标题：Alien tree invasion into a South African montane grassland ecosystem: impact of Acacia species on rangeland condition and livestock carrying capacity
摘要：The degree to which invasive Acacia species affect South Africa’s livestock production hasreceived little attention. We investigated the ecological impacts of Acacia mearnsii invasion onforage quality and quantity and on soil resources, along A. mearnsii invasion gradients, onSouth African rangelands and the subsequent conditions following clearing. Grazing capacitywas reduced by 72% in densely invaded sites, whereas clearing improved grazing capacity by66% relative to densely invaded sites within 5 years. In densely invaded sites total grass speciesbasal cover was reduced by up to 42%. As a result, A. mearnsii reduced grazing capacity, from 2to 8 ha required to support one large stock unit (ha/LSU) in uninvaded and densely invadedsites, respectively. Soil moisture content was lower in densely invaded sites compared withlightly invaded and cleared sites. Plant litter increased from 1.3% to 4.2%, carbon content of thesoil increased from 2.0% to 4.0% and nitrogen concentrations increased from 0.1% to 0.2% inresponse to invasion by A. mearnsii. Clearing resulted in improved grazing capacity within5 years. These results also showed that, if left uncontrolled, wattle species can reduce livestockcarrying capacity within montane grasslands in South Africa.
