Alastair J. Crawford

Volcán de Agua, also known locally as Hunahpú, is a largely unstudied volcano in Guatemala, situated less than 10 km south of the city of Antigua Guatemala, between the active volcanoes of Pacaya and Fuego. The population centres of Ciudad Vieja, Santa María de Jesús, Amatitlán and Palín also lie within 15 km of Agua’s summit, with a total population of approximately 550,000. There is little published work on either its eruptive behaviours or bulk chemistry, with no documented historical eruptions. Dating of its past activity is unknown, and the style of activity remains poorly constrained. Other volcanoes along the Guatemalan cordillera have shown a range of activities in the last two centuries, ranging from effusive to Strombolian at Pacaya in the south to the VEI 2–6 explosive eruptions at Santa Maria to the north west. As part of this study, we analysed samples from surface-exposed deposits that provide evidence for at least one phase of basaltic activity that generated pyroclastic density current (PDC) deposits. These deposits are poorly sorted and contain very angular to sub-rounded, weakly vesicular clasts. The deposit’s geometry suggests an overbank flow, indicating that it escaped an established drainage channel as the current changed direction. Charcoal fragments identified within the deposit were subjected to reflectance analysis, which indicates a depositional temperature of approximately ~300 °C. Radiocarbon dating of this charcoal yielded an age of 15,454 ± 41 BP. This represents the first published date of eruptive activity at Agua. Given the location of the dated deposit and lack of capping deposits, it may be possible that Agua has been inactive throughout the Holocene.

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.

Wildfire risk is increasing in temperate regions like the UK and NW Europe, but we lack operational tools to support wildfire management decision-making needs. We developed FireInSite to address the need for a user-oriented system for predicting fire behaviour. FireInSite is a fire behaviour prediction system in the form of a web-based application that forecasts the probability of ignition, surface fire rate of spread, flame length and fireline intensity for a user selected location for a set of core UK fire prone fuels. By seamlessly integrating geolocated weather forecasts up to 5 days ahead, topographic data, and in-built UK specific fuel models, FireInSite creates an accessible system that removes barriers like the need to gather data from multiple sources and is designed to minimise the number of inputs and decisions users must make before being able to predict fire behaviour. FireInSite can be used to assess the risk of fire in a particular area, plan for fire prevention and suppression, assess the potential effects of fuel load reduction, and educate the public about fire behaviour. We envision FireInSite being useful as a land management planning tool to assess the potential impacts of proposed landscape changes on potential fire behaviour.FireInSite is built on over four years of intensive data collection of fuel moisture, fuel flammability, and energy contents measured across the UK for key fire prone vegetation types, which have been used to develop fuel models that describe the fire prone fuel types of the UK landscape for the first time. No other fire behaviour prediction system contains fuel models that have been specifically designed and tailored to UK vegetation and are ready inbuilt for use in the system. It also allows the user to select custom developed fuel moisture models, explore past fire behaviour using historical weather records back to 1970, and compare weather and fuel moisture forecasts to conditions in previous years. As FireInSite fuel models capture seasonal variability in fuel flammability and moisture for a range of temperate, humid fuels, we anticipate that FireInSite will also be transferable and of interest for wildfire management in other temperate regions like north western Europe.

New fire vulnerable communities are emerging in traditionally non-fire prone regions of the world. But these communities are often largely unaware of the developing threat and do not hold the core wildfire knowledge to galvanise collective community-based action to mitigate the risk. Furthermore, we urgently require knowledge of fuel moisture dynamics and flammability of fuels in such regions to provide accurate assessments of fire danger at the national scale. Here we characterise the moisture content and flammability of heather through engaged environmental science, demonstrating the potential of the approach to develop a public consciousness and knowledge of wildfire within communities. Fuel sampling kits were sent to 150 samplers who collected ~1000 vegetation samples across the UK (from Land’s End to John O’Groats) over a period of two days during a single period of high fire danger. The validity of the volunteer approach for collecting high quality fuel moisture data was also assessed from the analysis of a separate ~1500 samples collected by 17 samplers in a single test plot. The approach provides a simple nationally available entry point for residents traditionally unaware of both the wildfire risk and the management of their community for wildfire mitigation. Empowering samplers offers potential future opportunity to create meaningful local datasets, to build communities, and in doing so give a strong voice to residents in regional and national policy discussions.

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.

Background: Charcoal increases in reflectance with increased intensity and/or duration of heating, and this has been proposed as a potential quantitative metric for fire severity. Because fuel properties also influence reflectance, relationships between heat exposure and reflectance must currently be considered fuel-specific, limiting the application of the method. Aims: We assessed the effect of wood density on charcoal reflectance, to test whether it could be used as a proxy for overall variation in wood properties. Methods: Wood samples from 25 tree species were charred under constant conditions in a microcalorimeter, and reflectance measured by microphotometry. Key results: A positive linear relationship was found between wood density and charcoal reflectance (r = 0.53). Wood density was highly correlated with total heat release per unit volume (r = 0.94). Conclusions: Wood density accounts for a substantial component of the variation in charcoal reflectance under constant heat exposure. Implications: The relationship of density to reflectance shown here is relevant to the assessment of charcoals formed anaerobically, where endogenous heating (combustion of the sample itself) does not occur. In fire-produced chars, an additional increase in reflectance from endogenous heating should produce a stronger correlation, and density might account for a large component of the variation in reflectance under such conditions.

Peat deposits that preserve charcoal particles can provide valuable archives for reconstructing fire histories. Palaeofire studies using lake sediments often use morphometric data or morphotype classifications of charcoal particles, from which information on fuel types and taphonomic processes may be derived. We present a preliminary assessment of whether such methods may be useful for peat charcoal studies, using a single Holocene peat core from an upland area in southwest England. Diverse charcoal morphotypes were preserved in the peat, some displaying plant anatomy and others amorphous, and with a variety of structures and textures. Quantitative measures of shape also varied widely, and aspect ratios appear to reflect shifts in dominance between grasses and woody taxa as is seen in lake sediments. Some of the morphotypes found could not be meaningfully described using only the categories established for lake sediment charcoal, indicating that peatlands may preserve distinctive charcoal morphologies. Detailed research on peatland charcoal morphotypes and their origins would enable greater understanding of the fire histories that peat archives can reveal.

Quantifying sedimentary charcoal content by estimation of volume from two-dimensional images is a relatively new and little-used method, but has the potential to improve the accuracy of fire histories. It requires a power transformation of area data, and multiplication by a coefficient to account for particle shape. The latter step has been routinely overlooked, or considered unnecessary, with volume estimates made simply by power transformation of the area data. Some researchers have used the method on the basis of the power transformation only, and others have rejected it as unnecessary on the same basis. However, the assumption that the shape coefficient can be ignored is likely to introduce very large errors, resulting in overestimation of charcoal volume. The magnitude of the error is indicated by a limited amount of empirical data obtained from volumetric measurement of individual charcoal particles, and accurate use of the method would require considerable further work to extend this data set. In a sedimentary sequence where particle morphology varies with depth, the errors identified could seriously distort the fire history produced. However, as such variation is easily identified, the method can still improve charcoal quantification where morphology is stationary.

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.