The aliens drank our water!

Understanding the impact of invasive alien vegetation on our water resources  

[With thanks to info from the Department of Environmental Affairs] 

The Working for Water (WfW) programme was launched in 1995 in response to the realisation of the gravity of the threat that invasive alien plants pose to water resources. A group of scientists and natural resource managers presented the idea to the late Kader Asmal, who was at the time Minister of Water Affairs and Forestry. Professor Asmal was instrumental in getting the government support needed for this programme and it was officially launched in September 1995 at a cost of R25 million. At the time Rand Water also formed an integral part of removing invasive plants in their catchment areas. 

Some of the core functions of the programme are to clear mountain catchments and other riparian zones of invasive alien plants and to restore natural fire regimes, the productive potential of the land, biodiversity and hydrological functioning, while at the same time creating employment opportunities for marginalised people and communities. 

What makes the WfW programme unique and somewhat unusual is that it was initiated and primarily funded as a poverty relief public works programme. In 2008, the WfW programme had an annual budget of more than R400 million, effectively making it the “largest single natural resource-based poverty relief and public works expenditure in the country”. 

The WfW programme has also diversified into several related projects, including the Working for Wetlands programme which deals with biodiversity and hydrological services, and the Working on Fire programme, which promotes the responsible and safe use of fire as an environmental management tool. The WfW programme now forms part of the Expanded Public Works Programme. 

Around 30 000 work opportunities have been created through the Working for Water projects since 1995. “The WfW programme successfully combines ecological concerns and social development benefits by addressing unemployment.” 

Job creation 

The WfW programme successfully combines ecological concerns and social development benefits by addressing unemployment, empowerment and skills training. In many developing countries, short-term economic growth and social delivery often takes precedence over environmental conservation and resource management. 

The WfW programme has gained international recognition and praise for the unique way in which it combines the need for social enhancement and job creation with that of managed ecosystems and water conservation. In the case of WfW, this is done primarily through the clearing of invasive alien plants in water catchment areas and sensitive ecosystems. 

The goals of the programme are to create opportunities for the most marginalised sectors of society, including the ‘poorest of the poor’, women, the disabled and the youth. There are currently over 300 projects around the country employing over 30 000 people. Of those employed, 54% have been women and the majority of people employed by the WfW programme come from poor and marginalised sectors of the community. Training and skills development give people the chance to create their own employment opportunities as well as setting up their own businesses, such as manufacturing furniture from cleared invasive plants, for example eucalyptus and poplar. 

Working for Water facts: 

  • Clearing invasive plants alongrivers typically results in streamflow increase of 800 to 12 000ℓ/ha/day in the winter rainfall region and up to 34 000ℓ/ha/day in the summer rainfall region, regardless of location and species. 
  • Between 1995 and 2011,WfWteams cleared over 2,1 million hectares of alien plant invasion. This clearing has yielded an estimated release of 48 million to 56 million cubic metres of additional water for alternative uses annually. 
  • Scientists have estimated that71% of grazing in South Africacould be lost to invasive alien plants if they were allowed to occupy all of the areas suitable to their growth. This is an unthinkable risk in terms of food security and jobs lost. It also threatens biological diversity. 
  • Of the estimated 9 000 alienplant species introduced to ourcountry, 379 are legally classified as invasive under the NEMBA AIS regulations. It is estimated that these plants cover about 20% of the country’s surface area and the problem is growing exponentially.  

Hermanus Municipality – a success story 

The township of Hermanus in the Western Cape derives its water from the De Bos Dam and has experienced severe water shortages at various times, where demand had outstripped supply. The WfW project cleared around 3 387 hectares of alien invasive plants around the catchment zones of De Bos Dam at a calculated expense of R4,9 million, while generating 91 person years of employment. It is estimated that this clearing operation has prevented water losses of between 1,1 and 1,6 million cubic metres annually. 

The real cost to our economy 

Scientists and researchers working on invasive alien plants have worked out that water lost to these plants runs into billions of rands. In one study, scientists Drs Willem de Lange and Brian van Wilgen suggested that “water lost to invasive alien plants every year was worth R6,5 billion.” They also noted that historic interventions, including the clearing programmes of the Forestry Departments in the 1970s and 1980s, biological control, and WfW, have saved the economy an estimated R41,7 billion a year by protecting ecosystem services. 

In an article in Engineering News, Dr Christo Marais of the WfW resource management programme, pointed out that since 1995, the budget of R25 million had grown to R1,4 billion for WfW and R540 million for Working on Fire in the 2014/2015 financial year. 

cientists have estimated that water lost to invasive plants each year equates to a net worth of R6,5 billion – more than the construction value of most dams. 

Long-term project 

Invasive alien plants are well established in South Africa and continue to encroach on land in different parts of the country. To date, the WfW programme has cleared around 2,1 million hectares and the department estimates that a further 19 million hectares still need to be cleared in the next few years. 

In addition to clearing operations, ongoing control to prevent further invasions will be needed. Because of the threat these plants pose to water security, the WfW programme will undoubtedly continue to create much needed employment well into the future. 

A report published by the Development Bank of South Africa, Trade and Industrial Policy Strategies and Industrial Development Corporation entitled “Green Jobs: An estimate of the direct employment potential of a greening South African economy” suggests that, “there is potential to create as many as 230 000 job opportunities in natural resource management. This includes secondary industries such as biofuel production and manufacturing from harvested biomass.”  

Impacts of invasives on water and soil 

Studies indicate that invasive alien plants have a detrimental effect on water flow and uality, as well as modify the soil. Numerous studies have been conducted in South Africa to measure the amount of water taken up by invasive alien plants. Many of these invasive plants flourish in our catchments, most notably the mountainous regions of the Western Cape as well as the Drakensberg and the escarpment of Mpumalanga and Limpopo. Grasslands are also acknowledged as important reservoirs for water. 

The removal of invasive alien plants from sensitive catchments and wetlands has enhanced
 the water quality, which in turn has revived biodiversity in these aquatic ecosystems. 

Invasive alien plants have invaded an estimated 10 million hectares in South Africa, according to a report published in 2008. In a more recent publication in Engineering News, this figure was estimated at closer to 19 million hectares. Left uncontrolled, these plants will increase exponentially, to the detriment of our water supply. 

How much water do we lose? 

In one of the studies undertaken to determine how much water is lost due to invasive alien plants, published in 2000, the estimated total incremental water use of invading alien plants was at about 3 300 million cubic metres of water per year. Catchments in the Western Cape lost up to 31% of mean annual run-off. A more recent study published in 2007 estimated the current loss of usable water to alien invasive plants at a much higher figure of 695 million cubic metres, or the equivalent of 4% of the total registered water use. It is predicted that if left uncontrolled, this could increase to over 2,7 billion cubic metres or 16% of registered water use. These figures may seem somewhat low, but in a country acknowledged as a water scarce country that regularly experiences regional drought, these figures can have a devastating effect on our water supply.  

Effect on water quality and biodiversity 

Invasive alien plants, once established and often with no natural enemies, often multiply exponentially to the detriment of the native plants. Invasive shrubs and trees often grow faster and taller than the surrounding natural vegetation, especially in fynbos and grassland. As a result, the indigenous vegetation is often swamped and dies out. This in turn has a detrimental effect on the animals which depend on these plants for food and shelter. In some circumstances, with indigenous plants and their inhabitants displaced, other invasive birds, mammals and insects move in and further displace indigenous species. 

Taller trees don’t allow many grasses and river bank plants to grow underneath due to shading out natural sunlight and depleting water. As a result, bare soil is exposed and when there is a flash flood, valuable topsoil is lost and erosion becomes a serious problem. Often the invading tree has deeply anchored roots, so these sporadic floods have little impact on the invader, but wash everything else away. Habitat and shelter for insects, small mammals and frogs is destroyed, often leading to local extinctions, or in the case of range restricted species, placing them in danger of complete extinction.  

Invasive alien plants have a negative effect on biodiversity and several rare and
 endangered frogs are threatened by these invasions. 

Water use by invasive plants 

How exactly do invasive alien plants deplete water? When large stands of invasive plants take over a wetland, they are often taller and denser than the original indigenous vegetation. In fynbos and grasslands, this vegetation is often made up of small reeds, sedges, grasses and small shrubs. Grasses in particular have a small surface leaf ratio compared to many invasive trees and shrubs. Because of the small surface area in natural vegetation, evaporation from indigenous vegetation is much less than that of exotic trees and shrubs. 

Another important factor contributing to high rates of evaporation is the height of the plants. Plants which are low to the ground, such as grasses and fynbos, are less prone to the effect of wind, which in tall trees has a much greater effect on evaporation from the leaf surface. This follows a similar principle of taking a wet towel and laying it flat on the ground, which will take much longer to dry than if it was elevated off the ground where it will dry faster.  

Grasses and fynbos plants also have short root systems, whereas exotic invasive trees have deep root systems which can travel further and absorb much more water. So even in the dry season, the exotic tree will continue to absorb soil water which in turn will evaporate from the leaf surface. In many regions, indigenous natural vegetation and grasses lose their leaves during the dry season. Grasses dry up and often burn. Therefore, very little, if any, water is lost through leaf evaporation. On the other hand, exotic invasive vegetation such as shrubs and trees continue to absorb water and often retain their leaves during the dry season. 

Tall trees such as eucalyptus have a high rate of evaporation and even in the dry season the
 trees will continue to absorb soil water which will evaporate from the surface of their leaves. 

Scientists have used numerous scientific methods to calculate the rate of water lost through invasive alien plants. The biggest culprits are the Australian wattles and gums, as well as certain pine species which come from North America and Europe. Other serious waterholic invaders include syringa, bugweed, lantana, triffid weed and hakea. These plants are estimated to use up over 2,5 billion cubic metres of water annually, a figure that will increase incrementally year on year. The 2,5 billion cubic metres equates to approximately 6,7% of South Africa’s annual run-off.  

Food for thought indeed!  


  • Working for Water createsemployment for around30 000 people annually. 
  • The programme has clearedmore than 2,1 million hectaresof invasive alien plants (IAPs). 
  • Additional programmeshave developed from theWfW programme, such as Working for Land, Working for Forests and Wildlife Economy, Working on Fire and Working for Wetlands. 
  • Without intervention bytheWfW programme, it is estimated that invasive alien plants are costing our economy R41,7 billion a year in lost ecosystem services. 
  • In addition to job creation,theWfW programme enhances water quality and rehabilitates natural habitats and ecosystems which in turn have a positive effect on biodiversity. In fact, many species of animals are directly threatened due to invasive alien plant infestations which have altered their habitat and dried up water sources. 
  • TheWfWprogramme has also trained thousands of people and given them skills which have greatly enhanced their chances of securing future contracts. 
  • IfWfWhad not invested in the removal of IAPs, scientists estimate that South Africa would have lost around R50 billion a year in ecosystem services.