dissertation submitted to the faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science. Johannesburg, 2015. / Global environmental change due to anthropogenic activity results in alterations to the Earth’s biogeochemical cycles. This study focused on nitrogen and sulphur deposition, which results in the acidification of ecosystems. Alterations to these processes will have an effect on the diversity and ecophysiology of the vegetation; moreover, little is known about the long-term impacts on the vegetation structure and composition. Increased development, mining and industrialization, within the Waterberg area, particularly with the construction of the Medupi power station, have resulted in this area coming under study. The impacts of additional air pollution to the vegetation in this area are currently unknown. The aim of this research was to determine whether increased ambient levels of atmospheric nitrogen and sulphur, resulting from the power stations, will impact the structure, functional type and the composition of the vegetation, and the resultant impacts on vegetation structure and growth as a result of the added nitrogen and sulphur to the system and increased acidity. A baseline of quantitative data was needed in order for future comparisons to be made to assess whether biodiversity is changing and at what rate. One part of the study involved the collection of baseline vegetation data along a pre-determined transect in the Waterberg area. A transect was identified which could serve as a vehicle for monitoring changes over time, with areas downwind of the Matimba and Medupi power stations assumed to be more impacted than areas upwind. The two downwind sites and the two sites closest to the power stations were found to have the highest beta diversities, with the two downwind sites having a value of 0.60 and the downwind Landelani site and upwind Withoutpan site having a value of 0.53. The high species variation between these sites may already be an indication of pollution impacts within the area. The downwind site closest to the power stations, Landelani, is particularly vulnerable as it has a high Shannon diversity index, with a value of 2.84, and high tree biomass, 46.64 tonnes/ha, with low tree density, 625 trees per hectare. iii Functional groups are assumed to react similarly under changing environmental conditions. The second part of this research focussed on photosynthetic pathways, by using two C3 woody species and two C4 grasses. The experiment was conducted in the greenhouse at the University of the Witwatersrand and showed that both tree and both grass species selected were sensitive to sulphur additions to varying degrees. Additionally Acacia sieberiana was found to be sensitive to nitrogen addition, however Combretum erythrophyllum responded to nitrogen when it was added alone. A positive response to nitrogen was seen in both grass species; however the positive response was negated by the addition of any sulphur in Eragrostis curvula. In Panicum maximum the positive response in growth to nitrogen addition exceeded any negative effects from the sulphur addition. The results of plant growth to increasing soil acidity were different between functional groups and within functional groups. A relationship between the increase in the average above and below ground mass was found to exist with a decrease in soil acidity in Acacia sieberiana (R2 = 0.45). A relationship between an increase in the average above and below ground mass with a decrease in soil acidity in Eragrostis curvula was also seen (R2 = 0.31). Changes to the structure and composition of vegetation in this area will impact land use and the management thereof, impacting land users and owners ability to generate an income and therefore their livelihoods. Changes to vegetation structure and composition will also have a greater overall effect by impacting ecosystem functioning and resilience to future disturbances.

Thesis (MTech (Applied Sciences))--Cape Peninsula University of Technology, 2007 / Changes in plant specIes richness and diversity were investigated in Rocherpan Nature Reserve across a fence (or old fence line) separating 34 years of conservation management, conservation management for 11 years south and north, natural veld grazed by cattle and goats, natural veld grazed by sheep, and strip-ploughed veld grazed by sheep. Vegetation surveys were conducted in September 2001. The modified 20 m x 50 m Whittaker plot design with its attractive features of long-thin plots and the original Whittaker plot design were used. Number of species (as richness data) and the numbers of individual recordings per species per land use (as abundance data) were used in calculations in the 20 m x 50 m (1000 m2 ) plots. The species richness index showed significantly smaller numbers of species in the conservation management 11 years south land. The results also showed an increase in species numbers under the grazing land use systems. The data from the comparative study of the five different species diversity indices showed no significant differences. As a result, the Shannon-Wiener index was selected for further assessing the species diversity index and the species diversity significance of different land uses in the West Coast Strandveld. In this particular study, the species that showed an increase in vegetation cover in response to grazing land use regimes were Hemimeris racemosa (annual herb) and Ehrharta brevifolia (annual grass).

Savanna degradation is an environmental problem occurring in most countries around the world and it poses threats to biodiversity conservation, the food industry, and other economic sectors. According to FAO, South Africa’s rangelands exhibit the highest rate of fragmentation in comparison to range ecosystems in neighbouring countries including Lesotho and Swaziland, and consensus among researchers is that communal rangelands are more degraded than commercial rangelands. Although researchers and communities have identified the occurrence of land degradation in communal savannas at a local scale, land degradation has been poorly estimated because little has been done to quantify the extent and dynamics of perceived and observed changes associated with land degradation. The main goal of this study is to provide empirical insights on the direction of changes in the communal savannas of Nkonkobe Local Municipality in order to inform policy formulation and implementation. Additional to the communal sites is a private farm included for comparative analysis of trends in communal and commercial savannas. Landsat imagery was used to map, assess, and quantify the extent of land degradation in Nkonkobe Local Municipality, over a period of 30 years between 1984 and 2014. Field investigations were undertaken in June 2015 to acquire reference data to guide supervised classification of Landsat images. Three algorithms (Mahalanobis-distance, Minimum-distance, and Maximum likelihood classification) were compared to identify a classifier that produced the best results. The maximum likelihood classifier produced the best results with classification accuracy levels of 95.24 percent, 89.66 percent, and 95.65 percent for Honeydale Farm, Thyume, and Sheshegu respectively. Regression analysis revealed that both communal and private lands have experienced statistically significant increases in bush encroachment and decreases in surface water. Communal savannas have been confronted more by expansion of built-up area, decrease in open grassland, abandonment of arable land, soil erosion, and a steady invasion by Acacia Karroo compared to the privately owned commercial farm. The land cover changes measured through this investigation suggest an environmental shift that threatens biodiversity and agricultural activity. The study provides empirically informed insights about the direction to which these savannas are changing with the hope that the findings will prompt formulation and implementation of effective policies.

Thesis (MTech. degree in Nature Conservation)--Tshwane University of Technology, 2011. / The study was conducted on the Botsalano Game Reserve with the support of the North West Tourism and Parks Agency. No formal management plan is available for the game reserve and therefore the need for an ecological management plan and guidelines for the formulation of a vegetation monitoring plan constituted the basis of the study. The objectives of the study were: 1. To classify and map the plant communities of the Botsalano Game Reserve; 2. To provide quantitative data, collected during a formal vegetation classification, for use by the reserve management in terms of current vegetation condition; 3. To ascertain whether a classification of the vegetation on the BGR could be used for the objective placement of vegetation monitoring sites. Monitoring site placement will be based on representation of plant communities, reflecting community and topographical unit utilization and thus stocking rates based on management decisions.

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.

Thesis (MSc (Conservation Ecology and Entomology)--University of Stellenbosch, 2006. / Swartland Shale Renosterveld is restricted to fertile fine-grained soils in the winter rainfall region of the Western Cape. Between 91% and 97% of this vegetation type is transformed, mostly due to agriculture. Remaining fragments have an irreplaceable conservation value due to a high richness of endemic geophytes. Information on renosterveld vegetation composition and response to disturbance is sparse. Research occurred at three sites near Wellington: Voëlvlei Provincial Nature Reserve (CapeNature), Elandsberg Private Nature Reserve (Elandsberg Farms (Pty.) Ltd.), and Krantzkop munitions factory (Armscor/Somchem) forming a contiguous fragment in the Agter- Groeneberg Conservancy. The primary research aim was to identify or ascertain patterns of plant succession in Swartland Shale Renosterveld and associated different-aged old fields (previously ploughed), with the interaction of grazing. The key research questions are: (1) What are the plant communities of unploughed renosterveld and different-aged old fields which originated in habitats of ploughed renosterveld? (2) What are the most characteristic features of the floristic and ecological relationship between the described plant communities in terms of ecological factors operating within the studied system? (3) Does total species and life-form group richness differ between natural vegetation and old fields? (4) Is life-form richness influenced by ploughing and grazing or the interaction between these disturbances? (5) Is life-form cover-abundance influenced by ploughing and grazing or the interaction between these disturbances? (6) Does alien plant species richness differ amongst seres, and with different levels of grazing intensity? A comparison of life-form richness and cover-abundance of old field vegetation was made with adjacent natural unploughed “controls”. The effects of ploughing on community structure, with the inclusion of grazing was established. These life-form richness comparisons also occur across a gradient of increasing large mammalian herbivore grazing intensity. Sampling was conducted in winter and spring using nested 1000m2 relevés. A hierarchical classification, description and floristic interpretation of renosterveld and old field vegetation were made using TWINSPAN, SYN-TAX 2000 and CANOCO. The samples were classified with TWINSPAN and two communities were described at the association level, namely: Ursinia anthemoides–Cynodon dactylon Grassland Community (with two variants) and the Pterygodio catholici–Elytropappetum rhinocerotis Shrubland Community (with two subassociations), respectively. The vegetation data were further hierachically classified using SYNTAX 2000 which revealed similar clustering of sample objects to that resulting from classification and ordination. Following ordination of sample objects with CANOCO, select groups of species were used to depict their response curves in relation to seral development. Briefly it was found that the effects of grazing vs. non-grazing was more pronounced on old fields than in unploughed vegetation. Overall total species and life-form richness was reduced by ploughing with old fields requiring a recovery period of 30 years to resemble unploughed vegetation. Keywords: Swartland Shale Renosterveld, phytosociology, vegetation patterns, life-forms, succession, disturbance, ploughing, grazing, old fields.

Thesis (MSc) -- University of Stellenbosch, 2004. / ENGLISH ABSTRACT: This thesis focuses on the effects of vegetation resting on biodiversity and community dynamics at Rocherpan Nature Reserve (320 36'S, 180 18'E) in the semi-arid coastal strip of the Succulent Karoo known as Strandveld. As a whole, the Succulent Karoo has an extraordinary high level of phyto diversity with high levels of endemism. This is particularly true for succulent shrubs belonging to the groups Mesembryanthemaceae, Crassulaceae and Asteraceae. The thesis begins with an investigation into effects that vegetation resting has on plant diversity. The aim was to determine if resting affected biodiversity levels and if so, which plant groups are affected and why. Through a numerical approach, it was determined that with resting overall species richness remained the same. However, different plant life forms responded to resting differently. With increased resting, abundance of succulent shrubs decreased, while richness of annuals increased. The second aspect under investigation was to determine how resting the vegetation affected community dynamics. The aim was to understand how vegetation structure and interspecific associations changed with resting and to apply these findings to known community models. Through an autocorrelation approach, it was found that horizontal patterning of long-lived woody species, that formed distinctive vegetation clumps, did not change with resting, while differences were found in woody matrix species and succulent species. These changes in structure were investigated further through a study on the demography of specific species. Demography of woody species associated with vegetation clumps did not change with vegetation resting, while significant changes were observed for woody matrix species and succulent species. In longer rested vegetation, woody matrix species showed a greater range in size class distribution (i.e. had both very large and smaller plants) with the tendency towards larger plant sizes. Succulents on the other hand, had a smaller range in size class distribution with a tendency towards larger plants. For all species investigated there were low seedlings counts. It was concluded that succulent shrub populations were 'mature' and continued resting could result in local extinction of some species due to the lack of regeneration. The overall lack of seedlings was attributed to a saturated establishment environment. Implications for conservation management were discussed. / AFRIKAANSE OPSOMMING: Hierdie tesis fokus op die gevolge van plantegroeirus op biodiversiteit en gemeenskapsdinamika by die Roeherpan Natuurreservaat (320 36'S, 180 18"0) in die halfdor kusstrook van die Sukkulente Karoo, bekend as die Sandveld. In die geheel gesien het die Sukkulente Karoo 'n buitengewone hoë vlak plantdiversiteit met hoë vlakke endemie. Dit is veral waar vir sukkulente struike wat tot die groepe Mesembryanthemaceae, Crassulaceae en Asteraceae behoort. Hierdie tesis ondersoek eerstens die gevolge wat plantegroeirus op plantdiversiteit het. Die doel was om te bepaal of rus die biodiversiteitsvlakke beïnvloed het en indien wel, watter plantgroepe en waarom. Deur middel van 'n numeriese benadering is bepaal dat die algehele diversiteit, numeries gesproke, met plantegroeirus dieselfde gebly het. Verskillende plantlewensvorme het egter verskillend gereageer. Met toenemende rus het die diversiteit van sukkulente struike afgeneem, terwyl die diversiteit van jaarplante verhoog het. Die tweede aspek wat ondersoek is, was om te bepaal hoe die plantegroeirus die dinamika van die omgewingsgemeenskap beïnvloed het. Die doel was om te verstaan hoe die struktuur van die plantegroei en die interspesifieke assosiasies verander het met rus en om dan hierdie bevindinge toe te pas op bekende gemeenskapsmodelle. Deur middel van 'n outokorrelasiebenadering is gevind dat die horisontale patrone van meerjarige houtagtige spesies wat in duidelik-uitkenbare plantegroeigroeperings voorkom, nie met rus verander het nie. Veranderinge is egter wel in die houtagtige matriksspesies en die sukkulente spesies waargeneem. Hierdie veranderinge in struktuur is verder ondersoek deur 'n studie te maak van die demografie van spesifieke spesies. Daar is gevind dat die demografie van houtagtige spesies geassosieer met plantegroeigroeperings nie met plantegroeirus verander het nie, maar beduidende veranderinge is waargeneem in die geval van houtagtige matriksspesies en sukkulente spesies. By plantegroei wat langer gerus het, het die houtagtige matriksspesies 'n wyer verspreiding in klasgroottes vertoon (d.i. daar was baie groot plante én kleiner plante) met 'n gemiddelde afname in plantgrootte. Sukkulente, aan die ander kant, het 'n kleiner verspreiding in klasgroottes vertoon met 'n neiging tot groter plante. Vir al die spesies wat ondersoek is, was daar lae saailingtellings. As gevolg van die "volwassenheid" van die populasies van sukkulente struike, sou voortdurende rus, weens die gebrek aan regenerasie, kon lei tot die plaaslike uitwissing van sommige spesies. Die algemene gebrek aan saailinge is toegeskryf aan die versadigde vestigingsomgewing. Die implikasies VIr natuurbewaringsbestuur word bespreek. v

Thesis (MSc)--University of Stellenbosch, 2005. / ENGLISH ABSTRACT: Invasive alien trees, especially Acacia species, are a great threat to biodiversity in South African rivers. The national Working for Water Programme is addressing the alien problem by removing alien trees from river margins. The concern is that this may be creating even further disturbance by affecting water quality and habitats. In particular, how is this affecting rare and endemic species? Benthic macro invertebrates and aerial odonates were assessed along five Western Cape rivers in alien-invaded, cleared and natural sites between December and March. The aim was to assess the effect of both alien invasion and alien clearing on aquatic invertebrates. Odonata, being easily sampled, were also assessed as they are severely affected by the lack of understorey plants in shaded, alien-invaded sites. Odonata and benthic macroinvertebrates were treated as two separate studies and no attempt was made to correlate the results obtained from both studies. SASS5, a qualitative, rapid bioassessment technique, based on the sensitivity of the families present, was used as a measure of river health and, indirectly, of water quality. SASS indicated a decline in water quality conditions after alien clearing, a likely response to the greater insolation as well as erosion of cleared banks, resulting in elevated temperatures and suspended solids and lowered oxygen levels. Community responses to alien disturbance and other environmental factors were analysed using PRIMER and CANOCO software. Assemblages of Odonata were found to provide a rapid, cost-effective means of assessment and monitoring. Potential indicator and detector species were also identified using the lndicator Value method. Assemblage patterns of aquatic invertebrates, however, were dominated by between-river and seasonal effects. Therefore, while SASS detected overall changes in river health, without identifying the cause, potential aquatic detector taxa were identified that may be useful for linking general disturbance to alien invasion or clearing. All indicator and detector taxa identified in both studies can be used for long-term monitoring and for identifying biodiverse areas for clearing or protection. In both studies, sensitive, endemic taxa were lost after clearing, being replaced by more tolerant, widespread taxa. Recovery of the biota appears to follow the recovery succession of the vegetation, with most sensitive or endemic taxa only appearing after the recovery of indigenous plants. A number of recommendations are made regarding the restoration of both water quality (particularly with respect to shade and soil erosion) and biotope availability (particularly in terms of the recultivation of indigenous plants) in order to achieve biodiversity objectives. The role of catchment management, prioritisation procedures and long-term monitoring are also discussed. / AFRIKAANSE OPSOMMING: Uitheemse, indringerbome, veral Acacia spesies, is 'n groot bedreiging vir biodiversiteit in Suid- Afrikaanse riviere. Die nasionale Werk vir Water-projek spreek hierdie probleem aan deur uitheemse bome van rivieroewers te verwyder. Die kommer is dat water kwaliteit en habitatte sodoende verder versteur kan word. Byvoorbeeld, hoe word endemiese en bedreigde spesies geraak? Akwatiese makroinvertebrate en volwasse Odonata in vyf Wes-Kaapse riviere is tussen Desember en Maart bestudeer en gemonster in natuurlike gebiede, in gebiede waar indringerbome teenwoordig is, en in gebiede waar hulle verwyder is. Die doel was om die effek van indringerverwante impakte op akwatiese invertebrate vas te stel. Odonata is ook bestudeer omdat hulle maklik gemonster kan word en omdat hulle ernstig geraak word deur indringers. Die uitheemse plantegroei oorskadu die oewers en verhoed die groei van inheemse oewerplante. Die bentiese makro-invertebrate en Odonata is as twee aparte studies behandel en geen poging is gemaak om die resultate van die twee te vergelyk nie. SASSS, 'n kwalitatiewe, bioasseseringsmetode wat op die sensitiwiteit van die aanwesige families baseer word, is gebruik om waterkwaliteit op 'n indirekte manier te bepaal. SASS het aangedui dat daar 'n afname in waterkwaliteit is nadat indringerplante verwyder is. Dit is moontlik as 'n gevolg van groter blootstelling aan sonskyn en erosie van rivieroewers wat veroorsaak dat temperature en die hoeveelheid gesuspendeerde materiaal verhoog word, en dat suurstof konsentrasies verminder word. Die gevolge van indringerplante en ander omgewingsfaktore op akwatiese gemeenskappe is met PRlMER en CANOCO sagteware ontleed. Groepering van Odonata kan gebruik word om op 'n maklike en koste-effektiewe manier om die impak van indringerplante en hul verwydering te bepaal en te monitor. Aanwyserspesies is ook deur middel van die 'Indicator Value' metode geïdentifiseer. Die verspreidingspatrone van invertebraatspesies word deur geografiese en seisoenale effekte oorheers. Dus, terwyl SASS veranderinge in waterkwaliteit kan aantoon, sonder om die oorsaak daarvan te identifiseer, kan aanwyserspesies gebruik word om meer spesifieke impakte deur indringerplantegroei, of indringerverwydering, te bepaal en te monitor. Hulle kan ook gebruik word om gebiede met hoë biodiversiteit vir bewaring of indringerverwydering te identifiseer. Beide studies dui aan dat sensitiewe en endemiese taksa na indringerverwydering verlore gaan, en vervang word met meer geharde, wydverspreide taksa. Herstel van die biota volg op die herstel van die plant gemeenskappe, en die mees sensitiewe of endemiese taksa herstel eers nadat die inheemse plantegroei herstel het. 'n Aantal aanbevelings in verband met die restorasie van waterkwaliteit (veral in terme van die hoeveelheid skaduwee en erosie) en die beskikbaarheid van biotope (veral in terme van inheemse plante) om biodiversiteitsdoelwitte te bereik word gemaak. Die rol van opvanggebied bestuur, voorrang prosedures en lang termyn monitering word ook bespreek.

Thesis (MSc)--Stellenbosch University, 2004. / ENGLISH ABSTRACT: Bush encroachment in savannas leads to reduced diversity, productivity and profitability of rangelands. This holds important implications for the livestock and eco-tourism industries, as well as for subsistence ranchers in the South African semi-arid savannas, who depend on this vegetation type for economic and livelihood purposes. Soil moisture, nutrients, rue and herbivory are generally regarded as the principal factors determining vegetation structure and function within savannas. The factors and processes involved in the determination of the tree:grass ratio within savannas are, however, not clearly understood. We investigated the role of soil type and management strategy (cattle, game and communal grazing) in the determination of the presence and distribution of plant species in general, and on the presence and distribution of the encroaching tree species, Acacia mellifera, specifically. Both shortand long-term trends were investigated. The study area, the Kimberley Triangle, (Northern Cape Province, South Africa), was ideal for this kind of study because it has different management strategies practised on several soil types, and bush encroachment is a widespread phenomenon. Contrary to the belief that heavy livestock grazing is the main cause of increases in the tree:grass ratio, we found that soil type, through its effects on plant growth and on the presence and availability of soil moisture and nutrients, is more important in determining vegetation composition than management strategy. It was found that the various types of grazing management mainly influenced vegetation structure and function by affecting the competitive interactions between Ns-fixing woody species and non-Ns-fixing grasses. Of the soil factors affecting vegetation composition, soil texture was a good indicator of the physical conditions for plant growth in an area, and also of the presence and availability of soil moisture and nutrients. We found that sand and clay soils are relatively resistant to bush encroachment as compared to loamy-sand and -clay mixes. This is because woody growth is impaired in the first-mentioned habitats by soil texture, soil moisture regimes and heavy utilisation. In soils with combinations of loam, sand and clay, soil texture and moisture are not limiting to woody growth and if the repressive competitive effect of grasses on woody vegetation is removed, opportunities are created for recruitment of woody species and encroachment. Additionally, rockiness increases soil moisture infiltration. In the study area, woody species, and specifically A. mellifera, are associated with these areas. We suggest that in the study area, rocky areas are naturally encroached. This is in agreement with the patchdynamic approach to savanna vegetation dynamics. Because soil moisture is such an important factor in the determination of the tree:grass ratio in the study area, we further suggest that in above-average rainfall years, when soil moisture conditions are optimal for woody seed germination, establishment and growth, heavy grazing should be avoided, as it would provide the opportunity for encroachment. Keywords: Bush encroachment; N2-fixing species; game, cattle, communal grazing; soil texture; soil moisture; soil nutrients; Acacia mellifera; tree-grass competition. / AFRIKAANSE OPSOMMING: Bosindringing in savanna gebiede het verlaagde diversiteit, produktiwiteit en winsgewendheid van natuurlike weivelde tot gevolg. Behalwe dat dit die Suid-Afrikaanse vee- en ekotoerisme bedrywe raak, is verskeie bestaansboerderye afhanklik van die plantegroei-tipe vir oorlewing. Grondvog, grondvoedingstowwe, vuur en beweiding word algemeen aanvaar as die belangrikste faktore wat die struktuur en funksie van savannas bepaal. Daar is egter nog nie duidelikheid oor die prosesse wat betrokke is in die bepaling van die boom-gras verhouding in savannas nie. In dié studie het ons ondersoek ingestel na die invloed van grond tipe en beweidingstrategieë (beweiding deur beeste, wild, of kommunale beweiding) op die algemene verspreiding van verskillende plant spesies, en ook op die van die indringer spesie, Acacia mellifera. Beide kort- en lang-termyn patrone is ondersoek. Die studiegebied, die Kimberley Driehoek in die Noord-Kaap, Suid-Afrika, was ideaal vir so 'n ondersoek omdat verskillende beweiding strategieë op verskeie grond-tipes beoefen word maar bosindringing steeds 'n algemene verskynsel in die gebied is. Ons bevinding was dat, ten spyte van die feit dat daar oor die algemeen geglo word dat swaar beweiding die hoof oorsaak van bosindringing is, grond-tipe belangriker is in die bepaling van die spesie-samestelling van 'n gebied. Dit is as gevolg van die feit dat grond-tipe die groei van plante beïnvloed deur die teenwoordigheid en beskikbaarheid van grondvog en -nutriënte te bepaal. Die verskillende beweidingstrategieë beïnvloed meerendeels die kompetatiewe interaksies tussen N2-bindende hout-agtige spesies teenoor nie-Nj-bindende gras-agtige spesies. Grond-tekstuur was 'n goeie aanduiding van die algemene toestande vir plantegroei en ook van die teenwoordigheid en beskikbaarheid van grondvog en -nutriënte. Ons het bevind dat sand en klei grond, relatief tot leem, sand en klei kombinasies, weerstandbiedend is teen bosindringing as gevolg van die tekstuur, water-regimes en swaar beweidings vlakke wat op die grond-tipes voorkom. Omdat grond-tekstuur en grondvog nie beperkend is op die leem-, sand- en klei-grond kombinasies nie, kan bosindringing maklik hier voorkom as die onderdrukkende effek wat grasse op houtagtige plantegroei het, deur swaar beweiding verwyder word. A. mellifera is ook oor die algemeen met klipperige gebiede geassosieer omdat klipperigheid lei tot verhoogde infiltrasie van grondvog. In die studie-gebied is klipperige areas dan ook van nature ingedring deur A. mellifera. Dit stem ooreen met die siening dat savannas bestaan uit "laslappe" van verskillende plantegroei (patch-dynamic approach). Dit was duidelik dat grondvog 'n belangrike bepalende faktor is in die bepaling van die boom-gras verhouding in die studiegebied. Ons stel dus voor dat in bo-gemiddelde reënval jare, swaar beweiding vermy moet word, omdat houtagtige saailinge gedurende die tydperke maklik kan ontkiem en vestig juis omdat grondvog dan nie beperkend is nie. Sleutelwoorde: Bosindringing; N2-bindende spesies; bees, wild, kommunale beweiding; grond tekstuur; grond-vog; grond-nutriënte; Acacia mellifera; boom-gras kompetisie.