South African Desert Becomes Global-Warming Lab

August 4, 2003

About 900 miles (1,450 kilometers) northwest of Cape Town, South Africa, lies the Succulent Karoo, one of the world's most plentiful, and most threatened, desert ecosystems.

The Washington-based Conservation International has designated the 45,000-square-mile (116,000-square-kilometer) Karoo as one of the world's 25 biodiversity "hot spots." The stark, arid landscape has a so-called Mediterranean climate that fosters an astonishing diversity of some 5,000 plants—40 percent of which are found nowhere else.

Many of the plants are succulents, which store water in their stems and leaves, giving them their plump, fleshy appearance.

"The greatest challenge to these plants may be a rapidly warming climate," says Guy Midgley, a plant physiologist at the National Botanical Institute (NBI) in Cape Town and lead scientist of a group that is investigating the effects of rising temperatures on the Karoo flora. The research is primarily funded by Conservation International.

The Karoo has become a laboratory for the study of climate's impact on ecosystems. Midgley had seen 50-year climate models for South Africa that predicted a 25 percent drop in winter rainfall and a two-degree rise in temperatures.

"I thought the predictions were so extreme that I was motivated to get in the field and look for the evidence," says Midgley.

Midgley and his colleagues, in the Karoo since 2001, are tracking signs of plant stress.

Signs of Change

"With some plants, like proteas and the cape reed, we have seen areas of local extinction," Midgley says—for example, the dried husks of adult plants, and no young plants.

In other areas, shriveled leaves and aborted flowers reveal the lack of water and nutrients. Without flowers, there are no seeds; without seeds, no future generation of plants.

In some areas, only adult plants remain. Young plants aren't thriving because they don't have the water storage capacity to survive the heat. "The adult plants are like living dead," Midgley says.

The researchers are also looking for shifts or contractions in species distribution—a fingerprint of climate change. As the climate warms and dries, the range of species in the Karoo may move south to cooler latitudes. Such shifts have been documented in regions of the Northern Hemisphere.

Continued on Next Page >>


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