- Title
- Associations between patterns of wild ungulate patch use, soil carbon and albedo in montane grasslands
- Creator
- Mc Gregor, Steven
- Subject
- Grassland ecology
- Subject
- Global environmental change
- Subject
- Climatic changes
- Date Issued
- 2024-12
- Date
- 2024-12
- Type
- Doctoral theses
- Type
- text
- Identifier
- http://hdl.handle.net/10948/69382
- Identifier
- vital:77250
- Description
- Grassy ecosystems are essential for human survival, providing key services including food production, water provisioning and moderating climate. Yet, grassy ecosystems remain undervalued due to misconceptions that they are remnants of degraded states of forest – a view that continues to influence climate change policies. This thesis explores the links between wild, free-roaming ungulate grazers and climate drivers, including carbon storage and surface albedo (i.e., reflectance of solar radiation), through their impacts on vegetation and soils. Using black wildebeest (Connochaetes gnou) as a model wild species, I compared their grazing patterns in an Afromontane grassland in the eastern Karoo, South Africa, to those of short-duration cattle grazing systems in similar nearby grasslands (Chapter 2). While short-duration grazing aims to mimic spatiotemporal wild ungulate grazing patterns to supposedly enhance ecosystem functioning and soil carbon stocks, I found that wildebeest had ~50% shorter grazing durations and much shorter rest intervals (1-5 days versus 60-365 days), revealing key differences in grazing patterns that may affect vegetation and climate feedbacks. Next, I examined spatial variations in soil organic carbon (SOC) stocks between grass growth forms that differ in grazing tolerance (Chapter 3). Red grass (Themeda triandra) tussock patches, sensitive to frequent grazing, had higher SOC to a soil depth of 20 cm (61.45 ± 1.59 Mg C·ha-1)than intensively grazed, prostrate-growing Cynodon dactylon grazing lawns (55.43 ± 3.40Mg C·ha-1), likely due to greater shading and soil moisture beneath tussocks which drives microbial decomposition. Seasonal albedo variations were then assessed across distinct grassland patch types among seasons to determine whether albedo varies seasonally at fine patch-scales between grass patches, between shrub and grass patches, and with grazing (Chapter 4). Albedo was lower during the growing season compared to dormancy, and was consistently lower in dwarf shrub (Pentzia incana) encroached patches compared to grass patches. No albedo differences between grazed and less-grazed tussock grass patches of the same species were found, although intensively grazed grazing lawns had consistently higher albedo than most patch types. Finally, I evaluated trade-offs between plant carbon, albedo, and their impacts on radiative forcing (i.e., atmospheric warming/cooling) resulting from patch type changes commonly found in grassy ecosystems (Chapter 5). The loss of perennial grass cover resulted in the highest net positive (warming) effect, mostly due to reduced root biomass. Additionally, shrub encroachment into all patches lowered albedo, but led to negative (cooling) effects from shrub encroachment into bare ground patches due to biomass gains. This thesis challenges current views of grassy landscapes and short-duration grazing systems, emphasizing the need to rethink climate change mitigation strategies to prioritize maintaining heterogeneity, while enhancing carbon sequestration and albedo in grassy ecosystems.
- Description
- Thesis (PhD) -- Faculty of Science, School of Environmental Sciences, 2024
- Format
- computer
- Format
- online resource
- Format
- application/pdf
- Format
- 1 online resource (178 pages)
- Format
- Publisher
- Nelson Mandela University
- Publisher
- Faculty of Science
- Language
- English
- Rights
- Nelson Mandela University
- Rights
- All Rights Reserved
- Rights
- Open Access
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Collections
NMU School of Environmental Sciences
| Thumbnail | File | Description | Size | Format | |||
|---|---|---|---|---|---|---|---|
| View Details Download | SOURCE1 | MCGREGOR, S.pdf | 3 MB | Adobe Acrobat PDF | View Details Download |