A Review Of The Impact Of Bush Burning On The Environment: Potential Effects On Soil Chemical Attributes

. Bush burning, whether the result of a wildfire or a controlled burn, has been shown to affect not only the appearance of the landscape, but the quality of the soil as well. Uncontrolled bush fires impact the soil in a variety of ways with the magnitude of the disturbance largely dependent upon the fire intensity, duration and recurrence, fuel load, and soil characteristics. The impact on soil properties is intricate, yielding different results based on these factors. Whereas burning off the vegetation during land clearing for cultivation is a common farming practice among farmers in many parts of the tropics, yet little is known by perpetrators of this practice about its impacts on the soil and its dwellers. This paper reviews research findings from a number of works conducted across the globe with the aim of gaining an insight the effects of wildfire and prescribed fire on the soil chemical and biological attributes. The knowledge of soils response in terms of these two properties to fire events can help in proper implementation of rehabilitation and restoration strategies at the short term, medium term, and long term.


INTRODUCTION
Bush burning, defined as the removal of the natural vegetation cover that protects the soil surface through the use of fire has detrimental effect on the environment, health and the economy (Otitoju et al., 2019) (Fig. 1).Fires are considered a destructive factor in most forest ecosystems of tropical and temperate climates (Fernández-García et al. 2019a, b), and are viewed as global phenomena affecting most land areas (Bento-Gonçalves et al. 2012; Agbeshie et al., 2022).Fires affect living organisms directly (causing their death) and indirectly, transforming their living environment (affecting food availability and quantity, heterogeneity of the environment, and pH increase) (Barreiro and Díaz-Raviña, 2021).The consequence of uncontrolled bush burning is most obvious in areas characterized by torrential rain fall, strong wind and intense solar radiation (Otitoju et al., 2019).This according to the authors, is because even slight disturbance of the vegetal Fig 1 : Images of a low-intensity prescribed fire to burn stubble during land clearing preparatory to planting a crop mantle may have very considerable impact on organic matter content and vegetation biodiversity.In addition, bush fire reduces not only the plant species composition, abundance, richness and biodiversity, but also disrupts the natural soil fertility (Salim et al., 2022).However, over the past 50,000 years, https://ijsenet.com102 anthropogenic fires have recurrently been used in livestock and agriculture, but fire frequency, extent and severity have greatly increased in the last few decades, bringing changes to the vegetation composition and soil nutrient stocks, particularly in the savanna ecosystems (Pellegrini et al., 2021).Bush fires are key ecosystem modifiers affecting the biological, chemical, and physical attributes of forest soils.Change in soil properties after fire produces varying responses in the water, vegetation dynamics, and faunal ecosystems.The wide range of effects is due to the inherent pre-burn variability in these resources, fire behavior, characteristics, season of burning, and pre-fire and post-fire environmental conditions such as timing, amount, and duration of rainfall (Clark, 2001;Verma and Jayakumar, 2012).Several studies have reported the impact of fire on soil chemical attributes (Table 1) with the extent of soil disturbance by fire largely dependent on fire intensity, duration and recurrence, fuel load, and soil characteristics (Agbeshie et al., 2022).Table 1 summarizes the findings of different studies pertaining to the impact of fire on soils of various ecosystems across the world.The impact on soil properties is intricate, yielding different results based on these factors.Studies have revealed that African savannas which constitute roughly 50% of the global terrestrial ecosystems (Lehmann et al. 2011) has in the recent past undergone a rapid transformation through anthropogenic activities including the indiscriminate use of fire (Dwomoh and Wimberly, 2017; Amoako and Gambiza, 2019).Fires, whether wild or prescribed defined as low-intensity fires used to achieve specific management objectives (Hiers et al. 2020;Francos and Úbeda, 2021) can have a marked effect on soil quality through its effect on the OM stock.This is evident because almost all OM which is the precursor of plant nutrients is consumed during fire thereby affecting long term crop productivity and soil fertility (Tadesse, 2016).Since fire and traditional practices of soil burning removes OM and their colloids fractions, and since such materials furnish most of the microbiological activities and the base exchange sites in the soils, the removal of such essential particles and their colloids decrease the fertility of the soils (Assefa, 1978).Rates of nutrient loss from slash fires are among the highest of any fires (Kauffman et al., 1995), and sustaining site fertility depends on a detailed understanding of the nutrient fluxes and losses that accompany such fires.Concerns about the threats posed by bush fire to sustainability of low input agriculture in many farming systems where the practice is prevalent is heightened by the current climate change predictions, coupled with more recurrent and prolonged droughts in many of these areas (Caon et al. 2014).There have been several predictions on the possible increase in fire duration, intensity, and frequency in forested regions, especially in the tropics, because of higher temperatures (Zhang and Biswas, 2017; Auclerc et al. 2019; Addo-Fordjour et al. 2020).Therefore, increased fire risk will not only affect forest flora, but also soil physical, chemical, and biological properties (Romeo et al. 2020).Fire influence forest soils in complex ways but have not been studied as comprehensively compared to the effects of vegetation (Agbeshie et al. 2022).Fires on forest soils influence a wide range of processes, including organic matter loss (Knicker, 2007), nutrient availability and their dynamics (Cavard et al. 2019), and revival of vegetation after the fire (Rodríguez et al. 2018).Consequently, information on the changes to soil properties following wild or prescribed fire is key to finding sustainable and adaptable management practices of soils and forests (Zhang and Biswas, 2017).In spite of its catastrophic effect on the ecosystem and physio-chemical properties of the soil, bush burning is among the several land clearing management options employed by farmers in many parts of the tropics (Edem et al. 2013;Ubuoh et al. 2017;Ibitoye et al., 2019).The practice is very common among the low input farmers in Nigeria with little or no knowledge about the consequent effects of such practice on the soil (Ibitoye et al., 2019).The objective of this paper is therefore to review the current knowledge regarding the impacts of fire on soil quality particularly as it relates to chemical and biological properties.

II. IMPACT OF FIRE ON CHEMICAL PROPERTIES OF SOIL Potential Impact on Soil Organic Matter (SOM)
SOM in agricultural soils is often concentrated on, or near, the soil surface and is made up of six easily recognized components: (1) the litter layer, consisting of recognizable plant litter; (2) the duff layer, composed of partially decomposed, but recognizable, plant litter; (3) the humus layer, consisting of extensively decayed and disintegrated organic materials, which are sometimes mixed with mineral soil; (4) decayed wood, consisting of the residual lignin matrix from decaying woody material that is on the soil surface or has been buried by the forest floor; (5) charcoal, or extensively charred wood mixed into the mineral soil; and (6) the upper mineral soil horizon (A horizon) of the underlying mineral soil (Harvey, 1982;DeBano, 1990).Nutrients contained in fuel and SOM are cycled by biological decomposition processes in environments where temperatures rarely approach 38°C and sufficient moisture is available for sustaining active microbial activity (DeBano, 1990).Under these mild conditions, soil microorganisms decompose SOM and slowly release many of the essential nutrients over time.In contrast, during a fire the nutrients stored in fuels and SOM are subjected to severe heating and, as a result, undergo various irreversible transformations during combustion.During the fire, heat transfer from burning biomass on the surface and within the soil is directly responsible for the changes that occur (

Impact on Nutrient Dynamics
Nutrients contained in fuel (litter) and SOM are cycled by biological decomposition processes in environments where temperatures rarely exceeds 38°C and sufficient moisture is available for sustaining active microbial activity (DeBano, 1990).Under these mild conditions, soil microorganisms decompose SOM and slowly release many of the essential nutrients over time.In contrast, during a fire the nutrients stored in fuels and SOM are subjected to severe heating and, as a result, undergo various irreversible transformations during combustion.Studies have shown that the responses of individual nutrients differ and each has its inherent temperature threshold.Threshold temperatures are defined as those temperatures where volatilization of a nutrient occurs.For discussion purposes, these thresholds can be divided into three general nutrient categories: sensitive, moderately sensitive, and relatively insensitive.Nitrogen (Hosking, 1938) and Sulphur (Tiedemann, 1987) are considered sensitive because they have thresholds as low as 200 to 375°C, respectively.Potassium (K) and P are moderately sensitive, having threshold temperatures of 774 °C (Raison et al., 1985).Magnesium (Mg), calcium (Ca), and manganese (Mn) are relatively insensitive, with high threshold temperatures of 1,107 °C, 1,484 °C, and 1,962 °C respectively (DeBano, 1990).However, because phosphorus is not readily mobile as nitrogen compounds, its concentration increases mainly in the ash and on, or near, the soil surface (DeBano 1989; DeBano and Klopatek 1988).However, the behaviour of micronutrients, such as Fe, Mn, Cu, Zn, B, and Mo, with respect to fire is not well known because specific studies are lacking (Certini, 2005, Verma andJayakumar, 2012).
Both wild and prescribed fires dramatically affect the nutrient cycling and other chemical and biological properties of the underlying soil.Burning increases the availability of most plant nutrients even though substantial amounts of carbon (C), nitrogen (N), sulphur (S), and phosphorus (P) can also be lost to the atmosphere by volatilization during the combustion of litter and SOM (DeBano, 1990).Fire acts as a rapid mineralizing agent that releases nutrients instantaneously as contrasted to natural decomposition processes, which may require years or, in some cases, decades (St. John and Rundel, 1976).Organic matter acts as the primary reservoir for several nutrients and, therefore, is the source for most of the available P and S, and virtually the entire available N (DeBano, 1990 ). Due to their high vaporization thresholds, losses of exchangeable cations in soils may arise only from erosion of ash and leaching of cations, coupled with plant uptake during post-fire succession (Caon et al. 2014).In contrast, under cooler soil-heating regimes, substantial amounts of NH4-N can be found in the ash and underlying soil (DeBano, 1990).Therefore, depending on the severity and duration of the fire, concentrations of NH4-N may increase, decrease, or remain unchanged.The ash which is the principal products of burnt material although rich in phosphorous, nitrogen and potassium can be easily washed away by rain.
Although the relationship between fire and soil nutrients is complex because of the interactions among many factors, fire intensity is usually the most critical factor affecting post-fire nutrient dynamics, with greater nutrient losses occurring with higher fire intensity (DeBano, 1990).Fire intensity both directly and indirectly impacts many of the mechanisms that affect nutrient pools and cycling.In the Southern part of Nigeria, slash and burn method of land clearing is an integral part of the traditional farming system, Ubuoh et al. (2017) investigated the effects of slash and burn method of land clearing on the soil nutrient dynamics of the upper 30 cm soil layer.The study revealed that at the upper 0-15 cm depth, the unburnt plot recorded decrease in pH, and an increase in K and base saturation, while the burnt plot recorded increase in SOM, Total N, Available P, Ca 2+ , Mg 2++ , Na + and EC.At the depth of 15-30cm, unburnt plot recorded a decrease in pH, Mg and EC while burnt plot recorded highest values in other selected parameters than unburnt plot.This and most other studies of slash-and burn documented an increase in soil nutrient availability after burning (De Rouw, 1994).Post-burn increases in soil fertility (Tables 2 and 3) have generally been attributed to nutrient-rich ash in nearly all tropical forest types where slash-and-burn has been examined (Maass, 1995  2+ and Mg 2+ levels in the A horizon (upper 5 cm) immediately after burning.In addition, Johnson et al. (2014) reported an elevated and consistent Ca 2+ content two years post-fire.However, other researchers have reported no change or a decline in exchangeable cations after fires.For example, in grassland vegetation, Liu et al. (2018) reported an insignificant amount of K + between pre-and post-wildfire-affected soils.In contrast, Raison et al. (1986) reported a reduction in nutrient pools even with low intensity fires.The study showed a decline of 50-75% of N, 35-50% of P, and 25-50% of Mg via volatilization and oxidation processes.Studies have shown that certain nutrients are also more vulnerable to fire than others.For example, levels of potassium (K), calcium (Ca), and magnesium (Mg) may be increased or unaffected by fire, while sulphur (S) and nitrogen (N) usually decline (Agbeshie et al. 2022).Some studies revealed that burned soils have lower nitrogen than unburned soils, higher calcium, and nearly unchanged potassium, magnesium, and phosphorus stocks (Neff et al., 2005).In contrast, Dzwonko et al. (2015) reported significantly higher exchangeable cations in burnt plots over controls in a Scots pine forest when a high severity wildfire occurred.Temperature specifically regulates the volatilization of nutrients within the soil.In organic matter, N begins to volatilize at 200 °C (Knicker, 2007), while Ca requires 1484 °C to vaporize (Johnston and Barati, 2013).https://ijsenet.com109

III. IMPACT OF FIRE ON BIOLOGICAL PROPERTIES OF SOIL Potential Effects on Soil Macro-organisms
Soil-dwelling organisms, most of whom live in the uppermost soil layer where fire-imposed temperatures on the ground are the highest suffer numerous consequences of fire disturbance.A large part of soil-dwelling organisms actually resides in the surface layer, where the organic fraction, which comprises mainly plant residue, animal remains and humic substances, often prevails over the inorganic inner materials.Whereas vertebrates can escape overheating death by running away, searching for wet niches or burrowing deep into soil the invertebrates and microorganisms, which have little or no mobility, succumb more easily to fire (Certini et al., 2021).Generally, the direct effects of fire on soil-dwelling invertebrates are less marked than those on microorganisms, due to a greater mobility which increases the potential for invertebrates to escape heating by burrowing deep into the soil (Certini, 2005).The general pattern of soil borne organisms i.e. macroinvertebrate responses to fire is often driven by changes in habitat structure, or by changes in the amount or the quality of food resources.Whenever fire affects vegetation, temperature or moisture, or the nutrient status of a soil, there is potential for impact on the soil invertebrate community (DeBano, 1990).Some arthropod groups increased in abundance but most decreased soon after fire.A study of litter dwelling and soil dwelling macroinvertebrates showed that the density of macroinvertebrates was significantly reduced one year after a prescribed fire (Kalisz and Powell, 2000).https://ijsenet.com110 The authors also reported reduction in the number of beetle larvae following fire, and further proposed that repeated fire in a single location could potentially have long-term negative effects on beetle populations and on the functions these beetles perform within the system.Findings of several studies conducted in grassland soils in Kansas that focused on the responses of soil macroinvertebrates to fire revealed that earthworm populations are strongly affected by fire in tall grass prairie soils, and the usual pattern observed is for fire to increase the abundance of earthworms in undisturbed areas (James, 1995).However, in more disturbed areas (i.e.close to human habitations), fire also has the interesting effect of limiting the colonization of non-native earthworms into prairie soils (Callaham et al. 2003).Results of this study suggested that the native earthworms in grassland soils are adapted to the warmer soil conditions frequently found in burned prairie, and that because fire improves the performance of grasses, the native earthworms may have strong habitat preferences for soils with abundant grass roots.Several studies have reported decreased microarthropod abundance immediately following fire (e.g.Sgardelis and Magaris, 1993).For example, Lussenhop, (1976) reported greater microarthopod abundance in a biennially burned prairie compared to an unburned prairie.Whereas a substantial resilience to fire in arthropod populations has also been documented in some studies.others found no effect of burning on microarthropod abundance.Coleman and Rieske (2006) examined the effect of early spring prescribed fires on forest floor arthropod abundance and diversity in mixed hardwood-pine of southeastern Kentucky (USA), and found that arthropod abundance, diversity, and richness did not differ among the pre-burned, unburned and single burned areas.The study by Swengel, (2001) suggest that leaf-litter and soil-dwelling arthropods might be directly affected by increases in temperature and exposure or indirectly affected through changes in habitat availability and quality.Findings from these and other similar studies suggest that there is no pattern of micro and mesofauna response to fire, instead several factors are implicated in the responses of these organisms to fire (Mataix-Solera et al., 2009).

Potential Effects on Soil micro-organisms
Microbial biomass reflects the microbial status of soil responsible for maintaining the nutrients and fertility of the soil and therefore, contributes to the biological properties of the soil (Mataix-Solera et al. 2009; Manral et al., 2020).Microbes are generally known to be solely responsible for nutrient cycling and play a major role in the transformation of nutrients and therefore, act as the soil health indicators (Singh et al., 2021).Fire affects biological properties by directly killing or denaturing soil biota through combustion or indirectly by post-fire plant recovery or changes in soil organic matter (Knelman et al. 2015;Jonathan et al. 2016;Ibáñez et al. 2021).It has been suggested that the changes in the nutrient supply due to the loss of plant residues could also be a reason for the reduction in microbial biomass after fire (Mabuhay et al. 2003;Smith et al. 2008).Singh et al., (2022) in their study on the impact of forest fire on soil microbial properties in the pine and oak forests of the Garhwal region of Uttarakhand Himalaya, India reported a reduction in microbial biomass (Cmic) of pine forests in Pauri and Tehri district were 61.7 and 17.4%, respectively, whereas in the oak forest, the percentage reductions of Cmic were much higher (75.8% in Pauri and 49.6% in Tehri district).The Cmic at the control and burnt sites of the oak forest was found to be greater as compared with the pine-dominated forest.This according to the authors could be attributed to the greater litter input with the oak forest which provides a greater carbon source pool for microbial utilization when compared to the pine forest.
Similar reduction in microbial biomass after the fire has been reported in many studies (Strand, 2011;Holden and Treseder, 2013;GironaGarcía et al. 2018).Several other researchers have documented the impact of forest fires on soil biological properties (Table 4ab).These studies revealed that the different microbial properties (related to mass, activity, and diversity) showed a different sensitivity to detect fire impact as well as different trend over time (immediate, short-, medium-, and long-term).In general, microbial activity and biomass changes can be transitory, and their values can reach pre-fire ones (Barreiro and Díaz-Raviña, 2021).Studies also suggest that the loss in microbial biomass during a fire depends upon the intensity and duration of the fire (Girona-García et al.In their review of prescribed burning on soil attributes, Alcañiz et al. (2018) noted that the temperature needed to kill most soil biological matter ranges from 50 to 120 °C.In other studies, Santín and Doerr (2016) also noted that temperatures from 50-150 °C result in the killing of fine roots, bacteria, fungi, and seeds within the soil.Microbial groups differ significantly in their sensitivity to temperature and nitrifying bacteria appear to be particularly sensitive to soil heating (Dunn et al. 1985).Aerobic heterotrophic bacteria, including the acidophilic and sporulating ones, were stimulated by fire while cyanobacteria, was clearly depressed (Verma and Jayakumar, 2012).Another important group of soil microorganism that are particularly sensitive to soil heating during a fire are endo-and ectomycorrhizae.Because most ectomycorrhizae are concentrated in the organic matter on or near the soil surface, the loss of shallow organic layers may be at least partially responsible for the reported fire-related reductions.For example, the study by Stendell et al. (1999) showed that the total ectomycorrhizal biomass in the upper soil layer of the unburned plots did not change to appreciable level, while in the burnt site, the destruction of the uppermost organic layer resulted in an eight-fold reduction in total ectomycorrhizal biomass.Mycorrhizal biomass in the two mineral layers was not significantly reduced by the fire.In a related study, forest fire was found to affect the proliferation of arbuscular mycorrhizal (AM) fungi by changing the soil conditions (Rashid et al., 1997).These workers also reported that compared with a nearby control area, the burnt site had a similar number of total spores but a lower number of viable AM fungal propagules.Regarding the impact of fire on the soil microbial diversity, Castano et al. (2020) observed a decrease in the relative abundance of ectomycorrhizal species four years after a medium-severity prescribed fire.However, in the long term, a decrease in the bacterial and fungal diversity was found 14 years after a wildfire (Huffman and Madritch, 2018).Long-term shifts in the composition of ectomycorrhizal fungal communities have been observed after wildfires and prescribed fires (Taudière et al., 2017).The fire impact on soil and the following postfire recovery of the microbiota can differ depending on the fire recurrence.
Table 4a.Summary of results from the reviewed articles concerning the fire effects on soil biological properties of samples taken mainly in the 0-5 cm of the A horizon top layer (part 1).Source: Barreiro and Díaz-Raviña, (2021).
PLFA: Phospholipid fatty acids; CLPP: Community Level Physiological Profiling; SIR: Substrate Induce Respiration example, a decrease in ectomycorrhizal fungal diversity (Pérez-Izquierdo et al., 2020) or alteration of the microbial community structure and no effect on microbial biomass have been described as a consequence of changes in the fire recurrence (Lombao et al., 2020; Barreiro and Díaz-Raviña, 2021).However, Barreiro and Díaz-Raviña, (2021) in their review of fire impact on soil microorganisms concluded that fire impact on soil microorganisms and the subsequent soil recovery depends on different factors such as the fire severity, the soil resilience, and the environmental conditions.They also asserted that the current situation of climate change favours more extreme environmental conditions (high fuel availability, low humidity, high temperatures, and high wind speed) that shift the fire regimes to more severe fires with large impact on the soil microorganisms.

IV. SUMMARY AND CONCLUSION
Both wild and prescribed fires occur frequently in many parts of the tropics.These fires dramatically affect many of the soil properties including the physical, chemical, and biological attributes of the underlying soil.From the literature reviewed it is obvious that cultural practices such as slash and burn method have both beneficial and detrimental effects on soil quality with the effects largely dependent upon such factors as fire intensity, duration and recurrence, fuel load, and soil characteristics.Fires, depending on severity and duration generally result in an increase in soil temperatures and higher pH, which in turn affect the nutrient dynamics via the combined processes of mineralization and nitrification.During combustion of soil organic matter some nutrients, such as N, P, and S, have low temperature thresholds and are therefore easily volatilized.Part of the nitrogen, that is not completely volatilized, is mineralized to NH4 + -N to minimize its loss or can be further nitrifed to NO3 --N under favourable conditions.Potassium (K) and phosphorus (P) are moderately sensitive, having threshold temperatures of 774°C while magnesium (Mg) and calcium (Ca) are relatively insensitive, with high threshold temperatures of 1,107°C, and 1,484°C, respectively.And as such, these nutrients are not readily volatilized from organic matter combustion temperatures.https://ijsenet.com114 However, some studies suggest that low-intensity fires result in little change or an increase in available nutrients (K + , Ca 2+ , Mg 2+ , PO4 3− , NH4 + ) and pH due to ash deposition.It is also evident from the present review that soil heating directly affects the soil borne organisms by either killing them directly or altering their habitats.Microbial groups in particular differ significantly in their sensitivity to temperature with the nitrifying bacteria in particular appear to be sensitive to soil heating.The review suggests that the responses of soil microbes to fires range from minor detectable effect under low intensity fires to total sterilization of the surface layers of soil under very intense fires.Studies have also shown that the impact of fire soil dwelling organisms particularly soil microorganisms and the subsequent soil recovery depends on a number of factors such as the fire severity, the soil resilience, and the environmental conditions (fuel availability, humidity, temperature, etc.).This study posits that uncontrolled use of fire for the purposes of hunting, charcoal production, or land clearing for crop production by most farmers in the tropics and other regions of the world has far reaching implications for sustainable management of ecosystems resources in these areas.

V.
RECOMMENDATIONS  Although little can be done to control OM loss during wildfires, effort should be made to revegetate the site so that organic litter can again be restored on the site as quickly as possible. When one plans prescribed fires, care should be taken to avoid bums that consume large amounts of surface litter and soil humus. Likewise, the total combustion of large woody debris on the soil surface (logs, etc.) during prescribed burning may not be a desirable practice. Repeated use of fire at frequent intervals probably should be avoided on relatively infertile sites where OM production is inherently low (for example, as the case with coarse textured soils found in most parts of drier environments). Further studies on susceptibility resilience of soil bourn organisms to fire events is critical to understanding the microbial response to fire and the subsequent implementation of rehabilitation and restoration strategies at the short term, medium term, and long term as opined in several studies (see for example, Barreiro and Díaz-Raviña, (2021) VI.
2018; Lucas-Borja et al. 2019).Oher studies attributed the observed reduction and diversity in soil microbial biomass after fire disturbance to factors such as unavailability of soil carbon and nutrients (Zhou et al. 2018) as well as topographic positions such as https://ijsenet.com111 ridge, middle slope, and valley bottom (Mabuhay et al. 2016; Girona-García et al. 2018).

Table 1 .
Summary of results from the reviewed articles on Soil chemical properties affected by forest fire https://ijsenet.com 103

Table 1 .
Summary of results from the reviewed articles on Soil chemical properties affected by forest fire (Continued) https://ijsenet.com 104

Table 1 .
Summary of results from the reviewed articles on Soil chemical properties affected by forest fire (Continued)

Table 1 .
Ummary of results from the reviewed articles on Soil chemical properties affected by forest fire (Continued)

Table 1 .
Summary of results from the reviewed articles on Soil chemical properties affected by forest fire (Continued) https://ijsenet.com 106

Table 1 .
Summary of results from the reviewed articles on Soil chemical properties affected by forest fire (Continued) Agbeshie et al., (2022) (2022).WF, PF and IAB indicates wildfire, prescribed fire, and immediately after burning, respectively.
Fernandez et al., (1997) changes in humus composition (Gonza ĺez-Pe ŕez etal., 2004).Low-intensity prescribed fire usually results in little change in soil carbon, but intense prescribed fire or wildfire can result in a huge loss of soil carbon(Johnson, 1992).Charcoal can promote rapid loss of forest humus and belowground carbon during the first decade after its formation, because charred plant material causes accelerated breakdown of simple carbohydrates(Wardle et al., 2008).Fernandez et al., (1997)suggested that in low intensity fire, lipids are least affected group whereas 90% of water-soluble cellulose, hemicelluloses and lignin are destroyed.Literature on the impacts of fire on soils are highly variable and suggest that low-intensity fires result in little or large change in the SOC, whereas high-intensity fires result in decreased SOC(Caon etal.2014).Elsewhere, Alcañiz et al. (2016) and Liu et al. (2018) also recorded up to 19.4% and 11.2% increase in SOC after a low intensity prescribed fire and a wildfire, respectively.Another study by Badía et al. (2014) showed a 27.9% reduction in SOC in the 1cm soil layer after a highly severe fire.Similarly, Moya et al. (2019) recorded a 21.0% reduction in SOM at a moderate to high intensity wildfire.Reduction in SOC after high-intensity fires may be due to several factors, including the combustion of SOM, increased rates of carbon mineralization, volatilization, and solubilization because of high pH (nutrient-rich ash) (RodriguezCardona et al. 2020).In contrast, Akburak et al. (2018) and Fernández-García et al. (2019a, b) did not observe any significant change in SOC following wildfire.Studies suggest that low-intensity fires are associated with increased SOC due to increased pyrogenic carbon resulting from incomplete combustion of organic matter, decomposition of incomplete burnt biomass, and the addition of ash (Sánchez Meador et al. 2017; Santín et al. 2018; Hu et al. 2020; Agbeshie et al. 2022).The combustion of carbon and the ash produced during low-intensity forest fires are referred to as black carbon (BC) (Thomas et al. 2017; Gao et al. 2018).Black carbons are highly condensed carbons, resistant to microbial attacks that are generated after a fire (Agbeshie et al. 2022).Their presence in the soil has been associated with an increased SOM pool (Nave et al. 2011; Caon et al. 2014; Agbeshie et al. 2022).
O'Brien et al. 2018).Generally, changes in SOC are variable and depend on fire duration, available biomass, and its moisture content, and fire type and intensity (Reyes et al. 2015; Agbeshie et al. 2022).Therefore, the effect on soil processes and their intensity influenced by fire are highly variable and no generalized tendencies can https://ijsenet.com107 be suggested for ).Studies have shown that concentrations of https://ijsenet.com108 exchangeable cations (Ca 2+ , Mg 2+ , K + , and Na + ), P and mineralized N (NH4 + and NO 3− ) increased with increasing fire intensity (Francos et al. 2019; Verma et al. 2019; Chungu et al. 2020).This increase in concentrations of the basic cations and phosphorus is as a result of their high vaporization thresholds compared to NH4 + and NO3− (James et al. 2018).However, the increase in soil exchangeable cation concentrations following fire disturbance may be short-lived and may soon return to their pre-fire levels (Granged et al. 2011; Maynard et al. 2014; James et al. 2018

;
Ubuoh et al. 2017; Numbere and Obanye, 2023)).Similarly, Muqaddas et al. (2015) and Francos et al. (2019) found increased soil pH in burnt soils following prescribed fire.In grassland vegetation, many researches have observed an increase in soil nutrients following a lowintensity wildfire (Inbar et al., 2014; Hosseini et al., 2017; Liu et al., 2018).Low-intensity fires with ash deposition on soil surfaces cause changes in soil chemistry, including increase in available nutrients and pH (Agbeshie et al. 2022).Under a low intensity prescribed fire in a Q. frainetto forest, Akburak et al. (2018) also found significantly high Ca

Table 2 .
The mean soil quality parameters for burnt and un-burnt land at different soil depths in the study area Ubuoh et al. (2017) (2017)

Table 3 .
Mean concentration of metals in burnt and unburnt soils at Eagle Island, Niger Delta, Nigeria

Table 4b .
Summary of results from the reviewed articles (part 2)