# Fire-Induced Changes in Soil and Implications on Soil Sorption Capacity and Remediation Methods
## 2 Factors Which Determine the Effect of Fire Events on Soil Properties
### Fire Intensity and Duration  
Fire intensity refers to the energy or heat released during various phases of a fire, and is determined by the type of fuel available and how fast this fuel burns [30]. Fire temperature is commonly used to describe fire intensity with low, medium, and high fire intensity having temperatures of 250 \({}^{\circ}\)C maximum, 400 \({}^{\circ}\)C maximum and above 675 \({}^{\circ}\)C, respectively [31; 32]. [PERSON] and [PERSON] [33] have also classified fire intensity according to the height of the flame produced by the fire relative to forest stands. This classification may, however, not be applicable where there are smoldering fires which may be flameless yet could have relatively high temperatures (high intensity based on the description of [PERSON] et al. [31] and [PERSON] and [PERSON] [32]), or where there are mainly grasses or shrubs present. Though several studies have indicated that only superficial and slight soil heating occurs during fire events, more recent studies have reported surface soil temperatures of 125 \({}^{\circ}\)C and 200 \({}^{\circ}\)C [34], 310 \({}^{\circ}\)C [35], 500 \({}^{\circ}\)C [31], ranges of \(<\)225 \({}^{\circ}\)C for grasslands to 700 \({}^{\circ}\)C in shrub lands [36], 704 \({}^{\circ}\)C [37], 1000 \({}^{\circ}\)C [38] and 1000-1500 \({}^{\circ}\)C [25] during various smoldering and flaming fire events on soils with different vegetation types. Subsurface soils also experience increases in temperature which are not necessarily proportional to the intensity of the fire. In a study of sugarcane burning in Cuba, [PERSON] [39] reported flame temperatures of between 600 \({}^{\circ}\)C and 750 \({}^{\circ}\)C, but soil temperature at a depth of 2 cm never exceeded 34 \({}^{\circ}\)C. [PERSON] [40] reported a soil temperature of 280 \({}^{\circ}\)C at depths of 1 cm, and 200 \({}^{\circ}\)C at depths of 2 cm for a fire which lasted 10 h. In grasslands, subsurface soil temperatures rarely exceed 50 to 80 \({}^{\circ}\)C during wildfire events according to [PERSON] et al. [41]. Generally, temperatures of 300 \({}^{\circ}\)C to 900 \({}^{\circ}\)C have been reported at the litter layer, 100 \({}^{\circ}\)C to 625 \({}^{\circ}\)C at the litter-duff interface, 80 \({}^{\circ}\)C to 210 \({}^{\circ}\)C at the mineral soil surface, and 25 \({}^{\circ}\)C to 200 \({}^{\circ}\)C at soil depths of 2.5 cm [41]. The variation of soil temperature with depth during fire events also varies. A steep temperature gradient of 590 \({}^{\circ}\)C at the surface to 131 \({}^{\circ}\)C at a depth of 3 cm in soil has been reported by [PERSON] et al. [28] during fire events, indicating a decrease in soil temperature with depth as the fire burns. This gradient, however, is determined by the moisture characteristics of the soil. Surface and subsurface soil temperatures attained during fire events are therefore highly variable, and may not be easily predicted. The higher the intensity of a fire, the more likely it is that the soil will experience changes in its properties. [PERSON] and [PERSON] [42] have shown that fire duration plays a more significant role in the changes observed in vegetation during fire events than fire intensity, which could also be the case with soils. Fire of longer duration would cause more, and lasting, changes in soil properties compared to fires that occur for shorter periods. The duration of a fire is influenced mainly by fuel type and soil characteristics. Fire on coarse-textured soils rich in woody species is likely to burn for a longer period than fire on fine-textured soil with grassland species [43], possibly because of the availability of fuel over a longer period of time. According to [PERSON] and [PERSON] [10], soils with organic matter richer in aromatic than aliphatic moieties are also likely to burn for longer periods. The effect of fire intensity on soil properties could be moderated by fire duration.