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California Bats Thrive in Forests Recovering From Wildfires

Wildfires leave behind a patchwork of forest densities that can give bats more room to fly and hunt

Pallid bats use relatively low-pitched sounds for echolocation, making them better at hunting in open spaces like grasslands. (Photo by Connor Long via Wikimedia Commons under CC BY-SA 3.0)
smithsonianmag.com

Fire suppression has been used as a forest management tool for decades, but a growing body of research shows that California’s forest ecosystems have evolved to live with, and even rely on, some amount of seasonal wildfire. A recent study published in Scientific Reports adds to that knowledge, finding that bat populations are doing better in areas recently affected by fire, compared to areas that grown thick from years of fire suppression.

The research, led by ecologist Zack Steel of University of California, Berkeley, focused on bats in the Sierra Nevada, a mountain range in central and eastern California. Of the 17 bat species the team studied, some are known to prefer wide open areas while others can maneuver in a cluttered canopy. Eight species were found in unburned areas, and 11 fluttered above the fire-affected ones. Only one species’ population fell after fires.

“We expected to see one group of species benefiting from fire—the more open-habitat-adapted species—and another group, the more clutter-adapted species, being negatively affected by fire, preferring the unburned areas,” Steel tells Scientific Americans Jason Goldman. “But even some of those species were occurring more often in burned areas.”

The researchers surveyed bat populations at six sites by recording the ultrasonic squeaks of bats doing echolocation. Three of the research sites hadn’t seen fire in recent years, while three recently faced wildfires: the 2013 Rim Fire, 2004 Power Fire and 2012 Chips Fire.

The research team recorded the ultrasonic squeaks that bats use for echolocation. Their calls are too high-pitched for human ears and supplement the flying mammals’ eyesight as they hunt. (Most bats can see about as well as humans, which is not necessarily well enough to catch a mosquito at twilight.) Audio of the sites revealed that the fires left behind a patchwork of differently burned areas, or ecological “pyrodiversity.” Some areas come out severely burned, while others just lost their underbrush, and all of these adjustments trickle up to the treetops.

Wildfires left to burn can change how tree cover density, introduce dead trunks for some bats to roost in, or kick up populations of insects for them to eat. All of these would be a boon for bat populations, which are facing a variety of threats, including a fungal disease called white-nose syndrome.

“When there’s lots of variation in habitat after a fire, many species benefit in different ways,” Andrew Stillman, a biologist at the University of Connecticut who was not involved in the study, tells Scientific American. “On the whole, the community becomes more diverse, and that’s a good thing for the landscape.”

Forests in the western United States were managed with a strict fire suppression policy for a long time, and are now beginning to adopt prescribed burning. In the Sierra Nevada, only two wilderness areas allow for managed wildfires, where fires started by lightning can burn themselves out.

“If we’re able to reintroduce fire to the Sierra Nevada, that’s going to improve habitat,” Steel told James Steinbauer at Sierra magazine in December. “If you have better habitat, you’ll have healthier bat populations that are more likely to withstand the threats caused by climate change.”

Steel added to Sierra that managed wildfires are more beneficial than prescribed burning, as the latter is intended to clear fire-starting underbrush without damaging the trees. Bats aren’t the only group that’s hurt by a lack of moderate wildfires. Birds including spotted owls, bees, and certain plants have evolved to rely on a healthy dose of heat.

“The crisis is not the number of fires, it’s that we have too many bad fires and too few good fires,” Stephen Pyne of Arizona State University, a leading scholar of forest fire history, told Smithsonian magazine’s Lyndsie Bourgon last July. “It’s equally a problem that we’re not doing the good burning that would calm bad fires.”

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