The autecology of Stipa Trichotoma Nees (Nassella Tussock) on Rhodes Estate, in the South-Western Cape

Harding, Graham Bruce

The autecology of Stipa Trichotoma Nees (Nassella Tussock) on Rhodes Estate, in the South-Western Cape

Thesis / Dissertation

1982

Abstract

[Page 1 missing] The autecology of Stipa trichotoma Nees (nassella tussock) was studied in the Mediterranean-type climate of the south-western Cape. The study site was Rhodes Estate, on the lower slopes of Devil •s Peak. The relative growth rate of tussocks in the field was studied using nondestructive methods while more accurate biomass experiments were undertaken on nursery grown plants. These experiments revealed that nassella tussock has a relatively low growth rate with maximum growth occurring in spring to early summer. The phenology was studied for two seasons. The times and duration of flowering were noted as well as the numbers of inflorescences and fruits produced. The stages of flowering were also noted. Floral initiation occurred in early summer with fruits being dispersed in January to February. Variation in fruit shape and colour was found. Cleistogamy was found to be common and to result in relatively short fat fruits. Cleistogamy occurred in shaded tussocks or inflorescences. The germination of nassella tussock was also studied. The pattern of germination was found to be variable which suggested that the evolution of localized ecotypes could have occurred. Dormancy was found to be limited and to occur after fruit dispersal: The degree of dormancy varied between the experimental sites. Germination could be enhanced by leaching fruits in running water for a few days. This and a simple bioassay suggested the presence of an inhibitor or complex of inhibitors, probably located in the lemma and palea. Reports that burning I enhanced the germination of nassella tussock could not be repeated by simulation in the laboratory. -Nassella tussock was found to have a limited distribution. This was thought to be controlled mainly by the state of the vegetation. Nassella tussock is, however, adapted to the climate of the south~western Cape.

Keywords

Botony

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