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You searched for +publisher:"Stellenbosch University" +contributor:("Midgley, Guy"). Showing records 1 – 3 of 3 total matches.

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Stellenbosch University

1. Davis-Reddy, Claire. Assessing vegetation dynamics in response to climate variability and change across sub-Saharan Africa.

Degree: PhD, Botany and Zoology, 2018, Stellenbosch University

ENGLISH ABSTRACT: Understanding and predicting how anthropogenic climate change is likely to impact terrestrial ecosystems across sub-Saharan Africa is a key question for both ecology and for regional and global climate policy development. This predictive understanding hinges on a far better ability to detect, interpret, and attribute changes in vegetation cover and productivity, which is the basis for ecosystem response and resilience to anthropogenic climate change. Monitoring and modelling of vegetation dynamics in the context of climate change requires long-term datasets of key ecosystem indicators such as vegetation productivity and phenology. The use of remotely sensed vegetation indices to detect vegetation change related to climate has become an important application of remotely sensed imagery. The third generation Normalized Difference Vegetation Index (NDVI3g) time series from the Global Inventory Modeling and Mapping Studies (GIMMS) has a 34-year long history (1982-2015) and provides unprecedented opportunity to examine vegetation dynamics in response to changes in temperature, rainfall, and increases in atmospheric carbon dioxide (CO2). This thesis makes use of the NDVI3g time-series to examine the influence of climate on vegetation productivity and phenology in order to (i) assess recent shifts in vegetation across sub-Saharan Africa (SSA) and (ii) facilitate improved simulations of vegetation by Dynamic Global Vegetation Models (DGVMs). The NDVI3g information was integrated with climate data and large-scale climate fluctuations and oscillations in sea surface temperature and atmospheric pressure to test hypotheses on the role of both climate variability and change on vegetation activity. Seasonal and long-term patterns of change were compared with projections of a dynamic global vegetation model, the "adaptive Dynamic Global Vegetation Model" (aDGVM) that was initially developed for application in sub-Saharan Africa. In the first component of the thesis results show that the vegetation of SSA is driven by rainfall and associated fluctuations and oscillations in sea surface temperature (SST) and atmospheric pressure, with the El Niño-Southern Oscillation (ENSO) being the most dominant driver of variability in both vegetation productivity and phenology over eastern and southern Africa. Vegetation tends to show a stronger positive response to rainfall in the 3 months preceding vegetation growth suggesting that time-lag effects are significant when assessing the influence of climate. In the second component, trend analyses provide evidence for a number of important spatial and temporal patterns of change in vegetation productivity and phenology over SSA, which are generally consistent with independently reported long-term trends. Significant added value was provided to previous studies through the use of productivity and phenology metrics, which facilitated an assessment of vegetation dynamics at both the seasonal and inter-annual scale. A clear latitudinal pattern of change was detected where… Advisors/Committee Members: Midgley, Guy, Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology..

Subjects/Keywords: Vegetation dynamics  – Su-Saharan Africa; Climate change  – Sub-Sahara Africa; UCTD

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Davis-Reddy, C. (2018). Assessing vegetation dynamics in response to climate variability and change across sub-Saharan Africa. (Doctoral Dissertation). Stellenbosch University. Retrieved from http://hdl.handle.net/10019.1/103595

Chicago Manual of Style (16th Edition):

Davis-Reddy, Claire. “Assessing vegetation dynamics in response to climate variability and change across sub-Saharan Africa.” 2018. Doctoral Dissertation, Stellenbosch University. Accessed October 17, 2019. http://hdl.handle.net/10019.1/103595.

MLA Handbook (7th Edition):

Davis-Reddy, Claire. “Assessing vegetation dynamics in response to climate variability and change across sub-Saharan Africa.” 2018. Web. 17 Oct 2019.

Vancouver:

Davis-Reddy C. Assessing vegetation dynamics in response to climate variability and change across sub-Saharan Africa. [Internet] [Doctoral dissertation]. Stellenbosch University; 2018. [cited 2019 Oct 17]. Available from: http://hdl.handle.net/10019.1/103595.

Council of Science Editors:

Davis-Reddy C. Assessing vegetation dynamics in response to climate variability and change across sub-Saharan Africa. [Doctoral Dissertation]. Stellenbosch University; 2018. Available from: http://hdl.handle.net/10019.1/103595


Stellenbosch University

2. Zietsman, Alta. Response of different plant functional types to environmental variability on Marion Island: Quantifying diurnal patterns over a seasonal cycle using the photochemical reflectance index.

Degree: MSc, Botany and Zoology, 2018, Stellenbosch University

ENGLISH ABSTRACT: Marion Island forms part of the Prince Edward Island group, situated near the latitude of 47° South. Seasonal and temporal variability in climate on Marion Island has been described as muted, due to the thermal buffering of the surrounding ocean. This is thought in turn to lead to an extended growing season. However, empirical in situ measurements of net primary production (NPP), are lower than estimations based on annual temperature and precipitation. The aim of this study was to explore which potentially limiting environmental factors exert control over photosynthetic behaviour at a range of sub-annual temporal scales, in order to better understand what limits production in plant functional types (PFTs) typical of Marion Island. The three main PFTs selected for study were lower plants, cushion plants and grasses. Spectral reflectance sensors were used in situ to investigate the diurnal and seasonal patterns of physiological stress and inferred photosynthetic behaviour. The Photochemical Reflectance Index (PRI) is calculated from a ratio of reflected versus incoming light wavebands, that are influenced by a change in carotenoid ratios, indicating photosynthetic efficacy through the activity of the xanthophyll cycle. The xanthophyll cycle is closely linked to photosystem II and thus an important component of the non-photochemical quenching (NPQ) process that acts as a photo-protection mechanism. PRI measurements require careful interpretation in the absence of any independent confirmatory measurements. Repeated ancillary measurements of leaf chlorophyll fluorescence and leaf chlorophyll content via independent instrumentation provided support for the PRI measurements as an indicator of physiological stress. This approach was also used to confirm that the point monitoring of individual canopies was representative of surrounding vegetation. Contrary to the assumption that climate variability is muted, fine temporal scale monitoring revealed remarkably high temporal climate variability on Marion Island. Although seasons sensu stricto could not be clearly defined, a shift in climate can be seen between “winter” and “summer” months, most notably by a replacement of cold, calm days by warm, windy days. PRI data revealed that different PFTs (and to an extent, individual species) showed somewhat distinct optimum growing seasons, with the seasonal shift in climate affecting PFTs differently. The three main PFTs showed distinct PRI patterns. Lower plants showed the deepest daily PRI depression, almost regardless of environmental conditions, confirming for thefirst time over an entire annual cycle their previously proposed low light adaptive characteristics. Cushion plants only showed a midday PRI depression on days withhigh temperatures, revealing their optimal adaptation to cooler diurnal conditions. Grasses had the highest PRI values, responding positively on days with higher temperatures, and revealing their more efficient performance under warmer and brighter conditions, in distinct contrast to the… Advisors/Committee Members: Midgley, Guy, Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology..

Subjects/Keywords: Different plant functional types; Photochemical Reflectance Index (PRI); Climate  – Marion Island; UCTD

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Zietsman, A. (2018). Response of different plant functional types to environmental variability on Marion Island: Quantifying diurnal patterns over a seasonal cycle using the photochemical reflectance index. (Masters Thesis). Stellenbosch University. Retrieved from http://hdl.handle.net/10019.1/103617

Chicago Manual of Style (16th Edition):

Zietsman, Alta. “Response of different plant functional types to environmental variability on Marion Island: Quantifying diurnal patterns over a seasonal cycle using the photochemical reflectance index.” 2018. Masters Thesis, Stellenbosch University. Accessed October 17, 2019. http://hdl.handle.net/10019.1/103617.

MLA Handbook (7th Edition):

Zietsman, Alta. “Response of different plant functional types to environmental variability on Marion Island: Quantifying diurnal patterns over a seasonal cycle using the photochemical reflectance index.” 2018. Web. 17 Oct 2019.

Vancouver:

Zietsman A. Response of different plant functional types to environmental variability on Marion Island: Quantifying diurnal patterns over a seasonal cycle using the photochemical reflectance index. [Internet] [Masters thesis]. Stellenbosch University; 2018. [cited 2019 Oct 17]. Available from: http://hdl.handle.net/10019.1/103617.

Council of Science Editors:

Zietsman A. Response of different plant functional types to environmental variability on Marion Island: Quantifying diurnal patterns over a seasonal cycle using the photochemical reflectance index. [Masters Thesis]. Stellenbosch University; 2018. Available from: http://hdl.handle.net/10019.1/103617


Stellenbosch University

3. Agenbag, Lize. A study on an altitudinal gradient investigating the potential effects of climate change on fynbos and the Fynbos-Succulent Karoo boundary.

Degree: Botany and Zoology, 2006, Stellenbosch University

Thesis (MSc (Botany and Zoology)) – University of Stellenbosch, 2006.

Global circulation models predict that the Cape Floristic Region (CFR), a biodiversity hotspot, in the near future will be subjected to rising temperatures and widespread droughts as a result of rising atmospheric CO2 causing global climate change. It is predicted that climate change will lead to a southward shift of the Succulent Karoo, a neighbouring more drought tolerant biome, and a possible invasion of Fynbos, the main vegetation type of the CFR, by succulent species. In this research project, the effects of climate change on Fynbos, and the likelihood of Succulent Karoo invading Fynbos are assessed by means of various monitoring and experimental studies on an altitudinal gradient spanning a natural transition between fynbos and succulent karoo vegetation. An analysis of plant species diversity and turnover on the gradient revealed high species turnover between succulent karoo and the rest of the gradient, associated with a boundary between two soil types: shale (associated with succulent karoo) and sandstone (associated with fynbos). Phenological monitoring of fynbos species across the gradient showed how growth of fynbos species is affected negatively by high temperatures, and that low but regular rainfall is required to sustain growth during the dry Mediterranean summer. Retrospective growth analysis of Proteaceae species pairs with contrasting range sizes revealed that small geographic ranges do not signify low tolerance of climate variation, but rather that faster growing species are more sensitive to interannual climate variation than slow growing species. Exposing fynbos species to experimental drought confirmed that faster growing species will be more severely affected by climate change than slow growing species with conservative water use strategies. This experiment also confirmed the importance of rainfall reliability for growth in fynbos species when a naturally occurring prolonged dry period affected some species more severely than the drought treatment of an average reduction in rainfall. A reciprocal transplant experiment exposed fynbos seedlings to both warmer and drier conditions when they were planted outside of their natural ranges in the succulent karoo. Soil type as a barrier to invasion of fynbos by succulent karoo was also tested. Soil type was found to be not limiting to succulent karoo species and competition and disturbance was revealed to be more important in determining the fynbos-succulent karoo boundary than climate. It was concluded that productivity in fynbos will be adversely affected by rising temperatures and that differing responses to climate change between slow and fast growing species will lead to shifts in dominance among species, and consequently altered community structures and vegetation dynamics. Fires are likely to facilitate invasions of marginal habitats by succulent karoo because of sensitivity of fynbos regeneration stages to high temperatures and drought.

Advisors/Committee Members: Esler, Karen J., Midgley, Guy F., University of Stellenbosch. Faculty of Science. Dept. of Botany and Zoology..

Subjects/Keywords: Botany; Climatic changes  – Environmental aspects  – South Africa  – Western Cape; Phytogeography  – Climatic factors  – South Africa  – Western Cape; Fynbos  – Climatic factors  – South Africa  – Western Cape; Fynbos  – Effect of temperature on  – South Africa  – Western Cape; Succulent plants  – Climatic factors  – South Africa  – Western Cape; Succulent plants  – Effect of temperature on  – South Africa  – Western Cape

Record DetailsSimilar RecordsGoogle PlusoneFacebookTwitterCiteULikeMendeleyreddit

APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Agenbag, L. (2006). A study on an altitudinal gradient investigating the potential effects of climate change on fynbos and the Fynbos-Succulent Karoo boundary. (Thesis). Stellenbosch University. Retrieved from http://hdl.handle.net/10019.1/1737

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16th Edition):

Agenbag, Lize. “A study on an altitudinal gradient investigating the potential effects of climate change on fynbos and the Fynbos-Succulent Karoo boundary.” 2006. Thesis, Stellenbosch University. Accessed October 17, 2019. http://hdl.handle.net/10019.1/1737.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7th Edition):

Agenbag, Lize. “A study on an altitudinal gradient investigating the potential effects of climate change on fynbos and the Fynbos-Succulent Karoo boundary.” 2006. Web. 17 Oct 2019.

Vancouver:

Agenbag L. A study on an altitudinal gradient investigating the potential effects of climate change on fynbos and the Fynbos-Succulent Karoo boundary. [Internet] [Thesis]. Stellenbosch University; 2006. [cited 2019 Oct 17]. Available from: http://hdl.handle.net/10019.1/1737.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Agenbag L. A study on an altitudinal gradient investigating the potential effects of climate change on fynbos and the Fynbos-Succulent Karoo boundary. [Thesis]. Stellenbosch University; 2006. Available from: http://hdl.handle.net/10019.1/1737

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

.