The comparison of selected life-history characteristics of Mesembryanthema species occurring on and off Mima-like mounds (heuweltjies) in semi arid southern Africa
✍ Scribed by K. J. Esler; R. M. Cowling
- Publisher
- Springer Netherlands
- Year
- 1995
- Tongue
- English
- Weight
- 842 KB
- Volume
- 116
- Category
- Article
- ISSN
- 1385-0237
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✦ Synopsis
Selected life-history characteristics of Mesembryanthema species occurring on and off mima-like mounds (heuweltjies) were compared at Tierberg in the southern Succulent Karoo, South Africa. Seed production, the number of seeds retained in seed capsules and germination behaviour were measured in fourteen species of Mesembryanthema which were representatives of two sub-families: the Ruschioideae and the Mesembryanthemoideae.
Species occurring on heuweltjies had low overall germination and high seed retention compared with those species occurring off heuweItjies. A strong negative correlation was found between the degree of seed retention and maximum germination. It was proposed that rapid germination and low seed dormancy in species occurring on the flats would be a viable strategy where competition for safe recruitment sites is strong. Species occurring on the flats are long-lived woody shrubs, thus the resulting high levels of seedling mortality probably do not have a major impact on population dynamics. HeuweItjies are sites of intense disturbance. Plant species that occur on heuweltjies can also occur off heuweltjies in disturbed vegetation. Opportunistic life-history characteristics allow these species to colonise disturbed areas. Heuweltjie species thus act as pioneers in a successional process which results ultimately in the re-colonisation of the long-lived flats species. Phylogenetic factors may also determine the species distributions.
Members of the Mesembryanthemoideae did not occur off heuweltjies in undisturbed areas. Most Ruschioideae were found on the flats but the few species that occurred on heuweltjies shared similar characteristics with the Mesembryanthemoideae. The primitive life-history characteristics exhibited by the Mesembryanthemoideae enable them to exploit disturbed conditions.