Small climate shifts having unexpectedly large changes in tropical rainforests
Slight rises in temperatures are triggering rainforest trees to produce more flowers, reports a new study published in the journal Nature Climate Change.
The research is based on observations collected in two tropical forests: a seasonally dry forest on Panama’s Barro Colorado Island and a “rainforest” with year-around precipitation in Luquillo, Puerto Rico. The authors, led by Stephanie Pau, currently at Florida State University but formerly from UC Santa Barbara, analyzed the impact of changes in temperature, clouds and rainfall on flower production. They found an annual 3 percent increase in flower production at the seasonally dry site, which they attributed to warmer temperatures.
The findings lend support to other research suggesting that tropical forests are seeing significant changes from small climate shifts.
“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,” said Pau in a statement. “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.”
“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 continued. “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.”
Canopy of the Panamanian rainforest
Other studies have found evidence of increased growth rates in tropical forests, which some have attributed to the fertilization effect from elevated atmospheric carbon dioxide concentrations. For example, a paper published in Geophysical Research Letters in May reporting “greening” in dry regions due to carbon dioxide fertilization. But that research added that rainforests are unlikely to see big increases in bioaccumulation.
“Leaf cover in warm, wet places like tropical rainforests is already about as extensive as it can get and is unlikely to increase with higher CO2 concentrations,” explained a statement from the American Geophysical Union, which publishes Geophysical Research Letters. “In warm, dry places, on the other hand, leaf cover is less complete, so plants there will make more leaves if they have enough water to do so.”
Still other studies, including a 2007 paper published in Ecology Letters by a co-author of the current Nature Climate Change paper, indicate that rising temperatures could eventually lead some tropical forest trees to hit a wall, where growth slows or even reverses due to increased respiration.
“Increases in atmospheric CO2 provide more substrate for photosynthesis and might lead to increased growths,” said Joseph Wright, a scientist at the Smithsonian Tropical Research Institute, in 2007. “Increases in temperature increase respiration rates and might lead to decreased growth, as appears to be the case in our study.”
CITATION: Stephanie Pau, Elizabeth M. Wolkovich, Benjamin I. Cook, Christopher J. Nytch, James Regetz, Jess K. Zimmerman & S. Joseph Wright. Clouds and temperature drive dynamic changes in tropical flower production. Nature Climate Change Letter | 7 July 2013
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