Researchers took sediment cores from Lake Kopello, located high in the Rwenzori mountains, to reconstruct fire history in the region since the last ice age.
Photo Credit: Jim Russell.
Scientific Frontline: Extended "At a Glance" Summary: Rwenzori Mountains Paleofire Research
The Core Concept: A recent study reveals that a devastating 2012 wildfire in the high-altitude alpine moorland of Africa's Rwenzori Mountains was the first large-scale blaze in the region in at least 12,000 years. This unprecedented event signals a modern threat to unique tropical alpine ecosystems driven by a shifting climate and human activity.
Key Distinction/Mechanism: By analyzing sediment cores from remote mountain lakes for charcoal deposits, researchers reconstructed a 12,000-year environmental record. This method distinguishes historical ecological baselines from modern disruptions, showing that while lower elevations experienced fires beginning 2,000 years ago, the highest glaciated peaks remained entirely fire-free until 2012.
Major Frameworks/Components:
- Sediment Core Analysis: Utilizing biomarkers such as pollen grains, leaf waxes, fossil bacteria, and charcoal extracted from lake beds to reconstruct ancient environments.
- Paleofire Reconstruction: Measuring charcoal concentration spikes to identify historical fire frequency and severity.
- Vegetation Succession Dynamics: Tracking historical pollen changes to observe ecosystem transformations, such as the documented shift from deciduous forests to bamboo and grasses following ancient fires at lower elevations.
Branch of Science: Paleoclimatology, Earth Sciences, Environmental Science, and Ecology.
Future Application: The findings emphasize the immediate need to develop strict land management and conservation plans to prevent ignitions in Afroalpine landscapes. This research will also aid in predicting and mitigating secondary hazards, such as the destructive flooding in lower-elevation villages caused by the reduced water retention of charred soil.
Why It Matters: The Rwenzori Mountains, alongside Mount Kenya and Mount Kilimanjaro, are UNESCO World Heritage Sites hosting endemic "sky island" species found nowhere else on Earth. The permanent transformation or loss of these ecosystems underscores the severe and unprecedented consequences of modern climate change and anthropogenic activity on isolated biomes.
In 2012, a wildfire ripped through 42 square kilometers of alpine moorland in Africa’s Rwenzori Mountains, a range of glaciated peaks on the border of Uganda and the Democratic Republic of the Congo. The blaze, which occurred at an elevation of over 13,000 feet, was shocking to those familiar with the mountains, as the climate had been assumed to be too cold and too wet for fire to spread.
Now, using sediment cores from a pair of remote mountain lakes, a research team led by Brown University scientists has assembled a record of fire activity in the Rwenzoris dating back thousands of years. The researchers show that the 2012 fire was the first large-scale blaze in the range’s highest elevations in at least 12,000 years. On the range’s lower slopes, at altitudes closer to 9,000 feet, the researchers found no evidence of fire until about 2,000 years ago, around the time archaeological evidence suggests there was an intensification of human activity in the region.
The findings, published in the journal Nature, suggest that changes in climate and human activities are having a profound and unprecedented effect on Africa’s unique alpine ecosystems.
“These findings imply that the diverse, endemic ecosystems on tropical Africa's highest mountains are vulnerable to fire and, particularly in the context of climate change, could be permanently transformed if fires become frequent,” said Andrea Mason, a PhD candidate in Brown’s Department of Earth, Environmental, and Planetary Sciences and an affiliate of the Institute at Brown for Environment and Society. “It is critically important to develop management plans that prevent ignitions to preserve these ecosystems.”
For the study, the researchers trekked into the Rwenzori Mountains to collect sediment cores from small lakes nestled along the slopes. The remnants of pollen grains, leaf waxes, fossil bacteria, and other biomarkers transported into the lakes by runoff and wind provide researchers with a well-preserved record of environmental activity dating back thousands of years. The team searched the sediments specifically for charcoal—the stable, telltale signal of past fire. The team collected sediment cores from two lakes: Lake Mahoma, on the lower slopes at about 9,000 feet, and Lake Kopello, in the alpine zone at around 13,000 feet.
The researchers found that the sediments from the past 12,000 years in the high-altitude Lake Kopello contain only tiny amounts of charcoal for most of that time—the exception being the most recent sediments deposited around the time of the 2012 fire. These recent sediments contain over 100 times more charcoal than older sediments, the researchers found.
“The charcoal peak associated with the 2012 fire is enormous,” Mason said. “It completely overwhelms any signal from the last 12,000 years, which is how we determined that the 2012 fire is unprecedented in the Holocene epoch.”
Lower on the slopes, at Lake Mahoma, the cores suggest fire was rare until around 2,000 years ago, when a sharp uptick in charcoal is recorded in the sediment. The onset of fire activity immediately preceded a profound change in the vegetation surrounding the lake, as detected by pollen grains sampled from the sediment. Pollen associated with deciduous trees declines after the period when fires are detected, while pollen associated with bamboo and other grasses increases.
These findings suggest that the “rise of fire permanently transformed these tropical African mountain forests 2,000 years ago,” said study coauthor Jim Russell, a professor of Earth, environmental, and planetary sciences at Brown.
Pinpointing the cause of the increase in fire activity is difficult, the researchers say, but the timing of the fire increase around 2,000 years ago coincides with archaeological evidence of intensified human activity in the region. At higher elevations, it is possible that the combination of increased tourist presence and a warmer, drier climate is allowing fire to spread in a way that it could not over the past 12,000 years.
The implications of this new fire regime are profound. The Rwenzoris—as well as Mount Kenya and Mount Kilimanjaro, which have also experienced recent fires—are all UNESCO World Heritage Sites. These high peaks are sometimes referred to as “sky islands” that are home to plant and animal species found nowhere else on Earth. All these ecosystems face an emerging threat from fire.
However, the risks are not confined to plants and animals. In the months following the 2012 Rwenzori fire, villages at lower elevations were subject to destructive flooding as the charred landscape above failed to hold rainwater as it normally would.
If fires like this are the new normal for Afroalpine landscapes, it will be necessary to plan for and manage them, the researchers say. For Russell, the findings were a startling reminder of how climate change and human activity are changing the planet in profound ways.
“People are starting to experience these environmental change moments when a place that they know and love has gotten wrecked,” Russell said. “That fire in 2012 was my moment. I’d been going to those mountains a lot for fieldwork, and to see them get scorched was really eye-opening.”
Funding: The research was supported in part by the National Science Foundation (DEB 2048669 and DGE 2040433).
Published in journal: Nature
Title: Twenty-first century emergence of alpine fire in Central African mountains
Authors: Andrea L. Mason, Eleanor M. B. Pereboom, Sarah J. Ivory, Richard S. Vachula, Meredith A. Kelly, Bob Nakileza, and James M. Russell
Source/Credit: Brown University
Reference Number: as051326_01
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