Globally, changes in plant community structure have occurred in ecosystems where humans have altered natural disturbance regimes. Many plants have adaptive life histories and morphological traits that have coevolved with fire and herbivory, which allows them to thrive despite repeated tissue losses. Therefore, altering the type, frequency, or severity of disturbance affects individual plant growth and competition among species. When these changes benefit or disadvantage different plant functional groups (i.e., grasses, shrubs, trees) it alters ecosystem structure and function. Understanding and predicting these vegetation changes, is critical for conservation and management of biodiversity, wildlife habitat, livestock forage, and water. Savannas are characterized by the codominance of grasses and trees, but the proportion of tree cover responds dynamically to changes in precipitation, fire, and herbivory. These factors often cause a ‘demographic bottleneck,’ which delays transitions from sapling size (1 m). In this dissertation, I investigated several fire × herbivory interactions to gain a mechanistic understanding of sapling recruitment processes that ultimately affect savanna structure. I made use of a long-term experiment that used semi-permeable fencing to manipulate presence and absence of different types of herbivores, to explore how fire and different combinations of domestic cattle, meso-wildlife, and megaherbivores (elephant and giraffe) affect sapling recruitment. First, I found clear evidence that a wide range of tree height classes resprout after being top-killed by fire, but they were all subsequently kept short by meso-wildlife browsing. Elephants played a key role in suppressing the largest resprouts after fire possibly because fire had reduced the presence of ant mutualists that defend the trees. Second, I found that in the absence of fire, cattle and wildlife indirectly affected saplings by altering competition with neighboring vegetation. Saplings competed with grass and trees during above-average rainfall years. Bare ground—a condition often caused by overgrazing—was positively associated with sapling growth. The highest sapling growth, however, occurred where large neighbor trees were absent, a condition maintained primarily by elephants browsing and damaging large neighbor trees. Finally, I found that saplings conditioned by pre-fire wildlife “browsing legacies” had high tolerance to combined fire and wildlife browsing. These results help explain how saplings tolerate repeated tissue loss to disturbance. Understanding how interactions between fire and herbivory affect sapling recruitment will help managers effectively use natural disturbance processes to manage savanna structure and function.

Thesis (M. Environmental Science)--North-West University, Potchefstroom Campus, 2008.

Thesis (M. Environmental Science)--North-West University, Potchefstroom Campus, 2008.

Thesis (M. Environmental Science)--North-West University, Potchefstroom Campus, 2008.

Land degradation is a process that causes the reduction in resource potential of natural rangelands and occurs widespread throughout southern Africa. This process is mainly characterized by the loss in vegetation cover, which leads to the occurrence of bare and denuded patches, increased soil erosion, changes in species composition as well as bush encroachment by indigenous and alien invasive plant species in savannah areas. Degradation of rangelands has drastically extended at an alarming rate during the last few decades with the main causes being overstocking, extended periods of drought, global climate change, overgrazing and general mismanagement of the land. Many researchers, however, feel that rangeland degradation is mainly caused by a combination of changes in land use practices and climate variability. Land users have, however, been applying a variety of technologies over the years in order to restore affected rangelands and mitigate the effect of degradation. These technologies include passive and active intervention methods, aimed at restoring bare and denuded areas and controlling indigenous bush and alien plant species encroachment. Bush control can be carried out by applying different technologies, involving chemical, mechanical, manual or biological control. The focal point of this study is on bush encroachment, the factors causing the problem, the possible ways of controlling this phenomenon and lastly the incorporation of such information into a user-friendly Decision Support System (DSS). The Decision Support System comprises of two databases as well as a related expert system. Bush encroachment is a matter of great concern in most southern African countries. This study therefore mainly included data from Namibia and to a lesser extent, South Africa, as the main study areas, seeing that this form of degradation greatly influences the biodiversity of rangelands in both these countries. The Namibia Agricultural Union (NLU) identified the need for the development of a user-friendly Decision Support System, in which case studies concerning the different bush control technologies could be stored in a database. Restoration technologies, regarding the occurrence of bare and denuded areas, that have been applied by the land users over a period of time and in a specific environment in the past, have been captured in a computerized database and expert system, serving as a Decision Support System (DSS) and user-friendly consulting tool in a similar study, carried out by Mr. Van der Merwe (1997). This DSS was based on CBR (Case Based Reasoning) methodologies by which a number of case studies, that have previously been stored in the database, can be searched by means of an expert system approach to advise the land user concerning the most appropriate solution (action) to similar degradation problems. The DSS developed by Mr. Van der Merwe was never published or made accessible to the land user in a format that could be consulted by either CD-ROM or the internet. Seeing that the NLU identified the need for a similar DSS containing bush control technologies, it was decided to incorporate both these databases into a single DSS, concerning bush control as well as the restoration of bare and denuded patches. The newly converted DSS is currently known as EcoRestore and consists on two databases: Grass Expert, which focuses on technologies to reclaim degraded rangelands, and Bush Expert, which is more focused on the control of bush encroachment and combating of alien invasives. As mentioned, this study focussed on the development of the Bush Expert database and will therefore only include results, discussions and conclusions of these case studies. The case studies in the Bush Expert database consist of results obtained by means of a questionnaire completed by the land user, in collaboration with the agricultural extension officer, as well as a quantitative vegetation assessment, to determine the success rate of the applied technology. The Bush Expert questionnaire, comprises of questions concerning personal information of the land user (e.g. location of the farm), the situation on the farm before bush control was applied (e.g. information on the environmental factors, such as density of problem trees), as well as the type of control technology applied and the situation of the rangeland after control (e.g. establishment of the herbaceous species). The quantitative vegetation assessments involved the sampling of the woody and herbaceous components in the area where a specific control technology was applied. The density and height classes of the woody component were determined by means of the belt-transect method. By using the descending-point method, the herbaceous component was surveyed to determine the abundance/frequency of the annual and perennial grass species. In order to increase the success of any restoration project, it is important to take the existing indigenous knowledge of local land users, concerning the problem of degradation and mitigation thereof, into consideration. By doing so, the local people and communities have greater control and responsibility over their resources and are able to command a greater range and level of resourcefulness. Taking indigenous knowledge into consideration finally enables the local land users to actively participate in and influence higher-level decision-making processes by which they are affected. A total of 175 case studies in Namibia and nine case studies in South Africa were surveyed. The Namibian case studies were surveyed in the central and northern arid and semi-arid regions, and South African case studies in a limited location within the Limpopo Province. Only 100 of the Namibian case studies have thus far been incorporated into the Bush Expert database. Multivariate data analyses techniques, analysis of variance and correlation analyses were used to analyse the data obtained from the questionnaires and quantitative vegetation surveys. Results were represented in the form of histogrammes, tables and multivariate analysis ordinations. From the results obtained for the Bush Expert database, it was clear that chemical control technologies were most often applied in Namibian and South African case studies (61%). The herbicides most commonly applied as chemical control technology in Namibia included Grazer (20%) and Savana (15%), whilst in South Africa these included Access (33.3%) and Tordon Super (33.3%). Herbicides were mostly applied by means of aerial application (46%) methods in Namibia and as cut-stump treatment (55.5%) by means of knapsack spraying or with a brush in South Africa. The dominant woody species causing bush encroachment problems in Namibia were found to be Acacia mellifera, Acacia reficiens and Dichrostachys cinerea, whereas in South Africa these species included Dichrostachys cinerea, Acacia erubescens and Acacia karroo. The wood of the controlled problem species (dead woody material) is mostly not utilized after control, but rather left on the land to disintegrate and thus contribute to the organic material content in the soil. Dead branches are also used for brush packing, which forms and ideal micro-climate for the germination and establishment of grass seeds, which serves as an erosion control medium and protects grass seedlings against grazing impacts. Some land users do however produce charcoal from certain controlled woody species, in order to recover some of the input costs of bush control. The majority of the case study sites (68%) in Namibia occurred within the 300-450 mm short- and long-term rainfall zones and in South Africa the majority of case study sites occurred within the short-term rainfall zone of 550-600 mm (66.6%) and 400- 500 mm long-term rainfall zone (55.5%). Case studies where chemical and manual bush control technologies were applied indicated the highest success rates after control (81.7% and 75.2% respectively). Success rate as an entity was greatly influenced by the type of control technology applied, the density of the problem woody species after bush control as well as environmental variables such as rainfall and soil clay percentage. No definite trend could be determined concerning the application of a specific bush control technology and a certain problem species. Land users tend to apply a chosen control technology, according to the resources available, such as labour, mechanical implements and finances. The only positive correlation between control technologies and the type of problem species could be found regarding Dichrostachys cinerea. This species was mainly chemically controlled by means of the application of certain herbicides. The most important lesson to be learnt from the surveys completed in the two countries is that it is an absolute necessity to apply a proper after-care programme as a management practice following the initial control of problem woody species. The implementation of after-care determines the final success rate of any applied bush control technology as a restoration practice within a rangeland. Only 11% of the case studies surveyed for Namibia and South Africa indicated the implementation of an after-care programme, which usually involved biological control (e.g. browsing by boer goats or the use of controlled or accidental natural veld fires). The EcoRestore Decision Support System is currently available as an online webversion (www.puk.ac.za/EcoRestore), as well as a CD-ROM version. The CD-ROM version is available in a package containing the CD and user's manual. An example of the package is included in this dissertation. In consulting the databases through question-and-answer procedures, the best action will be proposed to the land user for future rangeland restoration, either the reclamation of denuded areas or the control of bush encroachment. Since the case studies are based on past and existing experiences and research, the land user will have an indication of the expected outcome, should the same advised technology be applied. The EcoRestore DSS does not only offer a consulting tool for extension workers and technicians, but also creates networking and participation between land users and researchers, both locally and between neighbouring countries. The DSS is linked to other national and international websites and databases, to offer users a wider range of information and technologies with regard to agricultural and conservation practices. Better awareness is created amongst land users concerning the problem of rangeland degradation, which might encourage closer monitoring of the degradation and mitigation processes. The EcoRestore DSS was developed in such a way for it to be as user-friendly as possible, in order to reach as many parties involved in current or future restoration programmes. This study involved the development of the first version of the DSS (Version 1.0) and is thus only the prototype system. It is proposed that the Bush Expert database of the EcoRestore DSS, will be expanded in future and additional bush control case studies from other southern African countries will be included. The addition of such case studies will ultimately increase the effectivity of this DSS. / Thesis (M.Sc. (Botany))--North-West University, Potchefstroom Campus, 2004.

Land degradation is a process that causes the reduction in resource potential of natural rangelands and occurs widespread throughout southern Africa. This process is mainly characterized by the loss in vegetation cover, which leads to the occurrence of bare and denuded patches, increased soil erosion, changes in species composition as well as bush encroachment by indigenous and alien invasive plant species in savannah areas. Degradation of rangelands has drastically extended at an alarming rate during the last few decades with the main causes being overstocking, extended periods of drought, global climate change, overgrazing and general mismanagement of the land. Many researchers, however, feel that rangeland degradation is mainly caused by a combination of changes in land use practices and climate variability. Land users have, however, been applying a variety of technologies over the years in order to restore affected rangelands and mitigate the effect of degradation. These technologies include passive and active intervention methods, aimed at restoring bare and denuded areas and controlling indigenous bush and alien plant species encroachment. Bush control can be carried out by applying different technologies, involving chemical, mechanical, manual or biological control. The focal point of this study is on bush encroachment, the factors causing the problem, the possible ways of controlling this phenomenon and lastly the incorporation of such information into a user-friendly Decision Support System (DSS). The Decision Support System comprises of two databases as well as a related expert system. Bush encroachment is a matter of great concern in most southern African countries. This study therefore mainly included data from Namibia and to a lesser extent, South Africa, as the main study areas, seeing that this form of degradation greatly influences the biodiversity of rangelands in both these countries. The Namibia Agricultural Union (NLU) identified the need for the development of a user-friendly Decision Support System, in which case studies concerning the different bush control technologies could be stored in a database. Restoration technologies, regarding the occurrence of bare and denuded areas, that have been applied by the land users over a period of time and in a specific environment in the past, have been captured in a computerized database and expert system, serving as a Decision Support System (DSS) and user-friendly consulting tool in a similar study, carried out by Mr. Van der Merwe (1997). This DSS was based on CBR (Case Based Reasoning) methodologies by which a number of case studies, that have previously been stored in the database, can be searched by means of an expert system approach to advise the land user concerning the most appropriate solution (action) to similar degradation problems. The DSS developed by Mr. Van der Merwe was never published or made accessible to the land user in a format that could be consulted by either CD-ROM or the internet. Seeing that the NLU identified the need for a similar DSS containing bush control technologies, it was decided to incorporate both these databases into a single DSS, concerning bush control as well as the restoration of bare and denuded patches. The newly converted DSS is currently known as EcoRestore and consists on two databases: Grass Expert, which focuses on technologies to reclaim degraded rangelands, and Bush Expert, which is more focused on the control of bush encroachment and combating of alien invasives. As mentioned, this study focussed on the development of the Bush Expert database and will therefore only include results, discussions and conclusions of these case studies. The case studies in the Bush Expert database consist of results obtained by means of a questionnaire completed by the land user, in collaboration with the agricultural extension officer, as well as a quantitative vegetation assessment, to determine the success rate of the applied technology. The Bush Expert questionnaire, comprises of questions concerning personal information of the land user (e.g. location of the farm), the situation on the farm before bush control was applied (e.g. information on the environmental factors, such as density of problem trees), as well as the type of control technology applied and the situation of the rangeland after control (e.g. establishment of the herbaceous species). The quantitative vegetation assessments involved the sampling of the woody and herbaceous components in the area where a specific control technology was applied. The density and height classes of the woody component were determined by means of the belt-transect method. By using the descending-point method, the herbaceous component was surveyed to determine the abundance/frequency of the annual and perennial grass species. In order to increase the success of any restoration project, it is important to take the existing indigenous knowledge of local land users, concerning the problem of degradation and mitigation thereof, into consideration. By doing so, the local people and communities have greater control and responsibility over their resources and are able to command a greater range and level of resourcefulness. Taking indigenous knowledge into consideration finally enables the local land users to actively participate in and influence higher-level decision-making processes by which they are affected. A total of 175 case studies in Namibia and nine case studies in South Africa were surveyed. The Namibian case studies were surveyed in the central and northern arid and semi-arid regions, and South African case studies in a limited location within the Limpopo Province. Only 100 of the Namibian case studies have thus far been incorporated into the Bush Expert database. Multivariate data analyses techniques, analysis of variance and correlation analyses were used to analyse the data obtained from the questionnaires and quantitative vegetation surveys. Results were represented in the form of histogrammes, tables and multivariate analysis ordinations. From the results obtained for the Bush Expert database, it was clear that chemical control technologies were most often applied in Namibian and South African case studies (61%). The herbicides most commonly applied as chemical control technology in Namibia included Grazer (20%) and Savana (15%), whilst in South Africa these included Access (33.3%) and Tordon Super (33.3%). Herbicides were mostly applied by means of aerial application (46%) methods in Namibia and as cut-stump treatment (55.5%) by means of knapsack spraying or with a brush in South Africa. The dominant woody species causing bush encroachment problems in Namibia were found to be Acacia mellifera, Acacia reficiens and Dichrostachys cinerea, whereas in South Africa these species included Dichrostachys cinerea, Acacia erubescens and Acacia karroo. The wood of the controlled problem species (dead woody material) is mostly not utilized after control, but rather left on the land to disintegrate and thus contribute to the organic material content in the soil. Dead branches are also used for brush packing, which forms and ideal micro-climate for the germination and establishment of grass seeds, which serves as an erosion control medium and protects grass seedlings against grazing impacts. Some land users do however produce charcoal from certain controlled woody species, in order to recover some of the input costs of bush control. The majority of the case study sites (68%) in Namibia occurred within the 300-450 mm short- and long-term rainfall zones and in South Africa the majority of case study sites occurred within the short-term rainfall zone of 550-600 mm (66.6%) and 400- 500 mm long-term rainfall zone (55.5%). Case studies where chemical and manual bush control technologies were applied indicated the highest success rates after control (81.7% and 75.2% respectively). Success rate as an entity was greatly influenced by the type of control technology applied, the density of the problem woody species after bush control as well as environmental variables such as rainfall and soil clay percentage. No definite trend could be determined concerning the application of a specific bush control technology and a certain problem species. Land users tend to apply a chosen control technology, according to the resources available, such as labour, mechanical implements and finances. The only positive correlation between control technologies and the type of problem species could be found regarding Dichrostachys cinerea. This species was mainly chemically controlled by means of the application of certain herbicides. The most important lesson to be learnt from the surveys completed in the two countries is that it is an absolute necessity to apply a proper after-care programme as a management practice following the initial control of problem woody species. The implementation of after-care determines the final success rate of any applied bush control technology as a restoration practice within a rangeland. Only 11% of the case studies surveyed for Namibia and South Africa indicated the implementation of an after-care programme, which usually involved biological control (e.g. browsing by boer goats or the use of controlled or accidental natural veld fires). The EcoRestore Decision Support System is currently available as an online webversion (www.puk.ac.za/EcoRestore), as well as a CD-ROM version. The CD-ROM version is available in a package containing the CD and user's manual. An example of the package is included in this dissertation. In consulting the databases through question-and-answer procedures, the best action will be proposed to the land user for future rangeland restoration, either the reclamation of denuded areas or the control of bush encroachment. Since the case studies are based on past and existing experiences and research, the land user will have an indication of the expected outcome, should the same advised technology be applied. The EcoRestore DSS does not only offer a consulting tool for extension workers and technicians, but also creates networking and participation between land users and researchers, both locally and between neighbouring countries. The DSS is linked to other national and international websites and databases, to offer users a wider range of information and technologies with regard to agricultural and conservation practices. Better awareness is created amongst land users concerning the problem of rangeland degradation, which might encourage closer monitoring of the degradation and mitigation processes. The EcoRestore DSS was developed in such a way for it to be as user-friendly as possible, in order to reach as many parties involved in current or future restoration programmes. This study involved the development of the first version of the DSS (Version 1.0) and is thus only the prototype system. It is proposed that the Bush Expert database of the EcoRestore DSS, will be expanded in future and additional bush control case studies from other southern African countries will be included. The addition of such case studies will ultimately increase the effectivity of this DSS. / Thesis (M.Sc. (Botany))--North-West University, Potchefstroom Campus, 2004.

Bush encroachment is a major problem for the savannas supporting livestock in the Eastern Cape. Farmers employ chemical poisoning and mechanical clearing of woody vegetation to improve grass production. This thesis addressed the following questions. 1. Does soil fertility and hence, herbaceous production and/or quality increase beneath or between former bushclumps following woody clearing or poisoning? 2. Are chemical or mechanical control methods effective for all woody species? 3. Does bush density and height decline with increasing competition from the herbaceous layer? 4. Can fire and goats retard or revert woody re-establishment, thereby keeping these savannas open? A trial for assessing different methods of controlling bush was conducted near Kei Road. Initial treatments included chemical poisoning, mechanical clearing and a control, each replicated eight times in 0.36 hectare plots. Follow-up treatments were control, fire, goats, and the combination of fire and goats each replicated twice per primary treatment. Two additional mechanically cleared plots were oversown with Chloris gayana seeds. Herbaceous production, species composition, foliage quality and soil fertility, and mortality, recruitment, height increase and density of woody individuals were monitored for five seasons. Mechanical clearing of the woody vegetation increased soil fertility, except total nitrogen, and that explained the dramatic response in grass production that endured for the first four seasons since clearing. The periphery and ex-bushclump zones were characterised by increased colonization of Panicum maximum while there were no changes in frequencies of other key herbaceous species in all vegetation zones. Acacia karroo and woody "weeds" (Solanum incanum, Berkheya bipinnatifida) established from seed while all other woody species recruited mainly from coppicing. Seedling recruitment and resprouting resulted in high densities of woody stems and individuals by the second season after clearing when compared with the pre-clearing levels. Oversowing cleared areas with pasture grasses did not only increase grass production but also reduced the density of coppicing woody plants and "weeds". Chemical treatments mirrored the controls in terms of grass production, except during a very wet season, and species composition. Although encroaching woody species (e.g. Scutia myrtina, Maytenus heterophylla and Trimeria trinervus) were susceptible to poisoning, woody plant density was not reduced. Multi-stemmed woody individuals were resistant to poisoning. Fire and goats kept most coppicing woody plants short, less than half a metre, after three seasons of browsing and also improved grass production in the dense bushclumps suggesting that these clumps were being opened up. However, high browsing pressure forced goats to graze more hence this effect was masked. This study indicates that chemical and mechanical control of bush are economically unsustainable for beef and mutton production, at least in the medium term. Fire and goats are appropriate as a follow-up strategy for retarding woody regrowth, keeping bushclumps open, improving grass production and economic viability of mechanical clearing. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 2000.

Thesis (MSc. Agriculture (Remote Sensing)) -- University of Limpopo, 2015 / Savannas are the most important ecosystems for raising livestock in Africa. In the past 50 years, evidence has shown that savannas throughout the world are being altered by bush encroachment. This is an ecological succession process where perennial plants such as shrubs and trees replace annual vegetation. This reduces the amount of palatable fodder and directly threatens livestock productivity in many localities. This study evaluated long-term bush encroachment using multi-date Landsat Thematic Mapper (TM) images 1989, 1990, 1993, 1995, 1999, 2004 and 2008 to reconstruct changes in spatial distribution of trees and shrubs at the Towoomba Reseach Station over a period of 19 years, from 1989 to 2008. Grasses and woody species were classified using unsupervised classification and Normalised Difference Vegetation Index was used to assess forage productivity and change in vegetation with years. The study was carried out at Towoomba Research Station in Bela Bela, Limpopo Province, South Africa. The study revealed that bush encroachment is a natural process and is independent of the grazing patterns. The results show that if not monitored encroaching species will make it difficult for grazers to get underneath the trees and also disturb the photosynthetic process of grass thereby replacing the grass. The study further showed that satellite remote sensing has the potential for monitoring rangeland quality. Keywords: Bush encroachment, remote sensing, classification and Normalised Difference Vegetation Index

Thesis (M.Sc. Agriculture (Pasture Science)) -- University of Limpopo, 2020 / Bush encroachment is a major problem in arid and semi-arid savannas characterized by a grass layer interspersed with a shrub stratum. Land cover change as a result of rapid proliferation of woody species in previously open rangelands alters herbaceous species and impacts soil properties. So far, little is known about the threshold at which woody plant density and cover affects herbaceous cover and the underlying mechanisms driving bush encroachment in arid and semi-arid rangelands are still debated. The objectives of this dissertation were to (1) to assess woody species composition and structure along an encroachment gradient and to explore the relationship between woody vegetation and herbaceous vegetation. (2) To determine the effect of increasing tree density and cover on grass species richness, diversity, evenness and selected soil nutrients in a bush encroached rangeland. In order to address these objectives, a semi-arid rangeland was demarcated into three encroachment gradients spanning from open to intermediate and intensive. Within each encroachment gradient six plots of 10 m x 10 m were randomly selected, whereby woody and herbaceous vegetation were assessed and soil properties determined. A discernible increase in woody species diversity and evenness was found along the transition from open to intensive bush encroached rangeland. Leguminous woody species Vachellia spp. and Dichrostachys cinerea were dominant along the bush encroachment gradient. Tree height was found to be positively correlated with long crown diameter (LCD) and short crown diameter (SCD). Furthermore, increasing tree density resulted in a 53% decline in grass species richness (GR). A decline in GR mirrored an increase in the composition of the decreaser species Panicum maximum (90%). Increasing woody plant density and cover also increased macro-nutrients; total carbon, nitrogen, phosphorus, exchangeable calcium and magnesium by 21%-159% in the shallow rangeland soils. Such quantitative information will assist rangeland managers to better understand the effects of varying bush encroachment intensities on herbaceous species composition, richness and soil properties in semi-arid savanna rangelands.

Thesis (MSc. Agriculture (Pasture Science)) -- University of Limpopo, 2016. / The relationships between tree age, growth rings, and stem circumference correlated with establishment patterns may be a valuable instrument to reveal the functioning of woody species in the Savanna Biome. A study on tree age and establishment patterns of Acacia tortilis in the semi-arid regions of the Limpopo Province was conducted to aid an understanding of the causes of encroachment in savanna vegetation. This study aimed to determine the periodicity of growth ring formation at two study areas, correlate the number of growth rings with different tree characteristics and document tree population establishment patterns of Acacia tortilis, using stem circumferences. This was done in order to predict long-term bush encroachment using the interaction between rainfall and soil on the age, growth and establishment patterns of Acacia tortilis. Data was collected at three sites representing two study areas, two sites at the University of Limpopo’s Syferkuil Agricultural Experimental Farm and one site at the Sondela Nature Reserve in the Limpopo Province. The study incorporated two different soil forms and two rainfall regimes. Trees were divided into five height classes; namely, <0.5 m, >0.5 – 1.5 m, >1.5 – 2.0 m, >2.0 – 3.0 m and >3m. Fifty trees (ten in each class) were felled at each site, and the following recordings were made: tree height, stem circumference and crown diameter. Furthermore, each felled stump was taken to the laboratory and examined for growth rings. The results indicated that growth pattern of Acacia tortilis stems were more influenced by soil form than the amount of rainfall. Tree height was not significantly affected by soil form. However, rainfall proved to have a significant effect on the final height of the plant. Both rainfall and soil form did not have a substantial effect on the number of growth rings. Crown diameter was affected by soil form but rainfall did not prove to have the same effect. Correlations between growth rings and stem circumferences, tree height and crown diameter, proved to have significant relationships. However, the relationship between stem circumference and the number of growth rings was the most significant. iv A prediction model was created using the relationship between stem size and growth rings. Using this model tree age can be determined in a non-destructive manner. However, the absence of a correlation between rainfall and establishment strongly suggests that rainfall cannot be used, on its own, to determine the establishment sequence and the pattern of bush encroachment. The study suggests that natural developments responsible for establishment patterns and population dynamics of woody species are complex, and their effects are visible after an extensive period. Therefore, to understand these influential processes comprehensively, several seasons of observations and monitoring would be recommended. Future research on this particular topic should include more than one encroaching species, because this will provide a broader perspective on the encroachment patterns of bush communities. However, the focus should be on studying the influence of growth limiting factors such as soil and climatic impacts, as well as area-specific environmental factors on the growth of encroaching species, such as Acacia tortilis. Key words: Bush encroachment, dendrochronology, growth rings, tree age, savanna, stem circumference Note: The candidate and the supervisors are aware of the fact that the Acacia genus has been revised. However, in this dissertation, the genus and species Acacia tortilis is still used. Relevant changes will be used in future publications. / University of Limpopo’s Department of Agriculture and National Research Foundation