Biodiversity Under Threat

Biodiversity is lost when species disappear faster than new ones arise. The main causes in South Africa are:

1. Habitat destruction — ploughing grassland, expanding towns, mining, and clearing wetlands. This is the single biggest cause worldwide.
2. Invasive alien species — organisms brought from elsewhere that spread on their own and crowd out indigenous species. Water hyacinth chokes the Hartbeespoort Dam; black wattle and Port Jackson willow take over riverbanks and drink enormous volumes of water.
3. Pollution — sewage and mine drainage in rivers, litter, and smoke.
4. Over-harvesting — poaching of rhino and abalone (perlemoen), and over-fishing.
5. A changing climate — species that cannot move or adapt fast enough lose their range.

Why it matters to people. Biodiversity does unpaid work for us every day: wetlands and healthy soils clean and store water; insects pollinate the crops in the Western Cape's orchards; indigenous plants supply medicines; and our wildlife supports a tourism industry that employs hundreds of thousands of South Africans.

Worked example — Working for Water. Alien wattle trees along a river each draw far more water than the indigenous plants they replaced. If one wattle takes 120 litres of water a day, then clearing 250 wattles returns

to the river. That is why crews are employed nationally to cut alien trees out of catchments: it is a water project as much as a conservation project.