Impacts of Acacia mearnsii on pastures and grazing capacity
The ecological impacts resulting from the invasion by Acacia mearnsii (Fabaceae) and of the management measures applied in South African rangelands were investigated. The impacts of A. mearnsii in uninvaded, lightly invaded, densely invaded and cleared sites were examined in a grassland ecosystem in the Eastern Cape. The impacts of treatments on forage quality and quantity, as well as on soil resources were also examined.
The study revealed that invasion by A. mearnsii reduced grazing capacity by 56% and 72% on lightly and densely invaded sites respectively. Loss of grazing capacity during invasions was largely due to reduction in total groundcover (by up to 42%) and of herbaceous biomass. Subsequent clearing of invaded sites allowed both basal cover and biomass to return to pre-invasion levels. Soil moisture was also found to be significantly lower on densely invaded sites. Following invasion, plant litter increased (from 1.3 to 4.2%), carbon content of the soil increased (from 2 to 4%), and nitrogen concentrations (from 0.1 to 0.2%). Overall, the grazing capacity was reduced from 2 ha per livestock unit in uninvaded sites to 4 ha in lightly invaded sites, and from 2 ha to 8 ha in densely invaded sites.
Sources
Yapi T, O’Farrell P, Dziba L, Esler K (2014) Alien tree invasion into grassland ecosystems: impacts on range land condition and livestock production. Abstract of the 4th International Symposium on Environmental Weeds and Invasive Plants, Montpellier (FR), 2014-06-19/23.