Chapter 15
Impacts of Plant Invasions on Terrestrial
Water Flows in South Africa
David C. Le Maitre , James N. Blignaut , Alistair Clulow ,
Sebinasi Dzikiti , Colin S. Everson , André H. M. Görgens,
and Mark B. Gush
Abstract Considerable advances have been made since the first estimates of the
impacts of invasive alien plants on water resources in the early 1990s. A large body
of evidence shows that invasive alien plants can increase transpiration and evaporation losses and thus reduce river flows and mean annual runoff. Riparian invasions,
and those in areas where groundwater is accessible, have 1.2–2 times the impact of
invasions in dryland areas. The magnitude of the impacts is directly related to
differences between the invading species and the dominant native species in size,
rooting depth and leaf phenology. Information on the impacts has been successfully
used to compare the water use of invasive plants and different land cover classes, to
quantify the water resource benefits of control measures, and to prioritise areas for
control operations. Nationally, the impacts of invasive alien plants on surface water
runoff are estimated at 1.44–2.44 billion m
3 per year. The most affected primary
catchments (>5% reduction in mean annual runoff) are located in the Western and
Eastern Cape, and KwaZulu-Natal. If no remedial action is taken, reductions in
surface water runoff could increase to 2.59–3.15 billion m
3 per year, about 50%
D. C. Le Maitre (*)
Centre for Invasion Biology, Natural Resources and the Environment, Council for Scientific and
Industrial Research, Stellenbosch, South Africa
e-mail: dlmaitre@csir.co.za
J. N. Blignaut
South African Environmental Observation Network, Pretoria, South Africa
School of Public Leadership, Stellenbosch University, Stellenbosch, South Africa
A. Clulow · C. S. Everson
Centre for Water Resource Research, Department of Botany and Zoology, University of
KwaZulu-Natal, Pietermaritzburg, South Africa
S. Dzikiti · M. B. Gush
Natural Resources and the Environment, Council for Scientific and Industrial Research,
Stellenbosch, South Africa
A. H. M. Görgens
Aurecon, Century City, Cape Town, South Africa
© The Author(s) 2020
B. W. van Wilgen et al. (eds.), Biological Invasions in South Africa, Invading
Nature - Springer Series in Invasion Ecology 14,
https://doi.org/10.1007/978-3-030-32394-3_15
431
Impacts of Plant Invasions on Terrestrial
Water Flows in South Africa
David C. Le Maitre , James N. Blignaut , Alistair Clulow ,
Sebinasi Dzikiti , Colin S. Everson , André H. M. Görgens,
and Mark B. Gush
Abstract Considerable advances have been made since the first estimates of the
impacts of invasive alien plants on water resources in the early 1990s. A large body
of evidence shows that invasive alien plants can increase transpiration and evaporation losses and thus reduce river flows and mean annual runoff. Riparian invasions,
and those in areas where groundwater is accessible, have 1.2–2 times the impact of
invasions in dryland areas. The magnitude of the impacts is directly related to
differences between the invading species and the dominant native species in size,
rooting depth and leaf phenology. Information on the impacts has been successfully
used to compare the water use of invasive plants and different land cover classes, to
quantify the water resource benefits of control measures, and to prioritise areas for
control operations. Nationally, the impacts of invasive alien plants on surface water
runoff are estimated at 1.44–2.44 billion m
3 per year. The most affected primary
catchments (>5% reduction in mean annual runoff) are located in the Western and
Eastern Cape, and KwaZulu-Natal. If no remedial action is taken, reductions in
surface water runoff could increase to 2.59–3.15 billion m
3 per year, about 50%
D. C. Le Maitre (*)
Centre for Invasion Biology, Natural Resources and the Environment, Council for Scientific and
Industrial Research, Stellenbosch, South Africa
e-mail: dlmaitre@csir.co.za
J. N. Blignaut
South African Environmental Observation Network, Pretoria, South Africa
School of Public Leadership, Stellenbosch University, Stellenbosch, South Africa
A. Clulow · C. S. Everson
Centre for Water Resource Research, Department of Botany and Zoology, University of
KwaZulu-Natal, Pietermaritzburg, South Africa
S. Dzikiti · M. B. Gush
Natural Resources and the Environment, Council for Scientific and Industrial Research,
Stellenbosch, South Africa
A. H. M. Görgens
Aurecon, Century City, Cape Town, South Africa
© The Author(s) 2020
B. W. van Wilgen et al. (eds.), Biological Invasions in South Africa, Invading
Nature - Springer Series in Invasion Ecology 14,
https://doi.org/10.1007/978-3-030-32394-3_15
431