The formation of charcoal reflectance and its potential use in post-fire assessments

This is the final version of the article. Available from the publisher via the DOI in this record.Charcoal has an exceptional ability to reflect light when viewed using reflectance microscopy. The amount of light reflected is variable depending on the differential ordering of graphite-like phases within the charcoal itself. It has been suggested that this relates to the temperature of formation, whereby higher formation temperatures result in high charcoal reflectance. However, this explanation is derived from oven-based chars that do not well represent the natural combustion process. Here, we have experimentally created charcoals using a cone calorimeter, in order to explore the development of charcoal reflectance during pre-ignition heating and peak heat-release rate, through to the end of flaming and the transition to char oxidation. We find that maximum charcoal reflectance is reached at the transition between pyrolysis and char oxidation, before its conversion to mineral ash, and indicates that our existing understanding of reflectance is in error. We suggest that charcoal reflectance warrants additional study as it may provide a useful quantitative addition to ground-based fire severity surveys, because it may allow exploration of surface heating after the main fire front has passed and the fire transitions to smouldering phases.This research was funded by a European Research Council Starter Grant ERC-2013-StG-335891-ECOFLAM (awarded to CMB

Changes to Cretaceous surface fire behaviour influenced the spread of the early angiosperms

This is the final version of the article. Available from Wiley via the DOI in this record.Angiosperms evolved and diversified during the Cretaceous period. Early angiosperms were short-stature weedy plants thought to have increased fire frequency and mortality in gymnosperm forest, aiding their own expansion. However, no explorations have considered whether the range of novel fuel types that diversified throughout the Cretaceous also altered fire behaviour, which should link more strongly to mortality than fire frequency alone. We measured ignitability and heat of combustion in analogue Cretaceous understorey fuels (conifer litter, ferns, weedy and shrubby angiosperms) and used these data to model palaeofire behaviour. Variations in ignition, driven by weedy angiosperms alone, were found to have been a less important feedback to changes in Cretaceous fire activity than previously estimated. Our model estimates suggest that fires in shrub and fern understories had significantly greater fireline intensities than those fuelled by conifer litter or weedy angiosperms, and whilst fern understories supported the most rapid fire spread, angiosperm shrubs delivered the largest amount of heat per unit area. The higher fireline intensities predicted by the models led to estimates of enhanced scorch of the gymnosperm canopy and a greater chance of transitioning to crown fires. Therefore, changes in fire behaviour driven by the addition of new Cretaceous fuel groups may have assisted the angiosperm expansion.We thank two anonymous reviewers and the editor David Ackerly for providing useful comments that helped improve this manuscript. Thanks to Mark Grosvenor for technical support in the University of Exeter wildFIRE Lab and Nick Walding for assistance in plotting some of the figures. We thank the grounds teams at Bristol Botanic Gardens and the University of Exeter for providing plant material for our experiments. This research was funded by a European Research Council Starter Grant (ERC-2013-StG-335891-ECOFLAM); awarded to C.M.B

Latest Permian chars may derive from wildfires, not coal combustion

The Permian-Triassic boundary extinction event was the largest biological crisis of the Phanerozoic. One of the principle triggers for the mass extinction is thought to be greenhouse warming resulting from the release of CH4 from basalt-coal interaction during the extensive Siberian Traps (Russia) eruptions. Observations of organic matter interpreted to be coal combustion products (fly ash) in latest Permian marine sediments have been used to support this hypothesis. However, this interpretation is dependent upon vesicular chars being fly ash (coal combustion derived) and not formed by alternative mechanisms. Here we present reflectance microscopy images of vesicular chars from Russian Permian coals, and chars from modern tundra, peatland, and boreal forest fires, to demonstrate that despite a difference in precursor fuels, wildfires are capable of generating vesicular chars that are morphologically comparable to end-Permian fly ash. These observations, coupled with extensive global evidence of wildfires during this time interval, call into question the contribution of coal combustion to the end- Permian extinction event.We acknowledge funding from the Natural Environment Research Council and CASE Studentship grant NE/F013698/1 (Hudspith’s Ph.D. thesis, Royal Holloway University of London), for the late Permian coal samples from the Kuznetsk Basin, Siberia, Russia. National Science Foundation (NSF) grant ARC-0612366 (to F.S. Hu) funded the analysis of the boreal and tundra samples, and European Research Council Starter Grant ERC-2013-StG-335891-ECOFLAM funded Hudspith and Belcher for analysis of the modern peatland samples. We thank M.E. Collinson and A.C. Scott for use of reflectance microscope facilities at Royal Holloway University of London, and N. Holloway and S. Pendray for polished block preparation. We also thank four anonymous reviewers for their helpful comments

Quantitative charcoal reflectance measurements better link to regrowth potential than ground-based fire-severity assessments following a recent heathland wildfire at Carn Brea, Cornwall, UK

This is the final version. Available on open access from CSIRO Publishing via the DOI in this record.Charcoal has recently been suggested to retain information about the fire that generated it. When looked at under a microscope, charcoals formed by different aspects of fire behaviour indicate different ability to reflect the amount of light when studied using the appropriate technique. It has been suggested that this method, charcoal reflectance (Ro), might be able to provide a quantitative fire severity metric that can be used in conjunction with or instead of standard qualitative fire severity scores. We studied charcoals from a recent heathland wildfire in Carn Brea, Cornwall, UK, and assessed whether charcoal reflectance (Ro) can be linked to standard qualitative fire severity scores for the burned area. We found that charcoal reflectance was greater at sites along the burned area that had been scored as having a higher qualitative fire severity. However, there were clear instances where the quantitative charcoal reflectance measurements were able to better indicate damage and regrowth potential than qualitative scoring alone. We suggest measuring the reflectance of charcoals may not only be able to provide quantitative information about the spatial distribution of heat across a burned area post fire but that this approach is able to provide improvement to fire severity assessment approaches.European Research CouncilNatural Environment Research Counci

Holocene fire history: can evidence of peat burning be found in the palaeo-archive?

Smouldering wildfires in peatlands have the potential to release substantial amounts of the carbon currently sequestered in these ecosystems. However, past studies of Holocene fire history in peatlands have given little consideration to the identification of evidence left behind after peat burning, or to charring of the peat matrix. In this study, modern peat samples from peatlands across the globe were charred in order to assess the identifiable characteristics of charred peat. On this basis we believe that charred aggregates of partially decayed organics which can be identified in cores provide clear evidence that the peat matrix itself burned. A range of charred morphotypes could be found throughout a 2 m peat core from and we are able to identify charred partially decayed aggregates that appeared to correspond with peaks in fire activity on the bog. These may reflect periods when surface fires ignited the peat surface below, or when the radiant heat from surface fires was sufficient to pyrolyse the surface peat. We conclude that it is possible to find evidence of peat burning in the palaeo-archive, and that future studies should begin to document the occurrence of charred particles so that the discipline can begin to build a picture of possible past peat fire activity.CMB acknowledges a European Research Council Starter Grant ERC-2013- StG- 335891-ECOFLAM, and AGS acknowledges the NERC Millipeat grant: NERC Standard grant NE/I012915/1

What can charcoal reflectance tell us about energy release in wildfires and the properties of pyrogenic carbon?

Here, we explore how charcoal formation under different heating regimes and circumstances leads to chars of different physical properties. In order to do this, we have undertaken (1) carefully controlled laboratory experiments that replicate the different heating regimes that might be experienced during a wildfire and (2) two experimental wildfires where heat variations were monitored across the burn from which resulting charcoal has been studied. The charcoal properties were assessed using charcoal reflectance that measures the light reflected back from the charcoals structure and which links to changes in its structural properties. We find that increased total heat released during combustion positively correlates with increased charcoal reflectance and that this is evidenced from both our laboratory experiments and experimental wildfires. Charcoals that related to lower total heat release were found to have more lignin remaining than those subjected to greater heating indicating that charcoals formed in lower energy regimes are likely to be more susceptible to post-fire degradation. We conclude that charcoal reflectance may make a useful metric with which to determine the distribution of energy delivery across a burned area and that this may be utilized to inform both variations in fire severity and enable the prediction of long-term C budgeting for different types of wildfire

Floral Assemblages and Patterns of Insect Herbivory during the Permian to Triassic of Northeastern Italy

To discern the effect of the end-Permian (P-Tr) ecological crisis on land, interactions between plants and their insect herbivores were examined for four time intervals containing ten major floras from the Dolomites of northeastern Italy during a Permian-Triassic interval. These floras are: (i) the Kungurian Tregiovo Flora;(ii) the Wuchiapingian Bletterbach Flora;(iii) three Anisian floras;and (iv) five Ladinian floras. Derived plant-insect interactional data is based on 4242 plant specimens (1995 Permian, 2247 Triassic) allocated to 86 fossil taxa (32 Permian, 56 Triassic), representing lycophytes, sphenophytes, pteridophytes, pterido-sperms, ginkgophytes, cycadophytes and coniferophytes from 37 million-year interval (23 m. yr. Permian, 14 m. yr. Triassic). Major Kungurian herbivorized plants were unaffiliated taxa and pteridosperms;later during the Wuchiapingian cycadophytes were predominantly consumed. For the Anisian, pteridosperms and cycadophytes were preferentially consumed, and subordinately pteridophytes, lycophytes and conifers. Ladinian herbivores overwhelming targeted pteridosperms and subordinately cycadophytes and conifers. Throughout the interval the percentage of insect-damaged leaves in bulk floras, as a proportion of total leaves examined, varied from 3.6% for the Kungurian (N = 464 leaves), 1.95% for the Wuchiapingian (N = 1531), 11.65% for the pooled Anisian (N = 1324), to 10.72% for the pooled Ladinian (N = 923), documenting an overall herbivory rise. The percentage of generalized consumption, equivalent to external foliage feeding, consistently exceeded the level of specialized consumption from internal feeding. Generalized damage ranged from 73.6% (Kungurian) of all feeding damage, to 79% (Wuchiapingian), 65.5% (pooled Anisian) and 73.2% (pooled Ladinian). Generalized-to-specialized ratios show minimal change through the interval, although herbivore component community structure (herbivore species feeding on a single plant-host species) increasingly was partitioned from Wuchiapingian to Ladinian. The Paleozoic plant with the richest herbivore component community, the coniferophyte Pseudovoltzia liebeana, harbored four damage types (DTs), whereas its Triassic parallel, the pteridosperm Scytophyllum bergeri housed 11 DTs, almost four times that of P. liebeana. Although generalized DTs of P. liebeana were similar to S. bergeri, there was expansion of Triassic specialized feeding types, including leaf mining. Permian-Triassic generalized herbivory remained relatively constant, but specialized herbivores more finely partitioned plant- host tissues via new feeding modes, especially in the Anisian. Insect-damaged leaf percentages for Dolomites Kungurian and Wuchiapingian floras were similar to those of lower Permian, north-central Texas, but only one-third that of southeastern Brazil. Global herbivore patterns for Early Triassic plant-insect interactions remain unknown