Exploring the role of herbivory in Albany Subtropical Thicket restoration
- Authors: Hunt, Kristen Louise
- Date: 2024-04
- Subjects: Shrubs -- South Africa , Portulacaria afra -- South Africa , Grasslands -- South Africa , Plant communities -- South Africa
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/64060 , vital:73647
- Description: This dissertation attempted to investigate the influence of herbivory on the success of thicket restoration, addressing a critical gap in the current knowledge within the restoration initiative. Despite two decades of thicket restoration practices, the role of herbivory in influencing restoration success has been assumed and not yet quantified. This research aimed to observe and identify herbivore species and their interactions that may affect the survival of Portulacaria afra Jacq. material planted in thicket restoration contexts. This research took place on three game farms serving as case studies within the Albany Subtropical Thicket (Eastern Cape, South Africa). Multiple experiments were conducted to assess how the concept of different “natural refugia” might impact herbivore interactions with planted material, incorporating factors such as planting around rainfall, within open and semi-intact vegetation patches, and in proximity to water sources. Trail cameras were used for real-time monitoring of herbivore interactions within planted sites to understand and quantify herbivore interactions with P. afra cuttings and how they may impact plant survival. Results from the trail camera monitoring (Chapter 2) indicate varied herbivore interactions occurring on planted material, with the primary herbivore responsible for these interactions varying among farms. Species interactions were not consistent across farms, and herbivore interactions exhibited spatial and temporal variability. Notably, interactions declined soon after the start of the wet phase when surrounding vegetation could recover, indicating the influences of alternative forage availability on herbivore foraging choices. Different herbivore interactions were identified and quantified through trail camera images, ranging from minor biomass removal (estimated at <5 cm of stem and leaf material) to more detrimental actions such as uprooting and leaf stripping. Consistently, planted P. afra survival rates (Chapter 3) were significantly higher for protected material than those exposed to herbivores, regardless of whether planted in a dry or wet phase. Moreover, when exposed to herbivores, rooted material had significantly higher survival rates than unrooted material, indicating the potential advantage of a well-developed root system in faster recovery after a herbivory event. This research explored the influence of various factors, including rainfall, rooting state, protection, surrounding vegetation, and proximity to water, on P. afra survival and how some of these factors may affect P. afra survival in relation to herbivore interactions (Chapter 3). Significant differences in cutting survival were observed between dry and wet phases, rooted and unrooted material, and material protected vs exposed to herbivores. While survival was not significantly different in experiments involving surrounding vegetation and proximity to water, potential patterns were identified, warranting further investigation. A clipping and defoliation experiment under simulated seasonal conditions emphasised the significance of , Thesis (MSc) -- Faculty of Science, School of Environmental Sciences, 2024
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- Date Issued: 2024-04
Effects of fire on architecture and composition of canopy shrubs in subtropical dune thicket of the southeastern Cape Floristic Region
- Authors: Strydom, Tiaan , Grobler, Adriaan
- Date: 2023-12
- Subjects: Plant ecology -- Research , Plant communities -- South Africa , Browsing (Animal behavior)
- Language: English
- Type: Doctorial theses , text
- Identifier: http://hdl.handle.net/10948/62632 , vital:72899
- Description: Disturbance, such as fire and megaherbivory, is a pervasive phenomenon globally and has different effects on the flora and vegetation of different ecosystems. The Cape Floristic Region (CFR) of South Africa includes the distinctive Subtropical Thicket biome, which occurs as interrupted blocks that are not exposed to fire, but also as mosaics with the fire-prone vegetation of the Fynbos biome, especially on coastal dunes where thicket species are exposed to fire. Subtropical Dune Thicket (hereafter thicket) thus co-occurs with Fynbos, capable of supporting intense fires that can lead to thicket shrub defoliation and mortality. Thicket also experiences disturbance from meso- and megaherbivores that causes defoliation and mortality of shrubs. The aim of this study was to investigate the resilience of thicket shrub species to varying disturbance levels from fire and browsing to understand what drives thicket persistence in a fire-prone landscape. Firstly, I established the architectural traits of thicket species in long unburnt and post-fire contexts and investigated the relationships between these traits and the survival, resprouting ability and persistence of thicket shrubs. In mature thicket, I identified three distinct architectural guilds, namely hedge formers, lateral spreaders, and vertical growers. In post-fire thicket I identified three resprouting architectures, namely weak resprouters, moderate resprouters and strong resprouters. There was no strong relationship between the unburnt and post-fire resprouting architectures. Secondly, I compared thicket species and architectural composition in patches of landscape that experience different levels of fire exposure to assess the potential effect of fire frequency on determining thicket structure. I recognised three thicket vegetation units, each with a distinct structure and each corresponding to the level of fire exposure in the landscape. The first unit, forest-thicket, is exposed to low levels of fire frequency (> 100 years) and harbours forest species, many of which were vertical growers. The second unit, thicket, is exposed to moderate levels of fire frequency (50-100 years) and is dominated by lateral spreaders. The last unit, fynbos-thicket, is exposed to high levels of fire frequency (10-50 years) and here hedge-forming shrubs dominate the canopy cover. Forest-thicket and fynbos-thicket had a diverse set of shrub species with many being restricted to their respective vegetation type, whereas thicket had a lower diversity with no unique shrub species. , Thesis (DPhil) -- Faculty of Science, School of Natural Resource Management, 2023
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- Date Issued: 2023-12