Tropical trees and hanging vines burst into flower, showering the ground below with bright blossoms. Temperature, rather than cloud cover, may be key to the timing of tropical flowering events according to research at two sites in the Smithsonian Institution Global Earth Observatory Network published online in Nature Climate Change.

Scientists discovered a significant increase in flower production-about 3 percent more flowers produced on average per year since 1987-on Barro Colorado Island's Forest Dynamics Plot in Panama.

"Barro Colorado Island was chosen for this study because we have the longest quantitative record of flower production in the tropics," said S. Joseph Wright, Smithsonian staff scientist who has been tracking seasonal patterns in the tropics for about 30 years. At the other site in the study, the Luquillo Forest Dynamics Plot in Puerto Rico, flower production has been monitored since 1992 and shows no overall increase.

Both plots are part of the a worldwide network of 51 forest study sites that can be easily compared, making it possible to discover if forests in different places respond the same way to climate variables. In this case, they do not respond the same way to cloud cover.

Thicker clouds over Panama may limit flower production whereas thinner clouds over Puerto Rico may enhance flowering. Thin clouds diffuse light, which can offset the loss of absorbed radiation and increase light levels under the forest canopy.

The overall increase in flower production in Panama may be attributed to increasing maximum temperatures and/or precipitation.

Researchers from the U.S. National Center for Ecological Analysis and Synthesis, the University of British Colombia, NASA Goddard Institute for Space Studies and the Lamont-Doherty Earth Observatory teamed up with Smithsonian researchers at the two sites for this first study to link cloud cover to forest productivity. Led by Stephanie Pau, from NCEAS, they analyzed a new dataset, NOAA NCDC GridSat, which quantifies cloudiness at the two sites for several decades.

Half of the world's species live in tropical forests, which are also critical in the global carbon cycle, accounting for about a third of all terrestrial plant productivity.

Long-term studies in the tropics will continue to contribute to the understanding of climate change and its effects on global biological processes.