Climate change is affecting the globe's tropical forests, with even slight temperature increases causing them produce more flowers, U.S. scientists say.

"Tropical forests are commonly thought of as the lungs of the Earth and how many flowers they produce is one vital sign of their health," Stephanie Pau, a geology professor at Florida State University, said.

"However, there is a point at which forests can get too warm and flower production will decrease. We're not seeing that yet at the sites we looked at, and whether that happens depends on how much the tropics will continue to warm."

The researchers studied flower production in two contrasting tropical forests, a seasonally dry forest on Barro Colorado Island in Panama and an "ever-wet" forest in Luquillo, Puerto Rico.

The site in Panama has been producing more flowers at an average rate of 3 percent each year over the last several decades, an increase that appears to be tied to warming temperatures, Pau said.

Flow growth is a measure of the reproductive health and overall growth of the forests, she said, and is not often considered in climate change studies.

"With most projections of future climate change, people have emphasized the impact on high-latitude ecosystems because that is where temperatures will increase the most," Pau said. "The tropics, which are already warm, probably won't experience as much of a temperature increase as high-latitude regions.

"Even so, we're showing that these tropical forests are still really sensitive to small degrees of change."