The degradation of rangeland grass is currently one of the most serious environmental problems in South Africa. Increaser and decreaser grass species have been used as indicators to evaluate rangeland condition. Therefore, classifying these species and monitoring their relative abundance is an important step for sustainable rangelands management. Traditional methods (e.g. wheel point technique) have been used in classifying increaser and decreaser species over small geographic areas. These methods are regarded as being costly and time-consuming, because grasslands usually cover large expanses that are situated in isolated and inaccessible areas. In this regard, remote sensing techniques offer a practical and economical means for quantifying rangeland degradation over large areas. Remote sensing is capable of providing rapid, relatively inexpensive, and near-real-time data that could be used for classifying and monitoring species. This study advocates the development of techniques based on remote sensing to classify four dominant increaser species associated with rangeland degradation namely: Hyparrhenia hirta, Eragrostis curvula, Sporobolus africanus and Aristida diffusa in Okhombe communal rangeland, KwaZulu-Natal, South Africa. To our knowledge, no attempt has yet been made to discriminate and characterize the landscape using these species as indicators of the different levels of rangeland degradation using remote sensing. The first part of the thesis reviewed the problem of rangeland degradation in South Africa, the use of remote sensing (multispectral and hyperspectral) and their challenges and opportunities in mapping rangeland degradation using different indicators. The concept of decreaser and increaser species and how it can be used to map rangeland degradation was discussed. The second part of this study focused on exploring the relationship between vegetation species (increaser and decreaser species) and different levels of rangeland degradation. Results showed that, there is significant relationship between the abundance and distribution of different vegetation species and rangeland condition. The third part of the study aimed to investigate the potential use of hyperspectral remote sensing in discriminating between four increaser species using the raw field spectroscopy data and discriminant analysis as a classifier. The results indicate that the spectroscopic approach used in this study has a strong potential to discriminate among increaser species. These positive results prompted the need to scale up the method to airborne remote sensing data characteristics for the purpose of possible mapping of rangeland species as indicators of degradation. We investigated whether canopy reflectance spectra resampled to AISA Eagle resolution and random forest as a classification algorithm could discriminate between four increaser species. Results showed that hyperspectral data assessed with the random forest algorithm has the potential to accurately discriminate species with best overall accuracy. Knowledge on reduced key wavelength regions and spectral band combinations for successful discrimination of increaser species was obtained. These wavelengths were evaluated using the new WorldView imagery containing unique and strategically positioned band settings. The study demonstrated the potential of WorldView-2 bands in classifying grass at species level with an overall accuracy of 82% which is only 5% less than an overall accuracy achieved by AISA Eagle hyperspectral data. Overall, the study has demonstrated the potential of remote sensing techniques to classify different increaser species representing levels of rangeland degradation. In this regard, we expect that the results of this study can be used to support up-to-date monitoring system for sustainable rangeland management. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2011.

It is the purpose of this problem to classify the four major pastures of the McMurry ranch using the discussed classification system. The definite measurable qualities characterizing each condition of the system are used extensively in this study. The problem is concerned also with the observation of results of misuse, the present practices that could result in further depletion of portions of the McMurry ranch, and procedures being employed at the present time aimed toward the restoration of these depleted portions.

Degradation of rangeland resources leading to the desertification process is viewed in terms of human and climatic influences. While climatic impacts are important, resource utilization as practiced by man is the major cause of desertification. A multi-objective .decision methodology is developed here which is intended for the analysis of alternative management plans of rangeland watersheds under climatic variability. First, a system model is employed to portray the dynamics of a rangeland as it would respond to climatic changes and different grazing intensities. This approach allows for an interaction of inputs such as rainfall, solar radiation, and temperature with the state of the system which is a range condition index, and with outputs such as production and sediment yield. A simulation package is developed to implement the system model by actually using available data and providing some output values for production and sediment yield. At this stage a number of alternative management plans are identified. The information obtained from the simulation as well as other information of interest are represented by performance criteria, leading to an array of alternative versus criteria. Then, management plans need to be evaluated as they would impact the criteria. A multiobjective decision making technique is selected to perform the analysis for an identification of prefered management alternatives.

<p>Pastoralists in Africa have developed complex mechanisms by which they can alleviate the threat of drought. They practice mobility as one of the strategies to avoid the worst effects of natural stress and disperse grazing pressure. In the past in South Africa, the indigenous Nama people occupied large areas of land and moved around extensively to exploit seasonal differences in the availability of forage and water. With the settlement of the Europeans in the Cape the indigenous people lost most of their land to the colonists. The Nama people were, therefore, restricted to smaller rangelands and their patterns of rangeland use had to adapt to the spatial constraints. Descendants now herd livestock from semi-permanent stockposts that are scattered throughout the commons. Herders use a range of practices to manage their livestock. The aims of this study was to assess the agro-ecological knowledge of livestock keepers / assess the condition of the rangeland during drought / determine the herding strategies of herders during drought.</p>

Environmental issues are often complex with many different constituents operating according to a broad range of communication techniques. In order to foster negotiations, different perspectives need to be articulated in lucid ways sensitive to various viewpoints and circumstances. In my thesis I investigate how certain approaches to environmental discourse effect dialogue and negotiation. My first two chapters focus on environmental problems surrounding rangeland ecology along the U.S./Mexico border; whereas the last two chapters explore more theoretical conflicts concerning the philosophy of nature. Throughout the thesis I show the significance of nonhumans (prairie dogs, cattle, biological assessment sheets, environmental laws, etc.) in the human community. Only by considering the roles of nonhumans do we broaden and enrich the conversation between ourselves concerning environmental issues.

Comprendre les relations entre écohydrologie et structure fonctionnelle des communautés végétales est une problématique croissante en écologie. Cette thèse a pour objectif d'analyser les effets d'un gradient de ressource édaphique sur la structure et le fonctionnement de parcours herbacés dans le sud de la France, en intégrant les niveaux de l'écosystème à la plante. Par modélisation du bilan hydrique, les différences d'utilisation de l'eau au niveau de l'écosystème ont été quantifiées pour cinq années contrastées révélatrices de la variabilité des propriétés des sols et du fonctionnement végétal. Utilisation de l'eau et productivité des plantes sont proportionnelles à la réserve utile des sols et à son taux de remplissage, suggérant un équilibre fonctionnel entre les communautés végétales et la disponibilité de l'eau locale. Par une approche ‘traits', nous avons ensuite montré que le ratio entre surface foliaire et surface racinaire totales de la communauté est le facteur déterminant une relation 'allométrique' entre évapotranspiration potentielle et capacité de prélèvements hydriques. La coordination entre les compartiments racinaire et aérien de la végétation dépend d'une suite d'adaptations architecturales et morphologiques. Des modifications d'abondances relatives spécifiques et le turn-over d'espèces génèrent une variabilité de morphologie et de fonctionnement des communautés permettant leur adaptation à des ressources limitées. Au niveau plante, une expérimentation de transplantation a permis de quantifier l'importance relative de la disponibilité hydrique et des interactions entre plantes sur la productivité individuelle de trois espèces-cibles. L'importance de la compétition s'est révélée plus élevée sous fort niveau de ressource et dépendait plus des relations hiérarchiques entre traits que de la biomasse. La compétition entre plantes affecte les axes de niche fonctionnelle des espèces de façon indépendante, avec une convergence de la ‘teneur en matière sèche des feuilles' pour des faibles valeurs mais une plus forte divergence fonctionnelle pour la ‘hauteur des plantes'. Cette approche fonctionnelle a permis d'éclairer le rôle de la diversité végétale dans la réponse des systèmes écologiques à des ressources hydriques variables. De plus, ces résultats sur les propriétés écohydrologiques des communautés naturelles peuvent contribuer à la conception d'agro-écosytèmes complexes mieux adaptés aux sécheresses intenses prévues dans le contexte actuel de changement climatique. / Understanding the relationships between ecohydrology and functional structure of plant communities is a timely issue in plant ecology. From ecosystem to species levels, this works investigated the effects of a resource availability gradient on the structure and functioning of Mediterranean rangelands in Southern France. Using a water-balance modeling approach, differences in water-use at the ecosystem level were quantified across five contrasting years, accounting for the variability in both soil characteristics and vegetation functioning. Plant water-use and productivity scaled with soil water storage capacity and its filling rate, suggesting a functional equilibrium between plant communities and local water availability. Using a trait-based approach, we then showed that the ratio of total leaf area of the community on total root area determined an allometric relationship between potential evapotranspiration and water uptake capacity. The “coordination” between above- and belowground compartment of the vegetation was achieved by a suite of architectural and morphological adaptations. Modifications of species relative abundances and species turn-over explained morphological and functioning adaptations to cope with limiting resources. Finally at species level, a removal experiment allowed to quantify the relative importance of water limitations and effects of plant-plant interaction on individual plant productivity of three target species of graminoïds. The importance of competition increased with soil resource availability and depended more on trait-trait hierarchical distances among species than standing biomass. Competition among plants affects the axes of the functional niche of species independently, leading to the convergence of leaf dry matter content towards low values but to greater functional divergence for plant height. Overall, this functional approach provided an integrative understanding of the role of plant diversity in the response of ecological systems to changes in water availability. Furthermore, these results on ecohydrological properties of natural communities can contribute to the design of complex agro-ecosystem better adapted to intense droughts predicted under climate change.

Call number: LD2668 .T4 1986 W542 / Master of Arts / Geography

Understanding the factors which determine the distributions of species is challenging. In response to recent anthropogenic climate change species’ ranges are already changing, adding to the complexity of describing their ecological boundaries. The threat posed to species by climate change cannot be understated, and our ability to understand the drivers and mechanisms which underlie species’ responses is critical to our strategies to conserve them. The Ethiopian Bush-crow’s Zavattariornis stresemanni distribution was recently described by an envelope of cooler, drier climate than the surrounding area. This finding raised an intriguing possibility; could this abundant, generalist and charismatic species be limited to a tiny corner of the world by its response to climatic variables alone? That the White-tailed Swallow Hirundo megaensis occurs in a near identical area only adds to this curiosity; how can two unrelated species be globally restricted to the same small area? I address the following questions. What are the effects of temperature on the distribution and local density of the Ethiopian Bush-crow and White-tailed Swallow? How is Bush-crow behaviour affected by temperature? What are the effects of temperature on the breeding success of the White-tailed Swallow? What are the consequences of climatic range-restriction for the conservation of the two species? I found that both species’ ranges are neatly described by distribution models, in which the most important variable was maximum temperature of the warmest month. Bush- crow local density declines as temperatures rise, and their foraging behaviour is negatively impacted by high temperatures, compared to two sympatric starling species. The White-tailed Swallow shows similar negative trends in abundance, and displays a reduction in breeding success as ambient temperatures increase during its breeding season. In both cases, wider-ranging sympatric species do not show the same negative responses to temperature. Both the Ethiopian Bush-crow and White-tailed Swallow are projected to lose a significant proportion of their range over the coming century, raising the level of conservation concern for the species.

Promotion of a predictive understanding of plant community response to various forms, frequencies and seasons of disturbance, either through the direct physical effect on biota and or indirect effect on plants, through modification of microclimate and soil attributes is currently a major goal in plant ecology. In particular, the effect of disturbance on altering the ratio between available light and nutrients and their resultant effect on growth, shoot/root allocation, and thus community composition has gained considerable recognition in connection with the mechanisms of plant succession under a popular heading "the resource ratio hypothesis of plant succession". Contemporary and long-term (>50 years) burning and mowing experiments in KwaZulu-Natal (KZN) provide important sites for investigation that in the mesic grasslands of KZN, community composition changes in response to the frequency, time and type of disturbances such as burning, mowing and veld fertilization. However, the relationship between disturbance-resource-plant traits and their interactive role in species change is virtually unknown. This study sought to improve understanding of mesic grassland dynamics in. KZN, using short-term pot and plot experiments. The principal objectives were: 1) by subjecting plants to different levels of resources viz. light, nutrients, water and cutting to determine the relative above and below-ground growth performances (biomass allocation) of species from contrasting habitat preference in KZN, which implies their relative competitive ability for limiting resources and tolerance to cutting, 2) by using a short-term (one-season period) burning and mowing experiment to determine the effect of different veld management practices on microclimate and availability of soil resources and their subsequent effect on plant growth performances, 3) testing the relative shade tolerance of representative species from contrasting habitat preferences, 4) by combining the outcomes from these experiments, to provide a general synthesis concerning species' response to disturbance/resource which further signifies species change. The hypothesis that competitive ability as a function of biomass allocation is fertility dependent was supported by a pot experiment. In low nutrient treatments short grass species that predominate infertile soils in KZN viz. Aristida funcifarmis and Themeda triandra attained double the shoot biomass, more than double root biomass, initiated more tillers and re-grew better (after cutting) than those inherently tall species that predominate fertile sites viz. Eragrostis curvula and Hyparrhenia hirta. In contrast, in high nutrient treatments, tall species attained far higher shoot biomass and grew taller in height. Interestingly, short species had a smaller shoot: root ratio than tall species, consistent with the prediction of the resource ratio hypothesis. However, no evidence was obtained suggesting that tall species were more shade tolerant than short species. A field-based shade experiment rather showed that, those species that initiate tillers below-ground viz. Aristida junciformis, Eragrostis curvula and Tristachya leucothrix were more shade tolerant than those species that initiate tillers above-ground viz. Hyparrhenia hirta and Themeda triandra. On the other hand, the effect of disturbance/resource relationship in influencing the growth (biomass production, growth rate, and basal circumference) of contrasting species was examined by conducting a short-term (one season) burning and mowing experiment. The effect of disturbance, its form and frequency through its effect on light and soil moisture was able to account for a substantial difference in species vigour, which can potentially impact community composition. Short species (Themeda triandra and Tristachya leucothrix) showed their highest biomass production and higher basal circumference enlargement in burnt summer mown sites, whereas medium to tall species (Aristida junciformis, Eragrostis curvula and Hyparrhenia hirta) were less tolerant to summer mowing. Aristidajunciformis and Eragrostis curvula appeared to be more vigorous (both in terms of above-ground biomass production and growth rate) in burnt but not mown and control treatment respectively. High biomass and litter accumulation on sites protected from disturbance appeared to have a large influence on species vigour. Species such as Aristida junciformis, Eragrostis curvula and Tristachya leucothrix had high tolerance to litter accumulation while in contrast Hyparrhenia hirta and Themeda triandra were more vulnerable. In total this study has revealed that the association of some short species e.g. Themeda triandra with the reccurrence of disturbance is mainly due to increases in light availability and lowered dominance from tall species in frequently disturbed sites rather than nutrient related. However, this study has revealed that there are some indications whereby the notion that the inverse relationship between available light and nitrogen are important driving variables in species change is an important working theory in the mesic grassveld of KZN. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2004.

<p>Pastoralists in Africa have developed complex mechanisms by which they can alleviate the threat of drought. They practice mobility as one of the strategies to avoid the worst effects of natural stress and disperse grazing pressure. In the past in South Africa, the indigenous Nama people occupied large areas of land and moved around extensively to exploit seasonal differences in the availability of forage and water. With the settlement of the Europeans in the Cape the indigenous people lost most of their land to the colonists. The Nama people were, therefore, restricted to smaller rangelands and their patterns of rangeland use had to adapt to the spatial constraints. Descendants now herd livestock from semi-permanent stockposts that are scattered throughout the commons. Herders use a range of practices to manage their livestock. The aims of this study was to assess the agro-ecological knowledge of livestock keepers / assess the condition of the rangeland during drought / determine the herding strategies of herders during drought.</p>