenous large herbivores, and interaction of these two factors on the
establishment, growth and survival of transplanted Renosterveld seedlings on an
abandoned agricultural field. Experimental transplanting of indigenous shrubs into an
old field showed that most of the plants investigated competed for resources with
lawn grasses on the field, and competition affected the seedlings throughout the
experiment. Mortality was higher, and growth was reduced for seedlings exposed to
grass competition. With the exception of wild olive (Olea europaea spp.africana),
herbivory alone had no significant impact on the target species. Herbivory was at a
low intensity (20 ha/large animal unit); higher grazing pressures might have given
different results. No interaction between competition and herbivory was found for the
species investigated; competition and grazing therefore seem to influence the
seedlings independently. The second part of this study was conducted to examine the effects of different
management strategies, viz: brush cutting, burning and herbicide application on plant
species recruitment and community composition and to ascertain their applicability
by farmers for large scale restoration of Renosterveld. My comparison of the different
strategies for controlling annual alien grasses indicated that these did not differ
significantly in their effects on species richness. Burning reduced shrub cover and
increased overall species richness and diversity. Burning also reduced grass
biomass, and increased recruitment of indigenous seedlings. The use of herbicide
resolved the problem of grass biomass invasion and increased shrub species
richness. The herbicide application did not appear to have long-term negative effects
on the soil quality. Brush cutting did not remove grass biomass on the old field.
Experimental re-seeding with an indigenous grass and shrub species into treated
plots resulted in low recruitment.
My conclusion is that grass can reduce recruitment and growth of many indigenous
shrub species. My recommendation for the restoration of old fields in West Coast
Renosterveld is to apply herbicide to remove grass competition, and then, after the
herbicide has degraded, to oversow the field with seeds of indigenous shrub and
grass species of early successional stages to increase overall species diversity. / AFRIKAANSE OPSOMMING: Weskus Renosterveld is een van die mees bedreigde plantegroei soorte in Suid
Afrika. Minder as 5% van die oorspronklike omvang van hierdie plantegroei tipe is
oor, en dit hoofsaaklik (80%) op privaatlande. Saam met fragmentasie, is baie
Renosterveld areas ook omgeploeg vir boerdery en dan net so gelos, met die gevolg
dat uitheemse plante hierdie areas ingedring het. Restorasie of herstelling van sulke
bewerkte lande kan dalk die bewaringsstatus van hierdie plantegroei tipe verbeter.
Natuurlike vestiging van Renosterveld spesies op sulke ou bewerkte lande gebeur
nie, selfs al is daar Renosterveld direk langs so ‘n ou veld. Die hervestiging van
inheemse spesies is dus tot saadverspreiding or saailingbevestiging beperk. Die
doel van hierdie studie is om die stadige terugkoms van inheemse plantegroei na
verlate bewerkte velde te verduidelik.
Renosterveld is ‘n struikveld waarin die renosterbos (Eytropappus rhinocerotis)
domineer, maar kan ook ‘n grasveld of ‘n grasveld-struikland mengsel wees. Groot
herbivore was algemeen in die Wes Kaap toe die eerste settelaars gearriveer het,
maar intussen het omtrent al die groot wild spesies verdwyn. Dit is dus ontmoontlik
om die ekologiese prosesse en funksionering van Renosterveld presies so te herstel.
Die eerste deel van hierdie studie bestudeer die effek van graskompetisie, weiding
deur inheemse groot herbivore, en die interaksie tussen hierdie twee faktore op die
vestiging, groei en oorlewing van oorgeplante Renosterveld saailinge in ‘n verlate ou
veld. Die eksperimentele oorplanting van inheemse struike in ‘n ou land het gewys
dat die meeste van hierdie plante kompeteer vir hulpbronne met kweekgras wat op
die ou veld groei. Kompetisie het die saailinge deur die hele eksperiment
geaffekteer. ‘n Hoër mortaliteit en verminderede groei in saailinge wat aan gras
kompetisie blootgestel was, is waargeneem. Met die uitsondering van Olea
europaea spp. africana, het herbivorie alleen geen betekenisvolle impak op plant
spesies gehad nie. Weidingsdruk was laag (20 ha/groot vee eenheid); ‘n groter
weidingsdruk sou miskien ‘n ander uitkoms gehad het. Geen interaksie tussen
kompetisie en herbivorie is waargeneem in die bestudeerde plantspesies nie. Dit wil dus voorkom of kompetisie en weiding die saailinge onafhanklik van mekaar
beïnvloed.
Die tweede deel van hierdie studie was onderneem om die effek van verskillende
behandelings (kontrole, sny, brand en herbisied toediening) op plantspesie vestiging
en samestelling te bestudeer asook om bestuurmetodes te toets was deur boere op
groot skaal gebruik kan word om Renosterveld te herstel. In ‘n vergelyking van
verskillende bestuur metodes (kontrole, besnoeiing, brand en herbisied) om
eenjarige uitheemse gras te beheer, is gewys dat die behandlings nie betekenisvol
van mekaar verskil in hulle effek op spesierykheid nie. Vuur het struikbedekking
verminder en totale spesies rykheid en diversitiet verhoog. Die gebruik van ‘n
herbisied het die probleem van grasindringing opgelos en het ook
struikspesiesrykheid verhoog. Die herbisied het nie lang termyn negatiewe effekte op
grond kwaliteit gehad nie. Sny het nie gras biomassa verlaag op die ou land nie.
Eksperimentele plant van inheemse grasse en struike in die behandelde areas, het
lae vestiging tot gevolg gehad.
My algemene afleiding is dus dat gras die hervestinging en groei van baie inheemse
struikspesies verminder. Ek stel voor dat herbisied gebruik moet word om gras
kompetisie te verminder. Nadat herbisied residue in die grond afgebreek is, moet
die ou land met inheemse struik en grasspesies, wat in vroeë suksessie stadiums is,
beplant word om sodoende totale spesiediversiteit te verhoog en uiteindelik ou
bewerkte lande in Weskus Renosterveld te herstel.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/16390 |
| Date | 12 1900 |
| Creators | Midoko-Iponga, Donald |
| Contributors | Milton, Suzanne.J., Krug, Cornelia B., 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 | English |
| Type | Thesis |
| Format | xi, 126 leaves : ill., maps |
| Rights | University of Stellenbosch |
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