They like It HotTropical Biodiversity
Warm spell spurred it all
The diversity of pollen found in deposits from northern South America
Some like it hot, including the plants living in South America's tropical rain forests 56 million years ago. As global average temperatures spiked 5 degrees Celsius over a period of 10,000 years a geologic blink of an eye plant diversity in northern South America also soared, researchers report in the Nov. 12 Science. "We were expecting to find rapid extinction, a total change in the forest," says study leader Carlos Jaramillo, a biologist at the Smithsonian Tropical Research Institute in Balboa, Panama. "What we found was just the opposite a very fast addition of many new species, and a huge spike in the diversity of tropical plants." The study raises new questions about how tropical rain forests might respond as atmospheric carbon dioxide levels rise because of fossil fuel burning and other industrial activities. The researchers say that today's forests may not respond to warming in the same way that ancient forests did, but the findings do suggest that at least some plants are surprisingly adaptable. "This kind of work is critically important," says Scott Wing, a paleobotanist at the Smithsonian Institution in Washington, D.C., who was not involved in the study. "We're beginning to map out what happened in different places during this huge perturbation of the carbon cycle and climate system. It's our best bet at seeing the results of something that's already happened." Researchers call the warming the Paleocene-Eocene Thermal Maximum, because it took place at the boundary between the Paleocene and Eocene epochs of geologic time. Changes in ocean chemistry, such as "burps" of methane gas released from the seafloor, are thought to have rapidly built up greenhouse gases in the atmosphere and caused the warming. It's the closest analog scientists have to the global warming they expect in the future, though on a much slower scale; today, instead of a 5-degree increase over 10,000 years, researchers expect a 2-degree increase over just the next century, with more in store after that. Only a few places preserve evidence of how plants and animals responded to the Paleocene-Eocene heat, and most of those are in temperate or northern latitudes. In Wyoming, for instance, Wing and other researchers have found fossils suggesting that as things heated up, species from more southern regions moved into the area temporarily. But many tropical forests are already in the hottest places on the globe, hence there is no place from which warmer-adapted species might move. Many scientists think that tropical forests are already close to the maximum temperature they can survive.
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