Estimates of the impacts of invasive alien plants on water flows in South Africa

Abstract

The adverse impacts of alien plant invasions on water flows have been a prime motivation for South Africa's Working for Water Programme. The approach used in this study builds on a previous national assessment in 1998 by incorporating factors that limit plant water-use, information from recent research and improved flow reduction models. The total reduction in flows is estimated to be 1 444 million m . The taxon with the greatest estimated impact was wattles (Acacia mearnsii, A. dealbata, A. decurrens) with 34.0% of the total reductions, followed by Pinus species (19.3%) and Eucalyptus species (15.8%). The revised estimate is considered on the low side largely because the extent and impacts of riparian invasions have been underestimated. If the current estimates that 4-6% of Acacia mearnsii, Eucalyptus, Populus and Salix invasions are riparian, are adjusted to a more representative 20%, 50%, 80% and 80%, respectively, the total reductions increase by nearly 70% to ~2 444 million m 3 ·yr −1. Producing these estimates involved a number of assumptions and extrapolations, and further research is needed to provide more robust estimates of the impacts.

A four‐component classification of uncertainties in biological invasions: implications for management

“…), by using large amounts of water (Le Maitre et al. ). The rainbow trout ( Oncorhynchus mykiss ), native to the United States, was introduced to many countries for recreational fishing, and is viewed positively by recreational anglers, but has detrimental effects on native biodiversity (Shackleton et al.…”

“…In contrast to the range expansion of some Californian butterflies mentioned above, at least three other species of butterflies have been observed to lay eggs in alien species that are toxic to larvae (Graves and Shapiro 2003). Some of the above-mentioned Eucalyptus species introduced in South Africa for timber production cause major disruptions to invaded ecosystems, particularly riparian habitats (Tererai et al 2013), by using large amounts of water (Le Maitre et al 2016). The rainbow trout (Oncorhynchus mykiss), native to the United States, was introduced to many countries for recreational fishing, and is viewed positively by recreational anglers, but has detrimental effects on native biodiversity (Shackleton et al 2019).…”

Indicators for monitoring biological invasions at a national level

“…Relative invasive abundance NA 11. Impact of invasions Low Estimates are entirely based on three studies (de Lange & van Wilgen, 2010;Le Maitre, Forsyth, Dzikiti, & Gush, 2016;van Wilgen et al, 2008).…”

Alien tree invasion into a South African montane grassland ecosystem: impact of Acacia species on rangeland condition and livestock carrying capacity

“…The high root biomass of A. mearnsii is associated with high moisture and nutrient uptake ( In this study, dense invasion reduced soil moisture by 4.97%. Because of the reported comparatively excessive water use by Acacia species (Dye and Jarmain 2004;Gaertner et al 2011;Le Maitre et al 2016), we anticipated that all invaded sites would have significantly less soil moisture. However, local conditions and factors such as rainfall during the survey period played a more influencing role.…”