Yellowstone National Park 1988 Fire Burn Tour

Charred lodgepole pines fell in the area that burned in the 2016 Maple fire in Yellowstone National Park. The twin forces of wildfire and climate change could turn the forests of Yellowstone National Park into grasslands by the middle of this century, according to a new study.

The twin forces of wildfire and climate change could turn the forests of Yellowstone National Park into grasslands by the middle of this century, according to a new study.

The study, published in Ecological Monographs, found that warmer and drier conditions make it tougher for lodgepole pine trees and Douglas firs to regenerate after being consumed by fire. It also found that the trees that do regenerate have a tough time surviving for very long.

Winslow Hansen, a postdoctoral fellow at Columbia University and the study’s lead author, said the findings show that forests in and around the park are “at a tipping point.” He said intensified drought in the coming decades, especially after wildfires, could transform both Yellowstone and the surrounding ecosystem.

“What the results suggest is that the future will look very different,” Hansen said. “It will be a different place to live in and a different place to visit.”

Climate change impacts have shown themselves throughout the region — increased wildfire, declining snowpack, warmer temperatures. This study looks forward to get a sense of how the ecosystem will respond to projected climate conditions following wildfire. Though many plants in the Yellowstone region are adapted to fire, including lodgepole pine, this study showed that projected conditions made it harder for the young trees to establish and survive.

Hansen, and co-author Monica Turner, of the University of Wisconsin, combined two separate experiments — one in the field in Yellowstone and one in a greenhouse in Wisconsin. For each experiment, they planted lodgepole and Douglas fir seeds in soil from recently burned forests and tracked their ability to establish under different climatic conditions.

In the greenhouse study, they used special rooms to simulate climate conditions for different eras, including historical and future conditions. In each room, they set the temperature and relative humidity, and they watered the seeds in a precise way.

In Yellowstone, they used three seed plots at low elevations in the park’s northern range, near the road between Mammoth and Cooke City. They compared those to control plots farther south but at higher elevations — two near Yellowstone Lake, one in the area between Norris and Canyon, all in recently burned areas.

Hansen said the two sites in Yellowstone represent very different climates. While the areas in the southern part of the park are now dense, lodgepole forests at subalpine elevations, the northern range is a place where grasslands meet Douglas fir forests. The change in elevation makes for significantly different climates in the two locations, and Hansen said the northern range plots have the conditions expected for the plateau to the south in 50 years or so.

The seed plots in the northern range were made with soil transplanted from recently burned areas, since the study’s authors wanted to see post-fire recovery under a different climate regime. They found that far fewer seedlings established at lower elevations than at higher elevations. What seedlings did establish at lower elevations didn’t last long — all were dead within three years.

“None of those that did establish survived,” Hansen said. “That’s not a reduction. That’s a decimation.”

Hansen said there could be anomalies, like wet years that result in a bunch of tree production, but that the results suggest there will be more bad years than good in terms of tree growth. He said that will have consequences for wildlife and for the ways people use the forests now.

“People are going to have to think about how to adapt and maybe what kind of steps we want to take to try to shape that future in a way that’s favorable,” Hansen said.

Michael Wright can be reached at mwright@dailychronicle.com or at 406-582-2638. Follow him on Twitter @mj_wright1.

Michael Wright covers the environment and wildlife issues for the Chronicle.

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