Water Wheel Nov/Dec 2025: Invasive Alien Plants

Abstract

South Africa is one of the most water-stressed countries in the world. Rainfall is erratic, rivers often run dry, and climate change is intensifying the pressure. Yet, at the same time, millions of litres of precious water are being lost each year to invasive alien trees. These plants grow fast, spread rapidly, and use up far more water than native vegetation. They also fuel intense wildfires and crowd out biodiversity. Running from 2022 to 2025, the Mapping Woody invasive Alien Plant Species (MapWAPS) project was a trailblazing initiative which piloted remote sensing approaches for mapping alien trees in different biomes, with the long-term vision of producing a national map. The project used freely available satellite imagery and machine learning to map invasive alien trees within catchments that intersect with strategic water source areas (areas which cover 8% of South Africa’s surface but supply 50% of runoff ).

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