Browsing by Author "Yapi, Thozamile Steve"

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    Alien tree invasion into a South African montane grassland ecosystem : impact of Acacia species on rangeland condition and livestock carrying capacity
    (Taylor & Francis, 2018) Yapi, Thozamile Steve; O'Farrell, Patrick J.; Dziba, Luthando E.; Esler, Karen J.
    ENGLISH ABSTRACT: The degree to which invasive Acacia species affect South Africa’s livestock production has received little attention. We investigated the ecological impacts of Acacia mearnsii invasion on forage quality and quantity and on soil resources, along A. mearnsii invasion gradients, on South African rangelands and the subsequent conditions following clearing. Grazing capacity was reduced by 72% in densely invaded sites, whereas clearing improved grazing capacity by 66% relative to densely invaded sites within 5 years. In densely invaded sites total grass species basal cover was reduced by up to 42%. As a result, A. mearnsii reduced grazing capacity, from 2 to 8 ha required to support one large stock unit (ha/LSU) in uninvaded and densely invaded sites, respectively. Soil moisture content was lower in densely invaded sites compared with lightly invaded and cleared sites. Plant litter increased from 1.3% to 4.2%, carbon content of the soil increased from 2.0% to 4.0% and nitrogen concentrations increased from 0.1% to 0.2% in response to invasion by A. mearnsii. Clearing resulted in improved grazing capacity within 5 years. These results also showed that, if left uncontrolled, wattle species can reduce livestock carrying capacity within montane grasslands in South Africa.
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    An assessment of the impacts of invasive Australian wattle species on grazing provision and livestock production in South Africa
    (Stellenbosch : Stellenbosch University, 2013-12) Yapi, Thozamile Steve; O'Farrell, Patrick; Esler, Karen J.; Dziba, Luthando; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.
    ENGLISH ABSTRACT: I investigated the impacts of the invasive wattle species (Acacia mearnsii, A. dealbata, A. decurrens), on the ecological function and productivity of rangelands in South Africa and their ability to sustain livestock production. More specifically, this study set out to: (1) assess grazing areas at a national scale; (2) identify evidence of progressive impacts of these species on livestock production across a selection of magisterial districts; (3) determine the effects of A. mearnsii density on growth form dominance of indigenous plant species, and highlight how this translates into impacts in forage quality and quantity; (4) determine the effects of A. mearnsii invasion on soil resources and conditions (key determinates of ecological function) required to support grazing production; and finally (5) determine to effects that clearing operations have had on the provision of grazing resources. My results indicate that the level of overlap between wattle invasion and areas with a high grazing potential, at the national scale, is relatively low (2.9%). However, at a magisterial district scale, areas with a high grazing potential have a moderate (approximately 35.1% high grazing potential area under wattle invasion for highest invaded district) level of invasion. Scattered and moderate levels of invasion currently dominate or characterise these species invasion patterns. Both light and dense A. mearnsii invasions reduce grazing capacity. Dense invasion had the most severe effect reducing grazing capacity from 2 ha, required to support one large stock unit, to 8 ha. The clearing of this species was found to improve grazing capacity within 5 years. The reduction in grazing capacity following invasion was largely due to reduced basal cover and herbaceous biomass. The clearing of invaded sites was found to increase both basal cover and herbaceous biomass to pre-invasion levels. Acacia mearnsii invasion was found to affect certain soil properties. Under an A. mearnsii canopy, plant litter, carbon content of the soil and nitrogen concentrations were all found to be elevated. Overall, this study demonstrates that Acacia invasions have a significant effect on grazing resources at a local or site scale, and that for the eastern region of South Africa, these effects are ultimately scaled up to a district level. This is likely to have important financial and human well-being repercussions. However clearing and restoration programs are clearly able to reverse or mitigate these effects. This study therefore lends support to or complements other ecosystem service provision arguments for clearing alien invasive species.