Animal seed interactions in the Thicket Biome : consequences of faunal replacements and land use for seed dynamics

Abstract :

Vegetation transformation in the Thicket Biome of the Eastern Cape, South Africa has been extensively documented, and has been hypothesised to be irreversible. The irreversibility of transformation is attributed to the perceived inability of the vegetation to recover. The background against which this thinking is based is vegetative reproduction. Re-colonisation of extensively transformed landscapes through vegetative reproduction is obviously impossible. Reproduction through seedlings has received little attention, although the Thicket Biome is dominated by angiosperms. If the vegetation reproduces exclusively through vegetative means, what would be the value of seeds? It was therefore necessary to tease out the effect of transformation on seed dynamics in this thicket. It was hypothesised that “transformation of thicket vegetation alters the ecosystem processes critical to sexual reproduction”. Seed production, availability of germinable seed bank, the availability of seedlings, and the extent of seed predation across the transformation treatment was compared. On many private lands, indigenous herbivores are excluded it was therefore necessary to find out the consequence of their elimination in terms of seed dispersal. The effectiveness of birds as seed dispersers in areas where megaherbivores are excluded was also assessed. In tills research it is shown that transformation leads to reduced quantity and quality of seeds produced. It is shown that the Thicket Biome does not have an effective seed bank for woody species, so seedling recruitment is dependent on immediate germination of seeds produced in every fruiting event. It is also shown that pastoral operations reduce the opportunities for seed distribution, as goats are not effective dispersers. Birds, megaherbivores and kudu are effective dispersers of seeds in this thicket. It is also shown that regeneration through seedlings does occur in the Spekboom Thicket, and it occurs under canopy trees, which suggest directional seed dispersal. It is shown that transformation reduces the opportunities for seedling regeneration in thicket. In this research It is shown that vegetation transformation influences the distribution of small mammals, with high densities on untransformed than on transformed thicket. Seed predation in thicket is seasonally influenced, with dominant granivores being small mammals and birds. Granivory by small mammals is consistently more pronounced on untransformed thicket throughout the year. Granivory by birds was also higher in untransformed thicket for at least warm wet and cool dry seasons but higher in transformed thicket in cool wet season. It was concluded in this research that pastoralism in Thicket Biome does not only transform the vegetation but it also reduces the opportunities for sexual reproduction.



Author Sigwela AM
Date Accessioned 2016-09-22T13:17:30Z
Date Available 2016-09-22T13:17:30Z
Date Created 2000
Identifier URL 2004
Language English
Subject Resources, energy and environmental management
Subject 2 Resources, energy and environmental management
Alternative Title
Degree Type Doctoral degree
Degree Description  PhD