Fire Effects on Soil Properties

By Paulo Pereira

Wildland fires are occurring more frequently and affecting more of Earth's surface than ever before. These fires affect the properties of soils and the processes by which they form, but the nature of these impacts has not been well understood. Given that healthy soil is necessary to sustain biodiversity, ecosystems and agriculture, the impact of fire on soil is a vital field of research.

Fire Effects on Soil Properties brings together current research on the effects of fire on the physical, biological and chemical properties of soil. Written by over 60 international experts in the field, it includes examples from fire-prone areas across the world, dealing with ash, meso and macrofauna, smouldering fires, recurrent fires and management of fire-affected soils. It also describes current best practice methodologies for research and monitoring of fire effects and new methodologies for future research. This is the first time information on this topic has been presented in a single volume and the book will be an important reference for students, practitioners, managers and academics interested in the effects of fire on ecosystems, including soil scientists, geologists, forestry researchers and environmentalists.

• Language: English
• Publisher: CSIRO PUBLISHING
• Release date: Feb 1, 2019
• ISBN: 9781486308156

Book preview

PART 1

Review of fire effects on soil properties

1

The sedimentary record: the very early acquisition of fire by hominins

Ferran Estebaranz-Sánchez, Laura Martínez and Paulo Pereira

Introduction

The acquisition of the capacity to manipulate fire represents one of the major biological, behavioural and cultural changes in human evolution (Pyne 1994; Brown et al. 2009; Wrangham and Carmody 2010; Parker et al. 2016). Charles Darwin (1871) highlighted fire’s evolutionary importance in his book The Descent of Man, affirming that it was ‘probably the greatest [discovery], except language, ever made by man’. However, the use of fire has caused not only a paradigm shift for hominin evolution, but a change in the natural history of the Earth and life itself (Pyne 1994; Pausas and Keeley 2009), because biotas have been forced to adjust to new fire regimes and new fuel complexes (Pyne 1994). Despite its importance, there is no consensus concerning not only when hominins first developed the ability to make fire, but what it means to make fire, within the context of differentiating opportunistic/sporadic fires versus intentional/stable fires.

Some authors have suggested that evidence of occasional and opportunistic use of fire may be traced back more than 1 million years (Brain and Sillen 1988; Brain 1993; Beaumont 2011; Berna et al. 2012; Pickering 2012; Gowlett and Wrangham 2013; Bentsen 2014; Gowlett 2016) (Table 1.1; Fig. 1.1). Independently of the level of evidence of each case, all of them are African sites. This is not surprising, because Africa was the only continent inhabited by hominins (regardless of the species considered) until 1.8 Mya, when Homo ergaster/erectus began to move outside its boundaries (Gabunia et al. 2000). In East Africa, several sites have been suggested as having evidence of early burning and use of fire. At Chesowanja GnJi 1/6E, in the Chemoigut Formation near Lake Baringo, dated to more than 1.42 ± 0.07 Mya based on K-Ar dating of an overlying basalt, the presence of discoloured clay aggregates intermingled with Oldowan stone artefacts, fauna and bone fragments of a Paranthropus have been documented (Gowlett et al. 1981). Based on the results of the magnetic susceptibility analysis, which showed that the rubefied clay aggregates had been heated up to 400°C, the authors concluded that the artefacts had been intentionally burned (Gowlett et al. 1981). Another controversial site with regard to its possible association to intentional fire use is the Ethiopian site of Gadeb 8e, located in the Middle Awash, where stones with differential dark grey and red discolouration typical of burning have been reported (Barbetti 1986). Although magnetic analyses indicated that all stones had a thermal magnetisation from the time the volcanic rocks were formed, some of them also had a younger magnetisation signal with a maximum temperature of ~500°C (Barbetti 1986). Thus, these results are difficult to interpret, given the difficulty of distinguishing the archaeological magnetisation signal from that of geological origin, although some authors have suggested that this site could correspond to an early phase of a technological transition associated with Homo ergaster (Clark and Harris 1985; Clark 1987). Reports of the use of fire have also been proposed at the Kenyan site of Koobi Fora FxFj 20, an early Pleistocene archaeological site near Koobi Fora (northern Kenya, on the eastern shores of Lake Turkana) dating from 1.5 Mya (Bellomo 1994). In Koobi Fora FxFj 20, several fully oxidised and highly grouped sediment features have been identified at the base of the archaeological horizon. A total of five red patches were initially detected, of which four can be inferred as fireplaces, while an irregular narrow red patch at the edge of the excavation was suggested to be a burnt tree (Rowlett 2000). First archaeomagnetic analyses confirmed that these fires did not burn hotter than 400°C (Bellomo and Kean 1997). In addition to this, more recent differential thermal analysis (DTA) confirmed that fires did not attain 400°C (Rowlett 2000). However, ongoing debate still continues on whether these burnt traces could have been caused by wildfires. A recent high-resolution excavation at the FxJj20 AB site focused on the recovery and high-resolution spatial analysis of large and small finds (<2 cm), based on FTIR spectrometry analysis of the material recovered, has discounted that anthropogenic fire caused the spatial pattern of heated and unheated archaeological material (Hlubik et al. 2017).

Fig. 1.1.   Major African sites for which the presence of intentional fire has been described.

Table 1.1.   Putative earliest evidence of fire use by hominins

In Southern Africa, several sites have also been proposed as possible evidence of intentional fire. In Member 3, a depositional unit of the Swartkrans Formation, dating from 1.5 to 1.0 Mya, up to 270 burned fossil specimens have been recovered, including nine individuals of Paranthropus robustus (Brain 1993). Both osteological and chemical analyses suggested they had been exposed to high temperatures, ranging from 300 to 500°C. According to Brain (1993), this is evidence of the use of fire, because average campfire temperatures attain ~400°C, rarely exceeding 700°C (and discounting grass fires as the cause of burning, because, in this kind of fire, temperatures up to 800°C are attained). There are several pieces of evidence that reinforce that the fire was of human origin and not wildfire. For example, the presence of burnt bones in up to 23 excavation holes of 10 cm thick along Member 3, with a depth of 6 m, is evidence that bones were burned in recurring fires possibly over thousands of years (Brain 1993; Pickering 2012). These campfires were confined to the entrance of the gully, sheltered by a dolomite roof, around which hominins would process the food and discard pieces of bone into the ashes, which were dragged into the cave over time (Brain 1993). In addition, four of the burned bones have stone tool cut marks indicating defleshing butchery, which reinforces the hypothesis of meat eating and, consequently, its roasting/cooking (Pickering et al. 2008). Finally, there is no homogenous pattern of distribution of burned bones in the other deposits of the Swartkrans Formation, so it is difficult to infer that they were burned by natural wildfires. Despite this behavioural scenario, the presence of a burnt hominin phallanx (SKX35822), as well as the burning of two bone tools add some doubt to the behavioural reconstruction done by Brain (1993). Furthermore, the burned bones were in the filling of a gully (Brain 1993) and were probably transported short distances from their place of combustion (Pickering 2012). Thus, some authors suggest an alternative explanation that wildfire could have ignited detritus, including these burned bones, which were on the floor of the cave, and could have been later dragged into the gully from which the deposit of Member 3 was formed (Pickering 2012). If it is accepted that the Swartkrans fossils were actually burned, it would open the possibility that other species of a genus other than Homo could have controlled or opportunistically used the fire because, so far, the Member 3 has yielded remains of only Paranthropus robustus, but not of Homo ergaster (Brain 1993).

In South Africa there are other contemporary sites, or even older ones, with putative evidence of the use of fire by hominins. In the Wonderwerk cave, dating from 1.7 Mya, a level (MU9b) has been excavated comprising a composite accumulation of ash containing a large number of fragmented and charred-calcined bones that had been previously broken to access the marrow before being discarded into the fire (Beaumont 2011). In 2012, a new study applied micromorphological analysis and Fourier transform infrared microspectroscopy (mFTIR) to study intact sediments and associated archaeological finds (Berna et al. 2012). The authors stated that results confirmed an ‘unambiguous evidence’ of burning event in Wonderwerk Cave during the early Acheulean occupation, ~1.0 Mya (Berna et al. 2012), although other authors describe the results as ambiguous (Goldberg et al. 2017). The results of the microstratigraphic study in the Acheulean Stratum 10 indicate the presence of well-preserved ashed plant material and burned bone fragments that were not transported from distance to the basement either by water or wind, but were combusted and accumulated locally. Furthermore, the microscopic evidence of burning in Wonderwerk is supported by the presence of burned faunal, lithic and macrobotanical assemblages deposited on Stratum 10 (the same material previously studied and published by Beaumont (2011). In fact, up to 43.7% of the fauna (bones and teeth) from Stratum 10 had been exposed to fire, revealed by the presence of discolouration typical of burning. Moreover, FTIR analysis of the remains showed that some of the discoloured bone fragments displayed FTIR absorption spectra typical of bone mineral heated to more than 400°C, although no IR pattern characteristic of complete calcinations was found (thus, no specimen reached a temperature =700°C) (Berna et al. 2012), which consistent with using light vegetation, such as leaves and grasses, as fuel (Attwell et al. 2015). Finally, the authors stated that the prevalence of burning throughout the entire thickness of Stratum 10 minimises the likelihood that repeated wildfires were the source of the burning in the cave. Nevertheless, some authors suggest the archaeological evidence at Wonderwerk Cave indicates that early hominins did not maintain fire for long periods (Chazan 2017).

Middle and Lower Paleolithic

Unequivocal evidence for the early habitual use of fire (in contrast to early, sporadic use) (Alperson-Afil 2017) dates back to the beginning of the Middle Paleolithic, ~250–400BCE, despite the debate whether fire was used at the German site of Schöningen (Weiner et al. 1998; Gowlett 2006; Fluck 2007; Karkanas et al. 2007; Berna and Goldberg 2007; Roebroeks and Villa 2011; Shimelmitz et al. 2014; Stahlschmidt et al. 2015; Goldberg et al. 2017). Some authors claim that fire was first fully adopted almost 800kya: 790kya at the Israeli site of Gesher Ya’akov in the Jordan Valley, where burnt wood and flint have been recovered (Goren-Inbar et al. 2004; Alperson-Afil 2008, 2012); 780kya at the Spanish site of Cueva Negra del Estrecho del Río Quípar, where the presence of burning in association with lithics and fauna has been documented (Walker et al. 2013); and 770kya in the Chinese site of Zhoukoudian (Zhong et al. 2014; Gao et al. 2017), although some authors are reluctant to include Zhoukoudian as a site with an early evidence of fire use (Goldberg et al. 2017). From that time onwards, intentional use of fire became widespread and was associated with an increase in human social and intellectual complexity and capability (Gowlett 2006; Twoney 2013), as demonstrated by the heat treatment of lithic tools, which demanded an elevated cognitive ability (Brown et al. 2009). In this sense, all cultural process of access, maintenance, transport and protection of fire implied previous planning and cooperation, no matter whether it was directly obtained from nature or through stealing it from other hunter–gatherer groups (Twoney 2013). Neanderthal use of fire is well documented, both in Europe and the Levant, such as in Qesem Cave (380–200kya, Israel), for activities such as cooking (Karkanas et al. 2007; Henry et al. 2011; Sandgathe et al. 2011; Albert et al. 2012; Aldeias et al. 2012; Goldberg et al. 2012; Vallverdú et al. 2012; Blasco et al. 2016; Pop et al. 2016; Barkai et al. 2017; Henry 2017). For this purpose, Neanderthals tended to collect preferably dead wood from the surroundings, which enabled them to obtain a valuable resource without great acquisition effort (Vidal-Matutano et al. 2017). Despite this extensive record of cultural processes associated with the use of fire, it seems that Neanderthals did not influence fire regimes, although it could not be discounted that they used fire for ecosystem management (Daniau et al. 2010). However, some authors deny that use of fire was an essential aspect of Homo neanderthalensis behaviour, at least in Western Europe (Sandgathe et al. 2011; Dibble et al. 2017). In contrast, it has been suggested that Homo sapiens from the last glacial maximum (LGM) used fire for management of landscapes (burning forest cover through the ignition of wildfires in order to create a semi-open landscape to facilitate foraging), which provoked a dramatic reduction in forest cover in Europe (Kaplan et al. 2016).

Adaptive advantages of fire

Fire use might also have been important for the evolution of both biological and social traits. The acquisition of the ability to control fire enabled hominin populations to exploit new ecological niches (both physical and temporal) and habitats not previously occupied by other species. Campfires were a source of heat and light that provided an extension of light and warmth, which resulted in an increase in security against predators (Pyne 1994; Gowlett and Wrangham 2013; Attwell et al. 2015; Gowlett 2016). Furthermore, fire may have spurred the development and adoption of a new range of behavioural traits such as tool tempering, the improving of flaking properties, the extension of the activity time, and the beginning of cooking and preserving food (Bellomo 1994; Brown et al. 2009; Attwell et al. 2015; Henry 2017). Once adopted, the use of fire represented a new selective advantage for hominins (Twoney 2013; Dunbar and Gowlett 2014). This extension of light had a profound impact on cultural evolution, because it allowed the establishment of a temporal margin in which social connections were established around the campfire. Also, behavioural strategies to access fire would include complex actions, from using stealth or force to obtain fire from hostile groups to its amicable sharing, provisioning, transporting, protection and usage (Twoney 2013). One of the most immediate consequences of the acquisition of the ability to make fire is the prolongation of ‘daylight’ (Attwell et al. 2015), which has a marked effect on the photoperiodicity – the response of an organism to the length of exposure to daylight – of the early hominins (Attwell et al. 2015). The extension of ‘daylight’ has been suggested to have affected the production of melatonin by altering the body clock and sleep patterns and the timing of puberty (Burton 2009; Attwell et al. 2015).

Cooking and the origin of fire control

As mentioned earlier, the hominin species with the greatest consensus as a pioneer in fire control is Homo ergaster. This species is characterised by important anatomical changes, both at the gnatomasticator level – with a clear tend towards a directional reduction in the postcanine dentition compared with earlier hominins (Wood and Aiello 1998) and facial shortening (Lieberman et al. 2004) – and postcranial level (modification in trunk proportions, such as the barrel shape of the thoracic cage and narrowing of the pelvis along with a reduction of the gut volume) (Aiello and Wheeler 1995; Aiello and Wells 2002). Anatomical changes in Homo erectus were the result of a profound change in metabolic needs and tissue energy demand that entailed an increased in energy for brain metabolism at the expense of gut metabolism: this is known as the expensive tissue hypothesis (Aiello and Wells 2002). This reduction of the intestine, together with an increase in the energetic demands of the brain, reflected a dietary shift towards a higher quality and more easily digested diet based on meat consumption (Leonard and Robertson 1994; Aiello and Wheeler 1995; Milton 1999). An increase in meat consumption would have provided the necessary increase in valuable calories (Blumenschine and Pobiner 2007). Non-thermal processing methods, such as grinding and pounding, can increase meat digestibility a little (Carmody and Wrangham 2009). However, meat has certain toxicity, so the acquisition of the ability to use fire led to an increase in cooking food, especially meat, since it increases its digestibility and reduces its toxicity (Wrangham et al. 1999; Carmody and Wrangham 2009).

Digestion of cooked foods is easier because they become denatured (Parker et al. 2016). Cooking meat makes it more tender, easier to digest and reduces the possible toxicity associated with its consumption –reducing pathogens – in addition to increasing its energy value, which results in an increased rate of absorption in comparison with raw meat (Wrangham and Conklin-Brittain 2003; Carmody and Wrangham 2009; Zink et al. 2014; Smith et al. 2015). Evidence for meat consumption by early hominins can be traced back to at least 2.5 Myain Bouri and 2.6 Mya in Gona (de Heinzelin et al. 1999; Semaw et al. 2003), although unambiguous stone-tool cut marks for flesh removal and percussion marks for marrow access dating from 3.4 Mya have been recovered at Dikika (McPherron et al. 2010). This would suggest that meat consumption preceded its cooking, and that hominin species other than Homo erectus already ate meat, as could be the case of Australopithecus afarensis (from Dikika, Alemseged et al. 2006) and Australopithecus garhi from Bouri (Asfaw et al. 1999). However, the absence of cooking of the meat in these species would suggest an intake rate similar to that of the present chimpanzees, and clearly inferior to that of Homo ergaster (Wrangham and Conklin-Brittain 2003). The use of fire also allowed an increase in the range of consumable foods: some plants are inedible without cooking because they contain toxins or digestibility-reducing compounds (Stahl 1984). Cooking causes chemical alterations that increases the digestibility of starch, cellulose and plant protein, improving the energetic value of these foods (Stahl 1984; Wrangham and Conklin-Brittain 2003). Therefore, the reduction in tooth size in Homo ergaster limited the types of foods mechanically processable and is consequence of a dietary shift associated with major changes in food-processing techniques, such as the adoption of fire for cooking (Wrangham et al. 1999; Wrangham 2017), such that fibrous and difficult to masticate food items were no longer ingested by Homo erectus (Aiello and Wells 2002; Organ et al. 2011). However, the results of the microwear pattern analysis of Homo erectus are suggestive of consumption, at least occasionally, of a wider range of hard and/or tough items than early Homo (Ungar et al. 2006; Martínez et al. 2016) and are ‘not consistent with a highly specialized, mostly carnivorous diet; instead, they support the consumption of a wide range of highly abrasive food items’ (Martínez et al. 2016). These results are, a priori, contradictory, because they would indicate a tendency towards the acquisition not of a softer diet but of a more abrasive diet (in relation to early Homo). Nonetheless, we must consider that the consumption of hard or tough foods – such as USOs (tubers) or plant foods with silica particles abundant in East African open and arid environments – is constrained to the unfavourable season, when only low-quality foods are available in abundance (Martínez et al. 2016). In the specific case of USOs, it has been argued that cooking increases their digestibility (Schnorr et al. 2015) by neutralising toxicity and gelatinising starchy tissues (see Parker et al. 2016 and the citations therein) and increasing the fracture rate for some tubers by 49% (Dominy et al. 2008). This suggests that one of the main reasons Hadza hunter–gatherers made fire was to cook the USOs that the women had dug (Mallol et al. 2007; Mallol and Henry 2017). However, it seems that the process of roasting USOs was not so much to improve their digestibility by cooking the starch, but to improve their mechanical properties to allow peeling and chewing to extract edible tissues (Schnorr et al. 2015). This scenario would fit combination of anatomical adaptations of Homo ergaster, with both occlusal and buccal microwear patterns. Thus, the use of fire by Homo ergaster could have been a cultural mechanism to reduce mechanical demand of certain types of poor quality, yet abundant, food items, at a time when consumption is needed to survive the dry season. The aridity peak coincided precisely with the emergence of Homo ergaster 1.8 Mya and the earliest evidence of fire use in South Africa (Wonderweck with 1.7 Mya). The preference for cooked food (both tubers and meat) in captive great apes reinforces this assumption (Wobber et al. 2008), suggesting that early hominids would likewise have preferred cooked food to raw. However, although roasting food partially reduced the hardness of these foods, it did not completely eliminate it, and could also result in consumption of ashes that did not affect the mechanical properties of USOs, but left a significant signal on the enamel. As stated by Martínez et al. (2016), the dietary scenario for Homo ergaster does not exclude higher meat consumption, but states that consumption of plants and tubers might have been more important than previously assumed, as is the case with modern hunter–gatherer populations from arid environments (Dominy et al. 2008; Marlowe and Berbesque 2009). This scenario suggests new ways of using fire beyond softening meat, to improve the mechanical properties of USOs – foods that would have been outside of their dietary range – resulting in the dental reduction observed in this species. This higher available food energy resulting from cooking, as well as the detoxifying effect of heating, conferred an advantage in their fitness compared with Paranthropus.

How could the process of fire control be acquired?

The process of acquisition and development of pyrotechnology must have been a protracted and relatively complex cultural process (Sandgathe 2017). It has been proposed that initial stages of exploitation of fire would be based on observation and interaction with ubiquitous natural occurring fires (Burton 2009; Gowlett 2016; Pruetz and Herzog 2017; Henry 2017; Sandgathe 2017). In this context, savanna chimpanzees represent a good model to better understand the possible mechanisms by which early Pliocene hominins initially accessed the use of fire (Kano 1972; McGrew et al. 1981; Moore 1992, 1996; Sept 1992; Estebaranz-Sánchez et al. 2016) and they are subjected to similar limiting environmental factors (Moore 1996; Pruetz 2007). Savanna chimpanzees, which inhabit environments susceptible to fire, observe the fire and change their behaviour patterns in anticipation of the fire movement (Pruetz and LaDuke 2010) and even respond with relative calm to most intense fires (Pruetz and Herzog 2017). Moreover, western savanna chimpanzee are constantly exposed to burned landscapes during the dry season, when more than three-quarters of their home ranges may be burned annually (Pruetz and Herzog 2017).In addition to this, wild chimpanzees have been observed actively selecting seeds that have been heated by natural fires (Brewer 1978). Experimental studies in captivity have confirmed that hominoids tend to prefer cooked foods to raw, from tubers to meat (Wobber et al. 2008). The same happens with other primate species: in Chlorocebus aethiops, for example, an expansion of home range into newly burned, but previously unused, areas has been observed after a fire (Herzog et al. 2014). In fact, there are many examples in primates that forage in burned habitats, extracting freshly cooked resources, such as vervets and macaques (Harrison 1983, 1984; Berenstain 1986; Armelagos 2010; Herzog et al. 2014, 2016; Herzog 2015). Moreover, burning creates microhabitats characterised by a reduction of threat of dangerous snakes or larger carnivores, so primates begin showing less risk averse behaviour (Herzog 2015). Chimpanzees and other primates are accustomed to frequent fires and exploit burned environments. Using the chimpanzees as a model, it is possible to infer that the exposure of the first hominins to fire would be equivalent to that of Pan troglodytes verus from Senegalese savanna environments, giving the possibility of continued and repeated interaction with fire. This familiarity with fire in chimpanzees has been interpreted as the capacity for conceptualising fire behaviour: a skill that would be synapomorphic trait shared with hominins that would be a prerequisite or precondition for pyrolytic behaviour (Pruetz and LaDuke 2010; Attwell et al. 2015). Hominins may have habituated to fire, but it is difficult to discern their use, maintenance or even manufacture of fire (Henry 2017). Nevertheless, this scenario matches well with the theoretical framework of the process of fire acquisition described recently by Sandgathe (2017), in which initial use of fire was probably based on the exploitation of natural fires sources and, perhaps, fire maintenance for short periods of time. In fact, paleoenvironmental reconstruction show early hominins evolved in patchy dry savanna characterised by the accumulation of large amounts of flammable C4 grasslands, which constitute a source of propitious biomass for wildfires. Paleosedimentary records trace the existence of natural fires in Africa from the late Miocene onwards, corresponding to the emergence of both C4 grasslands in the hominin lineage (Jacobs 2004). In this sense, according to Sandgathe (2017), some of the early African sites associated with fire activities may simply reflect a process of habituation to natural fires (rather than a fully control or adoption of fire) or even only the ubiquitous nature of natural fires (Sandgathe 2017). Some authors have gone further by asserting that fire dependence is the result of a process of adaptation to these fire-prone environments (Parker et al. 2016). However, some authors pointed out that natural fires would not have been a reliable ignition source (Twoney 2013), but that an alternative consistent, but localised, source of fire for early hominis could have been active lava flows that were documented in the African Rift at that time (Medler 2011).

Acknowledgements

This work was supported by the postdoctoral grant Obra Social La Caixa (Caixabank, Barcelona, Spain) to Laura M. Martínez. We also recognise the contribution of E.M. Bruno to the development of this chapter.

References

Aiello L, Wells JCK (2002) Energetics and the evolution of the genus Homo. Annual Review of Anthropology 31, 323–338. doi:10.1146/annurev.anthro.31.040402.085403

Aiello L, Wheeler P (1995) The expensive-tissue hypothesis: the brain and the digestive system in human and primate evolution. Current Anthropology 36, 199–221. doi:10.1086/204350

Albert RM, Berna F, Goldberg P (2012) Insights on Neanderthal fire use at Kebara Cave (Israel) through high-resolution study of prehistoric combustion features: evidence from phytoliths and thin sections. Quaternary International 247, 278–293. doi:10.1016/j.quaint.2010.10.016

Aldeias V, Goldberg P, Sandgathe D, Berna F, Dibble HL, McPherron S, et al. (2012) Evidence of Neanderthal use of fire at Roc de Marsal (France). Journal of Archaeological Science 39, 2414–2423. doi:10.1016/j.jas.2012.01.039

Alemseged Z, Spoor F, Kimbel WH, Bobe R, Geraads D, Reed D, et al. (2006) A juvenile early hominin skeleton from Dikika, Ethiopia. Nature 443, 296–301. doi:10.1038/nature05047

Alperson-Afil N (2008) Continual fire-making by hominins at Gesher Benot Ya’aqov, Israel. Quaternary Science Reviews 27, 1733–1739. doi:10.1016/j.quascirev.2008.06.009

Alperson-Afil N (2012) Archaeology of fire: methodological aspects of reconstructing fire history of prehistoric archaeological sites. Earth-Science Reviews 113, 111–119. doi:10.1016/j.earscirev.2012.03.012

Alperson-Afil N (2017) Spatial analysis of fire:archaeological approach to recognizing early fire. Current Anthropology 58, S258–S266. doi:10.1086/692721

Armelagos GJ (2010) Creatures of the flame:light and heat in human evolution. Evolutionary Anthropology 19, 158–160. doi:10.1002/evan.20273

Asfaw B, White T, Lovejoy O, Latimer B, Simpson S, Suwa G (1999) Australopithecus garhi:a new species of early hominid from Ethiopia. Science 284, 629–635. doi:10.1126/science.284.5414.629

Attwell L, Kovarovic K, Kendal JR (2015) Fire in the Plio-Pleistocene: the functions of hominin fire use, and the mechanistic, developmental and evolutionary consequences. Journal of Anthropological Sciences 93, 1–20.

Barbetti M (1986) Traces of fire in the archaeological record, before one million years ago? Journal of Human Evolution 15, 771–781. doi:10.1016/S0047-2484(86)80009-4

Barkai R, Rosell J, Blasco R, Gopher A (2017) Fire for a reason:barbecue at Middle Pleistocene Qesem Cave, Israel. Current Anthropology 58, S314–S328. doi:10.1086/691211

Beaumont PB (2011) The edge: more on fire-making by about 1.7 million years ago at Wonderwerk Cave in South Africa. Current Anthropology 52, 585–595. doi:10.1086/660919

Bellomo RV (1994) Methods of determining early hominid behavioral activities associated with the controlled use of fire at FxFj 20 Main, Koobi Fora, Kenya. Journal of Human Evolution 27, 173–195. doi:10.1006/jhev.1994.1041

Bellomo R, Kean M (1997) Evidence of hominid-controlled fire at the FXFj 20 Site Complex, Karari Escarpment [A]. In Koobi Fora V: Plio-Pleistocene Archaeology. (Eds GL Isaac and B Isaac) pp. 223–236. Clarendon Press, Oxford, UK.

Bentsen SE (2014) Using pyrotechnology: fire-related features and activities with a focus on the African Middle Stone Age. Journal of Archaeological Research 22, 141–175. doi:10.1007/s10814-013-9069-x

Berenstain L (1986) Responses of long-tailed macaques todrought and fire in Eastern Borneo: a preliminary report. Biotropica 18, 257–262. doi:10.2307/2388494

Berna F, Goldberg P (2007) Assessing Paleolithic pyrotechnology and associated hominin behavior in Israel. Israel Journal of Earth Sciences 56, 107–121. doi:10.1560/IJES.56.2-4.107

Berna F, Goldberg P, KolskaHorwitz L, Brink J, Holt S, Bamford M, et al. (2012) Microstratigraphic evidence of in situ fire in the Acheulean strata of WonderwerkCave, Northern Cape province, South Africa. Proceedings of the National Academy of Science 109, E1215–E1220.

Blasco R, Rosell J, Sañudo P, Gopher A, Barkai R (2016) What happens around a fire: faunal processing sequences and spatial distribution at Qesem Cave (300 ka), Israel. Quaternary International 398, 190–209. doi:10.1016/j.quaint.2015.04.031

Blumenschine RJ, Pobiner BL (2007) Zooarchaeology and the ecology of Oldowan hominin carnivory. In Evolution of the Human Diet: The Known, the Unknown and the Unknowable. (Ed. Peter S. Ungar) pp. 167–190. Oxford University Press, Oxford, UK.

Brain CK (1993) The occurrence of burnt bones at Swartkrans and their implications for the control of fire by early hominids. In Swartkrans: A Cave’s Chronicle of Early Man. (Ed. CK Brain) pp. 229–242. Transvaal Museum, Pretoria, South Africa.

Brain CK, Sillen A (1988) Evidence from Swartkrans Cave for the earliest use of fire. Nature 336, 464–466. doi:10.1038/336464a0

Brewer S (1978) The Chimpanzees of Mt. Asserik. Knopf, New York, USA. Brown KS, Marean CW, Herries AIR, Jacobs Z, Tribolo C, Braun D, et al. (2009) Fire as an engineering tool of early modern humans. Science 325, 859–862. doi:10.1126/science.1175028

Burton FD (2009) Fire: The Spark that Ignited Human Evolution. University of New Mexico Press, Albuquerque NM, USA. Carmody RN, Wrangham RW (2009) The energetic significance of cooking. Journal of Human Evolution 57, 379–391. doi:10.1016/j.jhevol.2009.02.011

Chazan M (2017) Toward a long prehistory of fire. Current Anthropology 58, S351–S359. doi:10.1086/691988

Clark JD (1987) Transitions Homo erectus and the Acheulian: the Ethiopian sites of Gadeb and the Middle Awash. Journal of Human Evolution 16, 809–826. doi:10.1016/0047-2484(87)90025-X

Clark JD, Harris JWK (1985) Fire andits roles in early hominid lifeways. African Archaeological Review 3, 3–27. doi:10.1007/BF01117453

Daniau A-L, d’Errico F, Sánchez Goñi MF (2010) Testing the hypothesis of fire for ecosystem management by Neanderthal and Upper Palaeolithic modern human populations. PLoS One 5, e9157. doi:10.1371/journal.pone.0009157

Darwin C (1871) The Descent of Man, and Selection in Relation to Sex. Penguin, London, UK.

de Heinzelin J, Desmond Clark J, White T, Hart W, Renne P, WoldeGabriel G, et al. (1999) Environment and behavior of 2.5-Million-Year-Old Bouri hominids. Science 284, 625–629. doi:10.1126/science.284.5414.625

Dibble HL, Abodolahzadeh A, Aldeias V, Goldberg P, McPherron SP, Sandgathe DM (2017) How did hominins adapt to Ice Age Europe without fire? Current Anthropology 58, S278–S287. doi:10.1086/692628

Dominy NJ, Vogel ER, Yeakel JD, Constantino P, Lucas PW (2008) Mechanical properties of plant underground storage organs and implications for dietary models of early hominins. Evolutionary Biology 35, 159–175. doi:10.1007/s11692-008-9026-7

Dunbar RIM, Gowlett JAJ (2014) Fireside chat: the impact of fire on hominin socioecology. In Lucy to Language: the Bench Mark Papers. (Eds RIM Dunbar, C Gamble and JAJ Gowlett) pp. 277–296. Oxford University Press, Oxford, UK.

Estebaranz-Sánchez F, Hernández-Aguilar A, Martínez LM, Genis J, Pérez-Pérez A (2016) El acceso regular a recursos hídricos potables podría explicar la distribución de Australopithecus afarensis. Revista Española Antropología Física 37, 1–11.

Fluck HL (2007) Initial observations from experiments into the possible use of fire with stone tools in the manufacture of the Clacton Point. Lithics 28, 15–19.

Gabunia L, Vekua A, Lordkipanidze D, Swisher III CC, Ferring R, Justus A, et al. (2000) Pleistocene hominid cranial remains from Dmanisi, Republic of Georgia: taxonomy, geological setting, and age. Science 288, 1019–1025. doi:10.1126/science.288.5468.1019

Gao X, Zhang S, Zhang Y, Chen F (2017) Evidence of hominin use and maintenance of fire at Zhoukoudian. Current Anthropology 58, S267–S277. doi:10.1086/692501

Goldberg P, Dibble H, Berna F, Sandgathe D, McPherron SJP, Turq A (2012) New evidence on Neandertal use of fire: examples from Roc de Marsal and Pech de l’Azé IV. Quaternary International 247, 325–340. doi:10.1016/j.quaint.2010.11.015

Goldberg P, Miller CE, Mentzer SM (2017) Recognizing fire in the paleolithic archaeological record. Current Anthropology 58, S175–S190. doi:10.1086/692729

Goren-Inbar N, Alperson N, Kislev ME, Simchoni O, Melamed Y, Ben-Nun A, et al. (2004) Evidence of hominin control of fire at GesherBenotYa’aqov, Israel. Science 304, 725–727. doi:10.1126/science.1095443

Gowlett JAJ (2006) The early settlement of northern Europe: fire history in the context of climate change and the social brain. Comptes Rendus. Palévol 5, 299–310. doi:10.1016/j.crpv.2005.10.008

Gowlett JAJ (2016) The discovery of fire by humans: a long and convoluted process. Philosophical Transactions of the Royal Society of London. B 371, 20150164.doi:10.1098/rstb.2015.0164

Gowlett JAJ, Wrangham RW (2013) Earliest fire in Africa: towards the convergence of archaeological evidence and the cooking hypothesis. Azania 48, 5–30. doi:10.1080/0067270X.2012.756754

Gowlett JAJ, Harris JWK, Walton D, Wood BA (1981) Early archaeological sites, hominid remains and traces of fire from Chesowanja, Kenya. Nature 294, 125–129. doi:10.1038/294125a0

Harrison MJ (1983) Patterns of range use by the green monkey, Cercopithecus sabaeus, at Mt. Assirik, Senegal. Folia Primatologica 41, 157–179. doi:10.1159/000156129

Harrison MJ (1984) Optimal foraging strategies in the diet ofthe green monkey, Cercopithecus sabaeus, at Mt. Assirik, Senegal. International Journal of Primatology 5, 435–471. doi:10.1007/BF02692269

Henry AG (2017) Neanderthal cooking and the costs of fire. Current Anthropology 58, S329–S336. doi:10.1086/692095

Henry AG, Brooks AS, Piperno DR (2011) Microfossils in calculus demonstrate consumption of plants and cooked foods in Neanderthal diets (Shanidar III, Iraq; Spy I and II, Belgium). Proceedings of the National Academy of Sciences of the United States of America 108, 486–491. doi:10.1073/pnas.1016868108

Herzog NM (2015) Primate behavioral responses to burning as a model for hominin fire use. PhDdissertation. University of Utah, Salt Lake City UT, USA.

Herzog NM, Parker CH, Keefe ER, Coxworth J, Barrett A, Hawkes K (2014) Fire and home range expansions: a behavioral response to burning among savanna dwelling vervet monkeys (Chlorocebus aethiops). American Journal of Physical Anthropology 154, 554–560. doi:10.1002/ajpa.22550

Herzog NM, Keefe ER, Parker CH, Hawkes K (2016) What’s burning got to do with it? Primate foraging opportunities in fire-modified landscapes. American Journal of Physical Anthropology 159, 432–441. doi:10.1002/ajpa.22885

Hlubik S, Berna F, Feibel C, Braun D, Harris JWK (2017) Researching the nature of Fire at 1.5

Mya on the site of FxFj20 AB, Koobi Fora, Kenya, using high-resolution spatial analysis and FTIR spectrometry. Current Anthropology 58, S243–S257. doi:10.1086/692530

Jacobs BF (2004) Palaeobotanical studies from tropical Africa: relevance to the evolution of forest, woodland and savannah biomes. Philosophical Transactions of the Royal Society of London 359, 1573–1583. doi:10.1098/rstb.2004.1533

Kano T (1972) Distribution and adaptation of the chimpanzee on the eastern shore of Lake Tanganyika Kyoto Univ. African Studies 7, 37–129.

Kaplan JO, Pfeiffer M, Kolen JCA, Davis BAS (2016) Large scale anthropogenic reduction of forest cover in Last Glacial Maximum Europe. PLoS One 11, e0166726. doi:10.1371/journal.pone.0166726.

Karkanas P, Shahack-Gross R, Ayalon A, Bar-Matthews M, Barkai R, Frumkin A, et al. (2007) Evidence for habitual use of fire at the end of the Lower Paleolithic: site-formation processes at Qesem Cave, Israel. Journal of Human Evolution 53, 197–212. doi:10.1016/j.jhevol.2007.04.002

Leonard WR, Robertson ML (1994) Evolutionary perspectives on human nutrition: the influence of brain and body size on diet and metabolism. American Journal of Human Biology 6, 77–88. doi:10.1002/ajhb.1310060111

Lieberman DE, Krovitz GE, Yates FW, Devlin M, Claire MS (2004) Effects of food processing on masticatory craniofacial growth in a retrognathic strain and face. Journal of Human Evolution 46, 655–677. doi:10.1016/j.jhevol.2004.03.005

Mallol C, Henry A (2017) Ethnoarchaeology of Paleolithic fire. Current Anthropology 58, S217–S229. doi:10.1086/691422

Mallol C, Marlowe FW, Wood BM, Porter CC (2007) Earth, wind, and fire: ethnoarchaeological signals of Hadza fires. Journal of Archaeological Science 34, 2035–2052. doi:10.1016/j.jas.2007.02.002

Marlowe FW, Berbesque JC (2009) Tubers as fallback foods and their impact on Hadza hunter-gatherers. American Journal of Physical Anthropology 140, 751–758. doi:10.1002/ajpa.21040

Martínez LM, Estebaranz-Sánchez F, Galbany J, Pérez-Pérez A (2016) Testing dietary hypotheses of east African hominines using buccal dental microwear data. PLoS One 11, e0165447. doi:10.1371/journal.pone.0165447.

McGrew WC, Baldwin PJ, Tutin CEG (1981) Chimpanzees in a hot, dry, and open habitat: Mt. Assirik, Senegal, West Africa. Journal of Human Evolution 10, 227–244. doi:10.1016/S0047-2484(81)80061-9

McPherron S, Alemseged Z, Marean CW, Wynn JG, Reed D, Geraads D, et al. (2010) Evidence for stone-tool-assisted consumption of animal tissues before 3.39 million years ago at Dikika, Ethiopia. Nature 466, 857–860. doi:10.1038/nature09248

Medler MJ (2011) Speculations about the effects of fire and lava flows on human evolution. Fire Ecology 7, 13–23. doi:10.4996/fireecology.0701013

Milton K (1999) A hypothesis to explain the role of meat-eating in human evolution. Evolutionary Anthropology 8, 11–21. doi:10.1002/(SICI)1520-6505(1999)8:1<11::AID-EVAN6>3.0.CO;2-M

Moore J (1992) Savanna chimpanzees. In Topics in Primatology. (Eds T Nishida, WC McGrew, P Marler, MP Pickford and FBM de Waal) pp. 99–118. University of Tokyo Press. Tokyo, Japan.

Moore J (1996) Savanna chimpanzees, referential models, and the last common ancestor. In Great Ape Societies. (Eds WC McGrew, LF Marchant and T Nishida) pp. 275–292. Cambridge University Press, Cambridge, UK.

Organ C, Nunn CL, Machanda Z, Wrangham RW (2011) Phylogenetic rate shifts in feeding time during the evolution of Homo. Proceedings of the National Academy of Sciences of the United States of America 108, 14555–14559. doi:10.1073/pnas.1107806108

Parker CH, Keefe ER, Herzog NM, O’Conell JF, Hawkes K (2016) The pyrophilic primate hypothesis. Evolutionary Anthropology 25, 54–63. doi:10.1002/evan.21475

Pausas JG, Keeley JE (2009) A burning story: the role of fire in the history of life. Bioscience 59, 593–601. doi:10.1525/bio.2009.59.7.10

Pickering TR (2012) What’s new is old: comments on (more) archaeological evidence of one-million-year-old fire from South Africa. South African Journal of Science 108(5/6), 1–2. doi.org/10.4102/sajs.v108i5/6.1250.

Pickering TR, Egeland CP, Domínguez-Rodrigo M, Brain CK, Schnell AG (2008) Testing the shift in the balance of power hypothesis at Swartkrans, South Africa: hominid cave use and subsistence behavior in the Early Pleistocene. Journal of Anthropological Archaeology 27, 30–45. doi:10.1016/j.jaa.2007.07.002

Pop E, Kuijper W, van Hees E, Smith G, García-Moreno A, Kindler L, et al. (2016) Fires at Neumark-Nord 2, Germany: an analysis of fire proxies from a last interglacial Middle Palaeolithic basin site. Journal of Field Archaeology 41, 603–617. doi:10.1080/00934690.2016.1208518

Pruetz JD (2007) Evidence of cave use by savanna chimpanzees (Pan troglodytes verus) at Fongoli, Senegal: implications for thermoregulatory behavior. Primates 48, 316–319. doi:10.1007/s10329-007-0038-1

Pruetz JD, Herzog NM (2017) Savanna chimpanzees at Fongoli, Senegal, navigate a fire landscape. Current Anthropology 58, S337–S350. doi:10.1086/692112

Pruetz JD, LaDuke TC (2010) Brief communication: reaction to fire by savanna chimpanzees (Pan troglodytesverus) at Fongoli, Senegal: conceptualization of fire behavior and the case for a chimpanzee model. American Journal of Physical Anthropology 141, 646–650.

Pyne SJ (1994) Maintaining focus: an introduction to anthropogenic fire. Chemosphere 29, 889–911. doi:10.1016/0045-6535(94)90159-7

Roebroeks W, Villa P (2011) On the earliest evidence for habitual use of fire in Europe. Proceedings of the National Academy of Sciences of the United States of America 108, 5209–5214. doi:10.1073/pnas.1018116108

Rowlett RM (2000) Fire control by Homo erectus in East Africa and Asia. Acta Anthropologica Sinica 19, 198–208.

Sandgathe DM (2017) Identifying and describing pattern and process in the evolution of hominin use of fire. Current Anthropology 58, S360–S370. doi:10.1086/691459

Sandgathe DM, Dibble HL, Goldberg P, McPherron SP, Turq A, Niven L, et al. (2011) On the role of fire in Neanderthal adaptations in Western Europe: evidence from Pech de l’Azé IV and Roc de Marsal, France. PaleoAnthropology 2011, 216–242.

Schnorr SL, Crittenden AN, Venema K, Marlowe FK, Henry AG (2015) Assessing digestibility of Hadza tubers using a dynamic in-vitro model. American Journal of Physical Anthropology 158, 371–385. doi:10.1002/ajpa.22805

Semaw S, Roger MJ, Quade J, Renne PR, Butler RF, Domínguez-Rodrigo M, et al. (2003) 2.6-Million-year-old stone tools and associated bones from OGS-6 and OGS-7, Gona, Afar, Ethiopia. Journal of Human Evolution 45, 169–177. doi:10.1016/S0047-2484(03)00093-9

Sept JM (1992) Was there no place like home? A new perspective on early hominid archaeological sites from the mapping of chimpanzee nests. Current Anthropology 33, 187–207. doi:10.1086/204050

Shimelmitz R, Kuhn SL, Jelinek AJ, Ronen A, Clark AE, Weinstein-Evron M (2014) ‘Fire at will’: the emergence of habitual fire use 350,000 years ago. Journal of Human Evolution 77, 196–203. doi:10.1016/j.jhevol.2014.07.005

Smith AR, Carmody RN, Dutton RJ, Wrangham RW (2015) The significance of cooking for early hominin scavenging. Journal of Human Evolution 84, 62–70. doi:10.1016/j.jhevol.2015.03.013

Stahl AB (1984) Hominid dietary selection before fire. Current Anthropology 25, 151–168. doi:10.1086/203106

Stahlschmidt MC, Miller C, Ligouis B, Hambach U, Goldberg P, Berna F, Richter D, et al. (2015) On the evidence for human use and control of fire at Schöningen. Journal of Human Evolution 89, 181–201. doi:10.1016/j.jhevol.2015.04.004

Twoney T (2013) The cognitive implications of controlled fire use by early humans. Cambridge Archaeological Journal 23, 113–128. doi:10.1017/S0959774313000085

Ungar PS, Grine FE, Teaford MF, El Zaatari S (2006) Dental microwear and diets of African early Homo. Journal of Human Evolution 50, 78–95. doi:10.1016/j.jhevol.2005.08.007

Vallverdú J, Alonso S, Bargalló A, Bartolí R, Campeny G, Carrancho À, et al. (2012) Combustion structures of archaeological level O and mousterian activity areas with use of fire at the Abric Romaní rock shelter (NE Iberian Peninsula). Quaternary International 247, 313–324. doi:10.1016/j.quaint.2010.12.012

Vidal-Matutano P, Henry A, Théry-Paristo I (2017) Dead wood gathering among Neanderthal groups: charcoal evidence from Abric del Pastor and El Salt (Eastern Iberia). Journal of Archaeological Science 80, 109–121. doi:10.1016/j.jas.2017.03.001

Walker MJ, López-Martínez M, Carrión-García JS, Rodríguez-Estrella R, San-Nicolás del-Toro M, Schwenninger JL, et al. (2013) Cueva Nera del Estrecho del Río Quípar (Murcia, Spain): A late Early Pleistocene hominin site withan Achelo-Levalloiso-Mousteroid Palaeolithic assemblage. Quaternary International 294, 135–159. doi:10.1016/j.quaint.2012.04.038

Weiner S, Xu Q, Goldberg P, Liu J, Bar-Yosef O (1998) Evidence for the use of fire at Zhoukoudian, China. Science 281, 251–253. doi:10.1126/science.281.5374.251

Wobber V, Hare B, Wrangham R (2008) Great apes prefer cooked food. Journal of Human Evolution 55, 340–348. doi:10.1016/j.jhevol.2008.03.003

Wood B, Aiello LC (1998) Taxonomic and functional implications of mandibular scaling in early hominins. American Journal of Physical Anthropology 105, 523–538. doi:10.1002/(SICI)1096-8644(199804)105:4<523::AID-AJPA9>3.0.CO;2-O

Wrangham R (2017) Control of fire in the Paleolithic. Evaluating the cooking hypothesis. Current Anthropology 58, S303–S313. doi:10.1086/692113

Wrangham R, Carmody R (2010) Human adaptation to the control of fire. Evolutionary Anthropology 19, 187–199. doi:10.1002/evan.20275

Wrangham R, Conklin-Brittain NL (2003) Cooking as a biological trait. Comparative Biochemistry and Physiology. Part A, Molecular & Integrative Physiology 136, 35–46. doi:10.1016/S1095-6433(03)00020-5

Wrangham RW, Jones JH, Laden G, Pilbeam D, Conklin-Brittain NL (1999) The raw and the stolen: cooking and the ecology of human origins. Current Anthropology 40, 567–594.

Zhong M, Shi C, Gao X, Wu X, Chen F, Zhang S, et al. (2014) On the possible use of fire by Homo erectus at Zhoukoudian, China. Chinese Science Bulletin 59, 335–343. doi:10.1007/s11434-013-0061-0

Zink KD, Lieberman DE, Lucas PW (2014) Food material properties and early hominin processing techniques. Journal of Human Evolution 77, 155–166. doi:10.1016/j.jhevol.2014.06.012

2

Laboratory fire simulations: plant litter and soils

Paulo Pereira, Xavier Úbeda and Marcos Francos

Introduction

Laboratory simulations are a well-known technique used to imitate the direct impacts (e.g. heating) of temperature on plant litter and soil properties. Under laboratory conditions, we can observe the effects of a particular temperature and period of contact on a specific type and part of vegetation (e.g. litter, leaves, twigs), at different levels of moisture, density and volume. This test can also be carried out on soils to observe how temperatures change them. Normally, laboratory burns are carried out across a gradient of temperature, using one or several heating contact periods (García-Corona et al. 2004; Gray and Dighton 2006; Badía-Villas et al. 2014).

Laboratory simulations of the effects of fire on soils have been used since the mid-20th century (Tarrant 1953). Muffle furnaces have been the devices most frequently used to examine the impact of temperature on plant litter and soil properties (e.g. Úbeda et al. 2009; Bárcenas-Moreno and Baath 2009). However, some soil heating studies were carried out using blowtorches (Robichaud and Hungerford 2000; Hatten and Zabowski 2009, 2010; Badía-Villas et al. 2014; Aznar et al. 2016) or infrared lamps (Cancelo-González et al. 2014). In these studies, a thermal shock is applied over a period of time to the top of a soil column.

With the exception of smouldering fires and pile burns (Chapters 13 and 17), the time of residence of fire on soil surface is short, especially in fast-moving grassland fires. In this context, the time periods applied in the majority of studies may not correspond to reality. In addition, some authors have argued that the impact of temperatures on plant litter and soils in a muffle furnace is different from the impact in real fires, as a consequence of the lack of oxygen circulation (Raison and McGarity 1980; Soto and Díaz-Fierros 1993; Bryant et al. 2005). Despite this, several analyses have been carried out comparing the heating of plant litter and soils in muffle furnaces and real fires (Ketterings and Bigham, 2000; Galang et al., 2010; Pereira 2011; Mataix-Solera et al. 2013). The objective of this chapter is to summarise: (1) the methods used to mimic fire impacts on plant litter and soil properties in the laboratory; and (2) the impact on plant litter and soil properties, according to temperature and time of exposure.

Methods applied in the study of heating impacts on plant litter and soil properties

Table 2.1 summarises the studies focused on the heating impact on litter properties. The temperatures studied range from 70° to 950°C. The majority of works compared temperatures at intervals of 50 and 100°C, which can be considered large for the changes that occur along a temperature gradient. Studies with a better resolution are needed to understand the changes at shorter ranges and the impacts of temperatures in organic matter combustion. The majority of the works used between three and five samples, which is good for statistical purposes because it allows for comparisons between temperatures, species or treatments. The time periods of contact range between 60 and 1080 min. There is no specific protocol regarding this factor because the time of combustion in real fires is strongly dependent on the flammability of the species affected, temperature of the fire, fire behaviour (e.g. fire heads upslope or downslope), wind intensity, whether the material is alive or dead, moisture content and distribution (e.g. density, pack and connectivity) (Pereira et al. 2010). Thus, it would be interesting to study the impacts of fire temperatures on litter and fresh organic matter using different contact periods and moisture levels. To our knowledge, there is very little information available in the international literature. The majority of the works carried out have focused on Pinus species in environments located in Europe (e.g. Mediterranean) and the USA. Other areas of the globe have clearly been overlooked. The available works mainly focused on chemical transformations across a temperature gradient, especially in pH and water-extracted elements (Table 2.1). The studies carried out on soils are much more numerous than those carried out on litter. The range of temperatures studied is between 20° and 1000°C. The number of replicates is extremely variable across the studies, but normally averages around three to six replicates, as the time of exposure ranges from 0.15 to 930 min. The majority of the works studied the effects of temperature on the top 0–5 cm of the soil, where the effect of heating is more important in real fires. Despite the importance of soil moisture on heat propagation, very few works were focused on the impacts of different temperatures on soils with different moisture levels.

Table 2.1.   Summary of the studies of heating impacts on litter properties. Only studies using muffle furnaces were considered.

¹Mineralogical variables are underlined; physical variables are italic, chemical variables are bold, biological variables are underlined and italic

The soil heating experiments in muffles (Chapter 15) were especially focused on physical (e.g. texture and water repellency) (Chapters 4 and 5) and chemical (e.g. carbon, nitrogen, extractable cations) properties (Chapters 3, 7 and 8). Laboratory fire simulations using muffle furnaces are more developed for soils than for litter. The range of temperatures tested is wider in soil studies than in litter, and some works exposed soils to reduced temperatures (e.g. <100°C). Several studies were focused on changes in soil microbiology, which is more susceptible to reduced temperatures than are physical or chemical properties (Chapter 11). The period of contact used in soil studies has a better resolution than in litter analyses, and for future research it would be very useful if laboratory fire simulations exposing litter to different temperatures, could use several periods of contact as well (Table 2.2).

Heating impact on litter and soil mineralogical properties

The effect of heat on the mineral (Chapter 4) composition of litter and soils is related to the temperature to which they are exposed. Heat reduces the amount of some elements and increases and transforms others. These changes are also dependent on the type and amount of fuel combusted and on soil type (Misra et al. 1993; Ketterings et al. 2002; Grogan et al. 2003; Liodakis et al. 2007).

Liodakis et al. (2007) observed that calcium (Ca) and magnesium (Mg) content in Greek dominant species increased between the temperatures of 600 and 1000°C as a consequence of the decomposition of calcium carbonate (CaCO3), magnesium carbonate (MgCO3), potassium carbonate (K2CO3) and potassium oxide (K2O). On the other hand, the content of CaCO3 and hydroxyl decreased with increasing temperature. The ashes produced at temperatures of 600, 800 and 1000°C were mainly composed of sulphates, oxides and carbonates of Ca, Mg and K (Liodakis et al. 2007). Misra et al. (1993) observed that the contents of silica (Si), Mg, phosphorus (P), manganese (Mn), Mg, iron (Fe) and aluminium (Al) did not change relative to Ca, while potassium (K), sodium (Na), copper (Cu), sulphur (S) and boron (B) increased. At 600 °C, the main components of the ash were CaCO3, while at 1300 °C, the main components were oxides of Ca and Mg. Gabet and Booker (2011) ashed different parts of Pinus ponderosa (limb, needle, branches), grass and duff at different temperatures (450, 600, 800 and 950°C) and they found that quartz (SiO2) and CaCO3 were present in all types of fuel and periods of contact, while oxides were only identified at the temperatures of 800 and 950°C in Pinus ponderosa ashes. Etiegni and Campbell (1991) found, after ashing Pinus contorta at 538, 649, 760, 871, 982 and 1093°C, that CaCO3 content decreased with the increased temperature. CaCO3 and bicarbonates (HCO3–) were the most common elements at 500°C, while oxides were the most dominant mineral at temperatures higher than 1000°C. Iglesias et al. (1997) identified the formation of CaCO3 after exposing dead leaves and branches of Juniperus oxycedrus and Quercus pyrenaica at 300°C. Grogan et al. (2003) observed the formation of maghemite (Fe2O3, γ-Fe2O3) from goethite (FeO(OH)) after ashing leaf litter at 300 and 400°C. Brook and Wittenberg (2016) studied the effects of laboratory burning on the mineralogy of Mediterranean species and they found that heavy minerals content increased with the increasing temperature of combustion, as a consequence of the organic matter mineralisation. Audry et al. (2014) found that the most common mineral in ash produced at 500°C was CaCO3. The majority of the studies carried out were focused on temperatures above 300°C and further research is needed at low temperatures. At temperatures of 300°C changes in Fe minerals are observed. From 300° to 500°C, CaCO3 is formed, however, this depends on the burned species. In species rich in resins and with high flammability (e.g. Pinus) the formation of CaCO3 occurs at low temperatures, while in less flammable species (e.g. Quercus) it is created at high temperatures (Pereira et al. 2009). At temperatures higher than 500°C the amount of oxides became dominant as a consequence of the transformation of CaCO3 to CaO (Bodí et al. 2014) (Chapter 3).

Lugassi et al. (2014) found that goethite (FeO(OH)) was transformed to hematite (Fe2O3, a-Fe2O3) at 450°C in loess, terra rossa and rendzina soils. Heating the soils at 1000°C showed that CaCO3 and CaO are transformed into calcium hydroxide (Ca(OH)2). Zhang et al. (2018) identified that heating a soil at the temperature of 400°C, did not produce change in a loess soil mineralogy. However, when heated to temperatures higher than 500°C, they observed the dehydroxylation of kaolinite Al2Si2O5(OH)4. At temperatures higher than 600°C, CaCO3 disappeared as a consequence of decarbonation. Jiménez-Pinilla et al. (2016) observed a transformation of Fe (hydr)oxides into Fe2O3, γ-Fe2O3 and the disappearance of Al2Si2O5(OH)4 in a rhodoxeralf clay loam soil at the temperature of 700°C. Increases of dolomite (CaMg(CO3)2) and CaCO3 were observed in a xerorthent sandy silt loam soil. No changes were identified in a xerorthent sandy silt loam soil. Overall, changes in litter mineralogy do not depend only on the temperature, but also on vegetation flammability and the soil type affected (Chapter 3).

Heating impact on litter and soil physical properties

Heating reduces litter weight. As expected, there is a decrease with increasing temperatures, but this is not linear and varies according to the type of fuel combusted. Flammable fuels are more susceptible to temperature and mass loss occurs at a higher rate. The differences between flammable and nonflammable species are especially well observed at temperatures higher than 400°C. However, generally, the high mass loss occurs between 250° and 400°C. At 400°C mass loss is higher than 90%. The time of exposure is also a relevant factor. Mass loss increases with the time of exposure (Matthiessen et al. 2005; Gray and Dighton 2006; Pereira et al. 2011). Jiménez-Pinilla et al. (2016) observed a decrease of mass loss with increasing temperature in rhodoxeralf, xerorthent and haploxeralf heated at 300, 500 and 700°C. Rein et al. (2008) observed in a laboratory environment that the exposure of a peat soil to temperatures higher than 300°C, for 1 h, reduced the soil mass by more than 90%.

Litter/ash colour changes according to the different temperatures of contact. At lower temperatures of exposure (150°C), all water evaporates and the fuel has a brownish colour. At temperatures between 200° and 300°C the combustible material becomes reddish as a consequence of the oxidation of Fe minerals and at 300°C, the ash is black, due to the formation of carbon. At temperatures higher than 350–450°C, ash becomes grey and at temperatures between 450° and 550°C, it is white as a consequence of the total combustion of organic material and the formation of CaCO3. Differences are also found among species. In species with high flammability, ash becomes lighter at lower temperatures, compared with non-flammable species, showing that a high burn severity is observed at lower temperatures of contact (Úbeda et al. 2009; Pereira et al. 2010; Dudaite et al. 2011) (Chapter 3). Terefe et al. (2008) found an increase in soil darkness at temperatures between 25° and 300°C, as a consequence of the charring of organic material. Between the temperatures of 300° and 500°C, they observed an increase of soil redness as a consequence of the transformation of Fe hydrous oxides into maghemite and Fe2O3, α-Fe2O3. The redness ratio and chroma increase with the temperature and time of exposure (Wondafrash et al. 2005). Ketterings and Bigham (2000) found that the susceptibility of soil to heat was different according to the soil depth. The redness ratio increased faster in the top soil (0–5 cm) than at 5–15 cm depth with increasing temperature. The time of exposure was also important for the redness ratio increase. At a given temperature (300 or 600°C), samples became redder with the increase of the contact time. Cancelo-González et al. (2014) observed that soil organic matter content is a key determinant of colour in fire-affected soils. The amount of soil organic matter decreased significantly with the temperature, chroma and time of exposure. With increasing temperature, soils became lighter as a consequence of the organic matter consumption. Zhang et al. (2018) found that heated soil colour changes are related to the mineralogy. At 300°C soils had a yellow colour, turning to red and brighter colouring at temperatures between 300° and 600°C, as a consequence of the oxidation of Fe minerals. At 800°C, soils became grey, very likely due to the transformation of crystalline phases. Finally, Katsumi et al. (2016) observed that soil darkness increased with the amount of aromatic carbon (hydrophobic compounds) content and decreased with alkyl C and O- alkyl quantity (Chapters 7 and 18).

Table 2.2.   Summary of the studies of heating impacts on litter properties. Only studies using muffle furnaces were considered.

¹Mineralogical variables are underlined; physical variables are italic, chemical variables are bold, biological variables are underlined and italic

Abbreviations: Thermoluminescence (TL), near infrared spectroscopy (NIR), mid-infrared spectroscopy (MIR), calcium carbonate (CaCO3), aluminium oxide (Al2O3), iron oxide (Fe2O3), phosphorus pentoxide (P205), titanium dioxide (TiO2), silicon dioxide (SiO2), aluminium oxide (Al2O3), ferric oxide (Fe2O3), manganese oxide (MnO), calcium oxide (CaO), sodium oxide (Na2O), potassium oxide (K2O) colour (Col), Munsell hue (H), value colour (VC), chroma colour (CC), different thermal analysis (DTA), mass flow (MF), specific surface area (SSA), near-infrared spectroscopy (NIR), nitrogen volatilisation (NL), mass loss (ML), weight loss (WL), total porosity (TP), particle size (PS), aggregate stability (AS), aggregate sizes (ASi), stable aggregates (SA), macroaggregate stability (MS), microaggregate stability (MA) mean weight diameter (MWD), bulk density (BD), real density (RD), erodibility (ERO), hydraulic conductivity (HC), water loss (WAL), water stability index (WSI), dispersive value (DV), water holding capacity (WHC), field capacity (FC), wilting point (WP), water available (WA), water unavailable (WU), gravitational water (WG), total water (WT), water repellency (WR), water retention (WR), hydrogen (H), oxygen (O), electrical conductivity (EC), glomalin-related soil protein (GRSP), soil organic matter (SOM), water-extractable organic matter (WEOM), carbon losses (CL) carbon (C), Fourier-transform infrared (FTIR), total carbon (TotC), total organic carbon (TotOC) organic carbon (OC), dissolved organic carbon (DOC), dissolved organic carbon (DIC), extractable organic carbon (ExC), maleate (C4H4O4), acetate (CH3CO2) carbon mineralisation (CM), water soluble organic matter (WSOM), liquid-state hydrogen nuclear magnetic resonance (H NMR), humid acids (HA), fluvic acids (FA), alkali-insoluble fraction (AIC), lipids (LP), cellulose +hemicellulose (C+H), lignin (LG), pyrolysis-field ionisation mass spectrometry (Py-Fims), functional groups (XANES), nitrogen (N), kjeldahl nitrogen (KN), organic nitrogen (ON), total nitrogen (TotN), mineral nitrogen (MN), inorganic nitrogen (IN), nitrogen mineralisation (NM), potential mineralisable nitrogen (PMN), residual nitrogen (ResN), hydrolysable nitrogen (HydN), carbon/nitrogen ratio (C/N), carbon/hydrogen ratio (C/H), total solvent extracts (TSE), total sulphur (TotS), total potassium (TotK), total lithium (TotLi), ammonium (NH4+), nitrate (NO3–), nitrite (NO2 –), calcium (Ca), magnesium (Mg), sodium (Na), potassium (K), silica (Si), sulphur (S), phosphorus (P), aluminium (Al), manganese (Mn), iron (Fe), zinc (Zn), cobalt (Co), cadmium (Cd), cooper (Cu), chromium (Cr), nickel (Ni), lead (Pb), boron (B), barium (Ba), arsenic (As), beryllium (Be), mercury (Hg), lithium (Li), molybdenum (Mo), antimony (Sb), selenium (Se), tin (Se), titanium (Ti), thallium (Tl), vanadium (V), extractable calcium (ExCa), extractable magnesium (ExMg), extractable sodium (ExNa), sodium adsorption ratio (SAR), extractable potassium (ExK), extractable aluminium (ExAl), extractable manganese (ExFe), extractable iron (ExFe), extractable zinc (ExZn), extractable cooper (ExCu), extractable boron (ExB), extractable silica (ExSi), calcium/magnesium ratio (Ca/Mg), cation exchange capacity (CEC), base saturation (BS), organic phosphorus (OP), available phosphorus (AP), resin phosphorus (RP), bicarbonate inorganic phosphorus (HCO3IP), bicarbonate organic phosphorus (HCO3OP), sodium bicarbonate inorganic phosphorus (NAOHIP), sodium bicarbonate inorganic phosphorus (NAOHOP), residual phosphorus (ResP), labile phosphorus (LP), non-labile (NLP), total phosphorus (TotP), bray phosphorus (BP), inorganic phosphorus (IP), desorbed phosphorus (DP), phosphorus sorption (SP), extractable phosphorus (EP), diluted hydrochloric acid phosphorus (Dil. HCI-Pi), concentrated hydrochloric acid phosphorus (Conc. HCI-Pi), phosphate (PO4³), chloride (Cl), sulphate (SO4²–), microbial biomass (MB), soil respiration (SR), substrate induced respiration (SIR), total microbes (TotM), bacteria (Bac), actinomycetes (Act), cyanobacteria (Cya), algae (Alg), fungal propagules (Fpro), fungal hyphae (Fhyp), ammonifiers (Amm), basal respiration (Bres), normal respiration (Nres), specific respiration (Sres), biomass carbon (Bcar), bacterial growth (BacG), fungi (Fun), fungal biomass (FunB), ectomycorrhizal fungi (EcFun), phospholipids fatty acid (PLFA), soluble hexose sugars (SHS), malate-induced respiration (MIR),