Savanna vegetation predictions best done by continent

North Carolina State University Newsroom: A “one-size-fits-all” model to predict the effects of climate change on savanna vegetation isn’t as effective as examining individual savannas by continent, according to research published in Science this week.

Savannas – grasslands dotted with trees – cover about 20 percent of the earth’s land and play a critical role in storing atmospheric carbon, says Dr. William Hoffmann, associate professor of plant and microbial biology at North Carolina State University and co-author of the study.

A single global model can't predict savanna tree density as well as continent-specific models, according to research published in Science this week.

A single global model can’t predict savanna tree density as well as continent-specific models, according to research published in Science this week. Photo of a South African savanna courtesy of Dr. William Hoffmann, a co-author of the study.

“We wanted to find out what controls savanna vegetation – essentially the density of trees within the savanna – and whether we can use a single global model to predict what will happen to savannas if global temperatures rise,” Hoffmann said. “We found that the rules determining tree density are fundamentally different among the three continents studied – Africa, Australia and South America. That means a ‘one-size-fits-all’ approach won’t work.”

…“For example, greater moisture availability – a combination of rainfall, rainfall seasonality and drought indices – meant greater tree density in Africa and Australia, but it had almost no relationship with tree density in South America,” Hoffmann said.

Not surprisingly, he added, the study showed that fire reduces tree density. But the researchers found some strong counter-intuitive relationships between rainfall and fire frequency, namely that more moisture meant more fires. Hoffmann explained that more rainfall in a savanna meant faster-growing grasses, which meant any fires in that savanna would have ample fuel to spread quickly and easily…

A grassland in Slovenia, shot by Eleassar, Wikimedia Commons, under the Creative Commons Attribution-Share Alike 3.0 Unported license