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

초록

Escalating wildfire frequency and severity, driven by global climate change, are inducing profound physical, chemical, and biological shifts in forest soil ecosystems, necessitating the development of effective restoration strategies. This review critically evaluates the functional disparities between naturally occurring postfire residues (specifically ash and wildfire-derived charcoal) and engineered biochar (E-BC) used as an active soil amendment. While naturally occurring charcoal and ash can temporarily replenish nutrient pools, recent comparative analyses using solid-state & sup1;& sup3;C NMR spectroscopy and elemental profiling reveal fundamental limitations in the stability of wildfire-derived pyrogenic carbon (PyC). Unlike E-BC, wildfire charcoal is often produced under conditions of rapid heating, varying oxygen availability, and short heating durations. Consequently, even when formed at high temperatures, PyC retains significant chemical heterogeneity, characterized by a lower degree of aromatic condensation and the persistence of alkyl and O-alkyl compounds. These structural deficiencies result in lower chemical recalcitrance and reduced carbon sequestration potential compared to slow-pyrolysis biochar. Furthermore, the specific physicochemical properties of PyC, including higher acidity, lower ash fractions, and less thermally mature surface functionalities, lead to distinct leaching behaviors that may elevate the risk of heavy-metal mobilization and alter fluvial elemental transport. In contrast, E-BC produced under controlled, slow pyrolysis conditions exhibits superior porosity and a highly aromatic structure. The application of biochar has been shown to consistently improve soil water-holding capacity, enhance the sorption of hydrophobic organic contaminants, and stimulate beneficial microbial activity. Furthermore, the restorative efficiency of biochar depends heavily on the pyrolysis temperature. While low-temperature biochar (350-500 degrees C) enhances nutrient retention and microbial activity, high-temperature biochar (> 600 degrees C) offers superior surface area and aromatic stability. Consequently, for long-term carbon sequestration and contaminant immobilization in fire-affected landscapes, the application of highly recalcitrant, high-temperature biochar is critical. These mechanisms are crucial for facilitating the early-stage rehabilitation of fire-affected soils and mitigating secondary hazards, such as soil hydrophobicity and erosion. Crucially, this review challenges the prevailing methodological assumption that wildfire-derived charcoal and biochar serve as suitable proxies for one another in agronomy and global climate dynamics. The distinct environmental fates and residence times of PyC and biochar suggest that models based on wildfire-derived charcoal may significantly underestimate the longevity and sequestration benefits of E-BC. Therefore, this study advocates for a paradigm shift in postfire management: moving beyond reliance on natural recovery processes involving unstable PyC. Instead, it suggests that producing high-quality biochar from excess forest residues and re-applying it to burned landscapes represents an effective circular solution. This approach not only maximizes long-term carbon storage but also provides a chemically stable amendment to accelerate ecosystem restoration.

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