Purchase, NY - According to popular wisdom, the earth’s rainforests are a natural defense against the effects of climate change -- the “green lungs” that reduce the amount of carbon dioxide in the atmosphere.

Now startling new research by Susan Letcher, assistant professor of Environmental Studies at Purchase College, in partnership with Professor Deborah Clark of the University of Missouri-St. Louis, into the effects of climate on rainforests is telling a different story. A disturbing trend in the rainforest of La Selva, Costa Rica has emerged: as the climate grows hotter each year, the trees are producing—or “respiring”—greater amounts of carbon dioxide than they did when temperatures were cooler. What’s more, trees may be dying prematurely, long before reaching the natural end of their life spans.

In recognition of the critical importance of this research, the National Science Foundation has awarded Clark and Letcher a grant in the amount of $441,524 for a period of 60 months.

“With the recent elevated death rate of trees, it’s especially important now for us to get a clearer look at the link between climate and tree mortality,” says Letcher.

Deborah and David Clark initiated a study of the rainforest in northeastern La Selva in 1983, with the goal of examining the coexistence of various rainforest tree species. But the course of their research soon changed. As Letcher explains:

“Early in their research, the Clarks discovered that many different tree species were showing the same pattern of growth—experiencing good and bad years—at the same time, and they realized it was linked to climate. Good years for the trees tended to be cool, while bad years were warmer. As temperatures rose, the Clarks realized that this study was closely linked with carbon dioxide fluctuations in the atmosphere, suggesting negative impacts of warmer years on tropical forests worldwide.”

An additional, worrisome piece of data emerged in the early 90s: as heat steadily whittles away the number of trees, there has been a notable increase in lianas—plants similar to poison ivy, grapevine, and Virginia creeper. These plants are vital as food sources and pathways for rainforest animals, but can also damage trees.

“Lianas do better in heat, drought, and high levels of carbon dioxide than the trees do,” explains Letcher. “They compete with trees—with more lianas, you have more trees falling and dying. This is not only bad for the trees—it’s bad for the atmosphere as well.”

By February 2012 the study will have accumulated 29 years of data on the effects of climate on tropical trees, making it the longest-term study of its kind worldwide. It is also the most specific study of its kind because it measures data on an annual basis, which Letcher points out is critical to detecting patterns within a limited time frame.

But Letcher cautions that the study of rainforests is still a young discipline, and that additional research will be crucial to fully understand links between lianas, climate, and tree growth. One fact, however, is not in doubt: the rainforests are heating up, and it’s leading to more carbon dioxide in the atmosphere. She concludes, “The more we get the word out about how climate change is affecting tropical forests, the more we can motivate people to act.”

For more information about Purchase College, visit www.purchase.edu.