A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of requirements for the degree of Master of Science. August 2015. / iii
ABSTRACT
Global changes are likely to have negative impacts on many ecosystems including savannas. Semi-arid environments are notable for the wide range of seasonal patterns of leaf display in the tree communities. The environmental cues of leaf out and leaf drop are not consistent across species, and are not always directly linked to water availability, indicating that some species might be particularly sensitive to changes in climate. Strategies employed by trees which leaf early or drop their leaves late are likely to impact other aspects of their life-history and functioning so I expect particular plant functional types to be associated with particular vegetation functional traits. I assessed how variable savanna leafing strategies are among 28 species at a semi-arid savanna site at Nylsvley, and used this information to group species into plant functional types (PFTs). These PFTs were then assessed in terms of key vegetative traits to explore the life history consequences of different leafing strategies. Leaf phenology was monitored throughout one growing season and quantified using 8 key phenological metrics. The timing of leaf display tracks the timing of seasonal rainfall but with wide variation, with some species retaining their leaves throughout dry season. Other species loss some leaves throughout the growing season, some species only flushed their leaves after the first rains, and other flush before the first rains. I identified 4 clear PFTs using the MClust clustering integrated with subjective procedure. Four vegetative traits were measured: specific leaf area, leaf nitrogen, maximum stomatal conductance and wood density. I identified some clear trade-offs between vegetative traits and phenological strategies. There was also a positive relationship between degree of rain stimulated flushing metric and wood density. Using objective clustering methods to determine plant functional types has some clear advantages over more subjective methods but depends on good input data. Identifying plant functional types at Nylsvley has led to some insights into functioning of these savannas, but as there appear to be strong links between plant traits and particular leafing strategies it might be more appropriate to explore syndromes of vegetation functional traits when modelling responses to global change.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/19324 |
| Date | January 2016 |
| Creators | Masia, Nthambeleni Dalton |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf |
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