Abstract
Boophone disticha (L.f.) Herb (Amaryllidaceae) is a geophyte plant distributed across tropical Africa in open grassland and rocky areas. Although its global conservation status is Least Concern, it is categorised as declining in South Africa. To address the declining trend of its population, there is, first, a need to understand its survival and reproductive strategy. In the present study, a theoretical model was proposed and tested to explain the trade-off in the plant investment in size-dependent survival and reproductive strategies along an elevational gradient in Klipriversberge Nature Reserve, South Africa. This was done by testing 24 scenarios of metamodels following a Structural Equation Model apporach using the R function psem (library piecewiseSEM). In term of demographic structure, the analysis shows a bell-shaped structure for bulb and crown diameters, indicative of a dominance of intermediate-size class. This may result from episodic recruitment driven by sporadic fire or high rainfall, nonrandom harvest or a “bonsai effect”. The number of fruits, however, shows a reverse-J structure, which may not necessarily be a cause for concern, given that B. disticha is a long-lived slow-grow species. Although all metamodels tested are suitable to explain the trade-off (Fisher’s C = 0; P > 0.05), the best metamodel was selected as the one showing the highest R2 for all the models in the metamodels. Overall, the selected best metamodel reveals that grass competition (biotic factor) has the strongest direct impacts on the trade-off, suggesting that competition is a dominant ecological force structuring the population of B. disticha in a context of multiple stressors in KNR. The study recommends a multi-year demographic study of the population of B. disticha to explore the short- and long-term dynamic of the population in response to harvest.
M.Sc. (Environmental Management)