A review of the effects of forest fire on soil properties

Abstract

Forest fires are key ecosystem modifiers affecting the biological, chemical, and physical attributes of forest soils. The extent of soil disturbance by fire is largely dependent on fire intensity, duration and recurrence, fuel load, and soil characteristics. The impact on soil properties is intricate, yielding different results based on these factors. This paper reviews research investigating the effects of wildfire and prescribed fire on the biological and physico-chemical attributes of forest soils and provides a summary of current knowledge associated with the benefits and disadvantages of such fires. Low-intensity fires with ash deposition on soil surfaces cause changes in soil chemistry, including increase in available nutrients and pH. High intensity fires are noted for the complete combustion of organic matter and result in severe negative impacts on forest soils. High intensity fires result in nutrient volatilization, the break down in soil aggregate stability, an increase soil bulk density, an increase in the hydrophobicity of soil particles leading to decreased water infiltration with increased erosion and destroy soil biota. High soil heating (> 120 °C) from high-intensity forest fires is detrimental to the soil ecosystem, especially its physical and biological properties. In this regard, the use of prescribed burning as a management tool to reduce the fuel load is highly recommended due to its low intensity and limited soil heating. Furthermore, the use of prescribed fires to manage fuel loads is critically needed in the light of current global warming as it will help prevent increased wildfire incidences. This review provides information on the impact of forest fires on soil properties, a key feature in the maintenance of healthy ecosystems. In addition, the review should prompt comprehensive soil and forest management regimes to limit soil disturbance and restore fire-disturbed soil ecosystems.

Variability of soil properties with fire severity in pine forests and reforested areas under Mediterranean conditions

“…Moreover, forest fires result in ash deposition, changes in the structure, concentrations and forms of soil elements or compounds (Badía et al, 2017;Zavala et al, 2014) as well as in alterations of its biological properties (Agbeshie et al, 2022;Pellegrini et al, 2018). For instance, organic matter and nutrient contents decrease after fire, and changes in microbial communities composition and enzymatic activity are common (Carra et al, 2021;Inbar et al, 2014;Lucas-Borja et al, 2020c).…”

“…The post-fire physico-chemical and biological processes in soils can be extremely complex, due to the large variability of driving factors (ash release, vegetation cover, morphology as well as post-fire weather patterns and post-fire land management (Pereira et al, 2018;Robichaud et al, 2020;Salis et al, 2019)). With regard to the main chemical properties of forest soils, pH should not change following low to moderate fires (Agbeshie et al, 2022;Alcañiz et al, 2018;Valkó et al, 2016), while noticeable modifications are expected after high-intensity wildfires (Agbeshie et al, 2022;Zavala et al, 2014). Organic carbon content generally increases in burnt areas compared to unburnt soils after low severity fires (Agbeshie et al, 2022;Caon et al, 2014), but decreases after medium-or highintensity fires (Mataix-Solera et al, 2011).…”

“…With regard to the main chemical properties of forest soils, pH should not change following low to moderate fires (Agbeshie et al, 2022;Alcañiz et al, 2018;Valkó et al, 2016), while noticeable modifications are expected after high-intensity wildfires (Agbeshie et al, 2022;Zavala et al, 2014). Organic carbon content generally increases in burnt areas compared to unburnt soils after low severity fires (Agbeshie et al, 2022;Caon et al, 2014), but decreases after medium-or highintensity fires (Mataix-Solera et al, 2011). Burning volatilises part of the organic nitrogen in soils (Binkley and Fisher, 2019;Certini, 2005;Turner et al, 2007), which is converted into inorganic forms (Certini, 2005), thereby contributing to the maintenance of total nitrogen.…”

“…These investigations should give scientists and land managers insight about the type and magnitude of the expected changes in soil chemical properties after fire. The influence of fire on soils has not been comprehensively studied as compared to the effects on vegetation (Agbeshie et al, 2022), although several studies addressing soil properties in burnt forests have been carried out in different Mediterranean ecosystems (e.g., Inbar et al, 2014;Neris et al, 2013;Wittenberg et al, 2011). Less studies exist that have investigated changes in soil physico-chemical properties under different fire severities and different forest types (e.g., natural stands, reforested areas and managed forests).…”

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“…Another effect of fires is that they harden the soil surface and increase the soil water repellency (Weninger et al, 2019). In such a case, since the speed and amount of runoff increase on these hardened surfaces, it becomes more dangerous for the areas with loose soil (Agbeshie et al, 2022).…”