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