The historically poorly conserved subtropical transitional thicket (STT) of the Eastern Cape is overutilised by domestic stock and game in the more xeric areas, and has shown no signs of recovery from this grazing pressure. It has been postulated that no regeneration through seeding occurs. This project was undertaken to determine: 1) how much STT has disappeared between 1950 and present, and what the current conservation status is; and 2) whether regeneration of the xeric succulent thicket is taking place through seeding, and if so, where. The study was conducted at the Andries Vosloo Kudu Reserve near Grahamstown. Approximately one-third less STT was mapped in this study, based on 1981 Landsat images, than was mapped in 1950. Approximately 10 % of all remaining STT is conserved. The order Kaffrarian thicket is poorly conserved. Newly germinated seedlings of a wide range of shrub species occurred under the canopies of a wide range of shrubs which served as nurse plants, throughout a gradient of veld condition. Seedlings of Portulacaria afra, the dominant shrub in xeric succulent thicket, were most common. Similarly all saplings recorded in a survey of saplings were associated with bushclumps. One-third of all saplings have the potential to contribute to the spread of bushclumps. Regeneration of xeric succulent thicket through seeding probably does occur, contrary to current ideas. Ptareoxylon obliquum was the most common sapling, despite mature trees now being scarce following earlier heavier utilisation . P. obliquum was also the nurse plant which supported the highest density of newly germinated seedlings. The possible role of P. obliquum in the functioning of xeric succulent thicket is discussed. The confinement of seedlings and saplings to areas under the canopies of trees and shrubs implies that the xeric succulent thicket will not recover rapidly if allowed to rest. Active management techniques will be necessary if rapid recovery is required. Bare areas between bushclumps may no longer be suitable germination habitats because of high Al concentrations. There was no evidence to support the idea that germination and establishment of shrubs in clear areas is linked to episodic climatic events. Dung middens of recently reintroduced black rhinoceros may however aid in germination of seeds and establishment of seedlings under certain climatic conditions. Recommendations for further studies, based on the findings of this project, are made. Possible management techniques aimed at the rapid recovery of this veld are suggested, and management proposals for the Sam Knott Nature Reserve/Andries Vosloo Kudu Reserve complex are made.

Department of Geography and Geo-Information Sciences / MENVSC

Human activities are increasing the occurrence of megafires that have the potential to alter the ecology of forest ecosystems. The objective of this study was to understand the impact of a 610 km2 megafire on patterns of forest regeneration and herbivory of three forest types (aspen/fir, oak/maple, and pinyon/juniper) within the burn scar. Sapling density, meristem removal, and height were measured across a transect network spanning the area of the burn scar over three years from 2019-2021. The network consisted of 17 burned/unburned transect pairs in adjacent burned/unburned forest stands (6 aspen/fir, 5 oak/maple, and 6 pinyon/juniper). Species that regenerated through sprouting generally responded positively to fire while regeneration from seed showed very little post-fire response. Browse pressure was concentrated on deciduous tree species and tended to be greater in burned areas but the effect diminished over time. Meristem removal of sprouting species was below the critical threshold resulting in positive vertical growth across years. Our results indicate that forest regeneration within the megafire scar was generally positive and experienced sustainable levels of ungulate browsing that are likely to result in forest recruitment success. Novel fire regimes are becoming increasingly common and megafires have burned across ecotonal boundaries across multiple forest types. Plant community structure and composition may be critically affected by changing fire regimes. Our objective was to investigate how a megafire that burned across multiple forest types impacted understory plant community assembly and biodiversity. Paired vegetation transects were installed in burned and unburned areas across aspen/fir, oak/maple, and pinyon/juniper forests within the 2018 Pole Creek Megafire burn scar. Percent cover of understory plants was measured in the summer of 2022 and plants were identified to the species level. Richness and diversity indices were then calculated and analyzed using mixed effects models. Fire decreased species richness of the aspen/fir forest understory and increased plant cover in pinyon/juniper forests, while not significantly impacting oak/maple understories. The significant effects of fire were largely driven by changes in forb species. Fire decreased the richness of native plants in aspen/fir forests but increased the richness of non-native plants in oak/maple and pinyon/juniper forests. Non-native plant abundance also increased in post-fire pinyon/juniper forests. Our results suggest that forest understory communities show variable responses to megafires that burn across multiple forest types with important implications for post-fire plant community structure, diversity, and invasibility. Large mammal herbivores (ungulates) are increasing in number and spreading into novel habitats throughout the world. Their impact on forest understory plant communities is strong and varies by herbivore, plant growth form, and season. The objective of this study was to determine the individual and collective herbivory impacts of native versus domestic ungulates on the understory plant community composition of post-fire aspen forests. Four-way fencing treatments were installed in 2012 to separate ungulate species, and Daubenmire frames were used to collect percent cover estimates for each understory plant species. Vegetation data were later used to calculate richness and diversity indices. Total understory plant cover, richness, and diversity were not significantly impacted by the herbivory fencing treatment. However, woody plant species' percent cover was 90% greater in full ungulate exclusion plots than in the fenceless controls. Herbivores likely targeted woody plant species due to their high nutrient levels that last longer into the winter than those of forb or graminoid species. Herbivory treatment did not affect non-native species. Our results indicate that herbivore fencing can protect forest understory plant communities, particularly the woody species. Successful regeneration of woody species can benefit the diversity of the entire understory plant community and preserve forest structure.

No description available.

The Okavango Delta is an extremely dynamic system with variable vegetation comprised of permanent swamps, seasonal swamps, dry islands, floodplains and dry grassland, savanna and woodland. The system is largely driven by the interaction between fire and the annual flood, which filters down from the Okavango River catchments in Angola. While extensive research has been conducted on the flood-driven vegetation little is known about the dry woodland and savanna regions bordering these flood-driven habitats. A taxonomic classification of woody species composition resulted in eleven vegetation types. These data were then reanalyzed in terms of woody species morphology allowing these eleven vegetation types to be grouped into four functional response groups in order to provide a platform for improving the understanding of how dry woodland and savannas interact with the environment. These four groups were the savanna group mixed thornveld and the three woodland groups; mixed broadleaf woodland, shrub mopane woodland and tall mopane woodland. Burning in mixed thornveld and mixed broadleaf woodland was found to decrease woody species density and grass fuel loads and could be used for grazing management to remove unpalatable growth and improve grass species composition, while burning in shrub mopane woodland and mixed mopane woodland merely decreased the woody understory and is not recommended. Utilization dominated by grazing livestock resulted in overutilization of the grass sward leading to bush encroachment in both mixed thornveld and shrub mopane woodland, while utilization by goats alone resulted in underutilization of the grass sward and a dominance of herbaceous annuals. Livestock utilization had no effect on the occurrence of Pecheul-loeschea leubnitziae, a shrubby pioneer previously thought to be an indicator of overgrazing, however extensive P. leubnitziae cover was associated with a sward dominated by shade-tolerant grasses with low forage quality. Shrub mopane woodland and tall mopane woodland appear to be more stable vegetation states than mixed broadleaf woodland and mixed thornveld being less vulnerable to colonization by pioneer species and alteration as a result of utilization or environmental factors. For this reason management and monitoring of mixed thornveld and mixed broadleaf woodland is essential to prevent vegetation degradation and to ensure optimal forage availability for both livestock and wildlife. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2012.

The increase of woody vegetation (also known as bush or shrub encroachment) in savannas has become of global concern to conservationists and rangeland managers alike. Bush encroachment has been associated with a decrease in rageland palatability. In addition, the increase in woody biomass has consequences for climate change, carbon sequestration, rangeland hydrology and nutrient cycling. As a result of these large changes in ecosystem functioning with bush encroachment, biodiversity may be threatened. Fire is considered to be one of the most important management tools used to control woody biomass in savannas. However, despite the use of fire in Ithala Game Reserve, areas have become encroached. This thesis assesses the role of fire in bush encroachment in Ithala Game Reserve. I start this thesis with a discussion of the bottom-up (water, nutrients, and light) and topdown (fire and herbivory) ecosystem components in the literature review. This sets the foundation for an understanding of the factors that affect savanna tree:grass ratios for the rest of this thesis. In addition the review discusses the potential effects of climate change on savanna tree:grass ratios. Recently, it has been proposed that increasing atmospheric carbon dioxide concentrations result in an increased competitive ability for C3 woody plants against C4 grasses. Many models have been produced to explain savanna dynamics. By assessing the role of fire in Ithala Game Reserve, its functioning is assessed in light of the current issues of bush encroachment. Textural analysis is a remote sensing technique that has been used to detect changes in woody vegetation using aerial photographs. Textural analysis was used to assess changes in woody vegetation cover and density from 1943 (earliest period for which aerial photographs were available for the study area) to 1969, 1990 and 2007 in Ithala Game Reserve (IGR). Field surveys were performed to assess the effects of the fire regime in IGR on woody vegetation structure and composition. Transects were performed in areas with different fire frequencies. The effects of fire frequency were compared between similar vegetation communities. Textural analysis showed that woody vegetation cover (+32.5%) and density (657.9 indiv. ha-1) increased from 1943 to 2007. Importantly, in some areas of IGR, the suppression of fire led to the rapid invasion of woody plants from 1990 to 2007. Field studies demonstrated the importance of fire in controlling woody vegetation in IGR. The densities of the encroachers, Dichrostachys cinerea and Acacia karroo were resistant to annual burns. However, the height of these deciduous microphyllous woody encroachers was reduced by more frequent fires. Following the suppression of fire, these trees grew taller and their negative impact on the herbaceous layer increased. Consequently, fuel loads (grassy biomass) declined and prevented the use of frequent and intense fires by management. The reduction in fire frequency allowed the invasion of woody evergreen macrophyllous species. Continued development of fire-resistant patches of evergreen macrophyllous vegetation will further reduce the effectiveness of fire in controlling bush encroachment. To control bush encroachment in IGR and the consequential loss of biodiversity, an intermediate fire frequency (one burn every 2 to 4 years) is required. Burns also need to be hot enough to increase the current rate of topkill. Management should act to optimize the accumulation of grassy biomass to fuel fires. / Thesis (M.Sc.)-Unversity of KwaZulu-Natal, Pietermaritzburg, 2010.

This study looks at the impact of elephant feeding on the Xeric Succulent Thicket component of Eastern Cape Subtropical Thicket (ECST) in Addo Elephant National Park (AENP). Observations of elephant feeding were carried out and vegetation transects were surveyed for impact of elephant feeding. The results indicated that the Nyati elephants spent the majority of their time grazing (nearly 90%), particularly the cow-young herds, and especially when the herd gathered in larger numbers. Browsing events were concentrated on Acacia karroo (81%) and there was no significant difference between the sexes in their preference for this species. Despite being subjected to most of the browsing, the majority of A. karroo trees were undamaged and the effect of elephants was generally light. It appears unlikely that, three years after re-introduction to Nyati, the elephants have had an effect on community structure of the vegetation. Surveys were conducted on stands of the alien invasive weed prickly pear Opuntia ficus-indica, and it was recorded that elephants in Nyati have had a dramatic effect on prickly pear, utilising all adult plants assessed and destroying 70% of them. This level of destruction in such a short period of time suggests that prickly pear is a highly favoured species. The results from the present study suggest that elephants can play a role in the control of prickly pear. Results are discussed in terms of elephants as both megaherbivores and keystone species, and as agents of intermediate disturbance.

The 28-month study assessed the impacts of five syntopic medium-sized mammalian browsers and one fire event in a woodland savanna in the Matobo Hills, Zimbabwe. Aspects of herbivory, mechanical pressures, seed dispersal and nutrient cycling were investigated for three species of small antelope (common duiker [Sylvicapra grimmia]1, klipspringer [Oreotragus oreotragus] and steenbok [Raphicerus campestris]) and two medium-sized species (bushbuck [Tragelaphus scriptus] and greater kudu [T. strepsiceros]). Focusing on Burkea africana2 woodland, in a system that does not include elephant (Loxodonta africana), effects of browsing antelope on woody and herbaceous vegetation development were investigated using exclusion plots. Browsers regulated woody plant cover (measured as basal stem area), with smaller antelope having a greater impact than larger species. This was linked to feeding height, feeding selectivity and mechanical pressures (e.g. twig breakage and trampling). Fire caused an initial reduction in above-ground standing biomass, but in the presence of fauna, pre-fire equilibria were attained within 15 months. In antelope exclosures, herbaceous biomass increased and woody biomass decreased following fire. Responses by woody vegetation to browsing varied among species, with highly palatable species typically exhibiting compensatory regrowth. Woody species richness and abundance (especially of palatable species) increased in the absence of browsers, but species richness of the herbaceous layer was promoted by moderate disturbance (trampling or fire). Faecal deposition behaviour, primarily the use of latrines by small antelope, resulted in localised soil enrichment within defended territories. Decomposition rates (and therefore return of nutrients to the soil) varied among species and seasons, due to defecation site selection, accessibility to decomposers and desiccation rates of faecal pellets. Controlled seed germination experiments indicated that ingestion by small antelope enhances germination rates of large, hard-seeded fruits such as Sclerocarya birrea. However, germination of savanna seeds may require multiple cues. This study demonstrated the critical roles of small antelope in ecosystem functioning, and highlights the importance of the less visible impacts of frequently overlooked smaller mammalian herbivores. Perturbations to the faunal community, especially small antelope, are predicted to have substantial impacts on woody plant cover.

La coiffe racinaire est cruciale à la croissance et survie du méristème subapical de racine. Elle libère des cellules frontières (CFs) qui assurent la protection de l’apex racinaire. Les CFs associées à leur mucilage forment le piège extracellaire de racine (RET). La caractérisation du RET et des exsudats racinaires de trois essences ligneuses sahéliennes à partir de plantules cultivées in vitro a été réalisée. B. aegyptiaca et A. raddiana prospèrent dans les zones semi-arides, à l’opposé de T. indica. La morphologie des CFs et l’organisation du RET ont été déterminées par microscopie. La compostion en glycopolymères et la détection des arabinogalactanes proteines (AGPs) dans le RET et les exsudats racinaires ont été déterminées par des analyses biochimiques. L’effet des exsudats racinaires sur la croissance d’Azospirillum brasilense, une bactérie bénéfique pour la plante a été évalué. B. aegyptiaca produit des CFs de type border cells (BCs) alors que les autres Fabaceae produisent des BCs et des border-like cells. Les BCs sont entourées d’un dense mucilage riche en polymères de paroi. Le RET et les exsudats racinaires issus de B. aegyptiaca et A. raddiana sont plus riches en AGPs que ceux provenant T. indica. Les AGPs pourraient contribuer à la survie des plantules dans un contexte semiaride. Ce travail ouvre de nouvelles perspectives de recherche concernant l'implication du RET dans la survie des plantes à l'aridité. / The root cap is primordial for seedling growth and supports root apical meristem integrity. The root cap releases root border cells (RBCs) that surround the root tip and ensure seedling protection against numerous stresses. RBCs and their associated mucilage form the root extracellular trap (RET). Here, RET and root exudate characterization of three Sahelian woody seedlings are performed. In contrast to B. aegyptiaca and A. raddiana which thrive in semi-arid areas, T. indica is more sensitive to drought. B. aegyptiaca, A. raddiana and T. indica seedlings were sub-cultured in vitro. RBC morphologies and RET organization were determined using microscopic approaches. The polysaccharide composition and arabinogalactan protein (AGP) content were determined by biochemical approaches in the RET and the root exudates. Moreover, the effect of root exudates on the growth of Azospirillum brasilense a plant benefical bacteria has been performed. While B. aegyptiaca produces only border cell (BC) type, the two Fabaceae seedlings release both BCs and border-like cells (BLCs). BCs are enclosed in a dense mucilage enriched in cell wall polymers. Compared to T. indica, RET and root exudates of B. aegyptiaca and A. raddiana include more abundant AGPs. In this context, AGPs could contribute to woody seedling survival. This work opens new research perspectives regarding involvement of RET in plant survival to aridity.

MSc (Botanty) / Department of Botany / Background: Problem plants and alien invasive weed species are part of today‟s ecological transformation. Ethnobotanical literature on ecological prominence and ethical values of problem alien weeds is scant and should be documented to avoid loss of valuable species. Aim: The study was aimed at documenting problem weeds and alien invasive plant species considered to be beneficial in deep rural communities. Materials and method: Purposeful triangulation research methods were used to ensure the proper gathering of both qualitative and quantitative data sets. Results and conclusion: Some problem weeds and alien invasive plant species are being utilized by local people to maintain their livelihood. A total of 78 plant species from 33 families were recorded. These plant species belonged to diverse growth habits, namely: climbers, herbaceous, succulents, shrubs, trees as well as creepers. Recorded problem weeds and alien invasive plant species were contributing towards ecological, medicinal and social values. These included being utilized as a source of food (14), fruits (4), medicinal (31), ornamentals (7), firewood (3), social (2) and multiple purposes (17). The main utilized families were Asteraceae (14.1%) and Solanaceae (14.1%). These families were mostly utilized for the purpose of medicinal and food. Plant species that were widely used are as follows: Achyrathes aspera L., Agave sisalana L., Amaranthus spinosus L., Anredera cordifolia L., Canna indica L., Centella asiatica L., Chenopodium album L., Chenopodium ambrosioides L. and Chromolaena odorata (L.) R. M. King and H. Rob. The dominant category for problem weeds and alien invasive plant species was 1b (44%) followed by weeds (35%), category 2 (9%), invaders (5%), category 3 (4%) and 1% for both category 1, 1a as well as X3. The results revealed that the legislative listing of plant species as problem weeds and alien invasive species was based on single knowledge basis system, rather than on multi-dimensional knowledge systems. Therefore, this study recommended that for judgment to be considered in decision-making, it should be based on species-specificity as well as multi-dimensional-knowledge basis. The reconciliation of inherent grapples among scientific and indigenous knowledge systems could possibly be underpinned by equal legislative consideration for the aforementioned knowledge systems especially in the establishment and implementation of environmental regulations. This could also aid with the provision to support transformation in South Africa and worldwide.