25-06-2025
Alien plant removal pilot project adds massive water boost to Gqeberha's strained water supply
The lack of a standardised method to explicitly link water benefits to invasive alien plant removal left a significant opportunity untapped, according to the Roundtable on Sustainable Biomaterials, WWF South Africa and Stewards of Nature. In close consultation with local technical experts, they sought to address this, and they developed a Water Impact Calculator for water gains from invasive alien plant removals.
In a water-scarce South Africa, alien plants drink up to 6% of our freshwater annually. A new technology now proves the massive water savings from clearing them, potentially turning a costly problem into a valuable solution.
South Africa is a water-scarce country, and invasive alien plants like Black Wattle and Port Jackson are making this worse. They cover about 10% of the land and consume up to 6% of the country's freshwater.
These plants also harm natural ecosystems, reduce biodiversity, and increase the risk and severity of wildfires.
There are many projects in the NGO, private and government spaces that are working to remove these invasive plants.
But James Reeler, Senior Climate Specialist at World Wildlife Fund (WWF) South Africa, said, the biggest challenge had been getting projects to scale.
'Despite all of the money that's thrown at it and the work that's been done, we're still losing this battle. And the biggest problem is that it's really expensive,' said Reeler.
Another challenge has been to measure how much water is saved by removing these plants. To address this, the Roundtable on Sustainable Biomaterials, in partnership with WWF South Africa and Stewards of Nature (formerly Coega Biomass Centre), developed a new methodology and a special calculator tool.
In a webinar discussion on Tuesday, 24 June 2025, these groups explained how this ' Water Impact Calculator ' allows users to input details about the cleared area, such as the type of invasive species, their density, and the amount of land cleared, along with local rainfall and runoff data.
The tool then calculates the volume of water released back into local ecosystems after the plants are removed. This provides measurable evidence of water savings.
Their goal is to encourage more large-scale invasive alien plant removal by enabling companies, especially those purchasing the removed biomass (which can be used for energy like wood pellets), to make credible and independently verifiable claims about their contribution to water savings.
This, the team said, added value to the removed biomass, helping to make the expensive clearing process more financially viable and incentivising more companies to get involved.
The water impact indicator methodology and calculator
The lack of a standardised method to explicitly link water benefits to invasive alien plant removal left a significant opportunity untapped, according to the Roundtable on Sustainable Biomaterials, WWF South Africa and Stewards of Nature.
In close consultation with local technical experts Blue North and Blue Science, they sought to address this, and they developed a Water Impact Calculator for water gains from invasive alien plant removals.
The primary purpose of this tool is to quantify the positive water impact achieved by removing invasive alien plants and to 'stack more value' on the biomass feedstock to justify a price associated with its sustainable harvesting.
This could allow operators to calculate the volume of water released back into local ecosystems post-clearance, providing measurable evidence of water savings.
The scientific foundation for the methodology and calculator is rooted in the decade-long work of Dr David le Maitre, a key scientist who supported South Africa's Working for Water Programme, and his co-authors.
The calculator, an Excel-based spreadsheet tool, relies on several key inputs to perform its calculations:
Project and Target Area Definition: Users define the overall project area and then divide it into up to 10 smaller blocks, which allows for more accurate data entry as conditions can vary significantly across a large site.
Biome Type: Users must then select whether the area is dryland, non-riparian zone, Fynbos biome, or grassland/savanna biome. This choice determines a riparian multiplier (1, 1.5, or 2), reflecting how different biomes affect vegetation's ability to reduce runoff. For example, Fynbos has a higher multiplier (1.5) because more water is available for both native and invasive species, and invasives drink more than native species. In grasslands, native grasses go dormant in winter, while invasives continue to consume water year round.
Plant Stage: The tool requires users to classify the alien infestation as mature optimal, mature sub-optimal, young seedlings, or coppice. This choice influences the reduction factor used in calculations.
Species Reduction Factors: A drop-down menu lists various invasive alien plant species, each with pre-defined reduction factors based on their growth form (tree, shrub, sprouting tree) and maturity stage.
Percentage Density/Canopy Cover: Field surveyors must input the percentage of the site covered by invasive alien plants, representing the density of the infestation.
Mean Annual Precipitation and Mean Annual Runoff: While the tool incorporates average values for South Africa's 1,947 quaternary catchment areas, users are encouraged to use site-specific data from Cape Farm Mapper for greater accuracy. It's important to note that Cape Farm Mapper is a portal, with data sourced from the CSIR (for Mean Annual Runoff) and the South African Atlas for Climatology and Agro by Prodigy (for Mean Annual Precipitation, averaged from 1950-2000).
Follow-up Exercises: The tool allows for the capture of data from up to five follow-up clearing exercises to account for potential regrowth, helping prevent 'cherry-picking' of sites for water gain claims.
Dana Grobler, the director of BlueScience, explained that the calculator's output provides total water gains per annum in cubic metres, as well as cubic metres per hectare per year for standardisation. It can also tabulate results from initial clearing and subsequent follow-up work, offering a clear summary of restored water volumes.
However, there are some limitations to the tool. The tool is not automated for rainfall and runoff data. This means users must manually look up and enter these values from sources like Cape Farm Mapper. For large areas, dividing into smaller blocks and entering site-specific data is recommended for accuracy, as rainfall can vary greatly even within a single catchment.
Users must also be knowledgeable in their selections (e.g., biome type, plant stage) and understand their implications.
Boosting Gqeberha's strained water supply
In a pilot project, Stewards of Nature applied this methodology to their clearing activities in Gqeberha. Marilena Demetriou from Stewards of Nature explained they had eight harvesting teams currently active across 25 sites within a 200km radius of Gqeberha.
She said the pilot focused on seven sites, encompassing 269 hectares. Through the removal of 9,034 tons of invasive alien plant biomass, the project recovered an estimated 844,711m³ of freshwater.
This volume translated to approximately 94m³ of water savings per ton of biomass, or 144m³ of water savings per ton of pellets produced from the biomass. To put this into perspective, 844,711m³ of water is equivalent to the annual water usage of more than 16,000 households or the irrigation of more than 3,000 hectares of maize for one season.
Demetriou had before-and-after imagery that shows how clearing invasive alien plants restores ecological function, reduces wildfire risk, improves biodiversity, and frees up water in rivers and dams.
Looking ahead, the team said they would be continuously monitoring and following up on these activities to ensure long-term success in cleared areas. Beyond water, future efforts would also focus on tracking biodiversity gains, such as improved habitats, species recovery, and healthier soils, further solidifying the case for regenerative land management as a vital component of climate and environmental, social and governance action.
Reeler said they were hoping for a 'huge scaling of rural economies around the eradication of invasive aliens' to support biodiverse ecosystems and deliver real water benefits under a changing climate.
How invasive alien plants exacerbate water scarcity
The scale of the invasive alien plant problem in South Africa is staggering. By some estimates, these plants cover more than 10% of the landmass and consume up to 6% of the country's freshwater annually, a figure that could escalate without intervention.
This translates to 2.5 billion cubic metres of water lost each year due to evapotranspiration that would not otherwise occur. Beyond water depletion, invasive alien plants cause widespread ecological damage by degrading natural ecosystems, disrupting local biodiversity, and increasing the severity of wildfires, particularly in ecologically sensitive areas like the Cape Floral Region.
'In South Africa, there is a water availability issue. And unfortunately, this is not a problem that is known across the environment or the scientific community, but this a known problem across people, because it's already impacting their lives,' said Demetriou.
These impacts are further compounded by climate change, which generally leads to a drying climate in an already water-scarce nation, alongside more intense rainfall events, making the integrity of water flows and availability even more critical.
For a long time, the South African government has invested significantly in invasive alien plant clearing through initiatives like the Working for Water programme, primarily focusing on employment creation.
But as mentioned above, a persistent challenge has been effectively measuring the outcomes and ensuring consistent follow-up processes. Despite considerable financial investment and effort, the country continues to lose the battle against these invaders, largely due to the prohibitive cost of clearing biomass.
In the webinar on Tuesday, about the newly developed Water Impact Calculator tool, the partners of the project said that the biomass from invasive alien plant clearing itself had not historically been viable for many users, leaving a gap in sustainable funding models for large-scale eradication. This is what the tool hopes to address.
The primary purpose of this tool is to quantify the positive water impact achieved by removing invasive alien plants and to allow operators to calculate the volume of water released back.
Ariana Baldo, the programme director of Roundtable on Sustainable Biomaterials, said: 'This approach allows operators to calculate the volume of water that is released back into local ecosystem post clearance, and provides measurable evidence of water savings that can be documented and verified if necessary, through third party auditing, and then, finally, transfer to buyers who can use the water impact claims against their sustainability target.' DM
