South African Desert Becomes Global-Warming Lab

Bijal P. Trivedi
National Geographic Today
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.

"Midgley's work is right on the cutting edge," says Brett Orlando, the climate change adviser for the World Conservation Union in Gland, Switzerland. "He can't tell us when and what plants will be lost, but his work gives us a sense, a direction, of where things are headed."

"Other research teams have focused on the effects of climate change on particular species: birds in Mexico, mangroves in Southeast Asia, and amphibians, snakes, and birds in Costa Rica. But Midgley is one of the first to look at an entire ecosystem," says Thomas Lovejoy, conservation biologist and president of the H. John Heinz III Center for Science, Economics, and the Environment in Washington, D.C.

Watching the Heat Rise

Midgley and his colleagues at NBI are also conducting experiments to test plant survival in warming conditions. The researchers have erected 20 hexagonal Plexiglas chambers at several sites in the Karoo that trap heat and raise temperatures around the plants between four and six degrees during the day.

"This greenhouse effect kills 70 to 80 percent of the plants," says Midgley. "The models predict that the plants won't survive, and they don't."

The next stage in the experiment is to build more chambers to test a broader range of temperatures. "We want to know what is considered safe climate change," Midgley says.

Knowing the survival limits of plants in the Karoo may effect global energy policies and land use. If small increases in temperature threaten species, that adds to the pressure to reduce reliance on the fossil fuels believed to make the planet warmer.

More immediately, the research may reinforce the need for "friendly land management practices," as Midgley calls them, which allow species—plants and animals—to migrate in response to shifting temperatures and rainfall.

One result might be not grazing or farming "right up to the fence," says Midgley. "We need to ensure there are buffer zones next to protected areas, and generous wildlife corridors for all species to move and adapt to climate change."

As the work in the Karoo demonstrates, environmental groups increasingly need to consider climate in deciding the focus and the methods of conservation.

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