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Heating soil during intense wildland fires or slash-pile burns can alter the soil irreversibly, resulting in many significant long-term biological, chemical, physical, and hydrological effects. To better understand these long-term effects, it is necessary to improve modeling capability and prediction of the more immediate, or first-order, effects t...
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... fire has the potential to enhance these processes significantly by increasing the rate of molecu- lar diffusion, which increases as temperature increases, and by creating advective air cur- rents in soils. An example of these air currents can be easily be imagined (or hypothesized) for the case of a burning slash-pile (see Figure 4). Such a fire is usually ignited near the bot- tom of the pile and very quickly intensifies to the point that the whole (external) portion of the pile is burning. ...
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... However, not only extreme heat but also smoke can affect the animal's ability to navigate, causing disorientation while trying to escape [30,41,42]. Fossorial species with shallow burrowing behavior may also die, as fire can induce advective flows in soils (e.g., shallow-nesting mining bees) [43][44][45][46]. Species that take shelter in flammable or suffocating places, such as plants in the lower layers, litter, or cavities in small trees [46]. ...
... Fuel control can also be used to reduce fire intensity, minimizing damage to the tree layer [170]. Thus, nests in trees might escape smoke exposure and convective columns, while climbing species could take shelter in the upper strata of vegetation [25,[59][60][61][62]. Lower-intensity fires are also expected to cause lower mortality to soil microbiota and animals sheltering in rock crevices, tree holes, peaty soil, and shallow burrows [43][44][45][46]. Fuel management through prescribed burns is recommended and widely used in fire-prone vegetation but should be considered with caution, as some species are still vulnerable even to low-intensity fire (e.g., leaf-litter invertebrates) [24]. ...
Recent studies have argued that changes in fire regimes in the 21st century are posing a major threat to global biodiversity. In this scenario, incorporating species' physiological, ecological, and evolutionary traits with their local fire exposure might facilitate accurate identification of species most at risk from fire. Here, we developed a framework for identifying the animal species most vulnerable to extinction from fire-induced stress in the Brazilian savanna. The proposed framework addresses vulnerability from two components: (1) exposure, which refers to the frequency, extent, and magnitude to which a system or species experiences fire, and (2) sensitivity, which reflects how much species are affected by fire. Sensitivity is based on biological, physiological, and behavioral traits that can influence animals' mortality "during" and "after" fire. We generated a Fire Vulnerability Index (FVI) that can be used to group species into four categories, ranging from extremely vulnerable (highly sensible species in highly exposed areas), to least vulnerable (low-sensitivity species in less exposed areas). We highlight the urgent need to broaden fire vulnerability assessment methods and introduce a new approach considering biological traits that contribute significantly to a species' sensitivity alongside regional/local fire exposure.
... Vegetation combustion results in both short-and longterm alterations to the physical environment (Cass et al., 1984;Masterson et al., 2008;Massman et al., 2010). Several extralimital studies assessed if observable biases could be detected following the removal of cover (e.g., Craig et al., 2009;Driscoll et al., 2012) with varying results. ...
... Furthermore, this transport mechanism influences the rate of evaporation of soil water (Ishihara et al., 1992;Zeng et al., 2011), the sublimation rate of snowpacks (Albert, 2002;Drake et al., 2019), and the volatilization rates and fate of soil contaminants, such as jet fuel (Ostendorf et al., 2000) or other soil contaminants (Forde et al., 2019). In addition, knowledge of the advective velocities induced by pressure pumping may help improve the long term measurements of ecosystem CO 2 fluxes and carbon balance (Massman & Lee, 2002), the formulation of the soil surface boundary condition for land surface (soil-plant-atmosphere) models (e.g., Grifoll et al., 2005), the fluxes of soil-generated greenhouse gases for climate studies (e.g., Rains et al., 2016;Todd-Brown et al., 2012), the transport and deposition of combustion products into the soil during prescribed fires (Massman et al., 2010), and the exchange of atmospheric gases between the atmosphere and (a) cavities (e.g., mines, shafts, quarries, wells) within the Earth's surface (e.g., Harp et al., 2019;Levintal et al., 2018;Perrier & Richon, 2010;You et al., 2010) and (b) topographical features (e.g., snow drifts, sand dunes, furrows) on the Earth's surface (e.g., Colbeck, 1989;Louge et al., 2022;Poulsen et al., 2022). The fact that pressure pumping is an important and significant mode of the exchange between the vadose zone and the atmosphere (e.g., Etiope & Martinelli, 2002;Rutten, 2015) leads directly to one of the intentions of the present study, which is to expand the research horizons in the area. ...
... To keep the estimate of v θ reasonable only ∂θ/∂z = 0.33 m −1 is considered. Note that the data for some of these numerical estimates may not have included the temperature corrections appropriate to Time Domain Reflectometer (TDR) measurements of volumetric soil moisture (e.g., Massman et al., 2010;Or & Wraith, 2000; Appendix A). We found that these corrections did not introduce any significant differences into the order of magnitude estimate of v θ below or the conclusions drawn from them. ...
Changes in atmospheric pressure continuously ventilate soils and snowpacks. This physical process, known as pressure pumping, is a major factor in the exchange fluxes of H2O, CO2, and other trace gases between the soil and atmosphere. Thus models of pressure pumping are relevant to many areas of critical importance. This study compares the three principal models used to describe pressure pumping. Beginning with the fundamental physical principles and whether the flow field is compressible or incompressible, these models are categorized as linear parabolic (one model—compressible) or nonlinear hyperbolic (two models—incompressible). Using observed soil surface pressure data, measured vertical profiles of soil permeability and standard linear analysis and numerical methods, this study shows that nonlinear models produce advective velocities that are one to two orders of magnitude greater than those associated with the linear model. Incorporating soil temperature and moisture dynamics made very little difference to the linear model, but a significant difference in the nonlinear models suggesting that advective velocities induced by pressure changes associated with soil heating and moisture dynamics may not always be small enough to ignore. All numerical results are sensitive to the frequency of the pressure forcing, which was band‐pass filtered into low, mid and high frequencies with the greatest model differences at low frequencies. Partitioning the pressure forcing and model responses helped to establish that mid‐frequency weather‐related phenomena (empirically identified as inertia gravity waves and solitons) are important drivers of gas exchange between the soil and the atmosphere.
... Clearly, quantities can vary across sites. When pilings are burned, nutrient amounts can differ due to losses via volatilization or fly ash powder [18,19]; residue type/quantity and environmental conditions can influence nutrient-loss variability. Loss of N and S can be high, with some authors reporting most N and S being lost [20,21], while others reported 50% lost [22]. ...
The objective of this study was to evaluate the long-term effects of piling secondary forest residue (after 3 decades) on soil chemical properties, growth, and nutrition of Pinus taeda and weeds at three locations. After secondary forest removal and residue piling, areas were cultivated with P. taeda (22 years), followed by eucalyptus (7 years), and returned to P. taeda. At 2 years of age, tree height and needle-nutrient levels of ongoing P. taeda from areas influenced by residue piling and areas outside the piling zone were evaluated. Biomass and nutrient levels of herbaceous and shrub weeds, NDVI indices (via a drone), and soil chemistry were also evaluated. Residue-piled areas displayed a decrease in soil pH and an increase in available soil P and K. Although herbaceous and shrub-weed biomass increased 2.5 to 10 times in residue-piling areas, this did not compromise pine growth. While residue piling had little impact on the nutritional status of pine and weeds, NDVI values indicated greater plant growth in piling areas. In general, the long-term effect of residue piling was an important factor associated with the large variation in tree growth and weed incidence after 3 decades.
... However, soil temperatures can vary by hundreds of degrees Celsius within a fire event (Busse et al., 2013), which makes it challenging to generalize how soil properties can be transformed. Estimating belowground heat and mass transport, and associated temperature regimes (Massman, 2015;Massman et al., 2010), is essential for understanding how ecosystem services and processes, including carbon storage, primary production, and biogeochemical cycling, are changing across spatially complex fire footprints (Quigley et al., 2020). Many effects of interest, such as effects on soil biota, occur as temperature-dependent rate processes (e.g., Rosenberg et al., 1971) thus characterizing temperature regimes is central to understanding fire effects on soils. ...
... Attempts to understand how fireinduced heating affects soil properties must take soil depth into account because, in addition to heating, soil properties such as mineral content, moisture, and soil organic matter also vary with depth (e.g., Achat et al., 2012;Balesdent et al., 2018;Kramer et al., 2017). Physical models of soil heating have potential to characterize coupled heat and mass transport at high depth resolutions (e.g., Campbell et al., 1995;Massman et al., 2010) but they require much more development for practical use. Alternatively, instrumenting every possible soil depth of interest to directly record temperatures in the field is also not feasible. ...
... While there are situations where fire and soil conditions allow the model to make estimates for soil temperature at depths <0.1 cm from the surface, these estimates should be interpreted with caution because they have not been fully evaluated. To improve extrapolation, we need more soil surface temperature measurements and to improve our understanding and models of the physical processes that determine surface and subsurface heat fluxes during fire (Massman et al., 2010). ...
Fire has transformative effects on soil biological, chemical, and physical properties in terrestrial ecosystems around the world. While methods for estimating fire characteristics and associated effects aboveground have progressed in recent decades, there remain major challenges in characterizing soil heating and associated effects belowground. Overcoming these challenges is crucial for understanding how fire influences soil carbon storage, biogeochemical cycling, and ecosystem recovery. In this paper, we present a novel framework for characterizing belowground heating and effects. The framework includes (1) an open‐source model to estimate fire‐driven soil heating, cooling, and the biotic effects of heating across depths and over time (Soil Heating in Fire model; SheFire) and (2) a simple field method for recording soil temperatures at multiple depths using self‐contained temperature sensor and data loggers (i.e., iButtons), installed along a wooden stake inserted into the soil (i.e., an iStake). The iStake overcomes many logistical challenges associated with obtaining temperature profiles using thermocouples. Heating measurements provide inputs to the SheFire model, and modeled soil heating can then be used to derive ecosystem response functions, such as heating effects on microorganisms and tissues. To validate SheFire estimates, we conducted a burn table experiment using iStakes to record temperatures that were in turn used to fit the SheFire model. We then compared SheFire predicted temperatures against measured temperatures at other soil depths. To benchmark iStake measurements against those recorded by thermocouples, we co‐located both types of sensors in the burn table experiment. We found that SheFire demonstrated skill in interpolating and extrapolating soil temperatures, with the largest errors occurring at the shallowest depths. We also found that iButton sensors are comparable to thermocouples for recording soil temperatures during fires. Finally, we present a case study using iStakes and SheFire to estimate in situ soil heating during a prescribed fire and demonstrate how observed heating regimes would influence seed and tree root vascular cambium survival at different soil depths. This measurement‐modeling framework provides a cutting‐edge approach for describing soil temperature regimes (i.e., soil heating) through a soil profile and predicting biological responses.
... Heat is transferred down to colder areas deeper in the soil, which can lead to an increase in soil temperature in shallow subsurface layers up to 600 • C [7]. Such extremely high temperatures can irreversibly change the biological and chemical properties of the soil, significantly reduce the water content in the soil and damage all organisms contained within [8][9][10][11] computing technology based on cluster computing and Python high level programming language with specific library support. ...
Forest fires have a negative impact on the economy in a number of regions, especially in Wildland Urban Interface (WUI) areas. An important link in the fight against fires in WUI areas is the development of information and computer systems for predicting the fire safety of infrastructural facilities of Russian Railways. In this work, a numerical study of heat transfer processes in the enclosing structure of a wooden building near the forest fire front was carried out using the technology of parallel computing. The novelty of the development is explained by the creation of its own program code, which is planned to be put into operation either in the Information System for Remote Monitoring of Forest Fires ISDM-Rosleskhoz, or in the information and computing system of JSC Russian Railways. In the Russian Federation, it is forbidden to use foreign systems in the security services of industrial facilities. The implementation of the deterministic model of heat transfer in the enclosing structure with the complexity of the algorithm O (2N2 + 2K) is presented. The program is implemented in Python 3.x using the NumPy and Concurrent libraries. Calculations were carried out on a multiprocessor cluster in the Sirius University of Science and Technology. The results of calculations and the acceleration coefficient for operating modes for 1, 2, 4, 8, 16, 32, 48 and 64 processes are presented. The developed algorithm can be applied to assess the fire safety of infrastructure facilities of Russian Railways. The main merit of the new development should be noted, which is explained by the ability to use large computational domains with a large number of computational grid nodes in space and time. The use of caching intermediate data in files made it possible to distribute a large number of computational nodes among the processors of a computing multiprocessor system. However, one should also note a drawback; namely, a decrease in the acceleration of computational operations with a large number of involved nodes of a multiprocessor computing system, which is explained by the write and read cycles in cache files.
... Fire behavior, particularly flaming and smoldering combustion that drives heat transfer into soil, is a critical knowledge gap underlying other deficiencies in our understanding of physical and chemical transformations of soil organic matter (Dickinson and Ryan, 2010). Needed are measurements of fundamental processes that can be incorporated into fire behavior models (Massman et al., 2010). Additional interdisciplinary research is needed relating soil heating temperatures to soil biotic changes to better understand the biophysical processes initiated by fire (Dickinson and Ryan, 2010;Pingree and Kobziar, 2019). ...
Until recently, the processes of litter decomposition and soil organic matter formation in forests have been studied in isolation, which has hindered the development of a comprehensive understanding of the entire process. The last decade has brought considerable progress in this scientific endeavour in response to the challenge to sequester atmospheric C in forest soils. In this paper we review key recent developments in this field and describe our current collective understanding of litter decomposition and transformation processes and pathways in forest ecosystems.
Compelling evidence that most slow-cycling SOM has been microbially transformed forces us to rethink the standard technique of measuring mass remaining in litterbags during incubation to indicate litter decomposition rates. Rather than indicating the mass of litter that remains undecomposed, these measurements reflect the net outcome of two simultaneous processes: decomposition of plant material and accumulation of microbial and faunal transformation products. Measurement of both of these pools, rather than just the total mass of material in litterbags is necessary to understand decomposition processes. For example, the apparent retarding effect of available N on mass loss during late-stage decomposition may actually result from N promoting the production of microbial biomass and necromass, thereby increasing the accumulation of transformation products during late-stage decay. We recommend referring to the mass of material in litterbags as ‘net mass remaining’ or ‘residue mass’ rather than ‘litter mass’, to acknowledge its changing composition as decomposition proceeds.
Decomposition pathways in forests with abundant detritivorous meso- and macrofauna remain poorly understood as a consequence of the inability of the litterbag technique to capture their influences (even with differing mesh sizes). Long-term studies monitoring the transformation of litter to faunal faecal material and subsequent transformations of this material are urgently needed.
Roots and mycorrhizal fungal hyphae are important sources of SOM, including stable SOM. Fine roots (orders 1 and 2) decompose particularly slowly, as do some mycorrhizal hyphae, which has been attributed to cell-wall constituents such as lignins, melanin and glycoproteins. Convergence of mass loss curves of litters that initially decompose quickly and slowly indicates that leaf litter, root litter, and fungal residues with large labile contents can generate as much SOM as recalcitrant litters.
Transformation of litter into SOM can follow many pathways, depending on characteristics of the site. Key site and soil properties influence the biotic community present and together determine the pathway that decomposition follows on that site. As such, litter transformations occur along a continuum between situations in which aboveground litter is mainly transformed into humus that accumulates on the soil surface, and situations in which partially decomposed litter is transferred to the mineral soil via bioturbation. Predicting the most likely decomposition pathway should inform decisions on how to measure and interpret the transformations that occur on a particular site.
... In contrast, heating soils to 200°C likely caused greater mortality to the microbial community (Pingree and Kobziar 2019) and thus greater input of organic molecules, but 200°C is above or near the threshold at which these labile organic molecules are destructively distilled, volatized, or pyrolyzed (González-Pérez et al. 2004;Massman et al. 2010). Thus, although there was an overall increase in EOC after 200°C heating, this C may be in a less bioavailable form. ...
Wildfires cause direct and indirect CO2 emissions due to combustion and post-fire decomposition. Approximately half of temperate forest carbon (C) is stored in soil, so post-fire soil C cycling likely impacts forest C sink strength. Soil C sink strength is partly determined by soil microbial anabolism versus catabolism, which dictates the amount of C respired versus stored in microbial biomass. Fires affect soil C availability and composition, changes that could alter carbon use efficiency (CUE) and microbial biomass production, potentially influencing C sink recovery. Wildfire intensity is forecast to increase in forests of the western United States, and understanding the impacts of fire intensity on microbial anabolism is necessary for predicting fire-climate feedbacks. Our objective was to determine the influence of soil heating intensity and pyrogenic organic matter (PyOM) on microbial anabolism. We simulated the effects of fire intensity by heating soils to 100 or 200 °C for 30 min in a muffle furnace, and we amended the soils with charred or uncharred organic matter. Higher intensity soil heating (200 °C) led to lower microbial biomass carbon (MBC) accumulation, greater C respiration, and lower CUE proxies compared to unheated soils. Conversely, lower intensity heating (100 °C) yielded MBC accumulation and estimated CUE that was similar to unheated soils. Soils amended with PyOM exhibited similar MBC accumulation compared to uncharred organic matter, but lower CO2 emissions. These results indicate that high intensity soil heating decreases soil C-sink strength over the short-term by decreasing the amount of microbial anabolism relative to catabolism.
... Below the O horizon, lethal temperatures are confined to a few top centimetres because "mineral" soil is a poor conductor of heat (Enninful and Torvi, 2008). Nonetheless, the overall habitat can be so badly disrupted by fire that it becomes uninhabitable for most survivors for a variable time span (Massman et al., 2010). Possible hindrances to prompt soil biota recovery are various, e.g.: i) food shortage as the residual biomass from a fire is mostly scorched and charred and is a poor substrate for decomposer organisms, with a cascade effect on the whole soil food web structure (Gongalsky and Persson, 2013); ii) the persistent action of toxic compounds that form during fire, such as polychlorinated dibenzo-pdioxins (PCDDs), dibenzofurans (PCDFs) and polynuclear aromatic hydrocarbons (PAHs), which are redistributed on the burned area and in its neighbourhood (Kim et al., 2003); iii) the net loss of nutrients in spite of the initial positive pulse in their availability (Andreu et al., 1996); iv) the collapse of organo-mineral aggregates and the subsequent clogging of soil pores, which lead to compaction and sealing ; v) the establishment of a new "pedoclimate", i.e., soil temperature and moisture regimes (Harden et al., 2006). ...
Fire has always been a driving factor of life on Earth. Now that mankind has definitely joined the other environmental forces in shaping the planet, lots of species are threatened by human-induced variation in fire regimes. Soil-dwelling organisms, i.e., those organisms that primarily live in soil, suffer the numerous and different consequences of fire occurrence that are, however, often overlooked compared to those on vegetation and wildlife. Most of these organisms live in the uppermost soil layer, where fire-imposed temperatures on the ground are the highest insofar as they are lethal or dangerously upset natural habitats.
This contribution is a reasoned collation of findings from a number of works conducted worldwide that aims to gain insight into the immediate and longer-term impacts of single or repeated wild or prescribed fires on one group of soil-dwelling organisms or more.
In fire-prone ecosystems, fire is a controlling factor of soil biota biodiversity and activity, but also where it is infrequent its ecological footprint can be substantial and lasting. Generally, the immediate fire impact on soil biota is strictly related to the peak temperatures reached on the ground and their duration, and on a set of soil properties and water content. Vertebrates can escape overheating death by running away, searching for wet niches or burrowing deep into soil. Invertebrates and microorganisms, which have little or no mobility, succumb more easily to fire, but make up for this intrinsic vulnerability thanks to their greater fecundity at the population level.
Fire or burn severity, which can generally be defined as loss of organic matter aboveground and belowground, is the key factor of the indirect fire effects on soil-dwelling biota; whereas controlled burns do not often imply any substantial and lasting shift from the original situation, extreme and vast wildfires can have major consequences that may be severer than direct killing. In fact lairs are devastated, nutrient pools are heavily affected, food webs are upset, soil temperature and moisture regimes change, and toxic pyrogenic compounds remain in soil. All types of organisms can recolonise the burned area from their sanctuaries, provided that land use does not change, e.g., to pastures or arable fields, and prompt enough vegetation re-sprouting and/or encroachment prevent substantial soil erosion. Each major taxon has genera or species with useful traits and behaviours to resist fire or to recover from its unwelcome environmental legacy sooner than others. If burned soil does not undergo other fires that occur too closely together for the typical fire regime of that particular area, most of its living components are generally capable of returning to pre-fire levels in times that depend on a series of factors, such as fire severity and post-fire rainfall.
... Soil is an insulator and retards the downward movement of heat into the soil (Clarke et al., 2013;Valettel et al., 1994). Although there are few relevant field studies that directly manipulate fire energy, we expect that high-energy fires will result in greater heating at the soil surface (see Massman et al., 2010) as well as longer residence times of that heating due to high fuel loads. Studies have shown the impact of higher residence times on seed germination (Dayamba et al., 2010); it may be just as likely to have a significant effect on other plant tissues such as buds. ...
Increasingly, land managers have attempted to use extreme prescribed fire as a method to address woody plant encroachment in savanna ecosystems. The effect that these fires have on herbaceous vegetation is poorly understood. We experimentally examined immediate (<24 hr) bud response of two dominant graminoids, a C3 caespitose grass, Nassella leucotricha, and a C4 stoloniferous grass, Hilaria belangeri, following fires of varying energy (J/m²) in a semiarid savanna in the Edwards Plateau ecoregion of Texas. Treatments included high‐ and low‐energy fires determined by contrasting fuel loading and a no burn (control) treatment. Belowground axillary buds were counted and their activities classified to determine immediate effects of fire energy on bud activity, dormancy, and mortality. High‐energy burns resulted in immediate mortality of N. leucotricha and H. belangeri buds (p < .05). Active buds decreased following high‐energy and low‐energy burns for both species (p < .05). In contrast, bud activity, dormancy, and mortality remained constant in the control. In the high‐energy treatment, 100% (n = 24) of N. leucotricha individuals resprouted while only 25% (n = 24) of H. belangeri individuals resprouted (p < .0001) 3 weeks following treatment application. Bud depths differed between species and may account for this divergence, with average bud depths for N. leucotricha 1.3 cm deeper than H. belangeri (p < .0001).
Synthesis and applications: Our results suggest that fire energy directly affects bud activity and mortality through soil heating for these two species. It is imperative to understand how fire energy impacts the bud banks of grasses to better predict grass response to increased use of extreme prescribed fire in land management.
