In September 2018, a wildfire ravaged nearly 2,000 hectares of shrubland surrounding Pichu Pichu, an inactive volcano in the Peruvian Andes.
It wasn’t the first time. In recent years, this unique ecosystem has increasingly suffered from fires primarily caused by human activities such as deforestation and slash-and-burn agriculture. A new study published in the Spanish Journal of Soil Science has revealed that these fires not only damage vegetation but also harm the soil. Even 4 years after the 2018 fires, the study found, vulnerable volcanic soil had not recovered.
“The Peruvian Andes are not ready for wildfires.”
“The Peruvian Andes are not ready for wildfires,” said lead author Jorge Mataix-Solera, a soil scientist at Universidad Miguel Hernández in Spain who has spent more than 3 decades studying the impact of fires on different soils.
Located 3,700 meters above sea level in Peru’s Arequipa region, the Pichu Pichu shrublands are one of the most arid places in the world and considered a cold desert, with temperatures ranging from 4°C to 18°C. Unlike other arid ecosystems, such as the Mediterranean woodlands or the Cerrado grasslands of central Brazil, plants around Pichu Pichu have not developed traits such as thick bark or fire-germinating seeds to adapt to wildfire. To make matters worse, the region’s soil is naturally dry and highly water-repellent due to its sandy characteristics.
Soil Sampling and Plant Perusal
Researchers had already suspected that fires would have a significant impact on the region. But to better understand how, they collected 40 soil samples from Pichu Pichu 3 and 4 years after the 2018 disaster, half from burned areas and half from unburned areas.
Burnt shrubs in the Pichu Pichu region
Researchers analyzed the soil below two dominant species of shrubs affected by wildfire in the Pichu Pichu area. Credit: Jorge Mataix-Solera
Physical and chemical analyses revealed that the wildfires caused severe carbon loss in the soil, which persisted even 4 years after the incident. Soil carbon is a key indicator of soil health: It helps the earth trap water, it’s a proxy for the presence of organic matter, it’s a vital component of soil fertility, and it helps prevent erosion. Carbon loss also leads to compaction, making the soil more inhospitable to new plant growth.
In addition to assessing carbon loss, the researchers analyzed the impact that the combustion of different plant species had on the soil. For this, they collected soil samples directly below two native plants that dominate vegetation in the region: Berberis lutea, a large evergreen shrub known locally as palo amarillo, and Parastrephia quadrangularis, a smaller bush known as tola-tola.
During a wildfire, plants act like the wick of a candle, concentrating the fire in one spot and elevating temperatures on the ground. Not surprisingly, the researchers found that soils under the palo amarillo underwent greater degradation after a wildfire, likely because the large biomass of this shrub provided more fuel for combustion.
The burning of vegetation was another factor contributing to soil damage, as plants usually trap humidity and help water infiltrate the soil. Without plants, the water tends to flow across the soil surface, causing further erosion and loss of organic matter. “This is particularly problematic in ecosystems like in Arequipa, where rainfall occurs in short, intense bursts,” said study coauthor Minerva García Carmona, a soil scientist also at Universidad Miguel Hernández.
Moreover, Carmona noted that the destruction of native vegetation in these areas directly threatens biodiversity and can have long-lasting effects on ecosystem resilience.
Mataix-Solera observed similar results in previous research studying soils of Torres del Paine in Chilean Patagonia, which were affected by a large wildfire in 2011.
Intensifying Fires
For Stefan H. Doerr, an expert in wildfires and soils at Swansea University in the United Kingdom, the new study is especially important because Andean soils have been historically understudied. “We know little about the effects of fire on non-fire-adapted Andean ecosystems,” Doerr said, highlighting that volcanic soils are among the most fertile and support 10% of the world’s population.
In recent years, Peru has experienced a concerning increase in wildfires, mostly caused by agricultural burning, land clearing, and grazing practices. In 2024, more than 200 wildfires struck all but two of the country’s regions, and more than 2,200 hectares of natural grassland were destroyed, according to the Peruvian National Institute of Civil Defense.
“These ecosystems are very fragile, and the best thing we can do to recover them is to avoid more human activities that produce these kinds of fires.”
As the climate changes and world temperatures increase, such fires are expected to intensify, especially in arid regions like the Peruvian Andes, further hindering ecosystem recovery. “The problem with climate change is that it’s occurring in a very short time and ecosystems have no time for developing strategies to adapt to it,” Mataix-Solera observed.
Scientists said that some recovery strategies, such as mulching, could be tested for soil restoration. Mulching involves covering damaged soil with plant material like leaves or wood chips to reduce erosion and help plants grow.
However, the researchers stress, the ultimate solution to wildfire degradation is to prevent wildfires in the first place. “These ecosystems are very fragile, and the best thing we can do to recover them is to avoid more human activities that produce these kinds of fires,” said Mataix-Solera.
—Sofia Moutinho (@sofiamoutinho.bsky.social), Science Writer
Citation: Moutinho, S. (2025), Wildfires pose a threat to volcanic soils in the Peruvian Andes, Eos, 106,https://doi.org/10.1029/2025EO250104. Published on 20 March 2025.
Text © 2025. The authors. CC BY-NC-ND 3.0
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