MSc., Faculty of Science, University of the Witwatersrand, 2011 / Little is known about the longevity of grassland suffrutex plants and the relationship between longevity and
plant morphological structures and seedling growth strategies. The aim of this study was to determine the
longevity of four grassland suffrutex plant species, namely Berkheya insignis, Callilepis laureola, Protea insignis
and Tephrosia kraussiana. Seed viability, seedling growth, morphology, habitat and population structure and
demography were also assessed and related to plant age.
The rhizomes, seeds (if available) and canopies of B. insignis, C. laureola, P. simplex and T. kraussiana
were removed from a site near Port Edward in the Pondoland region, KwaZulu-Natal, South Africa in April
2008. Seeds were available for P. simplex and T. kraussiana only. Seed germination and viability were tested in
the field and laboratory using germination trials and tetrazolium tests. Greenhouse and field grown seedlings
were used to monitor seedling growth and to record seedling morphology. The aerial and rhizome morphologies
of adult plants excavated from the field were also recorded. The largest of these rhizomes were aged using
radiocarbon dating. Attempts were made to develop morphological surrogates for plant age as no method
currently exists. Plant density, demographies, number of inflorescences and various environmental variables of
wild populations of B. insignis, C. laureola, P. simplex and T. kraussiana were sampled from the Red Desert
Nature Reserve and the Umtamvuna Nature Reserve.
Species morphologies varied, however important similarities suggest convergent evolution. These
included a single vertical main stem rhizome with multiple side branches, early rhizome development in
seedlings, and high root: shoot ratios. Seed viability was high in the laboratory but low seedling emergence was
observed in the field. Seedling growth was rapid for T. kraussiana and slow for P. simplex. The population
stage structure for all four species comprised primarily adults with few or no juveniles. Wild population plant
height and main stem diameter followed normal distributions. Number of stems, basal area, canopy area and
the number of floral structures had distributions favouring the smaller size classes. Soil P, N, K and organic
carbon were important soil nutrients in a PCA analysis of the habitats of the four species. Radiocarbon dating
yielded the following ages: B. insignis: 49-51 years, C. laureola: 49-50 years, P. simplex: 49-51 years and T.
kraussiana: 51 years. There was a significant relationship between rhizome mass and canopy area, basal area,
height, number of stems and main stem diameter. Since rhizome mass had a positive relationship with age- a
relationship between age and aerial structures is likely. Therefore, creating surrogates for age may be possible.
Overall, these species have moderate longevity, are poor seed producers with possibly slow population
growth and are closely associated with soil nutrients. Therefore, these and other suffrutex species are
particularly vulnerable to habitat destruction and climate change. The results of this study indicate that there
needs to be a greater focus on below ground growth during ecological assessments in order to better
understand the ecology of our diverse grassland biome plants.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/11072 |
| Date | 18 January 2012 |
| Creators | Dayaram, Anisha |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf, application/pdf |
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