During wildfires, people are urged to stay indoors and keep windows closed to avoid breathing in the smoke. Surrounding trees don’t have that option, of course, but a new study suggests some species may also be able to protect themselves from dangerous air quality. Yale Environment 360 reports that a team of researchers from Colorado State University discovered this information by chance while out in the field for another project. As smoke from a nearby fire filled the air, they took the opportunity to observe what effect it had on the ponderosa pines they were studying. They found that the trees’ stomata — small pores on the surface of leaves that take in carbon dioxide and release oxygen — closed in the smoky conditions.

“Our months of data have shown that some plants respond to strong waves of wildfire smoke by ceasing their exchange with outside air,” the study’s authors write in the Conversation. “They’re effectively holding their breath, but not before they’ve been exposed to the smoke.” Studies of how wildfires affect plants and wildlife are harder to come by because they’re hard to predict and dangerous to deal with, so researchers aren’t usually on the ground to record data. While more information is needed to understand these new findings, the authors suspect that the leaves are actively closing the stomata, or that the smoke is plugging them — or some combination of both. (More wildfire stories.)