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Posted on: September 26, 2020

Indonesia forest fires surge, stoking global warming fears
How climate change is increasing forest fires around the world |  Environment| All topics from climate change to conservation | DW |  19.06.2017



  1. Climate change is driving the scale and impact of recent wildfires that have raged in California, say scientists. Their analysis finds an “unequivocal and pervasive” role for global heating in boosting the conditions for fire. California now has greater exposure to fire risks than before humans started altering the climate, the authors say.
  2. Land management issues, touted by President Donald Trump as a key cause, can’t by themselves explain the recent infernos. The worst wildfires in 18 years have raged across California since August. They have been responsible for more than 30 deaths and driven thousands of people from their homes.
  3. The cause of the fires have become a political football, with California Governor Gavin Newsom blaming climate change for the conflagrations. President Trump, on the other hand, has dismissed this argument, instead pointing to land management practices as the key driver.
  4. Now, a review of scientific research into the reasons for these fires suggests rising temperatures are playing a major role. Earlier this year, the same research team published a review of the origins of Australia’s dramatic fires that raged in the 2019-2020 season. That study showed that climate change was behind an increase in the frequency and severity of fire weather – defined as periods of time with a higher risk of fire due to a combination of high temperatures, low humidity, low rainfall and high winds.
  5. The new review covers more than 100 studies published since 2013, and shows that extreme fires occur when natural variability in the climate is superimposed on increasingly warm and dry background conditions resulting from global warming.
  6. In terms of the trends we’re seeing, in terms of the extent of wildfires, and which have increased eight to ten-fold in the past four decades, that trend is driven by climate change,” said Dr Matthew Jones from the University of East Anglia in Norwich, UK, who led the review.
  7. Climate change ultimately means that those forests, whatever state they’re in, are becoming warmer and drier more frequently. And that’s what’s really driving the kind of scale and impact of the fires that we’re seeing today.
  8. In the 40 years from 1979 to 2019, fire weather conditions have increased by a total of eight days on average across the world. However, in California the number of autumn days with extreme wildfire conditions has doubled in that period.
  9. The authors of the review conclude that “climate change is bringing hotter, drier weather to the western US and the region is fundamentally more exposed to fire risks than it was before humans began to alter the global climate”.
  10. The researchers acknowledge that fire management practices in the US have also contributed to the build-up of fuel. Normally, fire authorities carry out controlled burnings in some areas to reduce the amount of fuel available when a wildfire strikes – but these have also suffered as a result of rising temperatures. When you do prescribed burns, you can only do it when the conditions aren’t too hot and dry, because you need to be able to control the fire,” said Prof Richard Betts from the UK Met Office in Exeter, who was part of the review team.
  11. But once you’ve passed the point where you’ve got hot, dry conditions for much of the year, you’ve lost your opportunity to do lots of prescribed burnings. So that makes matters worse and makes the land management challenge even greater.
  12. Another factor in California has been the encroachment of human settlements into forested areas. This has put many more homes at risk of these blazes. Between 1940 and 2010, there was around a 100-fold increase in the number of houses built in dangerous fire zones in the western US. It’s like building on floodplains as well, you know, people are putting themselves in harm’s way, based on past statistics, which are no longer true,” said Prof Betts. The past is no longer a guide to the future, for flooding and for fire and lots of other ways in which climate change is played out.
  13. The researchers say that the conditions for wildfire are likely to continue to grow into the future, and according to Dr Jones, the resulting fires will likely get worse. It’s pointing towards increases in fire weather that become increasingly intense, widespread and dramatic in the future,” he said.
  14. And the more that we can do to limit the degree to which temperatures rise, is fundamental to how frequently we see dangerous fire weather in the future.
Staff | Geography | University of Exeter
Matthew Jones - Research Database, The University of East Anglia
University of Exeter - Massey University

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THE CONFIRMATION BIAS ISSUE IN POST HOC EVENT ATTRIBUTION Neither the Australian bushfires of 2019-2020 nor the California forest fires of 2020 were predicted by climate science, not even in probabilistic terms, and not even within large time or area spans and so these attributions derive only from the climate science position that global warming would exacerbate forest fire conditions where they occur. The nature and statistical weaknesses of these studies are found for example in the works of Leroy Westerling, Adam Pellegrini, and others described in a related post:


FROM THE LINKED POST: The assumed causal connection, that AGW climate change increases wildfire frequency, is derived from the various works of Leroy Westerling, Professor of Climatology, the University of California at Merced from 2006 to 2011 and some later works by other authors. The references are listed in the RELEVANT BIBLIOGRAPHY below. These research papers find that: “In certain specific regions (eg California), but not in others, wildfires have increased since the mid-1980s while at the same time AGW climate change was causing increased warmth, desiccation, and wind speed that could enhance wildfire conditions. These relationships are taken as evidence that AGW climate change did in fact cause an increase in wildfires.

The weaknesses in this argument are many as listed below.
(1) DATA SELECTION BIAS: Evidence of the effect of global warming on wildfire frequency or severity is not established globally; but rather for specific regions where rising devastation by wildfires is known to have occurred are selected for the evaluation. This procedure contains the data selection bias (2) A STATISTICAL WEAKNESS: That variable y is rising while at the same time variable x was also rising establishes neither correlation nor causation even when x and y could have a causation relationship in terms of theory. Yet this is the sole argument presented for the attribution of wildfire severity and/or frequency to AGW other than the rationalization that AGW is expected to cause increased warmth, desiccation, an wind speed (3) INCONVENIENT VARIABLES REMOVED FROM CONSIDERATION: Other factors that are also concomitant are not considered such as changes in California logging regulations that were made around the time when the Spotted Owl was declared to be an endangered species threatened by logging. Logging in California’s wilderness was banned. At the same time, prescribed forest management fires were banned or severely curtailed. These changes also occurred in the late 1980s and early 1990s but they have been removed from consideration to make way for a single minded focus on a pre-determined causation relationship between AGW climate change and wildfires. Even more egregious, if indeed the wildfire devastation in California is related to the failure of forest management by way of inadequate prescribed fires, the Pellegrini 2018 implication that prescribed fires are bad because of lost carbon sequestration is the exact opposite of the forest management change needed in California. (4) Computer modeling of the impact of AGW climate change on wildfires will of course show that relationship because it has been programmed into it. These results serve only to show that the model works the way it is supposed to work and can’t be presented as empirical evidence that the observed increase in California wildfire devastation since the 1990s must have been caused by AGW. Computer models of expected theoretical relationships are an expression of the theory itself and it cannot also serve as the data to test theory. The works listed in the AGW Wildfire bibliography below, particularly those by Professor Westerling are biased in this way. (5) Results of modeling studies and climate theories of the impact of AGW climate change on wildfires have created a sense that the truth of the causation relationship is a given and that the observational evidence plays the minor role of providing the kind of data that are expected in going through the required formality for a causation that has been fully accepted by the researchers apriori.

In other words, that AGW climate change increases wildfire devastation is the null hypothesis. However, it is necessary for empirical test of theory to be carried out in exactly the opposite way where the null hypothesis is the absence of the causation relationship and sufficient and convincing unbiased evidence must be presented before the null hypothesis can be rejected.

Thus, it was only after they had occurred that climate science found ways to attribute the event post hoc to fossil fueled anthropogenic global warming. There was no forecast of any kind not even in probabilistic language. This kind of attribution generally derives from confirmation bias where data analysis is carried out not with a null hypothesis that that the proposed hypothesis is false but with a null hypothesis that it is true. It is then defended with the burden of proof fallacy. A detailed presentation of confirmation bias and burden of proof fallacy in climate science is presented in a related post on this site.



The importance of the separating natural internal climate variability from the effects of anthropogenic global warming has been recognized in climate science in a recent series of papers published on this topic. See for example, Insights from Earth system model initial-condition large ensembles and future prospects, Clara Deser,et al: Nature Climate Change, 2020 or Quantifying the role of internal variability in the temperature we expect to observe in the coming decades Nicola Maher et al, 2020. The essential finding of these papers is that anthropogenic global warming {AGW} is a theory about long term trends in global mean temperature such that the reference climate in the climate change issue is long term changes in global climate such that ” Internal variability in the climate system confounds assessment of human-induced climate change and imposes irreducible limits on the accuracy of climate change projections, especially at regional and decadal scales“. The implication is that localized climate events – that is, a climate phenomenon that is constrained by a small geographical extent less than significant latitudinal sections of the globe and by a brief time scale less than 30 years is likely to be driven by natural internal climate variability to an extent that it does not have an interpretation in terms of AGW.

In the Internal Climate Variability context, we note in the chart below that Australia represents only 5% of the world’s land and 1.5% of the global surface. As for California, the state consists of 0.28% of the world’s land surface and 0.08% of global surface area. The corresponding figures for the western states that suffered through the dry lightning event and the fires attributed to that event represent 0.56% of the world’s land surface and 0.17% of global surface area. A further consideration in terms of Internal Climate Variability is that the entire event occurred within a time span of one calendar month, specifically the month of September in the year 2020. This time span, being less than 30 years, implies that the climate variability that created these weather events cannot be understood in terms of AGW and must be interpreted in terms of weather events that are creations of internal climate variability and separate from AGW.

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The arguments presented above as weaknesses of the climate science argument that the California fires were caused by AGW and that therefore they could have been avoided with timely climate action contains the climate science rebuttal that these fires are unusual and not part of the trend and pattern seen in historical data and so to question the AGW causation hypothesis of climate science, the critic must provide the unusual causation for this unusual event. In the absence of a convincing alternative unusual causation, the climate science theory that AGW caused these fires and that these fires underscore the urgency of climate action stands as scientific fact. This implied argument in climate science is an expression of the shifting the burden of proof fallacy. It cannot be claimed to be science.


Indonesia forest fires surge, stoking global warming fears
Staff | Geography | University of Exeter
Matthew Jones - Research Database, The University of East Anglia


  1. Fried, Jeremy S., Margaret S. Torn, and Evan Mills. “The impact of climate change on wildfire severity: a regional forecast for northern California.” Climatic change 64.1-2 (2004): 169-191.  We estimated the impact of climatic change on wildland fire and suppression effectiveness in northern California by linking general circulation model (GCM) output to local weather and fire records and projecting fire outcomes with an initial-attack suppression model. The warmer and windier conditions corresponding to a 2 × CO2 climate scenario produced fires that burned more intensely and spread faster in most locations. Despite enhancement of fire suppression efforts, the number of escaped fires (those exceeding initial containment limits) increased 51% in the south San Francisco Bay area, 125% in the Sierra Nevada, and did not change on the north coast. Changes in area burned by contained fires were 41%, 41% and –8%, respectively. When interpolated to most of northern California’s wildlands, these results translate to an average annual increase of 114 escapes (a doubling of the current frequency) and an additional 5,000 hectares (a 50% increase) burned by contained fires. On average, the fire return intervals in grass and brush vegetation types were cut in half. The estimates reported represent a minimum expected change, or best-case forecast. In addition to the increased suppression costs and economic damages, changes in fire severity of this magnitude would have widespread impacts on vegetation distribution, forest condition, and carbon storage, and greatly increase the risk to property, natural resources and human life. [FULL TEXT PDF]
  2. Westerling, Anthony L., et al. “Warming and earlier spring increase western US forest wildfire activity.” science 313.5789 (2006): 940-943.  Western United States forest wildfire activity is widely thought to have increased in recent decades, yet neither the extent of recent changes nor the degree to which climate may be driving regional changes in wildfire has been systematically documented. Much of the public and scientific discussion of changes in western United States wildfire has focused instead on the effects of 19th- and 20th-century land-use history. We compiled a comprehensive database of large wildfires in western United States forests since 1970 and compared it with hydroclimatic and land-surface data. Here, we show that large wildfire activity increased suddenly and markedly in the mid-1980s, with higher large-wildfire frequency, longer wildfire duration, and longer wildfire seasons. The greatest increases occurred in mid-elevation, Northern Rockies forests, where land-use histories have relatively little effect on fire risks and are strongly associated with increased spring and summer temperatures and an earlier spring snowmelt. In the Conclusions section of the paper the authors write “Robust statistical associations between wildfire and hydroclimate in western forests indicate that increased wildfire activity over recent decades reflects sub-regional responses to changes in climate. Historical wildfire observations exhibit an abrupt transition in the mid-1980s from a regime of infrequent large wildfires of short (average of 1 week) duration to one with much more frequent and longer burning (5 weeks) fires. This transition was marked by a shift toward unusually warm springs, longer summer dry seasons, drier vegetation (which provoked more and longer burning large wildfires), and longer fire seasons. Reduced winter precipitation and an early spring snowmelt played a role in this shift. Increases in wildfire were particularly strong in mid-elevation forests. [LINK TO FULL TEXT DOWNLOAD]
  3. Scholze, Marko, et al. “A climate-change risk analysis for world ecosystems.” Proceedings of the National Academy of Sciences 103.35 (2006): 13116-13120.  We quantify the risks of climate-induced changes in key ecosystem processes during the 21st century by forcing a dynamic global vegetation model (DGVM) with multiple scenarios from 16 climate models and mapping the proportions of model runs showing forest/nonforest shifts or exceedance of natural variability in wildfire frequency and freshwater supply. Our analysis does not assign probabilities to scenarios or weights to models. Instead, we consider distribution of outcomes within three sets of model runs grouped by the amount of global warming they simulate: <2°C (including simulations in which atmospheric composition is held constant, i.e., in which the only climate change is due to greenhouse gases already emitted), 2–3°C, and >3°C. High risk of forest loss is shown for Eurasia, eastern China, Canada, Central America, and Amazonia, with forest extensions into the Arctic and semiarid savannas; more frequent wildfire in Amazonia, the far north, and many semiarid regions; more runoff north of 50°N and in tropical Africa and northwestern South America; and less runoff in West Africa, Central America, southern Europe, and the eastern U.S. Substantially larger areas are affected for global warming >3°C than for <2°C; some features appear only at higher warming levels. A land carbon sink of ≈1 Pg of C per yr is simulated for the late 20th century, but for >3°C this sink converts to a carbon source during the 21st century (implying a positive climate feedback) in 44% of cases. The risks continue increasing over the following 200 years, even with atmospheric composition held constant. [FULL TEXT PDF DOWNLOAD] .
  4. Westerling, A. L., and B. P. Bryant. “Climate change and wildfire in California.” Climatic Change 87.1 (2008): 231-249.  Wildfire risks for California under four climatic change scenarios were statistically modeled as functions of climate, hydrology, and topography. Wildfire risks for the GFDL and PCM global climate models (note: GFDL and PCM are different resolutions of GCM climate models) and the A2 and B1 emissions scenarios were compared for 2005–2034, 2035–2064, and 2070–2099 against a modeled 1961–1990 reference period in California and neighboring states. Outcomes for the GFDL model runs, which exhibit higher temperatures than the PCM model runs, diverged sharply for different kinds of fire regimes, with increased temperatures promoting greater large fire frequency in wetter, forested areas, via the effects of warmer temperatures on fuel flammability. At the same time, reduced moisture availability due to lower precipitation and higher temperatures led to reduced fire risks in some locations where fuel flammability may be less important than the availability of fine fuels. Property damages due to wildfires were also modeled using the 2000 U.S. Census to describe the location and density of residential structures. In this analysis the largest changes in property damages under the climate change scenarios occurred in wildland/urban interfaces proximate to major metropolitan areas in coastal southern California, the Bay Area, and in the Sierra foothills northeast of Sacramento. [FULL TEXT PDF]
  5. Cannon, Susan H., and Jerry DeGraff. “The increasing wildfire and post-fire debris-flow threat in western USA, and implications for consequences of climate change.” Landslides–disaster risk reduction. Springer, Berlin, Heidelberg, 2009. 177-190.  In southern California and the intermountain west of the USA, debris flows generated from recently-burned basins pose significant hazards. Increases in the frequency and size of wildfires throughout the western USA can be attributed to increases in the number of fire ignitions, fire suppression practices, and climatic influences. Increased urbanization throughout the western USA, combined with the increased wildfire magnitude and frequency, carries with it the increased threat of subsequent debris-flow occurrence. Differences between rainfall thresholds and empirical debris-flow susceptibility models for southern California and the intermountain west indicate a strong influence of climatic and geologic settings on post-fire debris-flow potential. The linkages between wildfires, debris-flow occurrence, and global warming suggests that the experiences in the western United States are highly likely to be duplicated in many other parts of the world, and necessitate hazard assessment tools that are specific to local climates and physiographies. [FULL TEXT PDF]
  6. Abatzoglou, John T., and Crystal A. Kolden. “Climate change in western US deserts: potential for increased wildfire and invasive annual grasses.” Rangeland Ecology & Management 64.5 (2011): 471-478.  The influence of climate change on future invasions depends on both climate suitability that defines a potential species range and the mechanisms that facilitate invasions and contractions. A suite of downscaled climate projections for the mid–21st century was used to examine changes in physically based mechanisms, including critical physiological temperature thresholds, the timing and availability of moisture, and the potential for large wildfires. Results suggest widespread changes in 1) the length of the freeze-free season that may favor cold-intolerant annual grasses, 2) changes in the frequency of wet winters that may alter the potential for establishment of invasive annual grasses, and 3) an earlier onset of fire season and a lengthening of the window during which conditions are conducive to fire ignition and growth furthering the fire-invasive feedback loop. We propose that a coupled approach combining bioclimatic envelope modeling with mechanistic modeling targeted to a given species can help land managers identify locations and species that pose the highest level of overall risk of conversion associated with the multiple stressors of climate change. [FULL TEXT PDF]
  7. Girardin, Martin P., et al. “Vegetation limits the impact of a warm climate on boreal wildfires.” New Phytologist 199.4 (2013): 1001-1011.  Strategic introduction of less flammable broadleaf vegetation into landscapes was suggested as a management strategy for decreasing the risk of boreal wildfires projected under climatic change. However, the realization and strength of this offsetting effect in an actual environment remain to be demonstrated. Here we combined paleoecological data, global climate models and wildfire modelling to assess regional fire frequency (RegFF, i.e. the number of fires through time) in boreal forests as it relates to tree species composition and climate over millennial time‐scales. Lacustrine charcoals from northern landscapes of eastern boreal Canada indicate that RegFF regional fire frequency during the mid‐Holocene (6000–3000 yr ago) was significantly higher than pre‐industrial RegFF (ad c. 1750). In southern landscapes, RegFF was not significantly higher than the pre‐industrial RegFF in spite of the declining drought severity. The modelling experiment indicates that the high fire risk brought about by a warmer and drier climate in the south during the mid‐Holocene was offset by a higher broadleaf component. Our data highlight an important function for broadleaf vegetation in determining boreal RegFF in a warmer climate. We estimate that its feedback may be large enough to offset the projected climate change impacts on drought conditions. [FULL TEXT]  
  8. Westerling, Anthony LeRoy. “Increasing western US forest wildfire activity: sensitivity to changes in the timing of spring.” Philosophical Transactions of the Royal Society B: Biological Sciences 371.1696 (2016): 20150178.  Prior work shows western US forest wildfire activity increased abruptly in the mid-1980s. Large forest wildfires and areas burned in them have continued to increase over recent decades, with most of the increase in lightning-ignited fires. Northern US Rockies forests dominated early increases in wildfire activity, and still contributed 50% of the increase in large fires over the last decade. However, the percentage growth in wildfire activity in Pacific northwestern and southwestern US forests has rapidly increased over the last two decades. Wildfire numbers and burned area are also increasing in non-forest vegetation types. Wildfire activity appears strongly associated with warming and earlier spring snowmelt. Analysis of the drivers of forest wildfire sensitivity to changes in the timing of spring demonstrates that forests at elevations where the historical mean snow-free season ranged between two and four months, with relatively high cumulative warm-season actual evapotranspiration, have been most affected. Increases in large wildfires associated with earlier spring snowmelt scale exponentially with changes in moisture deficit, and moisture deficit changes can explain most of the spatial variability in forest wildfire regime response to the timing of spring. [FULL TEXT]


  1. Shakesby, Richard A., et al. “Impacts of prescribed fire on soil loss and soil quality: an assessment based on an experimentally-burned catchment in central Portugal.” Catena 128 (2015): 278-293.  Prescribed (controlled) fire has recently been adopted as an important wildfire-fighting strategy in the Mediterranean. Relatively little research, however, has assessed its impacts on soil erosion and soil quality. This paper investigates hillslope-scale losses of soil, organic matter and selected nutrients before and after a ‘worst-case scenario’ prescribed fire in a steep, shrub-vegetated catchment with thin stony soil in central Portugal. Comparison is made with soil erosion measured: (1) on a nearby hillslope burned by wildfire and monitored at the hillslope scale; and (2) on long-unburned terrain at small-plot, hillslope- and catchment-scales. Hillslope-scale pre- and post-fire soil erosion was recorded over periods of 6 weeks to 5 months for (1) 9.5 months pre-fire and 27 months post-fire in the prescribed fire catchment, and (2) c. 3 years post-fire at the wildfire site. Organic matter content, pH, total N, K2O, P2O5, Ca2 + and Mg2 + were measured in the eroded sediment and in pre- and post-prescribed fire surface soil. Results indicate that: (1) both the prescribed fire and the wildfire caused expected marked increases in erosion compared with unburned terrain; and (2) the hillslope-scale post-prescribed fire soil losses (up to 2.41 t ha− 1 yr− 1) exceeded many reported plot-scale post-prescribed fire and post-wildfire erosion rates in the Mediterranean. As a comparison, post-fire erosion for both fire types was less than that caused by some other forms of common soil disturbance (e.g. types of tillage) and even that on undisturbed shrubland in low rainfall areas of the region. Total estimated post-prescribed fire particulate losses of organic matter and nutrients represent only 0.2–2.9% of the content in the upper 2 cm of soil, suggesting only a modest fire effect on soil quality, although this may reflect in part a lack of extreme rainfall events following the fire. The longer-term implications for soil conservation of repeated prescribed fire in the Mediterranean are explored and future research priorities identified.
  2. Pellegrini, Adam FA, et al. “Fire alters ecosystem carbon and nutrients but not plant nutrient stoichiometry or composition in tropical savanna.” Ecology 96.5 (2015): 1275-1285.  Fire and nutrients interact to influence the global distribution and dynamics of the savanna biome, (Biome=large naturally occurring community of flora and fauna such as a forest) but the results of these interactions are both complex and poorly known. A critical but unresolved question is whether short‐term losses of carbon and nutrients caused by fire can trigger long‐term and potentially compensatory responses in the nutrient stoichiometry of plants, or in the abundance of dinitrogen‐fixing trees. There is disagreement in the literature about the potential role of fire on savanna nutrients, and, in turn, on plant stoichiometry and composition. A major limitation has been the lack of fire manipulations over time scales sufficiently long for these interactions to emerge. We use a 58‐year, replicated, large‐scale, fire manipulation experiment in Kruger National Park (South Africa) in savanna to quantify the effect of fire on (1) distributions of carbon, nitrogen, and phosphorus at the ecosystem scale; (2) carbon : nitrogen : phosphorus stoichiometry of above‐ and below-ground tissues of plant species; and (3) abundance of plant functional groups including nitrogen fixers. Our results show dramatic effects of fire on the relative distribution of nutrients in soils, but that individual plant stoichiometry and plant community composition remained unexpectedly resilient. Moreover, measures of nutrients and carbon stable isotopes allowed us to discount the role of tree cover change in favor of the turnover of herbaceous biomass as the primary mechanism that mediates a transition from low to high soil carbon and nutrients in the absence of fire. We conclude that, in contrast to extra‐tropical grasslands or closed‐canopy forests, vegetation in the savanna biome may be uniquely adapted to nutrient losses caused by recurring fire.
  3. Fultz, Lisa M., et al. “Forest wildfire and grassland prescribed fire effects on soil biogeochemical processes and microbial communities: Two case studies in the semi-arid Southwest.” Applied soil ecology 99 (2016): 118-128.  Fire is a natural disturbance that shapes many ecosystems. In semi-arid regions, where high temperatures and low soil moisture limit nutrient cycling and plant growth, fire is critical to supply nutrients and drive vegetation composition. We examined soil chemical and biological properties to assess the short-term impacts of wildfire and prescribed fires on soil functioning in semi-arid regions of Texas. Better understanding of soil organic matter transformation and nutrient cycling processes will aid land managers in predicting ecosystem recovery response post-fire. Soil samples were collected following both prescribed grassland fires in June of 2009 in Lubbock, TX and the April 2012 Livermore Ranch Complex Fire located in the Davis Mountains, TX. Prescribed fire samples (0–2.5 cm) were collected within 6 hours prior to burning and again at 0.5, 24, 48, and 168 hours post-fire to experimentally examine short-term influences of fire and fire frequency (1× vs. 2×) on soil carbon dynamics, inorganic nitrogen, and microbial community composition. Wildfire samples (0–5 cm) were collected two and six months following the wildfire. We evaluated the effects of three burn severity levels and sampled under three tree species (Juniperus deppeanaPinus cembroides, and Quercus grisea). Within 0.5 h of the prescribed fire, CO2 flux, NH4+-N concentration and total microbial biomass (as estimated by total fatty acid methyl esters) increased. A shift in the microbial community from a predominance of fungi to Gram positive bacteria occurred immediately following the fire. Chemical shifts were short lived (decreased within 24 h), but the biotic shift to a dominance of Gram negative bacteria and actinomycetes was measured in samples collected after 168 h. Soil pH and NH4+-N concentration increased at two and six months following the wildfire. In contrast, soil organic matter content decreased at two months post wildfire which, in combination of abiotic conditions such as low moisture content (<3.3%), resulted in reduced soil microbial biomass and enzyme activity. Increased soil moisture six months post fire created more favorable conditions for nitrification resulting in increased NO3-N concentration (0.8 to 36.1 mg NO3-N kg−1 soil), particularly following high severity fire. Prescribed fire did not have lasting impacts on soil nutrients, but both prescribed and wildfire resulted in increased NH4+-N, shifts in microbial community structure and decreased in microbial biomass. While the increase in nitrogen maybe be beneficial to the plant growth and revegetation, the loss of microbial biomass may have far reaching implications to the overall sustainability of the soils in these systems.
  4. Brown, Julian, Alan York, and Fiona Christie. “Fire effects on pollination in a sexually deceptive orchid.” International Journal of Wildland Fire 25.8 (2016): 888-895. Research into the effectiveness of prescribed fire in managing pollination has only recently begun. The effects of fire on pollination have not been explored in sexually deceptive systems. Further, the potential for multiple effects operating at different spatial scales has not been explored in any pollination system despite multi-scale effects on pollination observed in agricultural landscapes. We observed the frequency of pollinator visitation to flowers of sexually deceptive Caladenia tentaculata and related it to the post-fire age class of the vegetation at local and landscape scales. We also related the number of the pollinator’s putative larval hosts (scarab beetles) captured at these sites to age class. At the local scale (i.e. the sample location), visitation was highest in recently burnt sites. At the landscape scale, positive associations were observed between (1) putative pollinator hosts and vegetation burnt 36–50 years ago, and (2) pollinator visitation and vegetation burnt ≥50 years ago. Local- and landscape-scale effects on visitation were synergistic, such that visitation was greatest when fire age was heterogeneous within pollinator foraging range.
  5. Alcañiz, M., et al. “Long-term dynamics of soil chemical properties after a prescribed fire in a Mediterranean forest (Montgrí Massif, Catalonia, Spain).” Science of the total environment 572 (2016): 1329-1335.  This study examines the effects of a prescribed fire on soil chemical properties in the Montgrí Massif (Girona, Spain). The prescribed forest fire was conducted in 2006 to reduce understory vegetation and so prevent potential severe wildfires. Soil was sampled at a depth of 0–5 cm at 42 sampling points on four separate occasions: prior to the event, immediately after, one year after and nine years after. The parameters studied were pH, electrical conductivity (EC), total carbon (C), total nitrogen (N), available phosphorus (P), potassium (K+), calcium (Ca2 +) and magnesium (Mg2 +). All parameters (except pH) increased significantly immediately after the fire. One year after burning, some chemical parameters – namely, EC, available P and K+ – had returned to their initial, or even lower, values; while others – pH and total C – continued to rise. Total N, Ca2 + and Mg2 + levels had fallen one year after the fire, but levels were still higher than those prior to the event. Nine years after the fire, pH, total C, total N and available P are significantly lower than pre-fire values and nutrients concentrations are now higher than at the outset but without statistical significance. The soil system, therefore, is still far from being recovered nine years later.
  6. Armas-Herrera, Cecilia M., et al. “Immediate effects of prescribed burning in the Central Pyrenees on the amount and stability of topsoil organic matter.” Catena 147 (2016): 238-244.  Prescribed burning is the deliberate application of fire under selected conditions to accomplish predetermined management objectives. It is generally accepted that controlled use of fire has neutral or even positive effects on soils due to its lower temperature, intensity and severity compared to wildfires. However, very few studies have examined the effects of prescribed burning of shrub vegetation in humid mountain areas on soil properties. The objective of this work was to determine the immediate effects of prescribed burning on the quality and biochemical stability of soil organic matter (SOM) in areas encroached by shrubs in the Central Pyrenees (NE Spain). Soil samples were sampled in triplicate immediately before and after burning from the Ah horizon at 0–1, 1–2 and 2–3 cm depths. We quantified the variations as a direct result of burning in (1) the SOM content, (2) the content and mineralization rates of labile and recalcitrant C pools as inferred from incubation assays (141 days), and (3) the soil biological activity related to C cycling (microbial biomass C and β-D-glucosidase activity). Nearly all the soil properties studied were significantly affected by fire, varying in terms of extent of the effect and the soil depth affected. The total soil organic C (SOC), C/N ratio, β-D-glucosidase activity, C-CO2 efflux and estimated content of labile SOC decreased significantly up to 3 cm depth. The total N and microbial biomass C were significantly affected only in the upper cm of the soil (0–1 cm). These results describe a short-term stronger impact of the prescribed fire on topsoil properties than usually reported. However, comparing these findings to other studies should be performed with caution because of the different environments considered in each case, as well as the differing soil thicknesses found in the literature, typically between 5 and 15 cm, which can lead to a dilution effect associated with the actual impacts of fire on soil properties. In this sense, the choice of a suitable soil thickness or sampling just after burning can be relevant factors in the detection of the immediate effects of fire. Short- and medium-term monitoring of the soils is needed to assess the suitability of this practice for pasture maintenance and for adapting the frequency of prescribed fires in order to minimize its impact on soil.
  7. Sun, Hui, et al. “Bacterial community structure and function shift across a northern boreal forest fire chronosequence.” Scientific reports 6 (2016): 32411.  Soil microbial responses to fire are likely to change over the course of forest recovery. Investigations on long-term changes in bacterial dynamics following fire are rare. We characterized the soil bacterial communities across three different times post fire in a 2 to 152-year fire chronosequence by Illumina MiSeq sequencing, coupled with a functional gene array (GeoChip). The results showed that the bacterial diversity did not differ between the recently and older burned areas, suggesting a concomitant recovery in the bacterial diversity after fire. The differences in bacterial communities over time were mainly driven by the rare operational taxonomic units (OTUs < 0.1%). Proteobacteria (39%), Acidobacteria (34%) and Actinobacteria (17%) were the most abundant phyla across all sites. Genes involved in C and N cycling pathways were present in all sites showing high redundancy in the gene profiles. However, hierarchical cluster analysis using gene signal intensity revealed that the sites with different fire histories formed separate clusters, suggesting potential differences in maintaining essential biogeochemical soil processes. Soil temperature, pH and water contents were the most important factors in shaping the bacterial community structures and function. This study provides functional insight on the impact of fire disturbance on soil bacterial community.
  8. Badía, David, et al. “Burn effects on soil properties associated to heat transfer under contrasting moisture content.” Science of the Total Environment 601 (2017): 1119-1128. The aim of this work is to investigate the topsoil thickness affected by burning under contrasting soil moisture content (field capacity versus air-dried conditions). A mollic horizon of an Aleppo pine forest was sampled and burned in the laboratory, recording the temperature continuously at the topsoil surface and at soil depths of 1, 2, and 3 cm. Changes in soil properties were measured at 0–1, 1–2, 2–3, and 3–4 cm. Both the maximum temperature and the charring intensities were significantly lower in wet soils than in air-dried soils up to 3 cm in depth. Moreover, soil heating was slower and cooling faster in wet soils as compared to dry soils. Therefore, the heat capacity increase of the soil moistened at field capacity plays a more important role than the thermal conductivity increase on heat transfer on burned soils. Burning did not significantly modify the pH, the carbonate content and the chroma, for either wet or dry soil. Fire caused an immediate and significant decrease in water repellency in the air-dried soil, even at 3 cm depth, whereas the wet soil remained hydrophilic throughout its thickness, without being affected by burning. Burning depleted 50% of the soil organic C (OC) content in the air-dried soil and 25% in the wet soil at the upper centimeter, which was blackened. Burning significantly decreased the total N (TN) content only in the dry soil (to one-third of the original value) through the first centimeter of soil depth. Soluble ions, measured by electrical conductivity (EC), increased after burning, although only significantly in the first centimeter of air-dried soils. Below 2 cm, burning had no significant effects on the brightness, OC, TN, or EC, for either wet or dry soil.
  9. Dove, Nicholas C., and Stephen C. Hart. “Fire reduces fungal species richness and in situ mycorrhizal colonization: a meta-analysis.” Fire Ecology 13.2 (2017): 37-65.  Soil fungal communities perform many functions that help plants meet their nutritional demands. However, overall trends for fungal response to fire, which can be especially critical in a post-fire context, have been difficult to elucidate. We used meta-analytical techniques to investigate fungal response to fire across studies, ecosystems, and fire types. Change in fungal species richness and mycorrhizal colonization were used as the effect size metrics in random effects models. When different types of methods for assessing fungal species richness and mycorrhizal colonization were considered together, there was an average reduction of 28 % in fungal species richness post fire, but no significant response in mycorrhizal colonization. In contrast, there was a 41 % reduction in fungal species richness post fire when assessed by sporocarp surveys, but fungal species richness was not significantly affected when assessed by molecular methods. Measured in situ, fire reduced mycorrhizal colonization by 21 %, yet no significant response occurred when assessed by ex situ bioassays. These findings suggest that the putative magnitude of fire effects on soil fungal communities may be dependent on the approach and assessment method used. Furthermore, biome, but not fire type (i.e., wildfire versus prescribed fire) was a significant moderator of our categorical models, suggesting that biome might be a more useful predictor of fungal species richness response to fire than fire type. Reductions in fungal species richness and in situ mycorrhizal colonization post fire declined logarithmically and approached zero (i.e., no effect) at 22 and 11 years, respectively. We concluded that fire reduces fungal species richness and in situ mycorrhizal colonization, but if conditions allow communities to recover (e.g., without subsequent disturbance, favorable growing conditions), soil fungi are resilient on decadal time scales; the resiliency of soil fungi likely contributes to the overall rapid ecosystem recovery following fire.
  10. Girona-García, Antonio, et al. “Effects of prescribed burning on soil organic C, aggregate stability and water repellency in a subalpine shrubland: Variations among sieve fractions and depths.” Catena 166 (2018): 68-77.  Soil organic matter, aggregation and water repellency are relevant interrelated soil properties that can be affected by fire. The aim of this work was to analyse the effects of shrub prescribed burning for pasture reclamation on the soil aggregate stability, organic carbon and water repellency of different soil depths and aggregate sizes in a subalpine environment. Soil samples were collected from an area treated by an autumnal low-intensity prescribed fire in the Central Pyrenees (NE-Spain) at 0–1, 1–2, 2–3 and 3–5 cm depths just before and ~1 h, 6 months and 12 months after burning. Samples were separated as whole soil (<10 mm) and 6 sieve fractions, <0.25, 0.25–0.5, 0.5–1, 1–2, 2–4 and 4–10 mm. We analysed soil organic Carbon (SOC)aggregate stability (AS) and soil water repellency (SWR). In the unburned samples, SOC and SWR were higher in the <0.25 to 2 mm sieve fractions than the 2 to 10 mm sieve fractions. Fire severely and significantly decreased the SOC content in the whole soil and the <0.25 mm fraction at 0–1 cm depth and in the 0.25–0.5 mm fraction at 0–2 cm depth. SWR was reduced by burning mainly at 0–1 cm depth for the whole soil and the <0.25 to 2 mm sieve fractions. Nevertheless, the AS of the 0.25–0.5 mm aggregates increased after fire, while the rest of the sieve fractions remained virtually unaffected. One year after the prescribed burning, SOC slightly increased and SWR recovered in the fire-affected fractions, while the AS for all aggregate sizes and depths showed a considerable decrease. The results suggest that the direct effects of burning are still present one year after burning, and the post-fire situation may pose an increased risk of soil loss. Furthermore, our results indicate that fine soil fractions are more likely to be affected by fire than coarser soil fractions and highly influence the whole soil behaviour.
  11. Butler, Orpheus M., et al. “The phosphorus‐rich signature of fire in the soil–plant system: a global meta‐analysis.” Ecology letters 21.3 (2018): 335-344.  The biogeochemical and stoichiometric signature of vegetation fire may influence post‐fire ecosystem characteristics and the evolution of plant ‘fire traits’. Phosphorus (P), a potentially limiting nutrient in many fire‐prone environments, might be particularly important in this context; however, the effects of fire on Phosphorus   cycling often vary widely. We conducted a global‐scale meta‐analysis using data from 174 soil studies and 39 litter studies, and found that fire led to significantly higher concentrations of soil mineral Phosphorus as well as significantly lower soil and litter carbon:Phosphorus  and nitrogen:Phosphorus ratios. These results demonstrate that fire has a Phosphorus ‐rich signature in the soil–plant system that varies with vegetation type. Further, they suggest that burning can ease Phosphorus limitation and decouple the biogeochemical cycling of Phosphorus , carbon and nitrogen. These effects resemble a transient reversion to an earlier stage of ecosystem development, and likely underpin at least some of fire’s impacts on ecosystems and organisms.
  12. Alcañiz, M., et al. “Effects of prescribed fires on soil properties: a review.” Science of The Total Environment 613 (2018): 944-957.  Soils constitute one of the most valuable resources on earth, especially because soil is renewable on human time scales. During the 20th century, a period marked by a widespread rural exodus and land abandonment, fire suppression policies were adopted facilitating the accumulation of fuel in forested areas, exacerbating the effects of wildfires, leading to severe degradation of soils. Prescribed fires had emerged as an option for protecting forests and their soils from wildfires through the reduction of fuels levels. However such fires can serve other objectives, including stimulating the regeneration of a particular plant species, maintaining biological diversity or as a tool for recovering grasslands in encroached lands. This paper reviews studies examining the short- and long- term impacts of prescribed fires on the physical, chemical and biological soil properties; in so doing, it provides a summary of the benefits and drawbacks of this technique, to help determine if prescribed fires can be useful for managing the landscape. From the study conducted, we can affirm that prescribed fires affect soil properties but differ greatly depending on soil initial characteristics, vegetation or type of fire. Also, it is possible to see that soil’s physical and biological properties are more strongly affected by prescribed fires than are its chemical properties. Finally, we conclude that prescribed fires clearly constitute a disturbance on the environment (positive, neutral or negative depending on the soil property studied), but most of the studies reviewed report a good recovery and their effects could be less pronounced than those of wildfires because of the limited soil heating and lower fire intensity and severity.
  13. Koltz, Amanda M., et al. “Global change and the importance of fire for the ecology and evolution of insects.” Current opinion in insect science 29 (2018): 110-116.  Climate change is drastically altering global fire regimes, which may affect the structure and function of insect communities. Insect responses to fire are strongly tied to fire history, plant responses, and changes in species interactions. Many insects already possess adaptive traits to survive fire or benefit from post-fire resources, which may result in community composition shifting toward habitat and dietary generalists as well as species with high dispersal abilities. However, predicting community-level resilience of insects is inherently challenging due to the high degree of spatio-temporal and historical heterogeneity of fires, diversity of insect life histories, and potential interactions with other global change drivers. Future work should incorporate experimental approaches that specifically consider spatiotemporal variability and regional fire history in order to integrate eco-evolutionary processes in understanding insect responses to fire.
  14. Pellegrini, Adam FA, et al. “Fire frequency drives decadal changes in soil carbon and nitrogen and ecosystem productivity.” Nature 553.7687 (2018): 194. Fire frequency is changing globally and is projected to affect the global carbon cycle and climate. However, uncertainty about how ecosystems respond to decadal changes in fire frequency makes it difficult to predict the effects of altered fire regimes on the carbon cycle; for instance, we do not fully understand the long-term effects of fire on soil carbon and nutrient storage, or whether fire-driven nutrient losses limit plant productivity. Here we analyse data from 48 sites in savanna grasslands, broadleaf forests and needleleaf forests spanning up to 65 years, during which time the frequency of fires was altered at each site. We find that frequently burned plots experienced a decline in surface soil carbon and nitrogen that was non-saturating through time, having 36 per cent (±13 per cent) less carbon and 38 per cent (±16 per cent) less nitrogen after 64 years than plots that were protected from fire. Fire-driven carbon and nitrogen losses were substantial in savanna grasslands and broadleaf forests, but not in temperate and boreal needleleaf forests. We also observe comparable soil carbon and nitrogen losses in an independent field dataset and in dynamic model simulations of global vegetation. The model study predicts that the long-term losses of soil nitrogen that result from more frequent burning may in turn decrease the carbon that is sequestered by net primary productivity by about 20 per cent of the total carbon that is emitted from burning biomass over the same period. Furthermore, we estimate that the effects of changes in fire frequency on ecosystem carbon storage may be 30 per cent too low if they do not include multidecadal changes in soil carbon, especially in drier savanna grasslands. Future changes in fire frequency may shift ecosystem carbon storage by changing soil carbon pools and nitrogen limitations on plant growth, altering the carbon sink capacity of frequently burning savanna grasslands and broadleaf forests. CONCLUSION: In conclusion, our results reveal the sensitivity of surface soils to fire and the substantial effects that changes in soil pools have on long-term ecosystem C exchange. The large empirical and conservative modelbased
    estimates of soil C changes suggest that present estimates of fire-driven C losses7, which primarily consider losses from plant biomass pools, may substantially underestimate the effects of long-term trends in fire frequencies in savanna grasslands and broadleaf forests in particular. Our findings suggest that future alterations in fire regimes in savanna grasslands and broadleaf forests may shift ecosystem C storage by changing soil C levels and changing the N limitation of plant growth, altering the carbon-sink capacity of these fire-prone ecosystems.
  15. Pressler, Yamina, John C. Moore, and M. Francesca Cotrufo. “Belowground community responses to fire: meta‐analysis reveals contrasting responses of soil microorganisms and mesofauna.” Oikos 128.3 (2019): 309-327.  Global fire regimes are shifting due to climate and land use changes. Understanding the responses of below-ground communities to fire is key to predicting changes in the ecosystem processes they regulate. We conducted a comprehensive meta‐analysis of 1634 observations from 131 empirical studies to investigate the effect of fire on soil microorganisms and mesofauna. Fire had a strong negative effect on soil biota biomass, abundance, richness, evenness, and diversity. Fire reduced microorganism biomass and abundance by up to 96%. Bacteria were more resistant to fire than fungi. Fire reduced nematode abundance by 88% but had no significant effect on soil arthropods. Fire reduced richness, evenness and diversity of soil microorganisms and mesofauna by up to 99%. We found little evidence of temporal trends towards recovery within 10 years post‐disturbance suggesting little resilience of the soil community to fire. Interactions between biome, fire type, and depth explained few of these negative trends. Future research at the intersection of fire ecology and soil biology should aim to integrate soil community structure with the ecosystem processes they mediate under changing global fire regimes.

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