Subsequent to the impounding of the Pongolo river in the 1970's, development of irrigated agriculture on the Makatini flats has been reducing the area of vegetation available for grazing, and flooding patterns on the seasonally inundated Pongolo River Floodplain have been determined by the controlled release of water from the Pongolapoort dam. About 50 000 people live along the 10 000 ha floodplain within the 63 000 ha northern region of the flats which was studied. This population includes 2 970 registered cattle owners who own a total of 19 300 cattle. The objectives of this study were: to gain an understanding of the Makatini pastoral system which would facilitate prediction of the effects of potential developments, including agricultural expansion, modification of floodplain hydrology and changed cattle management practices on the utility value of cattle; and to provide guidelines for the management of pastoral resources on the Makatini and other traditional African pastoral systems. It was established that the value of cattle cannot be determined without understanding the importance of the subsistence utilities provided and that the value of utilities relative to each other influences the way in which the system is stocked and managed by the local people. The value of all marketed and non-marketed utilities was determined and the implications of the economic evaluation for the identification of management options in African pastoral systems assessed. Despite the "low productivity" of the Makatini system compared to western style ranches, cattle owners receive annual returns worth approximately 100 % of the asset value of their stock. This explains low market offtake rate in this and other subsistence systems. Non-marketed utilities, particularly milk production provide most of the returns to cattle owners. The mean stocking density on the floodplain vegetation was estimated to be three times that of dry-land areas, but only 23 % of all grazing time is spent on the floodplain. Although floodplain forage provides an important supplement to winter grazing, its use is not vital to maintenance of animal condition. The coincident occurrence of an annual "stress period"; greater acceptability of Echinochloa pyramidalis vegetation as forage; the absence of floods; and the reduced use of floodplain fields, results in increased floodplain use in winter to a stocking density approximately ten times that of dry-land areas. How the floodplain hydrology, rainfall and grazing interact with the crop growth rate and quality of E. pyramidalis stands was examined. The forage production potential of E. pyramidalis was found to be higher than that of other floodplain vegetation types and stocking densities of up to 4.5 AU/ha in summer and 2.5 AU/ha in winter are considered possible on the Pongolo floodplain. Echinochloa pastures may become wet and cause scouring if grazed exclusively, but grazing reduces plant moisture content and makes the forage more acceptable. Local pastoral management was found to depend on the collective activities of cattle owners in pursuit of personal needs in a dynamic socio-economic context. Motivation for the manipulation of cattle numbers and herd composition is dictated by a cattle owner's perception of his needs for utilities and his ability to access those benefits. Because of this, the pastoral practices were found to be closely linked to other socio-economic activities such as agriculture and migrant labour. stock owners have a narrow perspective of pastoral resource management and use strategies developed on small spatial and temporal scales. In contrast development planners tend to identify objectives on a regional scale and on long-term (10 - 50 year) time scales and to orient management towards maximising the value of marketable utilities and preventing long-term overstocking. Management of pastoral resources in traditional African systems requires that the needs of local people be met, that the resource base be maintained; that pastoral policy be developed as a component of regional development planning and that close liaison between interest groups be maintained. Failure to establish or maintain this liaison is considered the main reason for the failure of many African pastoral development programmes. It was recommended that local pasture management committees be established on the Makatini and that extension officers, trained specifically to understand management problems of Third World pastoral systems, be used to maintain liaison between stock owners and development planners. It was also suggested that formal cattle camps be established and managed by local people and that at least one flood (river flow> 200 cumecs) be released from the Pongolapoort darn each summer. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 1988.

A series of pot trials were undertaken to test the growth of indigenous grasses (Themeda triandra and Cynodon dactylon) on mine capping soil, treated with various soil ameliorants. The capping soils were obtained from open cast coal mines (Optimum Mine and Syferfontein Mine) in the Mpumalanga Highveld, south of Witbank. However, because mine soil was not available at the commencement of the project, the initial pot trial used soil from the Umlazi Landfill in Durban. The trials were the Umlazi Landfill Trial, Microbe Trial, Legume Trial and Fly Ash Trial. For the Umlazi Landfill Trial, landfill top and subsoil was used along with fertilizer, sewage sludge, K-humate, lime and microbes. The soil ameliorant treatments for the Microbe trial were Trichoderma harzianum (Eco'T), Bacillus subtilis Strain 69 (B69) and Bacillus subtilis Strain 77 (B77), for the Legume Trial, Medicago sativa, phosphorus and/or potassium were applied. For the Fly Ash Trial, lime and fly ash were introduced. From the Landfill trial it was shown that fertilizer and sewage sludge significantly increased the above ground, below ground and total biomass of T. triandra, further, there were no significant treatment differences between fertilizer and sludge. The lime treatment for this trial, surprisingly, significantly reduced below ground biomass but the application of microbes (B69 and BcoT) alleviated this negative effect. However, in the Microbe Trial the microbes (BcoT, B69 and B77) had a negative or no effect on the biomass of T. triandra and C. dactylon. In the Legume Trial it was shown that the above ground biomass of T. triandra was significantly reduced when grown with M. sativa. The Fly Ash Trial revealed that the lime and fly ash treatments had no effect on the biomass of M. sativa and T. triandra, and they did not maintain a reduction in soil acidity. The results therefore indicated that either organic fertilizer or sewage sludge could be used to significantly improve the growth of T. triandra. It was also suggested that lime not be applied to soils with an acid saturation of approximately 1%, as this could retard plant growth. The application of microbes and the growth of a legume with grass, although both have been recorded to have beneficial effects in aiding plant growth, in the short-term however, the application of T. harzianum, B. subtilis Strain 69 and 77 applied to the soil while growing T.triandra and C. dactylon and the growth of M. sativa with T. triandra is not recommended. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2004.

Abstract available in the print copy. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2010.

Climatic and market uncertainty present major challenges to livestock producers in arid and semi-arid environments. Range managers require detailed information on biological and economic components of the system in order to formulate stocking strategies which maximise short-term financial risk and minimise long-term ecological risk. Computer-based simulation models may provide useful tools to assist in this decision process. This thesis outlines the development of a bioeconomic stocking model for the semi-arid savanna of Natal. Grazing trials were established at two sites (Llanwarne and Dordrecht) on Llanwarne Estates in the Magudu area of the semi-arid savanna or Lowveld of Natal. The Lowveld comprises a herbaceous layer dominated by Themeda triandra, Panicum maximum and P. coloratum and a woody layer characterised by Acacia species. The sites differed initially in range composition. Llanwarne was dominated by Themeda triandra, Panicum maximum and P. coloratum, while Dordrecht with a history of heavy stocking was dominated by Urochloa mosambicensis, Sporobolus nitens and S. iocladus. Three treatments were stocked with Brahman-cross cattle at each site to initially represent 'light'(0.17 LSU ha-'), 'intermediate' (0.23 LSU ha-') and 'heavy' (0.30 LSU ha-') stocking. Data collected at three-week intervals over seven seasons (November 1986 to June 1993 or 120 measuring periods) provided the basis for the development of a bioeconomic stocking model (LOWBEEF - LOWveid BioEconomic Efficiency Forecasting) which comprised two biological sub-models (GRASS and BEEF), based on step-wise multiple linear regression models, and an integrated economic component (ECON) . The GRASS model predicted the amount of residual herbage at the end of summer (kg ha-') and the forage deficit period (days) over which forage supplementation would be required to maintain animal mass. Residual herbage mass at the end of summer (kg ha-') was significantly related (P < 0.01) to cumulative summer grazing days (LSU gd ha-'), rainfall (mm) (measured 1 July to 30 June) and range condition (indexed as the sum of the proportions of T. triandra, P. maximum and P. coloratum). The forage deficit period (days) over which herbage mass declined below a grazing cut-off of 1695 kg ha-' was significantly related (P < 0.01) to residual herbage mass at the end of summer. The BEEF model predicted the livemass gain over summer (kg ha¯¹) which was significantly related (P< 0.01) to rainfall (mm) stocking rate (LSU ha¯¹) but interestingly not to condition. The economic component (ECON) reflected the difference between gross income (R ha¯¹) and total costs, which were based on fixed and variable cost structures (using 1993 Rands), including demand-related winter costs, to reflect net returns to land management (R ha¯¹). A conceptual model of range dynamics based on three discrete states, was to developed to summarise the effects of rainfall and stocking rate in semi-arid savanna. State 1, characterised by iocladus and S. nitens, was associated with heavy stocking. Movement towards State 2, characterised by T. triandra and P. maximum, was associated with periods of above-average rainfall. Drought conditions, which comprised a major system disturbance led to stability at State 3, dominated by U. mosambicensis. Post-drought recovery was influenced by predrought composition and stocking levels where tuft numbers, basal cover and seedbank were significantly reduced by increased stocking within a sward dominated by species of low stature such as Aristida congesta subsp Urochloa mosambicensis, Sporobolus nitens, Sporobolus iocladus and Tragus racemosa. It was suggested that extensive soil loss may lead to stabilisation across an irreversible threshold at a forth state characterised by shallow species such as Tragus racemosa Aristida congesta subsp. congesta. Sensitivity of optimum economic stocking rate net return to price and interest rate fluctuations, and wage and feed cost increases were examined for various rainfall and range condition scenarios. Net return and optimum economic stocking rate increased as rainfall and range condition increased through the effect of increased residual herbage mass at the end summer, decreased forage deficit periods and reduced supplementary feed costs. Net return was highly responsive to changes beef price where an increase in beef price led to an increase in optimum economic stocking rate and net return. The effect of reduced prices may be compounded by dry where supply-driven decreases in price may occur. This suggested that for dry seasons the optimum stocking rate was the lightest within the range of economic stocking rates. Although an increase in interest rates would increase variable costs and lead to reduced returns, the influence of interest rates on enterprises will vary in relation to farm debt loads. Increased labour costs would result in a corresponding decline in net return although optimum economic stocking rate would remain unaffected. Increased supplementary feed cost had little influence on net return relative to the effect of demand-driven increases in feed costs as rainfall decreased . The distribution of net returns for stocking strategies of 0.20, 0.30 and 0.40 LSU ha¯¹ and climate-dependent stocking (where stocking levels were varied in relation to rainfall and hence forage availability) and range condition scores of 10, 50, 80 and a dynamic range model were examined for a 60 year rainfall sequence (1931- 1991). While a range score of 10 would see residual herbage mass decline to below a grazing cut-off of 1695 kg ha¯¹ before the end of summer, a range score of 80 suggested that, irrespective of stocking strategy within the range investigated, herbage would not become limiting. This suggested that irrespective of stocking strategy a range score of 10, established across an irreversible soil loss threshold, would reflect accumulated losses over the 60 year period. In contrast, a range score of 80 would lead to positive accumulated returns. A dynamic range model (where range composition was related to previous seasons rainfall) and a climate-dependent stocking strategy, suggested that herbage would not become limiting by the end of summer and forage deficit periods would be restricted to an average of 88 days per year. Such an approach would yield a higher accumulated cash surplus than fixed stocking strategies. Incorporation of stochastic rainfall effects allowed the development of cumulative probability distributions based on 800-year simulations to evaluate the risk associated with various stocking strategies. Range condition played a major role in determining the risk of financial loss where decreased range condition was associated with enhanced risk. An increase in stocking rate resulted in increased variability in returns. Although the risk of forage deficits and financial losses may be reduced with lighter stocking, this may be at the cost of reduced returns during wetter seasons. Increased stocking may increase the probability of higher returns during wetter seasons although this may at the cost of increased risk of forage deficits and highly negative returns during dry seasons. Importantly, ecological risk may increase as stocking is increased. A flexible or climate-dependent strategy, where stock numbers are adjusted according to previous seasons rainfall, combine financial benefits of each approach and reduce financial risk. Although errors may carry hig h ecological costs where, for example, the effect of an above-average rainfall season would be to increase stock numbers into a subsequent dry season, the probability of incurring such error was low. Current livestock production systems in the semi-arid savanna of Natal based on breeding stock may not be appropriate in a highly variable environment where low rainfall may require extended periods of supplementary feeding or force the sale of breeding stock. A change in emphasis from current systems to a mixed breeding system, where the level of breeding stock would be set at the optimum economic stocking rate for drier seasons, may decrease both financial and ecological risk. Growing stock may either be retained or purchased during wetter seasons to reach the optimum economic stocking rate for such seasons. Although growing stock may display a greater tolerance to restricted intake (during dry seasons) than would breeding stock, additional growing may be rapidly sold in response to declining rainfall with no influence on the breeding system. Integration of wildlife into current cattle systems may be an important means of reducing financial risk associated with variable rainfall and profitability and ecological risk associated with woody plant encroachment. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1994.

Data collected between 1992/93 and 1996/97 from two long-term grazing trials were used to investigate the interaction between grazing animals and veld grass. In the first trial, the impacts of stocking rate and time of stocking in spring on both livestock performance and veld vigour (defined as the ability of a grass plant to regrow after defoliation) and condition were investigated. In the second trial comparisons were made, firstly between the impacts of sheep and cattle grazing, and secondly between various types and frequencies of rest, on veld vigour and condition. Treatments applied in the first trial comprised four stocking rates, namely 7, 10, 13 and 16 sheep ha¯¹ for the duration of the grazing season, and two times of stocking, namely as early as possible after spring burning and three weeks later. Sheep grazed each treatment continuously throughout the growing season. Treatments were applied to alternate blocks in a two-year cycle with each block resting for a year within a grazing cycle. Animal performance (mass gains over the season) was measured to quantify livestock performance. Herbage availability was measured on a species basis at intervals throughout each season using a dry-weight-rank procedure to determine grazing patterns. Residual effects of the grazing treatments on vigour were determined by measuring herbage regrowth on a species basis during the rest season which followed a season of grazing and comparing these measures to a previously ungrazed control treatment. Effects of the grazing treatment on proportional species composition were determined using a nearest plant point technique. Stocking rate had a non-linear effect on livestock performance, with livestock performance on the lightest stocking rate being less than on the two intermediate stocking rates. The mass gains on the heaviest stocking rate were generally the smallest. Delaying the time of stocking in spring resulted in smaller mass gains during the resultant shorter season. The sheep from both the early and late time of stocking groups had similar mean masses at the end of the season. The advantage of stocking early can thus be attributed more to saving the cost of alternative feed for the interim period than to additional mass gains due to stocking early. Quantification of livestock performance in terms of selected and available feed quality, quantity and species availability throughout each season was extremely complex due to multiple thresholds in the measured variables and no simple cause and effect relations could be established that would hold for spatial or temporal extrapolation. The negative impact of grazing on veld vigour was severe. Stocking rate and time of stocking had a secondary impact with the vigour loss positively related to increasing grazing pressure. The main factor influencing vigour loss was grazing, irrespective of time of stocking or stocking rate, as opposed to no grazing. The impact of grazing on vigour was severely negative in the palatable species, variable in the species of intermediate palatability and positive in the unpalatable species that were rarely, if ever, grazed. The stocking rate and time of stocking rate had an impact on the proportional species composition, with the more palatable species declining in proportion. There was an observable relation between impact of grazing on vigour and on species composition. Treatments applied in the second trial involved applying a full growing season rest in alternate years, half a growing season rest (late season) in alternate years and no rest to veld grazed by sheep or cattle at similar stocking rates. Residual effects of the treatments on veld vigour were determined by measuring species regrowth using a dry-weight-rank technique during the season following treatment application, and comparing it to controls ungrazed for one and two seasons respectively. Changes in proportional species composition were determined using a nearest plant point technique. The vigour of veld grazed by sheep declined rapidly relative to veld grazed by cattle. The vigour of palatable species was severely impacted, vigour of intermediate species was variably impacted and vigour of unpalatable species increased dramatically on veld grazed by sheep compared to the control treatments. Similar trends occurred in veld grazed by cattle, but to a lesser degree. Resting was beneficial for vigour recovery in both sheep and cattle treatments but it seems that the grazing treatment between rests has a greater influence on the veld vigour and condition than the rest itself. The veld grazed by sheep remained at a substantially lower productivity level than veld grazed by cattle. This was particularly evident in the change in productivity balance between palatable and unpalatable species in the sheep treatments, where palatable species vigour declined and unpalatable species vigour increased relative to veld grazing by cattle. Species composition of veld grazed by sheep deteriorated over the trial period in contrast to the veld grazed by cattle, which improved in species composition. Grazing management recommendations for sourveld should include a bias towards cattle, optimising stocking rate for improved performance and resting for enhancing vigour of the palatable grasses. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1999.

The influence of herbivory, grass competition and grazing system on emergence, growth and survival of Acacia seedlings in burnt and unburnt areas was investigated in their first growing season, from September 1997 to May 1998. The study was aimed at determining possible reasons for the increase in woody plant density in semi-arid savannas, specifically the effect of excluding small-mouthed herbivores from domestic and livestock systems, and switching from continuous grazing to rotational grazing systems. The effect of fire intensity and maximum fire temperature on seed viability, germination and mortality, specifically with regard to back versus head fires and seed size , were investigated. Variability among species in the number of seedlings emerging generally resembled differences in viability. Emergence of Acacia karroo and Acacia tortilis was poorer than that of Acacia nilotica under grass competition. Emergence was lower in burnt and open areas, the latter depending on Acacia species. Herbivory did not affect seedling emergence, in both domestic and wildlife systems. Seedling survival and growth was adversely affected by small-mouthed herbivores in both domestic and livestock systems, whilst large-mouthed herbivores exerted no direct effects on woody seedlings, except to a small degree by trampling. Seedlings showed better growth and survival under low grass competition, which also resulted in greater leaf-to-height ratios , indicating that grass interference with irradiance affects woody seedlings. This effect appeared to be greater for cattle and rotational grazing, and for burning, in domestic and wildlife systems respectively. Woody seedling establishment was also better in burnt areas. Whilst seedling growth was better under rotational than continuous grazing, survival was not significantly different. Grass competition influenced seedling establishment to a greater extent than herbivory, whilst burning made a greater impact than grass competition. Seed mortality in response to maximum fire temperature was inversely related to seed size, and trends in seed germination and mortality, although very variable, appeared to be influenced by threshold fire intensities and maximum temperatures. Back fires had hotter maximum temperatures and fire intensities at ground level than head fires, which result in greater seed mortality following fire. Based on the current study it is likely that the removal of grass competition, burning, and a change from continuous to rotational grazing systems, and small-mouthed to large-mouthed herbivores, will result in an increase in woody seedling establishment. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 2001.

Considerable understanding of the functioning of semi-arid systems is still needed to enable range managers to formulate management policies, with a degree of confidence. Long term data sets that encompass a wide range of interactions between the various major components of a semi-arid system (vegetation, herbivory, animal performance, landscape and rainfall), are unfortunately rare but essential to provide sufficient depth of data to adequately test various hypotheses about rangeland dynamics. This study comprises an analysis of a ten year data set derived from two cattle stocking rate trials in the semi-arid savanna of KwaZulu/Natal. Statistical analysis revealed that the most pronounced and rapid compositional change was due to rainfall, but that stocking rates between 0.156 and 0.313 AU ha ¯¹ had an important effect as well. Sites on steeper slopes with heavy stocking rates, exhibited the greatest amount of compositional change between 1986 and 1996 (40 Euclidean points in heavy stocking rate treatments on slopes vs 21-24 Euclidean points in heavy stocking rate treatments on flatter land, or 11-24 Euclidean points in low stocking rate treatments). Heavy stocking rates in conjunction with low rainfall tended to cause decreases in densely tufted perennial grasses and increases in annuals and weakly tufted perennials. Multiple regression analysis revealed that seasonal peak grass production (measured as disc height) declined between 1986 and 1996 only at those sites on steeper slopes with heavy stocking rates. The camps that declined in productivity also underwent the greatest degree of compositional change. The decline in grass productivity in certain high stocking rate camps did not translate into a decline in cattle performance. Depending on rainfall, cattle gained on a seasonal basis between 112 and 241 kg at low stocking rates, 82 and 225 kg at medium stocking rates and 84 and 217 kg at high stocking rates Rainfall, compared with stocking rate, accounted for the greatest amount of variance in seasonal peak grass production and cattle performance. Cattle performance had a strong curvilinear response to rainfall, which also proved to be a better predictor of cattle performance than grass biomass. There were no clear trends in soil physical and chemical characteristics between low and high stocking rates that could provide convincing evidence that loss of soil nutrients was an important mechanism of range degradation. The total standing crop of plant nitrogen but not of phosphorus tended to decline at high stocking rates. Plant nutrient and van Soest analyses suggested that forage quality was higher at heavy stocking rates. The results of this study generally supported traditional concepts of rangeland dynamics with regard to rainfall and grazing effects on compositional change and seasonal grass production. The results were important in being able to show quantitatively that heavy stocking rates result in a decline in grass production and that this effect is dependent on an interaction between stocking rate and landscape position or slope, and that there is a link between a decline in seasonal grass production and compositional change. The results also highlighted areas for future research that would be useful for furthering our understanding of various aspects of rangeland dynamics and mechanisms of degradation. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 1998.

Data derived from a long-term grazing trial were used to determine short-term effects of mixed grazing by cattle and sheep in Highland Sourveld. Five cattle to sheep ratio treatments (viz. 1 :0, 3:1, 1 :1, 1 :3, 0:1) were applied, each at three stocking rates (viz. 0.5 (low), 0.71 (medium) and 1.0 (high) animal unit equivalents (AUE) ha¯¹). Ratios were expressed in terms of AUE cattle: AUE sheep. Stocking rate and ratio treatments were balanced at the start of each grazing season. Fourteen-month old Hereford steers and 'two-tooth' Merino wethers were used as experimental animals. The trial comprised two components, viz. an animal production component and a simulated component. The animal production component was conducted only in the medium stocking rate treatment where the effect cattle to sheep ratio on the performance of cattle and sheep was determined for each of four grazing seasons (viz. 1989/90, four-paddock rotational grazing The low and high stocking rate 1990/91, 1991/92, 1992/93). A management system was applied. treatments were implemented by simulating a four-paddock rotational grazing system and using a single paddock for each stocking rate/ratio combination. Grazing of the simulated treatments coincided with the grazing of a specific 'test' paddock in each ratio of the medium stocking rate treatment. These 'test' paddocks and the simulated treatment paddocks were monitored to determine the impact of mixed grazing by cattle and sheep on individual grass plants and the sward. The whole of the experimental area was rested during the growing season prior to the start of the trial and all paddocks were burnt in the dormant season just before the start of the first grazing season. The trial therefore commenced with a with a uniform sward of immature herbage in all paddocks allocated to each group of animals. ln the second and subsequent growing seasons only those paddocks which had been rested in the previous season were burned prior to the onset of growth in early spring. Rainfall for the first three grazing seasons was similar to the long-term mean of 790mm whilst the last season was considered 'dry' with 554mm recorded during 1992/93. In all grazing seasons, as the proportion of cattle in the species mix increased, sheep performance increased. A decline in sheep performance was recorded in each ratio treatment from the first to the third season. This decline was attributed to the increased maturity and thus lower quality of herbage on offer to the sheep, and the fact that only one paddock available to the animals in the second and third grazing seasons had been burned prior to the start of the season. Sheep performed best during the 'dry' season where herbage quality was maintained for longer into the grazing season than in previous seasons. In contrast, cattle performance was affected by the stocking rate (animals ha¯¹) of cattle rather than the presence of sheep. As the quantity of herbage on offer per steer declined steer performance declined. Animal performance data were also used to predict the effects of adding cattle to a sheep production enterprise and vice versa. The general trends were that the introduction of cattle into a low stocking rate, sheep-only production enterprise would allow for an increase in the stocking rate of sheep while maintaining the performance of the sheep. In this way the carrying capacity of a farm may be improved. Stocki ng rate and ratio treatments varied from those established at the start of each grazing season due to the differential performance of the cattle and sheep in each treatment. As the proportion of cattle in the species mix increased, stocking rate increased and the ratio widened in favour of cattle. Stocking rate (AUE ha¯¹), calculated a posteriori for each season, was the major influence on the severity of grazing on individual plants and within patches. As stocking rate of cattle and sheep at the various ratios increased, the extent and severity of grazing increased. At stocking rates in excess of O.8AUE ha¯¹ however, sheep-only grazing resulted in a greater proportion of plants, per species and per area, being grazed more severely than was the case for an equivalent stocking rate (AUE ha¯¹ ) of cattle. Furthermore, cattle and sheep had similar effects on patch size distribution when stocked at the same number of AUE ha¯¹. There were no measurable effects of stocking rate and ratio on proportional species composition and basal cover over a two year monitoring period. A technique for estimating basal cover in tufted grasslands was developed and is presented as an appendix to the thesis. Data were also used to evaluate the use of AUE as an integral part of the grazing capaci ty concept. Results indicated that cattle and sheep cannot be equated in terms of AUE when referring to the grazing impact. It is suggested that the definition of grazing capacity should include the species of livestock and assume a grazing management system appropriate to the grazing habit of the animals concerned. Resul ts of the trial provide strong indications that, in the long-term, the current recommendations of grazing cattle together with sheep in order to prevent the degradation or loss of veld condition which occurs in sheep-only grazing systems, will not succeed. A four-paddock rotation grazing system does not appear to be an appropriate veld management system for sustainable sheep production in sour grassveld. An alternative approach to veld management is suggested in which the sheep are confined to only those areas of the farm which were burnt at the start of the grazing season. Ideally, sheep should not allocated to the same paddock for two consecutive grazing seasons. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1994.

Plants are the major source of food or energy required to sustain life on the planet, but humans are grappling with the deteriorating conditions of natural ecosystems such as compositional change, desertification, invasive plants and soil erosion. In the face of global climate change and growing demands for agricultural productivity, future pressures on grassland ecosystems will intensify, therefore sustainable utilization of all plant resources is of vital importance to enhance food security within the limits of good conservation. The semi-arid grasslands of southern Africa represent major grassland resources for grazing. Herbage production in these areas is determined not only by water and nutrient availability, but also by controlled and uncontrolled fires. Since fire is regarded as a natural factor in savannas, it is essential to develop a deeper understanding of the role of fire in community structure and function for the development of appropriate burning regimes. A study was conducted in the Eastern Cape of South Africa where the rural communities are faced with the challenges of rangeland degradation in the form of encroachment by unacceptable bush, karroid, macchia and less desirable grass species, as well as soil erosion. The main objective of this thesis was to investigate the roles of competition and disturbance regimes (fire and simulated non-selective grazing) on species composition, habitat productivity and the performances of selected species from this semi-arid savanna. Long-term effects of burning frequency on herbaceous species composition, Leaf Area Index (LAI), Photosynthetically Active Radiation (PAR) within the herbaceous canopy, biomass production and soil chemical properties were investigated. These studies were conducted on a fire trial set up in 1980 at the University of Fort Hare research farm in the Eastern Cape, South Africa. The treatments comprise an annual, biennial, triennial, quadrennial, sexennial and no burn control, all replicated twice in a Complete Randomized Design. The data from the trial collected between 1980 and 2008 were used to determine compositional variation for herbaceous species using the Non-metric Multidimensional Scaling and Bray-Curtis Dissimilarity tests. The PAR ceptometer was used to determine LAI and intercepted PAR, while random samples were harvested from 1m² quadrats from each plot. Soil samples were taken at four depths (0-2 cm; 2-4 cm; 4-6 cm and 6-8 cm) from each plot and analyzed for pH, Ca, K, P, total C and total N. The Resin-Bag technique was used to determine nitrogen mineralization. Burning frequency caused significant variation in herbaceous species composition over time. The species were distributed along gradients of increasing burning frequency, and these responses were in three categories: Those that increased with burning frequency such as Themeda triandra; those that decreased with burning frequency such as Melica decumbens, and those that showed little response such as Panicum maximum. The three-year burn resulted in the highest compositional variation, light interception, Leaf Area Index, aboveground biomass production, while the annual, biennial and no burn treatments resulted in the lowest. The fact that infrequent burning resulted in higher species variation, improved habitat productivity due to increased leaf area for light interception shows that appropriate use of fire can maintain a more diverse and productive savanna system. Burning frequency had significant effects on the soil properties, while soil depth did not show any significance. Frequent burning increased soil pH, K, Ca, and Na, but reduced C, N, P and N mineralization. There was a negative correlation between burning frequency and N mineralization, but no correlation existed between N mineralization and total N, total C or the C:N ratio. These results imply that frequent burning can cause nutrient losses and a greater nutrient limitation to plants in the long-term, especially soil C and N loss from combustion of organic material in the soil top layer. The ability of shade-tolerant plants to persist under shade and regular defoliation such as in burnt and grazed systems may be of greater importance for long-term productivity and sustainability of forage crops. It is therefore imperative to explore the mechanisms by which some species were favoured by frequent burning which created low shade conditions, while others were favoured by high shade conditions where burning is infrequent or absent. A pot experiment was conducted to investigate the shade tolerances of seven grass species that were abundant in the long-term fire trial. The test species were Cymbopogon plurinodis, Digitaria eriantha, Eragrostis curvula, Melica decumbens, Panicum maximum, Sporobolus fimbriatus and Themeda triandra. Individual grass tillers of each species were collected from the natural vegetation, propagated in separate seedling trays and transplanted into individual pots, and were grown under five shading treatments: full sun (0 % shading), 55 %; 70 %; 85 % and 93 % shading respectively. Shading significantly reduced the dry matter production of all the species. Biomass production of all the species decreased linearly to varying degrees with an increase in shade intensity. Digitaria eriantha and Eragrostis curvula were most adversely affected by shading, hence are classified as shade intolerant, while Melica decumbens was the least affected by shading, and is hence classified as shade tolerant. Cymbopogon plurinodis, Panicum maximum, Sporobolus fimbriatus and Themeda triandra are classified as moderately shade-tolerant. From the results it was apparent that some species could perform optimally in partial shade than in full sunlight, and these results lead to a conclusion that for satisfactory natural regeneration and seedling growth of this savanna vegetation would require a gap large enough to provide at least 30 % of ambient light. Investigating patterns in competitive effects and responses of species in these communities may not only explain the abundance of each species, but may also provide insight into the nature of forces that affect the structure and function of that community. Since fire, herbivory and soil nutrients are natural drivers of savanna community structure and function, their influence on competitive interactions of selected species were investigated. Two experiments were conducted to investigate the competitive effects and responses of eight selected common species in the area. The test species (phytometers) included one woody shrub, Acacia karroo and seven grass species namely: Cymbopogon plurinodis, Digitaria eriantha, Eragrostis curvula, Melica decumbens, Panicum maximum, Sporobolus fimbriatus and Themeda triandra. In an outdoor plot experiment the responses of the phytometers to competition from neighbours (0; 2 and eight neighbours respectively), fertility (fertilized, unfertilized) and clipping (clipping, no clipping) were investigated. The second comprised a pot experiment where the competitive effects of the species were investigated. Each species was grown under 3 levels of fertility (0 %; 50 % and 100 % Hoagland‘s solution) and clipping (clipping, no clipping) in pots filled with fine river sand and 4 neighbours. Competition intensity, soil fertility and clipping had significant effects on the biomass production of the phytometer species. Acacia karroo and Melica decumbens, exhibited the weakest competitive effects and responses, and incurred the highest mortalities after clipping and with 8 neighbours. Digitaria eriantha and Panicum maximum exhibited the strongest competitive effects and responses, especially in high fertility, and experienced the lowest mortalities. T.triandra exhibited stronger competitive effect after clipping in low fertility, while A. karroo and C. plurinodis exhibited stronger competitive effects in moderate (50 %) fertility. Cymbopogon plurinodis, Eragrostis curvula and Sporobolus fimbriatus ranked between these two extreme groups in terms of competitive effects and responses. Relative Competitive Interaction increased with soil fertility and number of neighbours in the absence of clipping. These results indicate that in general, taller or broad-leaved grass species outgrow the shorter ones, and this gives them a competitive advantage over light and soil resources. One of the range management objectives in the False Thornveld of the Eastern Cape is to promote the abundance of Themeda triandra, which is of high forage value and an indicator of rangeland that is in good condition. The general situation under livestock farming conditions in this area is that if the grass sward is optimally grazed and rested then there is a great potential for Themeda triandra to dominate.The results of the competition experiments indicated that the species exhibits strong competitive interaction, and also exhibited stronger competitive effect after clipping in low fertility. These results imply that it has a low response and a high effect, an attribute that would enhance its performance if it is moderately grazed or the area is burnt. The species is also moderately shade tolerant, and this may explain why it thrives in burnt and moderately grazed areas. These studies have demonstrated the important role that competition and disturbance in the form of fire and herbivory play in the maintenance of this savanna grassland. Through natural selection species are able to occupy different niches in the same area and coexist in a heterogeneous environment and minimize their chances of extinction. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2012.

The purpose of this study was to develop and test a predictive understanding of the vegetation dynamics of the Lowveld of South Africa (30°35'E to 30°40'E and 24°00'S to 25°00'S). The study covered about 5000 km2 in Adjacent Private Protected Areas (APPA) adjoining the Kruger National Park (KNP). Data gathering (800 sites; 23 properties) commenced in 1989 and those recorded up to 2004 are reported here. The value, both ecological and economic, of the wildlife and tourism industry dependent on this savanna region is discussed in both historical and current perspectives. A range of land-use objectives and anthropogenic interventions were exposed. The properties ranged in size from 30 to 800 km2 and formed an effective and extensive manipulative experiment for investigating interaction of bush density, animal stocking, use of fire and landscape-scale processes. The first descriptive classification (at 1:250 000) of the area was developed using Inverse Distance Weighted interpolations. This confirms similar landscape/vegetation patterns in the KNP and Mocambique. The current mode of determining stocking density or carrying capacity was interrogated and indices suitable for complex multi-species systems developed. This was done in the context of equilibrial/disequilibrial paradigms. Application of the original indices resulted in drought-related declines in animal biomass of 4000 kg km2 over 20 years due to overestimation of carrying capacity. The model proposed here uses rainfall, animal type, biomass and vegetation parameters to determine stocking density for both coarse (regional) and ranch-specific scales. Principal driving determinants (rainfall, geology, soil type, tree density canopy cover, animal numbers, feeding classes and fire) of vegetation structure and their influence on the herbaceous layer were investigated. Groupings on ecological potential showed 'high' potential areas are less sensitive to animal impact than those classified as 'low' potential. Sustainability, embedded in a forward-looking component viz. Strategic Adaptive Management (SAM) with well-articulated endpoints viz. Thresholds of Potential Concern (TPCs) was used to study fluctuations in animal populations with Connochaetes taurinus (Blue wildebeest) as the case study. The TPC approach provides strong pointers for proactive management aimed at maintaining the system within bands defined by TPCs supporting operationally practical and periodically reviewed objectives. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2005.