[Truncated abstract] Annual grasses have colonised a diverse range of environments in southern Australia. The “Silvergrasses” of the genus Vulpia are excellent examples being widely distributed, are prevalent weeds of agriculture and have had a long history to naturalise on the continent. Research was undertaken on Vulpia populations to identify if naturalising species have reproductive traits that provide propagules with the best chances of success. Furthermore, research aimed at investigating if these traits vary between species and their populations and how this variability related to the environment. A herbarium and field study was undertaken to establish what Vulpia species occur in SW Australia and to investigate environmental factors affecting their distribution. 169 herbaria specimens was examined and a botanical field survey of 189 sites was carried out in September 1998. Four species occur in the region: V. fasciculata, V. muralis, V. bromoides and two variants of V. myuros (V. myuros var. megalura and V. myuros var. myuros). V. bromoides and V. myuros were introduced early into the region while V. fasciculata and V. muralis more recently. It is plausible that Vulpia invaded the region via early seaport settlements and was spread by agricultural expansion. 96% of field sites contained V. myuros var. myuros, 79% V. myuros var. megalura, 50% V. bromoides, 6% V. fasciculata and 6% contained V. muralis. 90% of sites contained a mix of species and 9% of sites contained pure species stands. V. myuros var. myuros is the most widespread species and dominant form of V. myuros. It is found from high rainfall regions through to arid locations occurring on mostly light textured low fertility soils. V. muralis and V. fasciculata occur infrequently with the former widely dispersed and the later occurring predominantly on sands. V. bromoides occurs extensively in high rainfall regions but rarely extends to locations receiving less than 400-450mm annual rainfall and northward above 30°00’ latitude. It is predominantly on light to loamy textured soils that are fertile and acid. The most common species V. myuros and V. bromoides often coexist within sites but the dominance of one over the other is strongly correlated with growing season length and false break frequency. V. bromoides is positively correlated to growing season length and V. myuros is negatively related. The distribution of Vulpia species is strongly influenced by climate and soils. Variability in distribution is a reflection of the ecological differentiation between species to colonise different environments

MESMEG / Department of Ecology and Resource Management / Invasive alien plants refer to plant species that show a tendency to escape from human control, go beyond the intended physical boundaries and cause environmental damage. The issue of letting the Invasive alien plant species grow and spread, with no attempts made to control the spread of the species beyond the limits of plantations, is not sustainable. All the attempted methods that the Department of Environmental Affairs used seemed to have failed in yielding the expected results. The main objective of the study was to determine the Wolkberg Working for Water programme’s level of success in terms of clearing invasive alien plant species. Wolkberg Project was used as a case study as it is one of the Working for Water Programme. The data were collected using random sampling methods on the worked areas, where work is in progress and those where no work has been done. Primary data were collected from land owners through field observations and questionnaires from the participants whilst secondary data were collected from the Department of Environmental Affairs. The study adopted a mixed methods approach which is both quantitative and qualitative. The data were analyzed using Statistical Package for the Social Sciences (SPSS) package. The research determined the level of success in terms of clearing invasive alien plant species, employment opportunities, tools/materials that have been used to clear the plants and the advice on the possible strategies that can be employed in the invasive alien plant species management. It was found out that the Invasive alien plant species require constant maintenance in order for them to be controlled. The Wolkberg project is mainly dominated by male workers compared to females. Each team comprised 3% underage workers. The study recommends that the project should make sure that the follow-ups are done at the correct time and stage. Looking at the statistics of males and females, the study revealed that transformation is not adhered to in this project. / NRF

This dissertation examines nursery/garden centre compliance with Invasive Alien Plant (IAPs) legislation in eThekwini and uMsunduzi, South Africa. Despite South African governmental programmes, an apparent lack of public awareness regarding IAPs persists. The cost to clear IAPs in South Africa is estimated to be 12 billion Rand over 20 years. Nurseries/garden centres should be able to increase customer awareness of IAPs. However, Government regulation/instruction of nurseries/garden centres seems inadequate. A mixed methods approach involving quantitative and qualitative analyses of questionnaires, observations and interviews was used in this study. There was little evidence that nurseries/garden centres stocked/sold CARA plants. However, they were stocking/selling NEMBA plants in spite of knowing CARA, NEMBA and indigenous alternatives. There is little interaction with relevant government/industry programmes. It is recommended that the Department of Environmental Affairs institute a IAPs Advisory Committee to see to the dissemination and provision of relevant information and training concerning IAPs to the industry.

Thesis (MSc)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Invasive alien plant species have devastating effects on the environments that they invade. Australian Acacias, a group of plants that has been planted globally for a range of uses, but has escape plantation areas and became invasive in many countries, are particularly problematic. Acacia mearnsii is one of these invasive alien plant species and in South Africa it is also an important forestry species. It is currently the fifth most widespread invasive alien plant in South Africa, only restricted by the very arid Karoo, thus it is important to assess the different habitats that it enters. The Afromontane forest complex in South Africa is highly fragmented and is one of the most threatened Biomes in the country. The widespread forest margin tree Virgilia divaricata occurs within these forest margins. It is ecologically similar to A. mearnsii as these two species share many characteristics (nodulating legumes, forest pioneer species, fast growing and fire adapted). These species occur sympatrically within invaded forest margins and within these sites, there is a potential for biological exchanges of associated pests and pathogens in the form of arthropods and fungal species. We hypothesize that these two species have different interactions with their pests and pathogens in accordance with the Enemy Release Hypothesis (ERH) and the Biotic Resistance Hypothesis (BRH), respectively. We first compared arthropod associates between these two tree species and found that they share many arthropod species. The native tree did, however, have much higher abundances of herbivores and overall arthropod associates than the invasive tree species, which supports the predictions of the ERH. The distribution of these two species also had an effect on their arthropod assemblages. We assessed their ophiostomatoid fungal associates and herbivore loads and then determined how these pests and pathogens were influenced by environmental conditions along a water gradient. We also compared the effect of plant nutrient content of the two tree species on pest and pathogen loads. A. mearnsii was unaffected by water limitation along this gradient, while δ12C/ δ13C analyses showed that V. divaricata trees experienced drought within drier sites. V. divaricata also had higher herbivore loads in drier sites. A. mearnsii had higher herbivore loads on nutrient deficient trees and higher disease development in trees with sufficient nutrient levels. Comparisons of the nutrient economies of the two legume trees showed that they had similar leaf nutrient contents and resorption efficiencies, but they differed in the use of Biological Nitrogen Fixation (BNF). The native tree utilized BNF more than the invasive. We also tested the physiological effects of a native fungal species on the two tree species. We found the infection elicited more response from the invasive, while the native plant was almost non-responsive. Both plants had significantly longer lesions on infected seedlings than on control plants after inoculation with this pathogen. This difference in response offers a measure of support to the BRH, as the invasive may be more vulnerable to infection. The importance of using related, ecologically similar species in the assessment of the impacts of invasive alien plants is highlighted here. This may provide more information on the actual ecological interaction between native and invasive species within invaded ranges. Forest margins are very vulnerable and dynamic habitats. The influx of a new species into this habitat in the form of an invasive alien plant may therefore have much negative effects. We found support for the exchange of pest and pathogens where these two tree species co-occur. The two host species were very similar in their nutrient economies, creating a potential for competition for similar resources between A. mearnsii and V. divaricata. The environment had an influence on how these plants responded to pest and pathogens and this may be important under the predicted scenario of future climate change. / AFRIKAANSE OPSOMMING: Uitheemse indringer plant spesies het vernietigende effekte op die omgewings waarbinne hulle indring. Australiese Acacias, ‗n groep plante wat reg oor die wêreld aangeplant is vir ‗n reeks gebruike, maar wat uit plantasie areas ontsnap het en indringers geword het in baie lande, is besonder problematies. Acacia mearnsii is een van hierdie indringer uitheemse plant spesies, en in Suid Afrika is ook ‗n belangrike bosbou spesie. Dit is tans die vyfde mees wydverspreide uitheemse indringer plant in Suid Afrika, en word slegs beperk deur die baie droë Karoo, so dit is belangrik om die verskillende habitatte wat dit binnedring te ondersoek. Woudrandte, the grense van die Afromontane woudkompleks in Suid Afrika, is hoogs gefragmenteerd en is dus een van die mees bedreigde Biome in die land. Die wydverspreide woudrand boom Virgilia divaricata kom in hierdie woudrandte voor. Dit is ekologies eenders aan A. mearnsii, aangesien hierdie twee spesies baie kenmerke deel (wortelknop-vormende peulplante, woudpionier spesies, vining groeiend, aangepas tot brande). Hierdie spesies kom simpatries voor binne woudrandte wat deur A. mearnsii ingedring is, en in hierdie lokaliteite bestaan daar die potensiaal vir biologiese uitruiling van geassosieerde peste en patogene in die vorm van geleedpotiges en fungi spesies. Ons stel die hipotese dat hierdie twee spesies verkillende interaksies met hulle peste en patogene het, in ooreenstemming met die Vyand-Vrystellingshipotese (VVH) en die Biologiese-Weerstandshipotese (BWH), onderskeidelik. Ons het eers die geleedpotige assosieasie tussen hierdie twee boom spesies vergelyk en het bevind dat hulle baie geleedpotige spesies deel. Die inheemse boom het egter baie hoër getalle herbivore en algehele geleedpotige-assosiasies gehad as die indringer boom spesie, wat die voorspellings van die VVH ondersteun. Die verspreiding van hierdie twee spesies het ook ‗n effek gehad op hulle geleedpotige samestellings. Ons het ook hulle geassosieerde ophiostomatiede fungus assosiate en hulle herbivoor ladings bestudeer, en het bepaal hoe hierdie peste en patogene deur omgewingstoestande beinvloed is langs ‗n water gradient. Ons het ook die effek van hierdie peste en patogene op die voedingstof-inhoud van hierdie twee spesies vergelyk. A. meansii is nie geaffekteer deur waterbeperkings langs hierdie gradient nie, terwyl δ12C/ δ13C analises aangedui het dat V. divaricata bome droogte stres in droër lokaliteite ervaar het. V. divaricata het ook hoër herbivoorladings gehad in die droër lokaliteite. A. meanrsii het hoër herbivoorladings gehad op voedingstof-beperkte bome, en daar was verhoogde siekte-ontwikkeling in bome met genoegsame voiding. Vergelykings van die voedingstof-ekonomië van die twee peulplant bome het aangedui dat hulle eenderse blaarvoedingstof-inhoude en resorpsie effektiwiteite het, maar het verskil in die gebruik van Biologiese Stikstof Fiksasie (BSF). Die inheemse boom het meer van BSF gebruik gemaak as die indringer. Ons het ook die fisiologiese effekte van ‗n inheemse fungus spesie op die twee boomspesies getoets. Ons het bevind dat infeksie ‗n sterker reaksie in die indringer ontlok het, terwyl die inheemse plant feitlik glad nie op infeksie gereageer het nie. Beide plante het beduidend langer wondmerke in geinfekteerde saailinge ontwikkel as in kontrole plante na innokulasie met die patogeen. Hierdie verskil in reaksie verleen ‗n mate van ondersteuning aan die BWH, aangesien die indringer meer vatbaar mag wees teen infeksie. Die belang daarvan om verwante, ekologies soortgelyke spesies te gebruik in die bepaling van die effekte van uitheemse indringer spesies word hier beklemtoon. Dit mag meer inligting verskaf oor die werklike ekologiese interaksie tussen inheemse en indringer spesies binne verspreidings wat binnegedring is. Woudrandte is baie weerlose en dinamiese habitatte. Die invoer van nuwe spesies in hierdie habitat in die vorm van ‗n uitheemse indringer plant mag daarom baie negatiewe effekte hê. Ons het ondersteuning gevind vir die uitruiling van peste en patogene waar hierdie twee spesies saam voorkom. Hierdie spesies was baie eenders in terme van hulle voedingstof-ekonomië, wat die potensiaal skep vir kompetisie tussen A. mearnsii en V. divaricata. Die omgewing het ‗n effek gehad op hoe hierdie plante gereageer het op peste en patogene, en dit mag belangrik wees onder die huidig voorspelde senarios van toekomstige klimaatsverandering.

Thesis (MScAgric (Soil Science))--University of Stellenbosch, 2009. / ENGLISH ABSTRACT: The sandy soils of the Riverlands Nature Reserve, near Malmesbury, and the neighbouring farm were studied to determine the effects of long term invasion of the legume Acacia saligna on the soil nutrient content of a soil previously vegetated with fynbos. The effect of the removal of this alien legume on general soil properties and groundwater quality were also studied. The changes in nitrates and nitrites (NOX) due to the invasion and removal of the alien legume were investigated in more detail than changes in other soil nutrients. In addition to that emphasis was placed on the effect of vegetation clearing on groundwater quality, specifically relating to potential contamination with nitrates. This study was initiated after Conrad et al., (1999) found increased NOX concentrations in ground water while studying the effects of pig farming on ground water nitrogen (N) near a site cleared of Acacia saligna by Working for Water (WFW). Since many sites are scheduled for removal of this alien vegetation it was deemed necessary to study the effects that clearing alone had on groundwater quality. It was suspected that there would be an increase in soil and groundwater NOX with vegetation removal due to the inputs from the legume alien invader. Soil sampling was done continuously throughout the rainy season of 2007 (From May to December) on three adjacent sites separated by some 50 m of distance, consisting of a natural fynbos site and two Acacia saligna sites. The sites were selected approximately on the same contour line to prevent interaction through lateral water flow. One of the Acacia sites was cleared by the Working for Water programme in the usual manner leaving slash on the ground. Soil samples were collected at regular intervals throughout the season from all three sites (fynbos, Acacia and cleared site) using a Jarrett soil auger. They were airdried (to achieve full oxidation of mineral N) and sieved though a 2mm sieve. Soils were analysed by atomic absorption spectroscopy for basic cations and by ion chromatography for anions, including nitrates and nitrites. Total carbon and nitrogen was determined by combustion, pH (1M KCl and H2O) and EC (1:5 H2O) were also measured. The present study was part of a wider investigation into the quality of groundwater, modelling flow and contaminant transport (Jovanovic et al., 2008). The largest changes in soil properties were observed in the top (0-5 cm) layer. The fynbos site had a lower nutrient status by comparison to the Acacia site and the cleared site. The sum of cations from the soils of the fynbos site at a soil depth of 0-5cm was 100mg/kg and soils from the cleared and Acacia sites were about 190mg/kg. The Acacia site had a higher NOX status and experienced a larger NOX fluctuation during the rainy season than the fynbos site; minimum NOX values were similar (below 10mg/kg) but the Acacia site had a maximum NOX value of near 60mg/kg and the fynbos site just below 30mg/kg. There was little difference in general soil characteristics (exchangeable cations, pH and EC, total soil C and N) during the first season after clearing, between the Acacia and the cleared sites. The effect of soluble nitrogen changes due to alien legume invasion and removal on groundwater quality, relating to NOX, during the first season after clearing, was determined. It was found that the Acacia site had higher NOX concentrations than the fynbos site. At 0-5cm the fynbos site NOX was less than 30mg/kg and the Acacia site was between 30 and 110mg/kg for most of the season, with values lower than 30mg/kg for the last four sampling dates only. N concentrations on the cleared site behaved in a similar manner to the uncleared Acacia site, but generally N values were lower on the cleared site, there were only two sampling dates where the cleared site had higher NOX values than the Acacia site at 0-5cm. The average groundwater N in NOX under the cleared site was 4.34 mg/l, and under the Acacia site 3.78mg/l, these values are both below the level determined for water contamination with nitrates. However, the increase in ground water nitrate levels after A. saligna clearing was significant. It was concluded that there is a change in the nutrient status of soil with Acacia invasion and again with removal. NOX migrates to the groundwater to a larger degree once vegetation has been removed, although during this study the nitrate pollution threshold of 10 mg/l nitrate N was not reached. / AFRIKAANSE OPSOMMING: Die sanderige gronde van die Riverlands Natuur Reservaat, naby Malmesbury, en die aangrensende plaas was bestudeer om die effek van die langtermyn indringing van die peulgewas, Acacia saligna, op die voedingswaarde van ‘n voorheen fynbos begroeide grond, sowel as die effek van die verwydering van die indringer op die algemene samestelling van die grond en grondwater kwaliteit. Oplosbare stikstof veranderings (NOX) wat plaasvind as gevolg van die indringing en verwydering van die indringer peulgewas, was in meer diepte bestudeer as die ander elemente. Klem was ook geplaas op die effek van die verwydering van plantegroei op grondwater kwaliteit, met spesifieke verwysing na potensiële nitraat besoedeling. Die studie was beplan na Conrad et al., (1999) ‘n toename van NOX konsentrasies in grondwater ontdek het, tydens ‘n studie van die effek wat vark boerdery het op grondwater N naby ‘n area waar Acacia Saligna verwyder was deur Working For Water (WFW). As gevolg van die feit dat verskeie areas in die proses is om skoongemaak te word van Acacia Saligna, is dit nodig geag om die effek daarvan of grondwater kwaliteit te ondersoek. Die hipotesis was dat daar ‘n toename in NOX konsentrasies in grond en grondwater sal wees as gevolg van die verwydering van plantegroei. Grond monsters was deurlopend geneem gedurende die reën seisoen van 2007 (Vanaf Mei tot Desember) uit nabygeleë areas wat omtrent 50 meter uitmekaar is. Die volgende tipes grond was verteenwoordig: ‘n Fynbos begroeide grond sowel as ‘n grond begroei met Acacia saligna. Die areas was geselekteer ongeveer op die selfde kontoer lyn om interaksie tussen areas te voorkom as gevolg van laterale water vloei. ’n Gedeelte van die A. saligna area was skoongemaak deur die Working for Water program op die gewone manier deur die afgesnyde plant materiaal op die grond te los. Grond monster was geneem met gereelde intervalle gedurende die seisoen op al drie areas (fynbos, A. saligna, en skoongemaakte area) deur die gebruik van ’n Jarret grondboor. Die monsters was lugdroog gemaak (om volle oksidasie van die mineraal N te verseker) en toe gesif deur ‘n 2mm sif. Die gronde was analiseer deur atoom absorpsie vir basiese katione en deur ioon chromatografie vir anione, insluitende nitriete en nitrate. Totale koolstof en stikstof was bepaal deur verbranding terwyl pH (1M KCl en H2O) en EC (1:5 H2O) ook gemeet was. Hierdie studie was deel van ‘n wyer ondersoek na die kwaliteit van grondwater, vloei modelering en vervoer van kontaminante (Jovanovic et al., 2008). Die grootste veranderinge in die grond eienskappe was in die boonste grondlaag (0-5cm) waargeneem. Die bevinding was dat die fynbos area ‘n laer voedingswaarde het as die area begroei met die indringer sowel as die die skoongemaakte area. Die som van katione onder fynbos grond by ‘n grond diepte van 0-5cm, was 100/mg/kg en die som van katione by die ander twee areas was omtrent 190mg/kg. Die Acacia area het ‘n hoër NOX inhoud en het ‘n groter NOX fluktuasie ervaar gedurende die reën seisoen as die fynbos area. Die minimum NOX waardes was soortgelyk (minder as 10/mg/kg), maar die Acacia area het ‘n maksimum NOX waarde van omtrent 60mg/kg terwyl die fynbos area se maksimum net minder as 30mg/kg gehad het. Daar nie veel verskil tussen die algemene grond eienskappe (uitruilbare katione, pH en EC, totale C en N) van die Acacia en skoongemaakte areas gedurende die eerste seisoen na die indringer verwyder is nie. Die effek van oplosbare stikstof veranderings as gevolg van die peulgewas se indringing en verwydering op grondwater kwaliteit, met verwysing na NOX, gedurende die eerste seisoen na verwydering van die indringer was bepaal. Dit was bevind dat die Acacia area ‘n hoër NOX konsentrasie as die fynbos area het. Op ‘n diepte van 0-5cm was die fynbos NOX laer as 30mg/kg terwyl die Acacia area tussen 30 en 110mg/kg vir die grootste gedeelte van die seisoen was met waardes laer as 30mg/kg vir die laaste vier datums waarop monsters geneem was. Veranderings in N op die skoongemaakte area en die Acacia area was soortgelyk, maar oor die algemeen was N waardes laer op die skoongemaakte area. Daar was slegs op twee datums gevalle gevind waar die skoongemaakte area ‘n hoër NOX inhoud as die Acacia area gehad het by ‘n diepte van 0-5cm. Die gemiddelde N in NOX in die grondwater onder die skoongemaakte area was 4.34mg/l en by die Acacia area was dit 3.78mg/l; hierdie waardes is onder die drempel vir nitraatbesoedeling in grondwater. Die nitraat inhoud van die grondwater het wel beduidend toegeneem as gevolg van verwydering van A. saligna. Die gevolgtrekking was dat daar ‘n verandering plaasvind in die voeding status van grond met Acacia saligna indringing en weer met verwydering. NOX migrasie na die grondwater verhoog met verwydering van plantegroei. In hierdie studie was die nitraat besoedeling drempel van 10mg/l nitraat N nie bereik nie.

Thesis (PhD)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: Invasive alien species are widely considered to be the second most significant threat to biodiversity globally following direct habitat destruction. The invasion of riparian systems worldwide by alien plants has contributed to profound changes in biodiversity and ecosystem functioning. In South Africa, river banks and river beds are amongst the most severely invaded landscapes, with the most damaging invaders, especially in the Fynbos Biome, being trees and shrubs of the Australian genera Acacia and Eucalyptus. Although large-scale management operations are underway to clear invasive trees and restore ecosystems, little is known regarding opportunities and constraints of native species recovery after alien clearing. The core aim of this thesis is to consider whether key aspects of two widely cited restoration models (successional and alternative-state models) are useful for guiding effective management of severely-invaded riparian vegetation. As a study system, I used the Berg River in the Western Cape, South Africa which is severely impacted by invasive trees, especially Eucalyptus camaldulensis. By linking the studies of constraints for restoration and opportunities for native species recovery, the aim was to provide new possibilities for restoration in riparian zones. The thesis starts by examining constraints to restoration following alien invasion, in particular allelopathy which is one of the factors that exacerbate the impacts of Eucalyptus invasion and inhibit recovery of natural vegetation after clearing. I further assess opportunities for both passive (based on the successional model) and active restoration (based on the alternative-state model) following different strategies for removing invasive trees. The aim is to determine the effectiveness of the different models for sustainable, goal-directed management. Finally, I investigate soil-related properties namely water repellency, soil moisture and infiltration that benefit from alien clearing and subsequent recovery of native vegetation. Work on allelopathy as a restoration constrain showed that the presence of E. camaldulensis along the Berg River negatively affects the recovery of native species. Eucalyptus camaldulensis is allelopathic and induces soil water repellency. I recommend the removal of E. camaldulensis from riparian systems as this has the potential to restore soils to a non-allelopathic and non-repellent state that can pave way for native vegetation recovery. Native vegetation recovery showed mixed results. Restoration based on the successional model was generally efficient, whereas restoration based on tenets of the alternative-state model was inefficient mainly due to the several constraints active restoration faced. Native species recovery was successful on both completely cleared and thinned sites that were treated four years ago. Cover of native trees and shrubs was higher in both completely cleared and thinned sites compared to invaded sites, indicating that both methods promote indigenous vegetation recovery and set the ecosystem on a trajectory towards recovery. To improve recovery through thinning, I propose a new four-stage process to guide management in ensuring good recovery of key native species. Numerous challenges associated with active restoration following fell & stack burning and fell & removal were observed on sites that were treated one year ago. Germination of introduced native species was low in both fell & removal and fell & stack burning sites. Secondary invasion of alien herbs and graminoids, dry summer conditions and low seed germination hindered early native species establishment and recovery. Therefore, for active restoration to achieve its goals, effective recruitment and propagation strategies need to be established. Recruitment of native species was non-existent in the sites that were not seeded; this is attributed to the dominance of alien herbaceous species and graminoids and the depletion of native species in the soil seed bank. Reduction of water repellency of soils after removal of the invasive trees is important as it has the potential to affect the success of native vegetation recovery. On sites where native vegetation was recovering well, soil water repellency ranged from moderately repellent in thinned sites to non-repellent in completely cleared sites. Therefore, successful native species recovery has the potential to improve soil-related ecosystem functions, which will possibly help towards restoring indigenous vegetation. I conclude that the invasive alien tree E. camaldulensis negatively affects the native riparian ecosystem and that strategies to remove the species are needed. Recovery of native vegetation composition, structure and ecosystem function depends on the degree of ecosystem degradation and remaining ecosystem resilience. Besides having clear and effective restoration goals, restoration efforts should also develop realistic solutions to overcome numerous challenges and constraints, before any restoration plan is implemented. Successfully restored riparian ecosystems have potential to increase river flow and may lead to increased availability of water to agriculture, recreation, conservation and for domestic use, resulting in significant water security in South Africa. Both the successional model and the alternative-state model emphasize the need to identify restoration constraints. This study identified allelopathy as an important constrain for restoration and recommends measures to address it so as to facilitate restoration. Recovery based on the successional model was more effective than recovery based on the alternative-state model, which faced several constraints. Models of alternative-states incorporate system thresholds and feedbacks that might explain why the degraded system faced recovery challenges and remained resilient to restoration. / AFRIKAANSE OPSOMMING: Naas habitatverlies word indringer spesies as die grootste bedreiging vir biodiversiteit beskou. Die indringing van riviersisteme wêreldwyd deur uitheemse plante dra by tot groot veranderinge in die biodiversiteit en ekosisteem funksie. In Suid-Afrika, veral in die Fynbos Bioom, is rivieroewers en -beddings van die landskappe wat die meeste ingedring word, meestal deur skadelike indringers soos bome en struike van Australiese genera soos bv. Acacia en Eucalyptus. Alhoewel grootskaalse bestuursoperasies besig is om die indringers te verwyder en ekosisteme te herstel, is min bekend omtrent die geleenthede en beperkinge vir die herstel van inheemse spesies na die verwydering van indringers. Die hoofdoel van hierdie tesis is om die nut te bepaal van die sleutel faktore van twee wyd aangehaalde restorasie modelle (suksessie en alternatiewe-toestand modelle) om die effektiewe bestuur van hewig ingedringde oewers te lei. Die Berg Rivier in die Wes Kaap, Suid-Afrika, is gebruik as studie area. Die Berg Rivier is hewig geimpakteer deur indringers, veral deur Eucalyptus camaldulensis. Die doel was om nuwe geleenthede vir restorasie in rivier areas te voorsien, deur die studies oor beperkinge vir restorasie en geleenthede vir inheemse spesie herstel te verbind. Hierdie tesis begin deur die beperkinge van restorasie na indringing te ondersoek, veral allelopatie wat een van die faktore is wat die impakte van Eucalyptus indringing verhoog en die herstel van natuurlike plantegroei na verwydering van indringer inhibeer. Verder bepaal ek die geleenthede vir beide passiewe (gebaseer op die suksessie model) en aktiewe restorasie (gebaseer op die alternatiewe-toestand model) wat volg op verskillende strategieë van verwydering van indringer bome. Die doel is om die effektiwiteit van die verskillende modelle vir volhoubare, doel georiënteerde bestuur te bepaal. Laastens het ek die grond verwante eienskappe ondersoek naamlik, water terugdrywing, grondvog en infiltrasie wat voordeel trek uit indringer verwydering en die daaropvolgende herstel van inheemse plantegroei. Resultate van allelopatie as ʼn restorasie beperking het getoon dat die teenwoordigheid van E. camaldulensis langs die Berg Rivier die herstel van inheemse spesies negatief beïnvloed. Eucalyptus camaldulensis is allelopaties en gee aanleiding tot grondwater terugdrywing. Ek beveel aan die verwydering van E. camaldulensis vanuit rivier sisteme omdat dit die potensiaal het om grond na nie-allelopatiese en nie-terugdrywende toestand te herstel wat die weg kan baan vir die herstel van inheemse plante groei. Die herstel van inheemse plantegroei het gemengde resultate gewys. Restorasie gebaseer op die suksessie model was oor die algemeen meer doelmatig, teenoor restorasie gebaseer op die idee van ʼn alternatiewe-toestand model, hoofsaaklik as gevolg van verskeie beperkinge wat aktiewe restorasie in die gesig staar. Inheemse spesie herstel was suksesvol op beide die totaal indringer verwyderde en uitgedunde areas, wat vier jaar vantevore behandel is. Dekking van inheemse bome en struike was hoër in beide heeltemal skoongemaakte en uitgedunde areas wanneer die vergelyk word met ingedringde areas. Dit dui daarop dat beide metodes inheemse plantegroei herstel promoveer en die ekosisteem op ʼn baan na herstel plaas. Om herstel deur uitdunning te verbeter stel ek ʼn vier-stadium proses voor om bestuurders te lei vir goeie herstel van sleutel inheemse spesies. Verskeie uitdagings geassosieer met aktiewe restorasie wat volg op val-en-stapel brand en val-en-verwyder is geobserveer in areas wat ʼn jaar van te vore behandel is. Ontkieming van aangeplante inheemse spesies se sade was laag in beide die val-en-verwyder en die val-en-stapel brand areas. Sekondêre indringing van uitheemse kruie en graminoiede, droë somers toestande en lae saad ontkieming hinder die vroeë inheemse spesie vestiging en herstel. Dus, vir aktiewe restorasie om sy doel te bereik moet effektiewe werwing en verspreidings strategieë in plek wees. Daar was geen werwing van inheemse spesies in die areas wat nie gesaai was nie. Dit kan toegeskryf word in die dominansie van uitheemse kruie spesies and graminoiede en die uitputting van inheemse spesies in die grond saadbank. Vermindering van water terugdrywing van grond ná verwydering van indringer bome is belangrik aangesien dit die potensiaal het om die sukses van inheemse plantegroei herstel te affekteer. Die areas waar inheemse plantegroei goed herstel het, het grondwater terugdrywing gevarieer van gemiddeld afstootlik in die uitgedunde areas na nie-afstootlik in die heeltemal skoongemaakte areas. Dus, suksesvolle inheemse spesie herstel het die potensiaal om die grondverwante ekosisteem funksies te verbeter, wat moontlik sal bydra tot die herstel van inheemse plantegroei. Ek kom tot die gevolgtrekking dat die indringer boom E. camaldulensis die inheemse rivier ekosisteem negatief affekteer en dat strategieë om hierdie spesie te verwyder nodig is. Herstel van inheemse plantegroei samestelling, struktuur en ekosisteem funksie hang af van die graad van ekosisteem verval en die oorblywende ekosisteem weerstandigheid. Behalwe die verwyderings en effektiewe restorerings doelwitte, moet restorasie pogings ook realistiese oplossings vir die oorkombaarheid van verskeie uitdagings en beperkinge ontwikkel voor enige restorasie plan geïmplementeer kan word. Suksesvolle herstel van rivier ekosisteme het die potensiaal vir verhoogde rivier vloei en mag moontlik lei tot ʼn verhoogde beskikbaarheid van water vir landbou, ontspanning, natuurbewaring en vir huishoudelike gebruik, en kan dus ʼn beduidende bydrae kan lewer tot water sekuriteit in Suid Afrika. Beide die suksessie model en die alternatiewe-toestand model beklemtoon die noodsaaklikheid om restorasie beperkinge te identifiseer. Hierdie studie identifiseer allelopatie as ʼn belangrike beperking tot restorasie en maak aanbevelings om dit aan te spreek en om restorasie te fasiliteer. Herstel gebaseer op die suksessie model was meer effektief as herstel gebaseer op die alternatiewe-toestand model wat verskeie beperkings in die gesig staar. Die alternatiewe-toestand modelle inkorporeer sisteemdrumpels en terugvoer wat moontlik kan verduidelik waarom gedegradeerde sisteme herstel uitdagings getoon het en weerstandig teenoor restorasie gebly het.

Thesis (MScAgric (Conservation Ecology and Entomology)--University of Stellenbosch, 2005. / Within the Table Mountain National Park (TMNP), Western Cape, South Africa, various management practices have been undertaken in the removal of alien vegetation. While considerable success in the control of alien plants is evident from the removal of standing plants, it is not known if this effort has actually made any long-term difference in the effort to eliminate alien vegetation from the TMNP. This is because no coordinated effort has been made to assess the extent of the alien seed bank, nor the effect that clearing (including the use of fire) has on this seed store. This study investigates the extent of pre- and post-fire Acacia saligna seed banks under differing stand ages, differing clearing techniques and different habitats in the Cape Peninsula National Park. Firstly, the focus is on two alien plant management techniques: The first technique involves clearing and stacking of biomass for burning during winter (stack burn technique), the second technique involves burning of standing alien plants (standing/block burn technique) to decrease heat release at the surface. Secondly, the extent of Acacia species seed banks along the Silvermine River is also investigated with the aim of determining the extent of alien seed stores in this habitat and therefore the long-term restoration potential of the riparian corridor. The primary question addressed in the first study is: “Under what clearing technique will most of the alien seed bank be reduced?” The secondary question reads: “Is seed bank density and distribution directly related to age of dense infestation of the alien vegetation stand and habitat?” The primary question addressed in the second study is: “What is the vertical, lateral and longitudinal distribution and density of Acacia species seed banks along the Silvermine River?” The secondary question reads: “Is seed density and distribution influenced by above ground density of alien vegetation?” In both riparian and terrestrial systems, alien soil seed banks accumulate in high densities where aboveground alien Acacia vegetation is dense. Most of the seed occurs in the upper soil layer, but seed density decreases with depth with an exception of a high seed density at a low depth in one of the samples in the riparian system. Intense fires are most effective in reducing seed stores and removing aboveground alien vegetation in both riparian and terrestrial fynbos systems. After burns, both stack and stand burns have shown a significant decrease in seed density especially in the upper layers but there is still much seed that remained in the matrix area between stacks. The cooler winter burns resulted in less destructive, lower temperatures that aided higher seedling recruitment. Mature stands of Acacia saligna tend to have greater seed stores than immature stands and habitats with deep colluvial soils have a greater density and also greater vertical distribution of seeds. The vertical distribution of the riparian system differed from the fynbos terrestrial system in that seeds were found down to lower depths. Along the river, seed density also increased laterally with more seeds occurring in the terrrestrial sections than in the channel. Seed density increased with longitudinal distribution with more seeds occurring at the sites in the lower catchment than upper catchment. Managers should be aware that fire is needed to reduce the seed bank in both riparian and terrestrial fynbos systems. The cooler winter stack burns is the best option as it results in less destructive, lower temperatures that aids higher seedling recruitment. It is important to know the site history as age of dense infestation, number of fires and geology of site could influence seed bank density. In riparian systems the vertical distribution of seed is deeper than in the fynbos area. In order for clearing to be effective it is imperative that follow-up takes place and should be done prior to flowering to stop reseeding.

Thesis (MScConsEcol (Conservation Ecology and Entomology))--Stellenbosch University, 2008. / The fynbos eco-region in the Western Cape lowlands has been extensively transformed by anthropogenic activities such as agriculture and urban development, as well as invasive alien plants. Elandsberg Private Nature Reserve and Farms lies on Swartland Alluvium Fynbos and has been largely fragmented by agricultural crop production, whilst Riverlands Nature Reserve together with the Pella Research Site, which lie on Atlantis Sand Fynbos, are under severe threat from the invasive woody alien Port Jackson Willow (Acacia saligna) which forms dense stands in the lands adjacent the nature reserve. Habitat transformation has resulted in subsequent loss of habitat and a reduction in habitat value for small mammal communities by creating a mosaic of optimal and sub-optimal habitats. The success of A. saligna is, in part, attributed to its production of copious amounts of small hard-shelled seeds and well established soil seed banks. In the first part of this study we investigated the effect of habitat transformation on resident small mammal communities by comparing small mammal species richness, diversity and abundance between natural and transformed habitats as well as between the two vegetation types. We also investigated the population demographics of the striped mouse (Rhabdomys pumilio) in the different habitats. Our study shows that whilst fragments of natural habitats, especially at Riverlands and Pella, may be playing an important role in harbouring rare and possibly endangered species, transformed habitats are also important as secondary habitats providing both cover as well as seasonal food resources. Reproduction and body condition in R. pumilio were dependent on seasonal changes such as availability of water and food resources in the habitats. The second part of this study was carried out to investigate the effect of alien plant invasion on the resident small mammal communities at Riverlands Nature Reserve and to determine the role of small mammals in the removal and predation of A. saligna seeds. Rodent species richness, diversity and abundance were very low in the A. saligna stands compared to the adjacent fynbos vegetation. The interaction of rodents with seeds (removal or predation) was dependent upon seed size and seed abundance in the habitats. Whilst rodents may play an important role in predator limitation in the acacias, it is also possible that they may be playing a significant role in dispersing the seeds of acacias into the fynbos. More work is required to fully understand the role small mammals play in seed predation, dispersal and limitation in alien invaded fynbos systems.

published_or_final_version / abstract / Sociology / Master / Master of Philosophy

Thesis (MScConEcol)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: Acacia saligna, or Port Jackson, is an Australian Acacia which has spread throughout the Western and Eastern Cape provinces of South Africa where it has become invasive and a prominent feature of the vegetation. In areas where A. saligna establishes it replaces natural vegetation, alters ecosystem processes and interferes with agricultural practices. Consequently large management efforts have been made to eradicate this invasive alien tree. However, its large and persistent soil stored seed bank, even in the presence of management and biological control agents, poses a serious obstacle to its successful removal. Furthermore the reproductive output and the size of the seed bank of A. saligna over its whole distribution as well as the variation of seed production and the seed bank with environmental conditions in time and space is poorly known. Understanding the seed bank dynamics of A. saligna in time and space is essential for reducing invasive success and achieving management objectives. This study has filled this knowledge gap through studying the seed production and seed bank of A. saligna over its invaded range in South Africa, including how environmental factors influence these factors in time and space. The seed rain of A. saligna was assessed at 10 sites across its distribution in South Africa. The seed rain of A. saligna at the sites was determined through the use of seed rain traps. Twenty five traps were placed out at every site during November 2010 (pre-dehiscence) which was collected again during April 2011 (postdehiscence). The seed bank of A. saligna was estimated through sampling at 25 sites across its distribution range in South Africa. The seed bank was sampled during April 2010 (postdehiscence), November 2010 (pre-dehiscence) and April 2011 (post-dehiscence) through taking 50 litter and soil samples at every site which gave a total sampling size of 3 750 for both the seed in the soil and litter over its distribution in South Africa. In addition the average tree diameter, tree density, average number of Uromycladium tepperianum induced galls per tree, the summer aridity index, De Martonne aridity index, winter concentration of precipitation, temperature of coldest month and the soil texture for every site was determined. The damage done by the seed feeding weevil, Melanterius compactus, was also estimated for the seed rain study sites. Water availability during the hot summer months was assessed as the most important factor governing seed production and seed bank size. Riparian and non-riparian water regimes were shown to be important in understanding the seed bank dynamics of A. saligna over its distribution range in the Cape Floristic Region. In non-riparian A. saligna populations the seed production and consequently the size of the seed bank and its rate of accumulation is limited by both water and temperature and in riparian A. saligna populations, only by temperature. Therefore, two environmental gradients influence the seed bank dynamics of Port Jackson in South Africa. In non-riparian A. saligna populations the number of seed produced and the accumulation of seed in the seed bank generally increases along the west coast of South Africa from Clanwilliam towards Cape Town and along the south coast from Cape Town towards Port Elizabeth. Seed banks are larger closer to the coast, when A. saligna populations of similar age are compared. In riparian A. saligna populations, the number of seed produced generally increases from Port Elizabeth towards Cape Town and from Cape Town towards Clanwilliam, again, with larger seed banks being accumulated closer to the coast, when populations of similar age are compared. This study provides managers with a useful tool for prioritising management efforts. / AFRIKAANSE OPSOMMING: Acacia saligna of Port Jackson is ‘n indringerplant in Suid-Afrika wat afkomstig is uit Suid-Wes Australië. Acacia saligna is ‘n onmisbare kenmerk van die plantegroei in die Wes en Oos-Kaap. Waar Port Jackson vestig, verplaas dit natuurlike plantegroei, verander dit ekosisteem prossesse en verhinder dit landbou praktyke. Gevolglik is groot bestuurspogings aangewend om hierdie indringer plant uit te roei. In die teenwoordigheid van bestuursprogramme en biologiese beheer bly A. saligna lewensvatbaar as ‘n gevolg van die plant se groot blywende grond saadreserwes. Verder is die saad produksie en saadbank grootte van A. saligna oor sy verspreiding bereike asook hoe dit met omgewingstoestande in tyd en ruimte interreageer en varieer grootendeels onbekend. ‘n Goeie en omvattende begrip van die saadbankdinamika is belangrik om die indringings vermoë van die plant te verlaag en om bestuursdoelwitte te bereik. Hierdie studie vul die bestaande gaping in die kennis aangaande die saadbank dinamika van A. saligna aan deur die saadproduksie en die saadreserves van die indringerplant oor sy verspreiding in Suid-Afrika te bestudeer, insluitend hoe omgewingstoestande die saadbankdinamika beïnvloed in tyd en ruimte. Die saadreën vir 10 A. saligna populasies was bepaal deur die gebruik van saadlokvalle. Vyf-entwintig lokvalle was uitgeplaas in elke bestudeerde Port Jackson perseel gedurende November 2010 (voor-saadval) wat weer gaan haal is gedurende April 2011 (na-saadval). Die saadbank van A. saligna was bepaal in 25 populasies van die boom gedurende April 2010 (na-saadval), November 2010 (voor-saadval) en April 2011 (na-saadval) deur die neem van 50 blaar- en grondmonsters by elke perseel wat ‘n totaal van 3 750 blaar- en grondmonster gee oor die hele verspreiding van A. saligna in Suid-Afrika. Verder is die gemiddelde boomdeursnee, boomdigtheid, gemiddelde Uromycladium tepperianum geinduseerde galle per boom, die somers droogtheids indeks, De Martonnes droogtheids indeks, die winter konsentrasie van presipitasie, die temperatuur van die koudste maand en die grond tekstuur van elke Port Jackson stand bepaal. Die skade wat die saad voedende kewer, Melanterius compactus, aanrig aan die sade van A. saligna is ook vir die persele waar die saadreën eksperiment uitgevoer is, bepaal. Die beskikbaarheid van water vir A. saligna in die droë somermaande is bepaal as die belangrikste faktor wat die grootte van die saadproduksie en saadbank beïnvloed. Oewer en nie-oewer water omgewings is bevind as noodsaaklik om die saadbank dinamika van A. saligna oor die indringerplant se verspreidingareas in die Kaap Floristiese Streek te verstaan. In nie-oewer A. saligna populasies word saadproduksie en gevolglik die grootte en tempo van akkumulasie van die saadbank deur beide water en temperatuur omstandighede beperk, terwyl in oewer A. saligna populasies word die indringerplant slegs deur temperatuur omstandighede beperk. Gevolglik blyk dit dat twee water beskikbaarheids gradiënte bestaan waarop die plant reageer wat dan uitgedruk word in die plant se saad produksie en gevolglik ook die plant se saadbank. In nie-oewer Port Jackson populasies neem die saadproduksie en die tempo waarteen die saadbank akkumuleer algemeen toe langs die weskus van Clanwilliam na Kaapstad en van Kaapstad na Port Elizabeth, met grootter saadproduksie en saadbank akkumulasie nader aan die kusgebiede, wanneer A. saligna populasies van dieselfde ouderdom vergelyk word. In oewer Port Jackson populasies neem die saadproduksie en die tempo waarteen die saadbank akkumuleer algemeen toe van Port Elizabeth na Kaapstad en van Kaapstad na Clanwilliam, met grootter saadproduksie en saadbank akkumulasie nader aan die kusgebiede, wanneer A. saligna populasies van dieselfde ouderdom vergelyk word. Hierdie studie verskaf bestuursplanne met ‘n nuttige raamwerk waarvolgens uitroeiing en beheer programme vir A. saligna beplan kan word.