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In September 2018, a wildfire burned nearly two thousand hectares of shrubland on the Pichu Pichu volcano, an ecologically significant area in the Peruvian Andes. Unlike Mediterranean ecosystems, where vegetation has evolved strategies to withstand fire, the volcanic soils of Arequipa—one of the driest regions in the world—are not adapted to wildfire disturbances.

A Miguel Hernández University of Elche (UMH) research team collected and analyzed soil samples from the burned area at 3,700 meters above sea level to understand how these fragile ecosystems respond to fire disturbances.

, published in the Spanish Journal of Soil Science, indicate that four years after the fire, vegetation and soil combustion, combined with post-fire erosion, have caused a severe loss of soil organic carbon (SOC)—a key element for soil fertility.

"The Peruvian Andes are not prepared for wildfires," warns UMH professor Jorge Mataix Solera, a scientist with more than 30 years of experience studying post-fire soil recovery. Mataix emphasizes that fire is a natural ecological force, but its effects vary significantly depending on the ecosystem.

The study's findings indicate that Pichu Pichu's soil has undergone significant physical and chemical degradation after the fire, hindering ecosystem recovery. Furthermore, post-fire erosion has triggered additional degradation, reduced clay content, and weakened soil structure.

Post-fire water repellency and soil vulnerability

One of the challenges identified in these arid soils is their natural tendency to repel water, a phenomenon influenced by organic matter characteristics and high sand content. This water repellency persisted after the fire, exacerbating erosion. Without vegetation to retain moisture, water runs off the surface rather than infiltrating the soil, accelerating erosion.

"While well-structured and evolved soils, such as Mediterranean soils, have a high water-holding capacity, young volcanic Andean soils, which are naturally sandy, lose this ability after fire-induced organic matter loss," explains UMH researcher Minerva García Carmona.

"This is why understanding the effects of fire on these young and fragile soils is crucial," García adds, "especially considering the role of plants, which form the combustible material in wildfires and influence soil degradation."

Key plant species and their influence on post-fire soil degradation

The study focused on two native plant species with a critical role in the ecosystem: Berberis lutea, known as "palo amarillo del Perú," and Parastrephia quadrangularis, or "tola."

Researchers examined whether fire had different effects on soils depending on the dominant vegetation. The results revealed that areas dominated by Berberis lutea experienced greater soil degradation. "This is likely because it is a larger plant with higher biomass, which intensified combustion effects," García clarifies.

The UMH research team has extensive experience studying wildfire impacts on Mediterranean forests, which have developed resilience strategies due to their long history of fire exposure. However, their findings in Pichu Pichu confirm that volcanic soils in Arequipa naturally retain less water and are particularly vulnerable to fire degradation. This highlights the increasing threat wildfires pose to these ecosystems.

A fragile ecosystem in the Andean volcanic belt

Pichu Pichu is located in the central volcanic zone of the Andes. UMH researchers collected soil samples at approximately 3,700 meters above sea level, where annual precipitation averages just 385 mm, concentrated over three to four months. This makes the Arequipa region a "cold desert," with temperatures ranging from 4 to 18°C. The vegetation consists mainly of highly drought-adapted shrubland.

Due to limited precipitation, the Andean Volcanic Belt is a crucial water source for surrounding areas. "Although Pichu Pichu is dominated by shrubland, its foothills support forests that host a rich diversity of plant and animal species," explains a UMH professor. These foothills include queñua forests (Polylepis), whose endemic species in Peru are currently endangered.

The rise of wildfires in Peru and climate change implications

In Peru, most wildfires occur between July and October. In September 2024, the satellite monitoring project Queimadas recorded an all-time high of 7,037 wildfire hotspots in the country. "In a region like Arequipa, located in a desert environment, understanding soil response under new fire regimes is essential for assessing ecosystem resilience to climate change," explains a UMH researcher.

Mataix believes that the more we learn, the better we can help design prevention strategies and post-fire treatments to mitigate the effects of rising temperatures and intensified droughts.

"This is as crucial in Peru as it is in Spain or California," Mataix concludes. "Although fire is a natural phenomenon, the climate crisis is exacerbating these events, and we must do everything possible to restore and protect these ecosystems."