According to Baker (1955), success of plant invasions can be attributed to autogamous breeding systems and generalist pollination systems. A test of Baker's rule was carried out on 19 invasive alien plant species in KwaZulu-Natal, South Africa. Natural levels of fruit set in these plants was high (median= 71.5% fruit set per plant). Breeding system experiments for 18 species showed that 17% of the species are allogamous, 72 % are autogamous and 11% are apomictic. This contrasts markedly with a general flora of 1472 species in which 65% are allogamous, only 14% are autogamous, and 21% are apomictic. Because the breeding systems of the alien species were largely autogamous, pollinators make only a small contribution to the overall reproductive success. Seventy one percent of the 14 alien species for which pollinators were obtained were pollinated by honeybees, which are super-generalists and ubiquitous in a generalist pollination systems. However, some species showed pre-adaptation to relatively specialized pollination systems, involving hawkmoths, butterflies and Xylocopa bees respectively. Thus, alien plants were not visited by a wide range of insects, but rather showed pre-adaption to one or more pre-existing guilds in the new habitat. Pollen limitation experiments showed no evidence that reproductive success in populations of the species is limited by pollen availability. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 2001.

Bracken fern (Pteridium aquilinum [L.] Kuhn) is an indigenous invasive plant and it is known to have a negative impact on biodiversity. This research focuses on infestations of bracken fern in two areas within the uKhahlamba Drakensberg Park World Heritage Site; the Royal Natal National Park and the Rugged Glen Nature Reserve. Prior change detection research on bracken fern were constrained due to the low resolution satellite imagery and the inability of hard classification techniques to account for the mixtures of land cover types that occur within pixels of low resolution imagery. To overcome these constraints this research applied the fuzzy image classification technique to multispectral digital aerial imagery of 0.5 m spatial resolution. Multi date imagery used for image classification was captured in the mid-winter of 2009 and mid-spring of 2011. Thereafter post-classification change detection analysis was conducted using the fuzzy classified images. The classified images were verified using ground truth surveys. The 2009 and 2011 fuzzy classified images produced overall accuracies of 81.4% and 94.4% with Kappa coefficients of 0.63 and 0.89 respectively. This research found that the distinct seasonal development pattern of bracken fern and the time of year imagery were captured were significant factors in its detection. As bracken fern was found to be more spectrally distinct in spring as compared to winter, due to the plant growth of bracken fern, grass and other shrubbery. These classified images were used in post-classification change detection analysis which revealed that the bracken fern infestation in the Royal Natal National Park and Rugged Glen Nature Reserve had increased at a rate of 24 % and 27 % per annum respectively. This showed that bracken fern is spreading in the Royal Natal National Park and Rugged Glen Nature Reserve, as expected. Fire regimes, slope and aspect were found as factors that could be promoting the spread of bracken fern, 67.5 % and 75 % of the bracken fern infestation in the Park and Reserve respectively, occurred in areas that were burnt by fire regimes and have gentle to moderately gentle slopes facing east, south east and south. / Thesis (M.Sc.Sur.)-University of KwaZulu-Natal, Durban, 2013.

Aristida junciformis subsp. junciformis Trin. et Rupr. is an indigenous, densely tufted, evergreen perennial grass associated with the degeneration of grasslands over large areas of South Africa. More than two hundred thousand square kilometres of veld, c. 17% of the total land area of South Africa, contains A. junciformis. The aim of this study was to improve our understanding of the mechanisms by which this species invades and dominates grassland, specifically in this study, Southern Tall Grassveld. Aristida junciformis also has a low nutritional value resulting in a very low grazing value. The unpalatability of the plant is due to the high tensile strength of the leaves, whose hard, fibrous laminas are very difficult for a grazing animal to crop once their length attains 30 cm or more. This species lack of response to conventional grazing practices has often resulted in a grassland in which the carrying capacity has diminished to such an extent as to be virtually useless for grazing in a relatively short time. The extent of encroachment of veld by A. junciformis appears dependant on the frequency of disturbance and rest afforded to the veld. Annual burning and mowing maintained the species composition of A. junciformis at levels <10% whilst protection from fire, burning or grazing allows this species to dominate the herbaceous layer at levels approaching 90%. Aristida junciformis does not become moribund and is unlikely to die if left undefoliated. As the abundance of A. junciformis increases, veld deterioration gradually accelerates through increased selective grazing on remaining palatable species. Competition from adult A. junciformis plants increases the mortality of seedlings and constrains growth of surviving seedlings. Tiller production of Aristida junciformis seedlings declined from an average of 5.2 tillers per seedling in a no competition situation to 2.2 tillers per seedling when subjected to full competition. Tiller production of T. triandra seedlings decreased from 9.6 tillers per seedling free from competition to 3.3 tillers per seedling subject to full competition for resources. Once these seedlings have become adult plants they are avoided by grazing animals and grazing pressure on the remaining palatable species consequently increases. This allows the A. junciformis plants to increase their size and density in the sward. Once this density is sufficiently high, grass seedlings of either A. junciformis or more desirable grass species such as T. triandra are unable to establish, eventually resulting in a monospecific stand of A. junciformis if left undisturbed. Large amounts of caryopses are produced by A. junciformis - up to a 19 000 caryopses from a large mature plant (c. 38 000 caryopses/m²). Of these c. 40% is likely to be infertile but the remaining c. 60% viable caryopses are dispersed in a typically leptokurtic distribution, the number of caryopses dispersed rapidly declining within a 10 metre radius. A large proportion of the caryopses was trapped in surrounding foliage but in open swards caryopses had greater opportunity to be blown further distances than in a closed sward. The density of A. junciformis caryopses on the soil surface was positively correlated with the density of flowering adult plants in the area and varied from 400 caryopses/m² (density of parent plants c. 0.6 plants/m²) in less effected areas to 11000 caryopses/m² (density of adult plants c. 6 plants/m²) in severely encroached areas. The primary function of the three awns appears to be orientating the caryopsis correctly for in its descent from the parent plant to expedite germination. Caryopses orientated vertically with the awns uppermost exhibited the highest and most rapid germination (67%) compared to caryopses lying horizontally (35%) whilst only 1% of inverted caryopses germinated. Caryopses trapped in litter and effectively held off the soil surface failed to germinate. Removal of the glumes from A junciformis seed greatly enhanced the rate and overall germination of the seed except for inverted seed of which <1% germinated. The highest numbers of A. junciformis seedlings (32 seedlings/m²) were found in those areas with the highest density of caryopses on the soil surface. Despite the large amounts of caryopses produced, dispersed and landing in apparently suitable micro-sites for germination, comparatively few A. junciformis seedlings (n=992) were found and overall germination ranged between 1 % and 4% of the initial caryopses density on the soil surface. Seedling survival through winter was low with only 13% surviving to the following spring. The basal areas of A. junciformis increased overall by 66% whilst that of other grass species increased overall by only 3% in the time monitored. These results suggest that the primary method of encroachment of A. junciformis in the grass sward appears to be through vegetative expansion and not seedling recruitment. Frequent defoliation of the sward and avoidance of overgrazing to enhance the competitive abilities of palatable species and provide as high a fuel load as possible appear to be the most economically and logistically feasible ways to remove or at least inhibit A. junciformis veld encroachment at present. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 1998.

The objective of this study was to describe the impacts of the density of Chromolaena odorata (chromolaena) on species composition in coastal grasslands and to investigate serial changes in the vegetation following the implementation of a burning programme. The thesis deals with key ecological concepts and issues, so a comprehensive literature review is included. Chromolaena invades coastal grasslands that are not burnt regularly (i.e. biennially). Grasslands that were not burnt for 30 years were seral to secondary forest. The successional pathway from open grassland to closed canopy forest varied according to soil type. Coastal grasslands on Glenrosa soils were characterised by savanna at an intermediate stage between the grassland and forest states. Shading ended the persistence of savanna species (e.g. Combretum molle, Dichrostachys cinerea and Heteropyxis natalensis) in forest, whereas forest precursors (e.g. Canthium inerme, Maytenus undata and Protorhus longifolia) only established where fire was absent. Chromolaena infestations were characterised by multi-stemmed adult plants of variable height (i.e. 1-3 m), depending on soil type. Regic sands did not support stratified woody vegetation and chromolaena infestations were self-supporting, reaching a maximum height of 1.5 m. Glenrosa soils supported tree communities and chromolaena reached more than 3 m in places. The density of chromolaena affected species composition in grasslands with moderate to dense stands (> 5 adult plants m ¯² or >50000 shrubs ha ¯¹). Chromolaena stands became monospecific when the number of adult plants exceeded 7 m ¯². Succession to forest also ceased once chromolaena became thicket-forming. Fire-induced mortality of the chromolaena depended on grass fuel loads. Grass cover of 30% (c. 1 000 kg ha ¯¹) was required to achieve 80% mortality of the parent infestation after the initial burn. Dense infestations could only be killed by running head-fires from adjacent grasslands into thickets. Under conditions where head-fires could not be used, infestations were slashed and burnt at the height of the dry season (July to August) to achieve an 80% kill rate. Seedlings were killed (99%) by annual burning in sparse (≤ 10000 shrubs ha ¯¹) to moderate < 50 000 shrubs ha ¯¹) infestations. The suppression of chromolaena and other alien species, establishing on bare ground after clearing dense infestations, required chemical control until grass cover was sufficient (i.e. 1 000 kg ha ¯¹) to effect uniform burning. Certain secondary alien invaders (e.g. Lantana camara, Psidium guajava and Solanum mauritianum) persisted by coppicing profusely after fire and herbicides need to be integrated into burning programmes when these species occur. Grasslands on regic sands (e.g. Ischaemum fasciculatum, Panicum dregeanum and Themeda triandra) were more resilient to the modifying effects of woody vegetation, than grasslands on Glenrosa soils. Grasslands on Glenrosa soils did not revert to an open state but persisted as ruderal savanna grassland (e.g. Eragrostis curvula, Hyparrhenia tamba and Cymbopogon validus) once fire-resistant tree species (e.g. Combretum molle and Heteropyxis natalensis) had established. Depending the objectives for land management and the vegetation's condition, coastal grasslands can be rehabilitated and managed in multiple states, i.e. grassland, savanna or forest communities. A state-and-transition model based on the empirical data recorded in the study is presented and shows chromolaena altering vegetation states from open grassland to chromolaena dominated thicket. The model illustrates chromolaena thickets as the dominant phase of a moist coastal forest/savanna succession, irrespective of soil type, in absence of appropriate land management practices (e.g. control burning and integrated control of alien vegetation). This model should aid in planning strategies for the control of chromolaena in subtropical grasslands in South Africa. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 2000.

The aim of the study was to find benefits derived from the natural propagation and the use of guava plants and fruit by people living in rural areas of KwaZulu-Natal, looking at guava as a source of food, income, medicinal uses, shade, a source of fuel and use for agricultural purposes like fencing; and also assessing Conservation of the Agricultural Resource Act (CARA), Act 43 of 1983 relating to guava plant as invasive species. The Act states that all alien invader species and weeds should be controlled or removed depending on the category. CARA states that plants in category one are declared as alien invasive plants and are not allowed to grow on the land or appear on the water surface. Plants under this category may not be transported or allowed to disperse e.g. Psidium x durbanensis (Durban guava). Category two plants are invader species that have a potential value, plants that are used by the people as a source of income and food. These species can be retained if they grow in special areas demarcated for the purpose (an orchard). If these species are found outside demarcated areas they are to be removed e.g. Psidium guava (guava). Category three species are mostly plants with ornamental value which are not allowed to occur anywhere unless they were already in existence when the regulation came into effect e.g. Psidium guineense (brazillian guava) and Psidium cattleianum (strawberry guava). The study focused on selected areas of KwaZulu-Natal,: Umgungundlovu district municipality (Richmond local municipality) and Uthungulu district municipality. Richmond represented the midlands areas and Uthungulu the coastal areas to reflect two different areas of KwaZulu-Natal. To investigate this study the researcher used telephonic interviews with 23 Extension officials, questionnaires to guide focus group discussions which were conducted with 28 community groups that were involved in guava usage. Informal observation surveys were also carried out with five markets (stall holders) selling guava and guava products. Informal observations in two supermarkets and two home industries were also conducted. The results showed that people in rural areas still use this resource (guava) as a source of fuel (wood), medicine (especially the leaves and bark), fruit for own consumption (either processed or raw) and income generation. The impact of the legislation on rural poor communities is negative as guavas sustain livelihoods and the costs of applying for permits are prohibitive. People are illiterate yet they have to apply for special permits to plant this useful species because the regulation stipulates that guava plants must be controlled if dispersed outside demarcated areas. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2008.