- Wildfires in the high elevation Rocky Mountains are burning nearly twice as often as in the past, according to a new study that looks back at 2,000 years of data.
- While fires in the Rockies, like in the U.S. West, are part of the natural cycle, the study authors say the current rate of burning puts us in “uncharted territory.”
- Fires are expected to continue, and increase in frequency, as climate change leads to hotter and drier summers.
- The findings add to growing calls to address the causes of climate change, while simultaneously working to adapt to and mitigate the impacts of wildfires on human communities.
High up in the Rocky Mountains, forests are burning more frequently than any time in the past 2,000 years. The overarching reason: climate change. Warmer and drier climate conditions mean the vegetation is also drier, making it easier for fires that ignite to spread, as the saying goes, like wildfire.
Researchers from the University of Montana and the University of Wyoming used lake sediment and tree ring data to look back over 2,000 years of fire history in the subalpine, high elevation Rocky Mountains in the U.S. state of Colorado. Their findings, which are the first to place modern fires of the region into such a far-reaching historical context, were published today in the Proceedings of the National Academy of Science.
When forest fires burn, they deposit charcoal on the surfaces of nearby lakes. That charcoal, along with pollen and debris from plants, lands on the surface, becomes waterlogged, and settles to the bottom. Because there’s little or no oxygen down there, these sediments are preserved for thousands of years. Using sediment cores, researchers can identify peaks in charcoal to determine when fires occurred around the lake.
“We can describe [sediment cores] like taking a big straw and pushing it into the bottom of the lake. Put your thumb over the top to create a seal, and pull that up,” Philip Higuera, a professor of fire ecology at the University of Montana and first author of the study, told Mongabay. “And we can collect, basically, the sediment undisturbed, as it was deposited in the bottom of the lake for thousands of years.”
The scientists compared the layers in the lake to the rings inside trees. When a tree is scorched by fire, sap floods the wounds, protecting it from wood rot decay for decades. Because trees grow a new layer each year, the story of fire becomes written in its rings.
“It’s only after 2020, that we can go back and look at all these records together,” Higuera said. “And now say … we have entered uncharted territory”
Fires, mostly sparked by lightning strikes, are naturally occurring in the Rocky Mountains, where landscapes and species have evolved with fire over millennia. Fire, there and across the U.S. West, play an important role in ecosystem health by clearing vegetation, encouraging seeds to grow, and controlling pests. What is “uncharted,” at least in the Rocky Mountains, is the frequency of those fires.
The research team found that the average rate of burning is now twice what it was in the past. They now expect an individual tree in the study region to experience a fire on average every 117 years. In the past, that number was every 230 years.
This rate is even higher than the maximum rate during the early Medieval Climate Anomaly (770 to 870 A.D.), when temperatures were approximately 0.3° Celsius (0.54° Fahrenheit) above the 20th-century average.
“Our results are sobering in that they clearly, clearly show us how climate change is impacting ecosystems at a really fundamental level,” Higuera said.
Climate change, high-intensity winds, dead trees from insect pests, and accidental ignition by humans mean more fires. This higher frequency of fires has important implications for the way we address climate change. As societies strive to meet climate goals such as those set by the Paris Agreement, interest in planting, protecting and managing forests has grown. But for forests to be good carbon-removal investments, they need to be relatively permanent, meaning that the plants and soil will absorb carbon and keep it locked away for decades or centuries. Having more frequent fires threatens that permanence.
“When we’re looking to the future and planning for the future, we can’t be doing it based on our expectations from even the 20th century,” Higuera said. “High elevation forests burn infrequently on human timescales, but if we’re planning for carbon storage, among other things, with the expectation that they burn once every 150 to 200 years, we’re going to be misguided as we move through the 21st century.”
The record-setting 2020 fire season doubled the total area burned in the central Rocky Mountains since 1984. Some 1,011,330 acres (409,270 hectares) burned in the Rocky Mountains in 2020—an area about three-and-a-half times as big as Los Angeles, California.
This higher rate of burning that we’ve seen so far in the 21st century is expected to continue. Climate projections point toward increasingly warmer, drier and longer summers. This, along with the amount of unburned forests at high elevations, means burning will continue. We may not see fires on the scale of 2020 every year, Higuera says, but high in the Rocky Mountains, the periods between years with extensive burning are going to become increasingly shorter.
As for 2021, Higuera says, the outlook is “a bit frightening.” Many regions across the U.S. West are in exceptional drought, setting up the conditions that make widespread fire activity like last year possible.
“This increase in burning,” Higuera said, “forces us to really decide if we want to accept the changes that are happening, if we want to resist them, or if we want to help direct how forest ecosystems are going to change under a warmer world with more frequent disturbances like wildfires.”
In short, humans need to reconcile our relationship with fire.
Many Indigenous groups developed fire-dependent culture that balanced and buffered the random cycles of fire dating all the way back to the last glacial period, Don Hankins, a Miwkoʔ (Plains Miwok) traditional cultural practitioner, professor at California State University, Chico, and expert in pyrogeography, wrote in Bay Nature.
“[F]ire became ingrained in the fabric of Indigenous cultures to the point of interdependence,” Hankins writes. “Rather than waiting for the rare lightning ignitions, people wielded fire as a process central to the landscape’s ecological function and structure.”
However, after just a few centuries of colonial rule and the resulting fire suppression, many Western ecosystems have a fire deficit. This means that when fires do occur, they are much more severe. It is these severe blazes that threaten our cities, infrastructure, crops and homes.
“It is time to rise to the occasion to build a relationship with fire, to be stewards of our lands and our shared future,” Hankins writes.
Higuera says we need to address the causes of climate change, while simultaneously working to adapt to and mitigate the impacts of wildfires on human communities. Governments cannot do this alone but will need partnerships with universities, NGOs, the public, and leadership from Indigenous people and cultural practitioners. The challenge will be to put plans into action quickly. If we don’t, Higuera says, “we’re going to watch our forests burn down.”
“Fire is codified in the law of the land, and it has been so since time immemorial; it has always been here and always will be,” Hankins writes. “To live in balance with this land, one must embrace and accept fire’s presence.”
Higuera, P. E., Shuman, B. N., & Wolf, K. D. (2021) Rocky Mountain subalpine forests now burning more than any time in recent millennia. Proceedings of the National Academy of Science, 118, e2103135118. doi:10.1073/pnas.2103135118
Banner image of Colorado’s East Troublesome Fire, on October 22, 2020, which jumped the Continental Divide and eventually became Colorado’s largest fire on record, at nearly 200,000 acres. NASA Earth Observatory images by Lauren Dauphin, using Landsat data from the U.S. Geological Survey.
Liz Kimbrough is a staff writer for Mongabay. Find her on Twitter: @lizkimbrough_
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