Guy Midgley has a more pessimistic view of atmospheric CO2’s apparently increasing influence. “We [South Africans] like our non-forest ecosystems,” he said, noting that aside from the impacts that an increase in woody plants will have on grassland wildlife and livestock ranching, the country’s grasslands form watersheds that feed rivers vital to the economy. Studies show that water yields of South African grassland catchment areas drop significantly when invaded by alien trees, one reason that the government spends millions of dollars a year to remove them.
South African ecologists are trying to figure out how best to stop trees from taking over savannas, perhaps with “fire storms” — controlled fires set on hot, dry days to maximize the heat they generate — or careful tree-thinning. But super-hot fires might have their own negative effects on ecosystems, and manual thinning could be too expensive. Midgley said that by reaching today’s level of 400 ppm of atmospheric carbon dioxide, “we’ve turned the evolutionary clock back 5 million years in under a century. It’s a massive change in how our ecosystems work.” He noted that atmospheric CO2 could hit 600 ppm by 2100, a level last seen during the Eocene epoch of 34 to 55 million years ago, when forests covered nearly all of the planet and long before modern grasses and the large savanna mammals that we know today evolved.
“We’re in a brave new world from a plant’s perspective,” said William Bond. “It’s a little frightening. Our plains animals have their backs against the wall.” The new invading trees won’t do anything meaningful to combat climate change, he said, because they’re a negligibly small carbon sink in global terms.
“We’ve got to stop the problem at source,” he said. “We’ve got to stop burning fossil fuels and sending carbon into the air.”
“Wangari Maathai was wrong,” he chuckled playfully, referring to the Kenyan environmentalist and Nobel Peace Prize winner who advocated a tree-planting campaign across the continent. “Trees aren’t always a good thing.”
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