In the Heat of the Night; October 1998; Scientific American Magazine; by Beardsley; 1 Page(s)

Researchers working in Costa Rica have discovered disturbing evidence that increasing temperatures have markedly slowed the growth of tropical trees over the past decade. The slowdown may explain calculations suggesting that tropical forests, which are usually considered to take up carbon dioxide, have actually added billions of tons of the greenhouse gas to the atmosphere each year during the 1990s, making them a huge net source, comparable in size to the combustion of fossil fuels. The trend could exacerbate global warming: as the mercury rises, tropical forests may dump yet more carbon dioxide into the atmosphere, causing still more warming.

In 1984 researchers Deborah A. Clark and David B. Clark of the University of Missouri, collaborating with Charles D. Keeling and Stephen C. Piper of the Scripps Institution of Oceanography in La Jolla, Calif., began measuring the growth rates of scores of adult tropical rain-forest trees at La Selva Biological Station in central Costa Rica. The sample includes six different tree species, with both fast- and slow-growing types represented. Using special measuring collars, the scientists obtain reliable data on aboveground growth each year. Deborah Clark presented the team¿s findings in August at a meeting of the Ecological Society of America in Baltimore.