A THREATENED HOTSPOT

Of all the predictions made in the South African Country Study report, the most worrying relate to the Succulent Karoo. Climate change models predict that within 50-100 years, areas that support Succulent Karoo vegetation today will become so arid that only the hardiest plants of that biome will be able to survive. Plants of the Desert Biome may colonise these areas, creating new plant communities not previously recorded. The main part of the country where the predicted climate might support Succulent Karoo vegetation is the Agulhas Plain. It is highly unlikely that plants will be able to migrate from Namaqualand and the Richtersveld, across the Cape Fold Mountains to this coastal plain in the southern Cape. The Succulent Karoo Biome faces an extremely fragile future.

TRANSFORMING GRASSLANDS

Frost helps to maintain the Grassland Biome by killing the seedlings of many trees and shrubs that would otherwise grow there. As the climate warms up and frost becomes less frequent, woody plants will be able to invade grasslands, transforming them into Savanna areas. Research done by NBI and UCT suggests that, in addition to affecting global warming, an increase in atmospheric carbon dioxide may also directly stimulate the growth of trees and shrubs in the following ways: Increasing carbon dioxide levels affect the metabolism of grasses such that they need less water to grow. Water that is not absorbed penetrates more deeply into the soil where it is available to the roots of shrubs and trees. Carbon is the raw material that plants use to build their cells and tissues. Plants absorb carbon in the form of carbon dioxide and convert it into building materials like cellulose and wood. Woody plants need much more carbon than grasses, so higher levels of carbon dioxide in the atmosphere will stimulate the growth of trees and shrubs.

THE SHRINKING KAROO

Climate change models predict that the Great Karoo will become drier and more desert-like, particularly in the west. Only in parts of the eastern Karoo will the climate still suit the vegetation of the Nama-Karoo Biome. Although we cannot predict exactly what the natural vegetation of the western Karoo will resemble in 50-100 years' time, we can get clues by comparing photographs of the Arid Karoo during drought years and years of good rainfall.