In the parched summer of 1988, wildfires ripped through more than one-third of Yellowstone National Park during the most severe fire year in park history. Approximately 1.2 million acres scorched by September. Some fires smoldered through November.
While new forests sprouted in most of Yellowstone’s charred woodlands, recent research has identified that 16 percent of the forests consumed by the fires still have few trees. A study published earlier this year found that much of this land has transformed into green meadows full of grasses and wildflowers.
Of the roughly 965 square miles of forest killed by the fires, 158 remain unforested, largely due to a lack of available seeds to start the next generation of trees, research has found. Seventy square miles of the previously forested land is now open meadow, while the remaining area has seen enough growth of young trees to eventually reestablish a forest.
Knowing how forests in Greater Yellowstone respond to fire over a span of decades helps scientists understand how the ecosystem will adapt to a hotter, more fiery future.
“A big reason why people care about the Greater Yellowstone Ecosystem is for its beauty and recreation opportunities,” said the study’s lead author Nathan Kiel, a postdoctoral researcher at the State of New York College of Environmental Science and Forestry. If forest coverage shrinks, he added, the region’s beauty and recreation will be impacted.
The forests that bounced back quickly after the Yellowstone’s fires of 1988 were full of lodgepole pines that possessed a trait called serotiny. The cones of serotinous pines spring open and release their seeds when exposed to intense heat, an adaptation to fire that ensures enough seeds can start the next generation of growth. The forests that these trees reseeded are now impenetrable thickets of skinny pines.
Alternatively, the areas that remain unforested were mainly above 8,200 feet in elevation and dominated by subalpine fir, Engelmenn spruce and non-serotinous lodgepole pines. Compared to the regions where recovery was quick, these places have a cooler, wetter climate.
“At higher elevations, [trees are] more likely to die of old age than fire because the fire return intervals are more like 300 years,” said study co-author Monica Turner, ecologist at the University of Wisconsin-Madison. Forests in these areas have few adaptations to fire and take much longer to recover, she added.
Although the 1988 fires were severe, they were not abnormal. Research suggests that large fires have razed Yellowstone’s forests every 150–300 years.
Turner and Kiel identified the areas burned in 1988 where forests have not returned using Google Earth. They published their findings in 2022, the same year they trekked into the Yellowstone backcountry to examine whether forests would ever return to these scorched areas.
The researchers created 55 study plots scattered across former forests in and around most of Yellowstone National Park. (They couldn’t study the park’s northeast portion at the time since it had been cut off by the year’s floods.)
“At higher elevations, [trees are] more likely to die of old age than fire because the fire return intervals are more like 300 years.”
Monica Turner, ecologist, University of Wisconsin-Madison
Turner and Kiel surveyed the vegetation interspersed among the charred trunks of scorched forests to determine whether tree cover would ever return. Large numbers of saplings on 32 plots suggested that they were just on a slow path to reforestation. The other 23 had few trees of any age and were dominated by meadow plants like sticky geranium. Extrapolated across the entire tree-scarce burn area, they say the 23 plots represent about 70 square miles of forest that have turned into meadows.
Many of these new meadows are on the Two Oceans Plateau south of Yellowstone Lake, Turner said. “There were places where we could walk for half a mile and not even see a single seedling.”
But these findings must be considered alongside the scale of the fires of 1988, said Cathy Whitlock, ecologist and climate change expert at Montana State University who was not involved with the study. “The ‘88 fires burned a huge area,” she said. “These places [where forests have not returned] are still a pretty small percentage of the area that was burned.”
In addition, the areas that look like meadows today might simply be on an exceptionally slow path to reforestation, according to Kiel. “These high elevation forests that didn’t have any serotonous lodgepole pine might have historically taken 300 or 400 years to come back,” he said.
But in a changing climate, all three scientists agree that the interval of time between fires is decreasing. “The important point here is that they might not have that time anymore with fire becoming more frequent as the climate gets warmer and drier,” Kiel said.
In one example of increasing fire frequency, the 2016 Maple Fire reburned forests previously scorched in 1988. In areas that burned in both fires, one-sixth as many new trees sprouted after the 2016 fire when compared to the 1988 fire, subsequent field research led by Turner revealed. The young lodgepole pines that sprung up between the fires did not have enough time to produce the bounty of seeds needed to regenerate a dense forest, the authors argued. Repeated fires could cause a gradual collapse in forests across the GYE, they added.
But it is unlikely that all forests will meet this fate. “I don’t think Yellowstone is going to completely become deforested in the future,” Whitlock said. “But I do think we will have more fires.”
