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The study, based on computer models created by a team of ecologists from three universities, modeled the effects of higher temperatures on fires. It centered on the Greater Yellowstone Ecosystem, which includes both Yellowstone and Grand Teton national parks as part of 20 million acres in Wyoming, Montana and Idaho. Special emphasis was on the health of forests: mostly lodgepole pines, but also including Ponderosa pine, Douglas fir, spruce fir, aspen and whitebark pine.
There’s already been much discussion and litigation over the fate of the whitebark pine; most recently the U.S. Fish and Wildlife Service held that although the whitebark pine is in peril, endangered-species protections would not be extended.
The new study went far beyond the whitebark pine. In a paper published yesterday in the Proceedings of the National Academy of Sciences, the effect of warmer temperatures on lodgepole-pine fires was examined and how they affect the entire ecosystem.
Traditionally, lodgepole-pine forest fires in Yellowstone are intense affairs, with entire forests consumed by intense flames — intense flames needed to open pine cones needed to create the next generation of lodgepoles. Lodgepoles are stubborn pines, hanging onto their slow-growing cones while other pines easily drop them regularly. Intense heat causes the lodgepole cones to pop open on the ground and release their seeds. This cycle is needed to keep forests healthy, and the resulting regeneration takes decades to take root. We’re talking about major wildfires of over 500 acres in size.
“The vegetation really needs about 90 years to fully recover,” said Erica A. H. Smithwick, assistant professor of geography and ecology in Penn State’s College of Earth and Mineral Sciences, and principal investigator on the project, “although there would probably be some cones at 15 years and more at 30 and 60 years. We need to know more about the forest’s capacity to recover rapidly under frequent fire conditions.”
If you map the history of wildfires in Yellowstone, you’d find that in years when temperatures are higher by just a small amount — 2 degrees Fahrenheit — you’ll also find more incidents of large fires. (Makes sense: warmer years are usually dry years as well.) Now, the sampling is just a speck in the sands of time — the records run between 1972 and 1999 — but it’s been correct in recent years, and so it was extended out to 2099.
“Large, severe fires are normal for this ecosystem. It has burned this way about every few hundred years for thousands of years,” said study author Monica Turner, the Eugene P. Odum Professor of Ecology at the University of Wisconsin-Madison and a landscape ecologist who has worked in the Greater Yellowstone area for more than 20 years. “But if the current relationship between climate and large fires holds true, a warming climate will drive more frequent large fires in the Greater Yellowstone Ecosystem in the future.”
The result: as it ends up, it takes the right combination of higher temperatures and lack of moisture and summer precipitation to create the right conditions for large-scale wildfires. Add the wild card of windy conditions, and you’ve got the makings of a perfect storm. And those conditions, which rarely occurred over the last 200 or 300 years, will become more common in coming years, with the potential of becoming the norm by 2099.
“What surprised us about our results was the speed and scale of the projected changes in fire in Greater Yellowstone,” said lead author Anthony Westerling, professor of environmental engineering and geography, University of California, Merced. “We expected fire to increase with increased temperatures, but we did not expect it to increase so much or so quickly. We were also surprised by how consistent the changes were across different climate projections.”
Scientists who specialize in climate change say it only takes a degree or two for the Earth’s surprising fragile ecosystem to change; we’re seeing that with Yellowstone’s threatened whitebark pine. The model says we’ll see more change: while today the norm is to have a summer season with no major fires, by 2034 we’ll see major fires every 30 years and by 2099 the conditions will be ripe for major fires every summer.
Which is not sustainable: as lodgepole-pine forests are burned down, it takes decades for forests to recover, and if fires are more frequent, they may not get the chance. Nature abhors a vacuum, so there’s the chance more aggressive tree species like the fast-growing aspen and Douglas fir may fill the void; there’s also the chance the forest will become a permanent grassland. This then impacts other vegetation and animals used to protection under the lodgepole pines; their habitat is endangered.
This isn’t to say lodgepole pines will disappear forever from Yellowstone. Indeed, the scientists are quick to point out they’re working with a model that represents the best available data.
“Our research after the immense 1988 fires revealed surprises and tremendous resilience in Yellowstone’s ecosystems, and Yellowstone is likely to surprise us again in the future,” Turner says. “It is an incredibly valuable natural laboratory for studying how natural ecosystems adapt to changing environmental conditions.”
Also participating in this research were Michael G. Ryan, research ecologist, U.S. Forest Service; and William H. Romme, professor emeritus, Colorado State University.
The Joint Fire Science Program, U.S. Forest Service Southern Research Station Joint Venture Agreement and the National Oceanic and Atmospheric Administration supported this work.
Image from the 1988 Yellowstone National Park fires courtesy of the National Park Service.
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