Ideas

Ideas | Kelly Kasulis

How some trees can defend themselves against fire

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THESE DAYS, FLAMES CONSUME many of the earth’s forests more frequently than ever before. Now, a study from Princeton University suggests that trees in traditionally fire-prone areas have a competitive edge for survival: thicker bark, which helps shield their stems from growing conflagrations.

Scientists combined data to compare 572 species of trees: where they live, their bark thickness, and how often fires occur in their area. Researchers found that bark is, on average, three times thicker in savannas — where fires are a natural part of the ecosystem — than in forests. In other words, savanna trees have adapted to cope with their surroundings.

“It’s a big step forward in our understanding of the biogeography of fire and plant species,” says Park Williams, a bioclimatologist at Columbia University’s Lamont-Doherty Earth Observatory.

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Identifying fire-resistant traits in trees is key to predicting whether a species will withstand climate change or other man-made destruction. Increasingly hot, dry weather from climate change makes some regions more flammable, while deforestation and land development regularly expose forests to fire. The frequency of wildfires in the American West between 1970 and 1986, for example, nearly quadrupled over the following 16 years, according to a study published in Science Magazine. Many regions are expected to get worse.

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“[The study] is saying, ‘OK, where are we going to have more fire, and which trees are prepared for dealing with that fire?’ ” Williams said.

But a tree’s thick bark is kind of like an oven mitt — it only protects up to a point. Even thick-bark trees could die if their forests are set ablaze more often than they can handle.

“The caveat is, let’s say you take a particular species and you start to expose it to more frequent fires. It won’t necessarily change its investment in bark over a few decades,” said Adam Pellegrini, the study’s lead author and a NOAA climate and global change postdoctoral fellow at Stanford University.

In rain forests, tree species could be especially vulnerable. Their trees typically have thin bark, since fire-resistant traits weren’t traditionally needed.

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“When you start to burn an area where the species don’t contain adaptations to tolerate fire, you’re going to see a large amount of tree death,” Williams said. “This is not just a bark thickness story, but it’s a story about how we’re seeing huge changes in fire now.”

It’s certain that large-scale tree loss would threaten entire ecosystems. But for now, scientists are at least one step closer to predicting how the earth will fare under growing pressures.

Kelly Kasulis is a journalist living in Boston and the deputy digital editor of The GroundTruth Project. Follow her on Twitter @KasulisK.