Abstract
ABSTRACTThe 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.EDITED BY James Aronson
Highlights
Invasion of rangelands by alien plants is a threat to livestock production in South Africa (Wise et al 2012; Shackleton et al 2015; Ndhlovu et al 2016; Stafford et al 2016)
Impacts of A. mearnsii invasion and clearing on individual species basal cover The mean distance between wattle stems on densely invaded sites was significantly shorter (F = 4.467, p < 0.001) than on lightly invaded sites
The results demonstrate a severe decline in grazing capacity as a result of A. mearnsii invasion
Summary
Invasion of rangelands by alien plants is a threat to livestock production in South Africa (Wise et al 2012; Shackleton et al 2015; Ndhlovu et al 2016; Stafford et al 2016). Fast-growing invasive Acacia species use more water than grasslands and indigenous tree species and alter nutrient flows, potentially reducing the ability of rangeland ecosystems to provide forage (De Neergaard et al 2005; Moyo and Fatunbi 2010). Little work has been done to quantify the impacts of invasive alien plant invasions on livestock production in South Africa, at local scales (Ndhlovu et al 2016; Stafford et al 2016). This is important because it has clear implications for both land management and human wellbeing in rural areas
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