Burned and barren: How wildfires transform volcanic soils

In 2018, a wildfire engulfed nearly two thousand hectares of shrubland in the ecologically critical area of Pichu Pichu volcano, located in Peru’s Andean region.

Unlike Mediterranean ecosystems, vegetation on the volcanic soils of Arequipa – one of the world’s driest regions – has not evolved to recover from fire disturbances.

A team of researchers from the Miguel Hernández University of Elche (UMH) embarked on a study to assess the impact of wildfire events on such fragile ecosystems.

Unprepared for wildfire

The researchers dug deep into the soil, collecting and examining samples from the fire-charred area, 3,700 meters above sea level.

The findings of the study, published in the Spanish Journal of Soil Science, reveal that the fire not only burned the vegetation, but also scarred the soil. This was evident even four years after the event.

Post-fire erosion has resulted in a severe loss of soil organic carbon (SOC), which is an essential factor for soil fertility. The loss of SOC also leads to compaction, making the soil more inhospitable to new plant growth.

“The Peruvian Andes are not prepared for wildfires,” noted Jorge Mataix Solera, a scientist who has spent over three decades studying post-fire soil recovery.

Slow and difficult recovery in the Andes

Solera further explained that the consequences of wildfires vary significantly based on the ecology of the region, but that in the Andes the combined effect of loss of vegetation and loss of soil organic carbon made recovery extremely difficult and slow.

The study highlighted that Pichu Pichu’s soil was severely affected by the fire and showed substantial physical and chemical degradation, which further hampered the ecological recovery process.

Burned soil, lost resilience

The study identified the soil’s natural propensity to repel water, which was aggravated by the loss of the vegetation, as a significant impediment to recovery.

Without vegetation to retain moisture, water just slides off the surface of the volcanic soil, leading to accelerated 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,” explained UMH researcher Minerva García Carmona.

With the soil’s inability to hold water directly influencing its degradation, scientists need to understand the impact of fire on these young, fragile soils.

Plant species and soil degradation

Of particular importance is the role of different plant species, which serve as the combustible material in wildfires and affect soil degradation.

The research focused on two native plant species that dominate the vegetation: Berberis lutea, known locally as “palo amarillo del Perú,” and Parastrephia quadrangularis, or “tola.”

The study revealed that soils under Berberis lutea bushes underwent greater degradation after a wildfire. This could have been due to the fact that this shrub is a larger plant with a higher biomass, which would have provided more fuel for combustion.

Wildfires on the rise

Peru’s wildfire season typically peaks between July and October, but recent years have seen a troubling surge in fire activity.

In September 2024, the Queimadas satellite monitoring project recorded an unprecedented 7,037 wildfire hotspots across the country – the highest on record.

This escalation in fire activity highlights the urgent need to understand how soil in fire-prone regions responds to these new fire regimes.

“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,” noted the researchers.

Global significance of wildfire research

Solera emphasized the global significance of wildfire research. He believes that the more we study these impacts, the better we can design prevention strategies and post-fire treatments to mitigate the long-term effects of rising temperatures and prolonged droughts.

“This is as critical in Peru as it is in Spain or California. 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,” concluded Solera.

The full study was published in the journal Spanish Journal of Soil Science.

Image Credit: Jorge Mataix Solera

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