• Premise of the study: Charcoal particles preserved in sediments are used as indicators of paleowildfire. Most research focuses on abundance as an indicator of fire frequency, but charcoals also convey information about the vegetation from which they are derived. One potential source of information is their morphology, which is influenced by the parent material, the nature of the fire, and subsequent transportation and burial.• Methods: We charcoalified 26 materials from a range of plant taxa, and subjected them to simulated fluvial transport by tumbling them with water and gravel. We photographed the resulting particles, and used image analysis software to measure morphological parameters.• Results: Leaf charcoal displayed a logarithmic decrease in area, and a logarithmic increase in circularity, with transportation time. Trends were less clear for stem or wood charcoal. Grass charcoal displayed significantly higher aspect ratios than other charcoal types.• Conclusions: Leaf charcoal displays more easily definable relationships between morphological parameters and degree of breakdown than stem or wood charcoal. The aspect ratios of fossil mesocharcoal can indicate the broad botanical source of an assemblage. Coupled to estimates of charcoal abundance, this will improve understanding of the variation in flammability of ancient ecosystems.

Loss of peat through increased burning will have major impacts on the global carbon cycle. In a normal hydrological state, the risk of fire propagation is largely controlled by peat bulk density and moisture content. However, where humans have interfered with the moisture status of peat either via drainage, or indirectly via climate change, we hypothesise that its botanical composition will become important to flammability, such that peats from different latitudes might have different compositionally-driven susceptibility to ignition. We use pyrolysis combustion flow calorimetry to determine the temperature of maximum thermal decomposition (T_max) of peats from different latitudes, and couple this to a botanical composition analysis. We find that tropical peat has higher T_max than other regions, likely on account of its higher wood content which appears to convey a greater resistance to ignition. This resistance also increases with depth, which means that loss of surface peat in tropical regions may lead to a reduction in the subsequent ignitability of deeper peat layers as they are exposed, potentially resulting in a negative feedback on increased fire occurrence and severity.

Sedimentary charcoal is a widely used tool for reconstructing past fire histories. These fossil charcoals are normally quantified as the number or area of particles present in a sediment sample, but it is not known how well either measure is correlated with their volume. Areal measurements are often treated as the true measure of quantity, which may introduce bias to fire histories. The relationship of measured area to volume is a function of shape, and if this relationship can be understood, areal measurements may be adjusted to better reflect volume. We show that particle elongation may be particularly important when making such adjustments. We also establish a high degree of correlation between volume and area in a mid-Holocene mesocharcoal assemblage, which indicates that the bias may be small in similar cases.

Background: Fires in temperate dry heaths burn dead and live fuels and are increasing in frequency. Models that describe these fuels and their contribution to fire behaviour is becoming of greater importance. Aims: We sought to identify variations in fuel moisture and flammability in dry heath fuel types throughout the year and assess the strength of phenological shifts to influence predicted fire behaviour. Methods: Six plant species from three dry heaths in the United Kingdom (UK) were collected throughout the year, their moisture content and effective heat of combustion measured. Data were used to parameterise a dynamic fuel model and undertake a sensitivity analysis using BehavePlus. Key results: Phenological changes in live fuel moisture had the greatest effect on predicted fire behaviour where variations between late winter–early spring and late spring–summer, led to a four-fold difference in fire rate of spread. Dead fuel moisture had an effect in the summer months but was dampened significantly by phenologically high live fuel moisture content. Conclusions: Phenological drivers of live fuel moisture in temperate shrubland fuels must be included in models that predict fire behaviour. Implications: Using the data presented, models such as BehavePlus can be adapted to include this variability to predict fire behaviour in temperate heathland ecosystems.

Charcoal morphometry is increasingly employed in the analysis of Quaternary sediments, but has not been applied in studies of earlier sediments. We present findings relating to charcoal morphometry and morphotypes in a Toarcian sequence, which contains a preponderance of highly elongate forms, and morphometric values well outside expected ranges. SEM imaging reveals elongate particles of two distinct kinds. One originates in conifer xylem, and may be associated with formation at high levels of heating. It is proposed that the other may derive from tree ferns, or from plants with similar growth forms. Our results show the importance of recognizing the wide morphological variation that exists in sedimentary charcoal. Failing to do so may result in serious errors in its identification, interpretation and quantification.