JUser: :_load: Unable to load user with ID: 504


Thank you for visiting our website.

Please note that the site is not fully functional at the moment as we are in the process of re-developing. We hope that you will find the available resources helpful in the meantime.

German wasp | Vespula germanica

German wasp

Vespula germanica

Coral bush | Ardisia crenata

Coral bush

Ardisia crenata

Purple loosestrife | Lythrum salicaria

Purple loosestrife

Lythrum salicaria

Pom pom weed | Campuloclinium macrocephalum

Pom pom weed

Campuloclinium macrocephalum

Canarybird bush | Crotalaria agatiflora

Canarybird bush

Crotalaria agatiflora

Peanut butter cassia | Senna didymobotrya

Peanut butter cassia

Senna didymobotrya

Rubber vine | Cryptostegia grandiflora

Rubber vine

Cryptostegia grandiflora

1 2 3 4 5 6 7

Environmental Programmes

In order to tackle our country’s socio-economic challenges, the government adopted the Outcomes based approach to improve government performance and providing focus on service delivery. find out more

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

Estimates of the impacts of invasive alien plants on water flows in South Africa
David Le Maitre, Greg Forsyth, Sebinasi Dzikiti and Mark Gush
Natural Resources and the Environment, CSIR, P O Box 320, Stellenbosch

This paper summarises the results of a new assessment of the impacts of invasive alien plants on the water flows in South Africa based on the mapping done by Kotzé et al. (2010). The approach took into account basic hydrological principles and factors which limit plant water-use and the accumulated information on water-use by these species in both plantation settings and those typically invaded since the publication of the previous national assessment in 1998. The unit area reduction of 97 mm/yr found in this assessment is about half the 190 mm/yr reported by Versfeld et al. (1998). The total reduction in mean annual runoff is about 1 444 million m3/yr or 2.9% of the naturalised mean annual runoff (see Table A below) which is much lower than the 3 300 million m3/yr estimated in 1998. The main reason for this is the lower flow reduction, but the decrease in the condensed are from 1.76 million ha in 1998 to 1.50 million ha in this study also reduced the impacts. The greatest reductions were recorded in primary catchment T (former Ciskei & Transkei,

322 million m3/yr, 4.5%), followed by U (southern KwaZulu-Natal, 154 million m3/yr, 5.0%) and W

(Northern KZN, 149 million m3/yr, 2.3%). The greatest proportional reductions were in K (Mossel

Bay-Tsitsikamma, 8.4%),  M  (Port  Elizabeth  coast-Coega, 6.5%),  H  (Breede,  6.1%)  and  G  (Berg- Agulhas, 6.0%). The taxon with the greatest impacts was the wattles (Acacia mearnsii, A. dealbata, A. decurrens) which account for 33.5% of the total reductions, followed by Pinus species (18.9%) and Eucalyptus species (15.1%). The unit area flow reductions due to pines were 212.1 mm/yr, followed by Hakea species (199.5 mm/yr) largely because they occur mainly in high yielding montane fynbos catchments.

This estimate is considered conservative for the following reasons. The approach we used probably underestimates the extent of riparian invasions within the mapped areas. The mapping was limited to catchments which cover only about 54% of the country (but do yield more than 80% of the MAR). There are also extensive riparian invasions by eucalypts, wattles and other species along perennial rivers in semi-arid and arid environments (e.g. middle and lower Orange R, lower Vaal River) whose impacts have not been included in this assessment.  In addition, Prosopis invasions in the Northern Cape result in a further reduction of about 8.94 million m3/yr. There are extensive invasions of Prosopis species in the North West, Free State and Western Cape provinces which have not been adequately mapped so their impacts cannot be quantified at the moment.

Read 3641 times

General News Updates

2019 National Symposium on Biological Invasio…


This is your invitation to South Africa's 2019 National Symposium on Biological Invasions. The convention is hosted by the Centre for Invasion Biology (CIB), University of Stellenbosch, and the Biolo... Read more

2019 Invasive Species Training


During the past five years (2014-2018), ISSA invasive species trainers have trained 4 000 in the identification of invasive species and laws pertaining to invasive species across South Africa.  ... Read more

Alien Grass Working Group


Who are we? The South African National Alien Grass Working Group was jointly initiated by the South African Biodiversity Institute (SANBI) and the Centre for Excellence in Invasion Biology (C·I·B) in... Read more

Permits for planting indigenous Cynodon?


On 16 February, 2018, South Africa's Department of Environmental Affairs issued amendments to the regulations and lists relating to the National List of Invasive Species.  Updates to the draft&n... Read more

Invasive species training 2018 dates released


Interested in invasive species?  How much do you know about NEMBA invasive species compliance for landowners and organs of state? The South African Green Industries Council (SAGIC) have released... Read more

Communications post for Africa advertised


The Nature Conservancy has advertised a brand new post:  Communications Manager, Africa Region. Knowledge of invasive species and water would be an asset in this post. See details below:    Job Titl... Read more