When Meredith Kelly arrived in the Rwenzori Mountains in June 2012, she walked into the aftermath of a fire that, as a new study in Nature she co-authored now shows, had no precedent in 12 millennia.
Kelly, a professor in the Department of Earth Sciences, had already spent about a week doing geological fieldwork in the Rwenzoris, a glaciated range on the border of Uganda and the Democratic Republic of Congo, before trekking into the burned area. In January, the fire ripped through more than 16 square miles of alpine moorland at elevations above 13,000 feet in a range long assumed to be too cold and wet to carry fire.
“The vegetation in the mountains is a unique tropical alpine vegetation that I had never seen or experienced before,” Kelly says. “It was heartbreaking seeing the extent of the damage—burned vegetation and ecosystems where a great diversity of animals had lived.”
The study in Nature confirms how out of place that blaze was before the influence of climate change and encroaching human activity. Using sediment cores from two remote mountain lakes, the team, led by Brown University researchers, constructed a fire record for the Rwenzoris stretching back 12,000 years and found that the 2012 fire was the first large-scale blaze at those elevations in all of that time. The results suggest that high-elevation ecosystems worldwide may face a greater future risk of fire that they are not adapted to withstand or recover from, Kelly says.
The researchers built that record by trekking into the Rwenzori Mountains and extracting sediment cores from two lakes amid the towering slopes: Lake Kopello at roughly 13,000 feet, and Lake Mahoma at about 9,000 feet. Over centuries, runoff and wind carried biological material into these lakes—pollen grains, leaf waxes, fossil bacteria—where it accumulated in layers that preserve a record of changes to the surrounding landscape. The team searched specifically for charcoal, the stable chemical signal of past fire.
The team building the coring raft used to obtain sediments from Lake Kopello in January 2019 (Laura Hutchinson ’19 is pictured at center.)
From Lake Kopello, the picture was stark. Sediments from the past 12 millennia contained only trace amounts of charcoal—until the very top layer. Material deposited around the time of the 2012 fire contained more than 100 times the charcoal of any older layer.
From Lake Mahoma, lower on the slopes, fire appears in the record starting about 2,000 years ago, roughly when archeological evidence suggests an intensification of human activity in the region. That uptick coincided with a major vegetation shift: pollen from deciduous trees dropped off, while grasses and bamboo moved in.
The effects of the 2012 fire didn’t stay in the mountains. Intact alpine vegetation normally absorbs rainfall, but scorched ground doesn't. As a result, there was devastating flooding in the Ugandan village of Kilembe, at the southern end of the range, and the nearby city of Kasese in spring 2013. Kelly believes the fire also hit Kilembe’s economy hard, with tourism shifting to the hiking trails on the east side of the Rwenzoris after 2012. The village depends on trekking and its residents work as guides, cooks, and porters, Kelly says.
Kelly and her colleagues have returned to the area five times since 2012, most recently in January 2019, watching the landscape slowly recover. That most recent trip was also when the team collected their sediment cores, which required hiring ~70 people to carry the coring equipment into the mountains.
Professor Meredith Kelly conducted fieldwork in the Rwenzoris in 2016 with David Cavagnaro ’17, Margaret Jackson GR ’21, and former Neukom postdoc Alice Doughty.
A warning for other mountain ranges
Mount Kenya and Kilimanjaro also have experienced recent fires. Like the Rwensoris, they are sometimes called “sky islands,” isolated ecosystems in the archipelago of high-altitude peaks that make up the continent's unique Afromontane regions. These cool, moist habitats are home to plant and animal species found nowhere else, species that evolved without fire and have no defenses against it.
Kelly sees the findings reported in Nature as a warning that extends well beyond East Africa. High-elevation regions are often thought of as “water towers” for the communities below, storing freshwater that lowlands draw on during dry seasons, Kelly says.
“Fires may put these critical regions at risk,” she says.
She draws a direct line to mountains closer to home. Glaciers are melting at rapid rates in the western United States, leaving high-elevation areas in the Sierra Nevada, Cascades, and Rockies drier and more susceptible to fire.
“I think the findings show that high-elevation tropical regions, which are generally quite cool and wet, are becoming more at risk for fires," Kelly says. “This is unexpected and can have the impact of significantly altering these unique high-elevation ecosystems.”