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.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/1737 |
| Date | 12 1900 |
| Creators | Agenbag, Lize |
| Contributors | Esler, Karen J., Midgley, Guy F., University of Stellenbosch. Faculty of Science. Dept. of Botany and Zoology. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Rights | University of Stellenbosch |
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