Varieties of Lantana camara (lantana) have been introduced into many countries of the world as ornamental plants and have become invasive weeds in many countries including South Africa. In South Africa, it mostly invades the sub-tropical eastern and northern range. Mechanical and chemical control options are expensive and ineffective. A biocontrol programme was initiated in South Africa in 1961. To date, 22 insect species, and a fungus have been introduced, of these 10, and the fungus have established. Three indigenous lepidopteran species and an exotic generalist pest mealybug are also associated with the weed. The variable success of some of the agents released on L. camara worldwide has been ascribed to a few factors. One important aspect is the large range of varieties encountered in the field. It is therefore essential to be able to predict the possible establishment and impact of agents on many varieties. Laboratory trials on five of the established agents showed clear varietal preferences. In the field, most of the biocontrol agents had limited geographic ranges, linked to altitudinal conditions, as higher populations were recorded at low lying warm summer rainfall areas. A pink and orange flower corolla lobe and throat colour combination and plants with few to medium leaf hairs were most abundant in South Africa. Most of the agent species had individual preferences towards different flower colour combinations, as the agents built up different population levels on varieties in the field, within the suitable geographic region for the insect species. Eight agents preferred smooth leaved varieties, while three preferred hairy leaves, and three had no specific preference to leaf hairiness. Varietal preferences thus did play a significant role in agent populations and accompanied impact achieved in the field. New candidate agents need to be proven specific under quarantine conditions and the results extrapolated to predict specificity in the field, while avoiding potential non-target effects. Many authors have questioned the validity of laboratory host specificity trials. The conventional wisdom is that insects portray a far wider host range in the laboratory than what they would do in the field. In other words, laboratory studies measure the physiological host range of an agent and are conservative and usually don’t reflect the ecological host range of agents in the field. To avoid unnecessary rejections of biocontrol agents, this study has made a retrospective study of the host specificity of agents established in the field. Their laboratory and field host ranges were compared and it was found that virtually all the agents reflect similar or less non-target effects in the field than predicted during multiple choice trials. Of the 14 agents, only one introduced species, Teleonemia scrupulosa, and the indigenous species, Hypena laceratalis and Aristea onychote were able to sustain populations on non-target species in the field in the absence of L. camara. Insect populations on non-target species were much reduced compared to that on L. camara. Furthermore non-target effects were only recorded on plant species closely related to the target weed. The multiple choice trials therefore predict field non-target effects accurately. Predictions of non-target effects of candidate agents can therefore be accurately predicted by laboratory studies, in terms of species likely to be affected and to what extent. One field that need further study though is the impact of non-target effects, especially on Lippia species by L. camara biocontrol agents.

This study sought opportunities to mitigate the pressures of land transformation and alien invader plants on commercial farm land in the thicket biome in the lower reaches of the Fish Kowie Corridor. It had two aims. Firstly, to determine the role incentives could play in mitigating these pressures. Secondly, to determine the characteristics of an incentive programme that would most effectively achieve this. In order to do this, an understanding of landowner activities, needs, opinions and barriers to behaviour; the nature of the pressures on thicket and the nature of the required behaviour to reduce these pressures; and current and past institutional arrangements needed to be achieved. This was done predominantly through a current literature review and personal interviews with landowners and key informants. These findings were used to make recommendations for an effective incentive programme. Landowners showed a preference towards tangible incentives, in particular management assistance, financial compensation and law enforcement. They indicated an aversion to an incentive programme implemented by a government agency, particularly district and provincial government. Rather, landowners showed a propensity towards a nongovernment organisation (NGO) or a farmers group implementing an incentive programme. It was recommended that the two major pressures, namely land transformation and alien invader plants, required different interventions by different agencies in order to be mitigated. The pressure of land transformation required a stewardship model response, with the primary drive being a non-contractual environmental extension service to landowners. The extension service should focus on promoting pro-conservation practises, raising awareness and disseminating information. It should also build a relationship of trust between landowners and the implementing agency. The pressure of alien invader plants would be most effectively addressed through the Working for Water programme. Tangible incentives must be provided to the landowner to induce the costly exercise of alien invader plant control. In particular, the high cost of labour must be addressed. The regulatory incentive of applying laws requiring landowners to control alien invader plants on their land should also be enforced.

Lygodium microphyllum, native to the Old World tropics, has invaded central and southern Florida, destroying native habitats, reducing biodiversity and altering fire regimes. Prescribed fire, one of several methods used to manage L. microphyllum infestations, reduces fern biomass over large areas, but its effects on spore viability are unknown. To provide tools to evaluate whether fire-dispersed spores are viable, this research determined how heat affects spore viability. Spores were exposed to temperatures of 50°C to 300°C for durations of 5 seconds to 1 hour, then allowed to germinate on agar in petri plates. Percent germination was assayed after two weeks. Temperatures of 50°C had little effect; 300°C killed spores for all durations. Results indicate that while viability of unburnt spores decreases with increasing temperature and duration of heat exposure, spores are killed when exposed to relatively low temperatures compared to those in fires.

Torpedograss (Panicum repens) was first observed in Lake Okeechobee in the 1970s and appears to have displaced an estimated 6,400 ha of native plants, such as spikerush (Eleocharis cellulosa), where inundation depths are often less than 50 cm. Two series of studies evaluated substrate exposure and water depth influences on torpedograss establishment and competitiveness. Results revealed that fragments remain buoyant for extended periods and so facilitate dispersal. Once anchored to exposed substrate fragments can readily root and establish. Subsequently, torpedograss thrives when subjected to inundations to 75 cm and survives prolonged exposure to depths greater than 1 m. These findings suggest that fluctuating water levels contribute to torpedograss dispersal and colonization patterns and that low water levels increase marsh area susceptible to invasion. The competition study found that spikerush grown in monoculture produces significantly more biomass when continually inundated to shallow depths (10 to 20 cm) than when subjected to drier conditions (-25 cm) or greater inundations (80 cm). In contrast, torpedograss establishes more readily on exposed substrate (-25 to 0 cm) compared to inundate substrates. During the first growing season biomass production increases as substrate exposure interval increases. However, during the second year, established torpedograss produces more biomass when grown on intermittently wet (0 cm) compared to permanently dry (-25 cm) or intermittently inundated (10 cm) substrates. No difference in production was observed between substrates permanently inundated (10 cm) and any other regime tested. During the first two years of torpedograss invasion, regardless of treatment, spikerush suppresses invasion and torpedograss had little effect on established spikerush, indicating that spikerush-dominated areas are capable of resisting torpedograss invasion. Even so, disturbances that might cause mortality of long hydroperiod species, such as spikerush, may create open gaps in the native vegetation and thus facilitate torpedograss establishment and expansion.

The Important Bird Areas (IBAs) network of BirdLife International aims to identify sites that are essential for the long-term conservation of the world’s avifauna. A number of global change events have the potential to negatively affect, either directly or indirectly, most bird species, biodiversity in general and associated ecological processes in these areas identified as IBAs. To assist conservation decisions, I assessed a suite of ten landscape scale anthropogenic pressures to 115 Important Bird Areas (IBAs) in South Africa, both those currently placing pressures on IBAs and those that constitute likely future vulnerability to transformation. These threats are combined with irreplaceability, a frequently used measure of conservation importance, to identify the suite of IBAs which are high priority sites for conservation interventions: those with high irreplaceability and are highly vulnerable to anthropogenic threats. A total of 22 (19%) of the South African IBAs are highly irreplaceable and are highly vulnerable to at least some of the pressures assessed. Afforestation, current and potential future patterns of alien plant invasions affect the largest number of highly irreplaceable IBAs. Only 9% of the area of highly irreplaceable IBAs is formally protected. A total of 81 IBAs (71%) are less than 5% degraded or transformed. This result, together with seven highly irreplaceable IBAs found outside of formally protected areas with lower human densities than expected by chance provides an ideal opportunity for conservation interventions. However, all the pressures assessed vary geographically, with no discernible systematic pattern that might assist conservation managers to design effective regional interventions. Furthermore, I used the newly emerging technique of ensemble forecasting to assess the impact of climate change on endemic birds in relation to the IBAs network. I used 50 endemic species, eight bioclimatic envelope models, four climate change models and two methods of transformation to presence or absence, which essentially creates 2400 projections for the years 2070-2100. The consensual projection shows that climate change impacts are very likely to be severe. The majority of species (62%) lose climatically suitable space and 99% of grid cells show species turnover. Five species lose at least 85% of climatically suitable space. The current locations of the South African Important Bird Areas network is very likely ineffective to conserve endemic birds under climate change along a “business a usual” emissions scenario. Many IBAs show species loss (41%; 47 IBAs) and species turnover (77%; 95 IBAs). However, an irreplaceability analysis identified mountainous regions in South Africa as irreplaceable refugia for endemic species, and some of these regions are existing IBAs. These IBAs should receive renewed conservation attention, as they have the potential to substantially contribute to a flexible conservation network under realistic scenarios of climate change. Considering all the global change threats assessed in this study, the Amersfoort-Bethal-Carolina District and the Grassland Biosphere Reserve (IBA codes: SA018; SA020) are the key IBAs in South Africa for conservation prioritisation. / Dissertation (MSc)--University of Pretoria, 2008. / Zoology and Entomology / unrestricted

Intraspecific plant-soil feedback is a relationship in which plant affects the composition of the soil and such modified soil affects growth of the same plant species. This relationship and its intensity may be linked with plant dominance and invasiveness. Dominant species can alter the composition of the soil in their favor and thus show positive intraspecific plant-soil feedback. As the invasive species are commonly being dominant in their new environment, it can be expected that intraspecific positive plant-soil feedback could be an important factor allowing the invasive species to achieve their dominant position and become invasive. To test if the existence of positive intraspecific feedback could be a general mechanism underlying plant invasiveness I compared intraspecific plant-soil feedback in a group of invasive and introduced, but non-invasive, plants in the Czech Republic. I did this using a preselected set of 34 species - 17 invasive and 17 non-invasive. For realization of the project I used the method of two-phase experiment. The first phase is called soil conditioning - influencing of soil by the plant. In the second phase the same plant species are planted in conditioned soil from the first phase and in control (unconditioned) soil. Then I compared plant biomass from conditioned and...

Plant-soil feedback (PSF) is a mechanism which may contribute to the success of invasive plant species. Which of the soil components have the greatest impact on PSF? In a two-phase experiment, I observed changes in germination and growth of plants in reaction to intraspecific plant cultivation: selected plant species were grown in substrate consisting of cultivated or uncultivated soil, containing different composition and amounts of soil biota. The effect of changes in abiotic and biotic components of the soil was then assessed and compared among pairs of closely related invasive and native plant species. The main observed phenomenon was species-specificity of plant responses to changed soil conditions. The cultivation-induced changes in soil composition affected germination and biomass of the test plants positively, negatively, or were neutral, their effect differed between tested species - some of the observed species were more affected by changes in abiotic properties of the soil, some reacted to changes in soil biota composition. Nevertheless, the composition of soil biota affected germination and biomass of plants even regardless of cultivation: the presence of all biotic components of the soil had negative effect on biomass - with growing representation and amount of pathogens, fungi, micro-...

Michaela Kubátová Alien species of plants and biotic resistence of invaded communities This study is about problems and questions of alien plants and their relation to native communities in their new range. Ecologists are increasingly aware that soil organisms may affect plant communities because they are part of the processes that affect them. The soil organisms may affect the success of alien species invasion. Each species of plants differ in interaction with soil organisms, these interactions can result in specific feedback that will influence the future growth of other plants. According to Darwin's naturalization hypothesis related species should have similar enemies. This implies less successful invasion of alien plants at home with relatives. The practical part consists of two experiments. Using plant-soil feedback I studied under controlled conditions the importance of kinship of native plants and their soil organisms on the growth of three species of alien plants Impatiens, Parviflora, Stenactis annua and Epilobium ciliatum. There were used soil samples from localities with related and unrelated species; the soil was used as inoculums for growing first-generation plants, where there were original related, unrelated and alien plants. In the second phase only alien species were grown. Part of...

Invasive plants can outcompete native plants, replacing diverse plant communities with monocultures, which can negatively impact the whole ecosystem. One invasive plant, Phragmites australis, has invaded wetlands across North America. In Utah’s Great Salt Lake, it has greatly reduced the area of native plants that are important habitat for migratory birds. Here we describe experiments that assess multiple treatments for Phragmites removal and evaluate the return of native plants after Phragmites management. The treatments were applied to Phragmites patches at two scales (small 1/4-acre plots and large 3-acre plots) and across multiple sites to evaluate how patch size and environmental differences can influence the plants that return after Phragmites removal. The treatments (applied over 3 years and monitored two more) compared two different herbicides (glyphosate and imazapyr) and different herbicide and mowing timings. The treatments evaluated in the large patch study were 1.) untreated control 2.) fall glyphosate, winter mow, 3.) summer imazapyr, winter mow, 4.) summer glyphosate, winter mow. The treatments evaluated in the small patch study included treatments 1-4 above plus 5.) summer mow, fall glyphosate, 6.) summer mow, then black plastic solarization. In the small patches, we also monitored the seeds in the soil to assess how Phragmites management treatments can change the densities of Phragmites and native seeds. Fall glyphosate treatments were superior for Phragmites cover reduction. After the initial treatment, summer herbicide and mow treatments reduced Phragmites seed production, while fall glyphosate did not. Phragmites seeds were plentiful in the soil but were reduced following three years of all herbicide treatments. Native plant recovery following Phragmites management was extremely variable across sites. Sites with high soil moisture had better Phragmites removal and more native plants. But when flooding was deep, native plants were rare. Native seed density in the soil did not change due to Phragmites management, but soil seed densities were different across sites, which influenced native plant recruitment. Phragmites was removed more effectively and native plants returned in greater numbers in small patches compared with large. This was because small patches were typically near established native plant communities, which likely provided more native plant seeds and had hydrology that was less disturbed by human activity. In sites where native plants do not return after Phragmites management, practitioners may need to try revegetation with native plant seeds to restore important native plant communities.

The effects that mutualistic soil biota have on invasive species success is a growing topic of inquiry. Studies of the interactions between invasive plants and arbuscular mycorrhizal fungi (AMF) have shown changes in AMF community composition, reductions in AMF associations in invasive plants, and changes in native species fitness and competitive outcomes in invasive-shifted AMF communities. These findings support the degraded mutualist hypothesis, where invasive species alter the mutualist community composition, resulting in detrimental associations with the new mutualist community for native species. Here I present two studies that examine various aspects of the arbuscular mycorrhizal fungal (AMF) mutualism in the success of a newly invasive bunchgrass, Brachypodium sylvaticum. The first chapter is a field survey of AMF associations between a native bunchgrass, Elymus glaucus and B. sylvaticum in the invaded range. The second chapter presents a test of reduced mycorrhizal dependence between invasive and native-range populations of B. sylvaticum. For the field survey, AMF colonization and spore density of root and soil rhizosphere samples from B. sylvaticum and E. glaucus from the two regions of introduction of the B. sylvaticum invasion were measured. In this survey I found lower AMF colonization and spore density in B. sylvaticum compared to the native species in the invaded ranges. The reduction in AMF associations in B. sylvaticum was predicted to be due to the evolution of reduced mycorrhizal dependence in invasive populations compared to native populations of B. sylvaticum. I tested the prediction for reduced mycorrhizal dependence by measuring the fitness gains or losses with AMF inoculation compared to sterile conditions in both fertilized and unfertilized treatments for individuals of B. sylvaticum from each of the introduction sites in Oregon, USA and source populations from the native range in Europe. There were no differences in plant or AMF fitness between the invasive and native populations of B. sylvaticum. Under high nutrients the interaction between all B. sylvaticum plants and AMF was mutualistic. Under low nutrient treatments both B. sylvaticum and AMF had reduced fitness measures, suggesting a competitive interaction. Nutrient levels of inoculated unfertilized soils are similar to field conditions. It is likely that the reduction in AMF associations in B. sylvaticum observed in the field is due antagonistic interactions between AMF and B. sylvaticum.