Biochar Outperforms Natural Residues in Restoring Burned Soils

Forest fires, increasingly frequent and intense due to climate change, profoundly transform forest ecosystems and soils. These fires destroy soil organic matter, disrupt microbial communities, and alter the very structure of the earth, making it vulnerable to erosion, landslides, and water contamination. In the face of such damage, natural residues like ash and charcoal from fires play an ambiguous role. Ash, rich in nutrients such as calcium, magnesium, or potassium, provides an immediate fertilizing effect and temporarily neutralizes soil acidity. However, these highly soluble nutrients are quickly washed away by rain before plants can benefit from them, thus impoverishing the soil in the long term. Additionally, fine ash particles clog soil pores, reducing its water absorption capacity and promoting surface runoff.

Charcoal produced by fires, on the other hand, has an unstable chemical structure. Formed under rapid and variable combustion conditions, it retains volatile organic compounds and substances toxic to plants, such as phenols or aromatic hydrocarbons. These characteristics limit its effectiveness for carbon sequestration and can even worsen soil hydrophobicity—that is, their ability to repel water—which prevents infiltration and increases erosion risks.

Faced with these limitations, biochar—a vegetable charcoal produced by controlled pyrolysis of biomass—emerges as a far more effective solution. Unlike natural charcoal, biochar is produced under precise, oxygen-free conditions and at adapted temperatures, giving it a porous and stable structure. This porosity allows it to retain water, improve the soil’s cation exchange capacity, and trap contaminants such as heavy metals. By retaining nutrients, it acts as a slow-release fertilizer, synchronizing their availability with the needs of recovering plants. Additionally, its surface, rich in functional groups, promotes the fixation of pollutants, thereby reducing their toxicity to young shoots.

Biochar also plays a key role in the biological revitalization of soils. After an intense fire, the top layers of soil are often sterilized, eliminating microorganisms and fungi essential for tree growth. Biochar creates a protective micro-environment, called the biocharosphere, where bacteria and fungi find refuge from drought and predators. Its micropores provide an ideal shelter for beneficial microorganisms, thereby accelerating soil recolonization and vegetation recovery.

Another major advantage of biochar lies in its ability to restore the hydrological properties of soils. Acting like a sponge, it increases water retention and breaks down the hydrophobic layers formed by fires, thus facilitating infiltration and reducing runoff risks. This improvement in soil structure also limits erosion on slopes, a recurring problem after fires.

Producing biochar from burned wood or forest waste represents a circular solution. By transforming fire residues into biochar on-site, the risk of new fires is reduced while enriching depleted soils. This approach, combined with the use of high-temperature biochar, enables durable carbon sequestration and rapid ecosystem restoration. Biochars produced at over 600 degrees indeed offer superior chemical stability and better resistance to microbial degradation, ensuring prolonged carbon storage in the soil.

However, the application of biochar must be carefully tailored to each site. For example, excessive use of alkaline biochar can unbalance soil pH and make certain nutrients inaccessible to plants. Similarly, surface application can increase the absorption of solar heat, further stressing young plants in dry climates. Incorporation into the top layers of soil is therefore preferable.

In conclusion, while natural fire residues have long been considered sufficient for soil regeneration, their effectiveness remains limited in the face of the scale of modern megafires. Biochar, on the other hand, offers a controlled and sustainable alternative capable of addressing the physical, chemical, and biological challenges posed by these natural disasters. Its targeted use, particularly in high-risk areas, could thus become a cornerstone of post-fire management and the fight against forest ecosystem degradation.

Credits and Attributions

Primary Source

DOI: https://doi.org/10.1186/s13765-026-01098-x

Title: Ecological restoration of wildfire-affected areas: a review on the impacts of natural combustion residues (charcoal/ash) versus engineered biochar application

Journal: Applied Biological Chemistry

Publisher: Springer Science and Business Media LLC

Authors: Jae-Hoon Lee; Seul-Rin Lee; Jun-Suk Rho; Dong-Cheol Seo