Anthropogenic Ignition Research Articles

Combustion characteristics of water-oil emulsion droplets with special additives

Relevance. Fuel oil application in power plants is characterized by increased values of underburning and anthropogenic emissions. One way to reduce anthropogenic emissions is the use of oil-water emulsions. Also, additional specialized additives are used to reduce anthropogenic emissions and improve fuel combustion characteristics. Aim. To determine the optimal fuel oil additive to reduce anthropogenic emissions and ignition delay times. Methods. The following additives: ION-M, Rosneft R503V3, Rosneft R502V1 (relative mass concentration 0.5%) were added to the water-oil fuel. The physicochemical properties of fuel oil M-100, as well as the elemental composition of CHNSO, were determined. The rheological characteristics of water-oil fuel compositions were established. Using high-speed photography, the droplet ignition delay times were determined. Using the gas analyzer, it was possible to prevent anthropogenic emissions. Results and conclusions. The results of the study showed that the additive based on a special combination of positively and negatively charged ions (ION M) reduces ignition delay times by 20–60%, when the gas temperature varies in the range from 700 to 900 °C. The addition of the additive based on fatty vegetable acids (P502B3) reduced the ignition delay times by 7–10%, when the temperature changed in the range from 700 to 900 °C relative to water-oil fuel. It was found that when using the P502B1 additive in water-oil fuel, it was possible to reduce the ignition delay times by 15–50%. It was determined that in the presence of combustion catalysts, water binds with heavy hydrocarbons and thus the release of volatile substances occurs faster, i. e. the supplied heat is not wasted on heating water into droplets, but evenly affects the entire volume of fuel. The results of the study of anthropogenic emissions showed that the use of additives when burning water-oil fuel reduces the concentrations of CO, CO2, NO, SO2 by 8, 6, 10 and 13%, respectively, compared to fuel oil.

Improvement of human-induced wildfire occurrence modeling from a spatial variation of anthropogenic ignition factor in the CLM5

Wildfire is an essential form of natural disturbance for the Earth system, and it is challenging for the current numerical models to accurately retrieve the spatiotemporal distributions of wildfire occurrence. One of the deficiencies could result from the parameterization of anthropogenic impact on wildfire occurrences. This study develops an approach to advance human-induced wildfire modeling by calibrating the parameter of human ignition count (HIC) in the fire module of the Community Land Model version 5. This study modifies the source code to allow a grid-scale variation of HIC. Sensitivity experiments with different grid-uniform HIC values are conducted to quantify the model biases with satellite-based observation data as the reference. The theoretically optimal HIC for each grid is obtained by linear rescaling the HIC based on the model biases in the sensitivity tests. The model evaluation takes place in southwest China where there is complex terrain and land use/land cover features. The involvement of grid-scale HIC significantly reduces the model bias in the climatology of wildfire occurrence. The pattern correlation coefficient increases from 0.57 to 0.78, and the root mean square error (RMSE) decreases from 0.58 to 0.18. The correlation coefficient of the annual sums of wildfire occurrences increases from 0.69 to 0.77, and the RMSE decreases from 560.8 to 146.4. A global-scale test verifies that such an approach can be extended to multiple regions with a reasonable scale of population density and economy.

Too much, too late: Fires and Reactive Wildfire Management in Northern Botswana’s Forests and Woodland Savannas

Across much of southern Africa’s savanna wildernesses, wildfires burn unchecked. This is particularly true in the woodland savannas of northern Botswana, where wildfires originate outside of management activities, and are left to burn uncontrolled, because of limited resources and remoteness. There is concern that severe annual wildfires are resulting in the ‘savannisation’ of large tracts of wooded land across forest reserves, protected areas and surrounding wilderness areas. Because the current fire regime is unknown, management interventions are hard to introduce. We examine the recent 20-year (2001–2020) fire history in northern Botswana using MODIS satellitederived fire products to reveal fire frequency and seasonality. Six wildfire hotspots are identified for exploration of fire frequency and possible origins. Annual fire frequencies are far higher than would be expected without anthropogenic ignition. Extensive areas in some hotspots are shown to have burned between 14 and 16 out of the 20-year period. Fires peak in September, several weeks before the onset of the rainy season and associated lightning strikes, and when the fuel load is at its maximum and conditions at their driest. Adaptive fire management practices, such as those being followed in neighbouring South Africa and elsewhere should inform Botswana’s fire management policies.

Coupling interactive fire with atmospheric composition and climate in the UK Earth System Model

Abstract. Fire constitutes a key process in the Earth system (ES), being driven by climate as well as affecting the climate by changing atmospheric composition and impacting the terrestrial carbon cycle. However, studies on the effects of fires on atmospheric composition, radiative forcing and climate have been limited to date, as the current generation of ES models (ESMs) does not include fully atmosphere–composition–vegetation coupled fires feedbacks. The aim of this work is to develop and evaluate a fully coupled fire–composition–climate ES model. For this, the INteractive Fires and Emissions algoRithm for Natural envirOnments (INFERNO) fire model is coupled to the atmosphere-only configuration of the UK's Earth System Model (UKESM1). This fire–atmosphere interaction through atmospheric chemistry and aerosols allows for fire emissions to influence radiation, clouds and generally weather, which can consequently influence the meteorological drivers of fire. Additionally, INFERNO is updated based on recent developments in the literature to improve the representation of human and/or economic factors in the anthropogenic ignition and suppression of fire. This work presents an assessment of the effects of interactive fire coupling on atmospheric composition and climate compared to the standard UKESM1 configuration that uses prescribed fire emissions. Results show a similar performance when using the fire–atmosphere coupling (the “online” version of the model) when compared to the offline UKESM1 that uses prescribed fire. The model can reproduce observed present-day global fire emissions of carbon monoxide (CO) and aerosols, despite underestimating the global average burnt area. However, at a regional scale, there is an overestimation of fire emissions over Africa due to the misrepresentation of the underlying vegetation types and an underestimation over equatorial Asia due to a lack of representation of peat fires. Despite this, comparing model results with observations of CO column mixing ratio and aerosol optical depth (AOD) show that the fire–atmosphere coupled configuration has a similar performance when compared to UKESM1. In fact, including the interactive biomass burning emissions improves the interannual CO atmospheric column variability and consequently its seasonality over the main biomass burning regions – Africa and South America. Similarly, for aerosols, the AOD results broadly agree with the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Aerosol Robotic Network (AERONET) observations.

Influences of climate fluctuations on northeastern North America’s burned areas largely outweigh those of European settlement since AD 1850

There is a pressing need for a better understanding of changing forest fire regimes worldwide, especially to separate the relative effects of potential drivers that control burned areas. Here we present a meta-analysis of the impacts of climate fluctuation and Euro-Canadian settlement on burned areas from 1850 to 1990 in a large zone (>100 000 km2) in northern temperate and boreal forests of eastern Canada. Using Cox regression models, we tested for potential statistical relationships between historical burned areas in 12 large landscapes (reconstructed with dendrochronological data) with climate reconstructions, changes in the Euro-Canadian population, and active suppression (all reconstructed at the decadal scale). Our results revealed a dominant impact of climate fluctuations on forest burned areas, with the driest decades showing fire hazards between 5 to 15 times higher than the average decades. Comparatively, the Euro-Canadian settlement had a much weaker effect, having increased burned areas significantly only during less fire-prone climate conditions. During periods of fire-prone climate, burned areas were maximum independent of fluctuations in Euro-Canadian populations. Moreover, the development of active fire suppression did not appear to reduce burned areas. These results suggest that a potential increase in climate moisture deficit and drought may trigger unprecedented burned areas and extreme fire events no matter the effects of anthropogenic ignition or suppression.

Wildfire history of the boreal forest of south-western Yakutia (Siberia) over the last two millennia documented by a lake-sediment charcoal record

Abstract. Wildfires, as a key disturbance in forest ecosystems, are shaping the world's boreal landscapes. Changes in fire regimes are closely linked to a wide array of environmental factors, such as vegetation composition, climate change, and human activity. Arctic and boreal regions and, in particular, Siberian boreal forests are experiencing rising air and ground temperatures with the subsequent degradation of permafrost soils leading to shifts in tree cover and species composition. Compared to the boreal zones of North America or Europe, little is known about how such environmental changes might influence long-term fire regimes in Russia. The larch-dominated eastern Siberian deciduous boreal forests differ markedly from the composition of other boreal forests, yet data about past fire regimes remain sparse. Here, we present a high-resolution macroscopic charcoal record from lacustrine sediments of Lake Khamra (south-west Yakutia, Siberia) spanning the last ca. 2200 years, including information about charcoal particle sizes and morphotypes. Our results reveal a phase of increased charcoal accumulation between 600 and 900 CE, indicative of relatively high amounts of burnt biomass and high fire frequencies. This is followed by an almost 900-year-long period of low charcoal accumulation without significant peaks likely corresponding to cooler climate conditions. After 1750 CE fire frequencies and the relative amount of biomass burnt start to increase again, coinciding with a warming climate and increased anthropogenic land development after Russian colonization. In the 20th century, total charcoal accumulation decreases again to very low levels despite higher fire frequency, potentially reflecting a change in fire management strategies and/or a shift of the fire regime towards more frequent but smaller fires. A similar pattern for different charcoal morphotypes and comparison to a pollen and non-pollen palynomorph (NPP) record from the same sediment core indicate that broad-scale changes in vegetation composition were probably not a major driver of recorded fire regime changes. Instead, the fire regime of the last two millennia at Lake Khamra seems to be controlled mainly by a combination of short-term climate variability and anthropogenic fire ignition and suppression.

Spatial accessibility of anthropogenic fire ignition sources of grassland fire in northeast China

Fires can have an enormous impact on grassland systems, affecting their ecology as well as their economic productivity. As most grassland fires are caused by human activities, understanding the relationship between anthropogenic activities that cause fires and where fire ignitions occur is essential in determining where grassland fires pose the greatest risk. Any potential model to predict the spatial distribution and intensity of anthropogenic activities that cause grassland fire ignition needs to take into account the size of residential areas, roads and area of land that is cultivated. The spatial accessibility of human activities that cause grassland fire ignitions was predicted by the model to represent the ability of human driving factors that influence the occurrence of grassland fire ignitions. An index of spatial accessibility of anthropogenic fire ignition sources was overlapped with artificially generated neural networks. Within the index, five categories were created to adequately assess the level of ignition risk to grassland fires: extremely low, low, medium, high and extremely high. The percentages of actual fires in each ignition risk zone from low to high were 2.94%, 18.82%, 20.01%, 22.35% and 35.88%. This methodology provides new insight into how human factors affect the occurrence of wildland fire.

Assessing Spatio-Temporal Variability of Wildfires and their Impact on Sub-Saharan Ecosystems and Air Quality Using Multisource Remotely Sensed Data and Trend Analysis

Globally, wildfires are considered the most commonly occurring disasters, resulting from natural and anthropogenic ignition sources. Wildfires consist of burning standing biomass at erratic degrees of intensity, severity, and frequency. Consequently, wildfires generate large amounts of smoke and other toxic pollutants that have devastating impacts on ambient air quality and human health. There is, therefore, a need for a comprehensive study that characterizes land–atmosphere interactions with regard to wildfires, critical for understanding the interrelated and multidimensional impacts of wildfires. Current studies have a limited scope and a narrow focus, usually only focusing on one aspect of wildfire impacts, such as air quality without simultaneously considering the impacts on land surface changes and vice versa. In this study, we use several multisource data to determine the spatial distribution, frequency, disturbance characteristics of and variability and distribution of pollutants emitted by wildfires. The specific objectives were to (1) study the sources of wildfires and the period they are prevalent in sub-Saharan Africa over a 9 year period, i.e., 2007–2016, (2) estimate the seasonal disturbance of wildfires on various vegetation types, (3) determine the spatial distribution of black carbon (BC), carbon monoxide (CO) and smoke, and (4) determine the vertical height distribution of smoke. The results show largest burned areas in December–January–February (DJF), June–July–August (JJA) and September–October–November (SON) seasons, and reciprocal high emissions of BC, CO, and smoke, as observed by Modern-Era Retrospective Analysis for Research and Applications version 2 (MERRA-2) and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO). In addition, the results reveal an increasing trend in the magnitude of BC, and CO concentration driven by meteorological conditions such as low precipitation, low relative humidity, and low latent heat flux. Overall, this study demonstrates the value of multisource remotely sensed data in characterising long-term wildfire patterns and associated emissions. The results in this study are critical for informing better regional fire management and air quality control strategies to preserve endangered species and habitats, promote sustainable land management, and reduce greenhouse gases (GHG) emissions.

Developing and testing models of the drivers of anthropogenic and lightning-caused wildfire ignitions in south-eastern Australia

Considerable investments are made in managing fire risk to human assets, including a growing use of fire behaviour simulation tools to allocate expenditure. Understanding fire risk requires estimation of the likelihood of ignition, spread of the fire and impact on assets. The ability to estimate and predict risk requires both the development of ignition likelihood models and the evaluation of these models in novel environments. We developed models for natural and anthropogenic ignitions in the south-eastern Australian state of Victoria incorporating variables relating to fire weather, terrain and the built environment. Fire weather conditions had a consistently positive effect on the likelihood of ignition, although they contributed much more to lightning (57%) and power transmission (55%) ignitions than the 7 other modelled causes (8–32%). The built environment played an important role in driving anthropogenic ignitions. Housing density was the most important variable in most models and proximity to roads had a consistently positive effect. In contrast, the best model for lightning ignitions included a positive relationship with primary productivity, as represented by annual rainfall. These patterns are broadly consistent with previous ignition modelling studies. The models developed for Victoria were tested in the neighbouring fire prone states of South Australia and Tasmania. The anthropogenic ignition model performed well in South Australia (AUC = 0.969) and Tasmania (AUC = 0.848), whereas the natural ignition model only performed well in South Australia (AUC = 0.972; Tasmania AUC = 0.612). Model performance may have been impaired by much lower lightning ignition rates in South Australia and Tasmania than in Victoria. This study shows that the spatial likelihood of ignition can be reliably predicted based on readily available meteorological and biophysical data. Furthermore, the strong performance of anthropogenic and natural ignition models in novel environments suggests there are some universal drivers of ignition likelihood across south-eastern Australia.

Improvement of fire danger rating and vegetation fire behaviour prediction on protected areas

Protected areas (PAs) are established to conserve biological diversity, to maintain nature complexes and objects in their natural condition. Strict nature reserves prevail in Russia by their total area. The whole nature complex is forever extracted from economic use in nature reserves. Here it is prohibited to pursue any activity which might disturb or damage the nature complexes. Even under the existing strict protection from anthropogenic ignition sources, vegetation fires do occur on their territory. Besides, lightnings − these natural ignition sources − are impossible to exclude. Since large destructive fires are impermissible in nature reserves, the later especially need vegetation fire behavior prediction for fire management. Fire behavior prediction includes fire spread rate, development (from surface fire into crown or ground one) and fire effects. All this is necessary for taking optimal decisions on how to control each occurring fire and how to suppress it. The Sukachev Institute of Forest SB RAS has developed a method to improve forest fire danger rating and a technique of vegetation fire behavior prediction using vegetation fuel maps (VF maps).

Smokey Bear and the pyropolitics of United States forest governance

Wildfire prevention advertisements featuring Smokey Bear represent the longest-standing and most successful government advertising and branding campaign in U.S. history. As the public face of U.S. fire control policy, Smokey Bear uses mass media to influence the attitudes and behavior of U.S. citizenry in order to accomplish particular outcomes related to wildfire prevention and suppression, forest protection, and resource management. Smokey Bear can therefore be viewed as a governmental instrument that simultaneously targets the behavior of the U.S. public and the biophysical materiality of combustible forests. Examining the evolution of Smokey Bear and related wildfire prevention media, we explore connections between state management of people, territory, and flammable landscapes. Borrowing from Nigel Clark (2011), we use the term pyropolitics to describe the resulting more-than-human assemblage of citizenship, fire suppression and forest ecology. Importantly, this pyropolitical assemblage has substantive and recursive impacts on state practice. Through aggressive wildfire prevention and suppression that include and extend beyond Smokey Bear, the U.S. state has transformed fuel loads, species compositions, and ecosystem dynamics across North America. One result is a heightened propensity toward catastrophic wildfire, requiring additional and sustained state intervention to maintain an imposed and unstable equilibrium. Thus even as the economic, social and cultural realities of U.S. civic life have changed over the course of the 20th and early 21st centuries – and even as knowledge of the ecological benefits of fire to ecosystem health has developed over time – the message of Smokey Bear has remained remarkably consistent, communicating an official imperative to prevent anthropogenic ignition.

Quantifying the human influence on fire ignition across the western USA.

Humans have a profound effect on fire regimes by increasing the frequency of ignitions. Although ignition is an integral component of understanding and predicting fire, to date fire models have not been able to isolate the ignition location, leading to inconsistent use of anthropogenic ignition proxies. Here, we identified fire ignitions from the Moderate Resolution Imaging Spectrometer (MODIS) Burned Area Product (2000-2012) to create the first remotely sensed, consistently derived, and regionally comprehensive fire ignition data set for the western United States. We quantified the spatial relationships between several anthropogenic land-use/disturbance features and ignition for ecoregions within the study area and used hierarchical partitioning to test how the anthropogenic predictors of fire ignition vary among ecoregions. The degree to which anthropogenic features predicted ignition varied considerably by ecoregion, with the strongest relationships found in the Marine West Coast Forest and North American Desert ecoregions. Similarly, the contribution of individual anthropogenic predictors varied greatly among ecoregions. Railroad corridors and agricultural presence tended to be the most important predictors of anthropogenic ignition, while population density and roads were generally poor predictors. Although human population has often been used as a proxy for ignitions at global scales, it is less important at regional scales when more specific land uses (e.g., agriculture) can be identified. The variability of ignition predictors among ecoregions suggests that human activities have heterogeneous impacts in altering fire regimes within different vegetation types and geographies.

People, El Niño southern oscillation and fire in Australia: fire regimes and climate controls in hummock grasslands.

While evidence mounts that indigenous burning has a significant role in shaping pyrodiversity, the processes explaining its variation across local and external biophysical systems remain limited. This is especially the case with studies of climate-fire interactions, which only recognize an effect of humans on the fire regime when they act independently of climate. In this paper, we test the hypothesis that an anthropogenic fire regime (fire incidence, size and extent) does not covary with climate. In the lightning regime, positive El Niño southern oscillation (ENSO) values increase lightning fire incidence, whereas La Niña (and associated increases in prior rainfall) increase fire size. ENSO has the opposite effect in the Martu regime, decreasing ignitions in El Niño conditions without affecting fire size. Anthropogenic ignition rates covary positively with high antecedent rainfall, whereas fire size varies only with high temperatures and unpredictable winds, which may reduce control over fire spread. However, total area burned is similarly predicted by antecedent rainfall in both regimes, but is driven by increases in fire size in the lightning regime, and fire number in the anthropogenic regime. We conclude that anthropogenic regimes covary with climatic variation, but detecting the human-climate-fire interaction requires multiple measures of both fire regime and climate.This article is part of the themed issue 'The interaction of fire and mankind'.

Modeling the Landscape Drivers of Fire Recurrence in Sardinia (Italy)

Although recurrent fire events with very short return periods have the most dangerous effects on landscape degradation, only a few papers have explored the landscape ecological factors that drive the probability of fire recurrence. In this paper we apply a habitat suitability model for analyzing the spatial relationship between a selected set of landscape factors (mainly land use types) and fire recurrence in Sardinia (Italy) in the years 2005-2010. Our results point out that fire occurrence in already burned areas is lower than expected in natural and semi-natural land cover types, like forest and shrublands. To the contrary, like in all regions where human activity is the main source of fire ignitions, the probability of fire recurrence is higher at low altitudes and close to roads and to urban and agricultural land cover types, thus showing marked preference for those landscape factors denoting higher anthropogenic ignition risk.

Woodland history in the upper Harz Mountains revealed by kiln site, soil sediment and peat charcoal analyses

Charcoal is abundant in various soils and soil sediments and is basically the result of either natural wildfires or of anthropogenic ignition. Compositions of charcoal assemblages are the result of several taphonomical processes. Beside this, little is known about the influence of charcoal from anthropogenic origin, like charcoal production sites (kiln sites) on soil charcoal assemblages. To elucidate how human charcoal production as well as erosion of the relicts of kiln sites influenced charcoal assemblages in soils and mires, a multi-proxy approach was applied at two transects on the Renneckenberg, a steep slope in the low mountain range Harz, Germany. On this slope, three types of archives (soil/soil sediments, kiln sites and peatland) were investigated each with different methods on a local scale (soil charcoal analyses, kiln site charcoal analyses, peat macro-/micro-charcoal and pollen analysis). The kiln site charcoal records are taxonomically richer in wood taxa than those from colluvial assemblages, especially regarding deciduous tree species. Fagus sylvatica and Acer sp. are rare or absent in the colluvial charcoal assemblages which are dominated by Picea charcoal. At the bottom of the slope, the soil charcoal concentration is very high and indicates strong erosion of charcoal from the upper part of the slope. Significant taxonomical discrepancies between the colluvial and the kiln site charcoal assemblages may be related to different fire intensity throughout the Holocene and to human woodland usage. Additionally, changes in the run-off intensity and fire frequency are detected in the peat macro-charcoal record reflecting vegetation change in the early Holocene. The micro-charcoal content coincides with the main mining phases in the late Holocene and the 9.2 k climatic anomaly.

Predictive modelling of burn probability and burn severity in a desert spring ecosystem

Little is known about the fire ecology of desert springs, despite their importance for biodiversity and for provision of ecosystem services. Desert spring ecosystems are characterised by high and continuous fuel loads compared with surrounding uplands, suggesting that fire may play a significant ecological role. For the Ash Meadows spring complex in the south-western USA, we used ecological-niche factor analysis and a Bayesian model averaging regression technique to characterise the environmental conditions associated with spatially explicit burn probability and burn severity over a 24-year period. Burn probability and burn severity were both more strongly associated with fuel availability than with proximity to anthropogenic ignition sources; however, areas with more homogeneous vegetation cover were positively associated with high-severity burns but were negatively associated with burn probability. Burn probability was greater near areas of high anthropogenic influence, whereas areas further from anthropogenic alteration were more likely to experience high-severity fire. Riparian forest and emergent wetland vegetation were most likely to burn although they were among the rarest vegetation types. Human activities may strongly influence fire regimes in desert spring wetlands through groundwater pumping and introductions of exotic plants that alter fuelbed heterogeneity and shift the balance among woody and herbaceous vegetation.

An MIS 5a/b to MIS 3 bog sequence from Henderson Bay, northern New Zealand

A discontinuous Late Pleistocene pollen record from an eroding coastal cliff section at Henderson Bay on the east coast of Northland, New Zealand, reveals changes in vegetation composition and associated palaeosol development under both stadial and interstadial climatic conditions ascribed to the last interglacial–glacial cycle, probably MIS (Marine Isotope Stage) 5a/b to early MIS 3. An increase in charcoal towards the top of the sequence is believed to be due to natural rather than anthropogenic ignition sources which resulted in the development of scrub rather than forest vegetation. The sequence is capped by gravel previously inferred to have been emplaced by tsunami event(s) some time after early MIS 3. A lack of Agathis pollen in our sequence despite unequivocal evidence for the parent trees (gum) strengthens a call for caution when inferring climatic conditions from the abundance of Agathis pollen in New Zealand pollen records.

Human versus climatic influences on late-Holocene fire regimes in southwestern Nicaragua

Fire regimes in the lowland Neotropics are affected both by anthropogenic land use practices and natural climate variability. In Central America it is widely recognized that fire has been used as an agricultural tool for thousands of years, but the role of anthropogenic ignition as a determinant of past biomass burning frequency and magnitude has been debated. Little is known about the effects of short-term climate variability on fire regimes in this region of the world because of both the low temporal resolution of the available charcoal records and the obfuscating effects of anthropogenic burning throughout the late Holocene. Here we reconstruct 1400 years of fire history and environmental change on Ometepe Island, Lake Nicaragua, and perform statistical wavelet analysis on multiple proxy records to identify natural cycles of environmental variability possibly related to climate forcing. Our results indicate that extensive indigenous burning and landscape modification largely mask any climate signal in the paleo-fire record from AD 580 to 1400, with the exception of the period AD 775—1000 where high wavelet power exists at scales of 2—24 years. This time period coincides with a severe, two-century long regional drought that has been identified at other locations in Central America. High wavelet power at climate-relevant scales after ~AD 1400 in the Ometepe fire record suggests that periodic drought possibly caused by the El Niño Southern Oscillation and/or high-frequency solar cycles may have played a significant role in influencing the post-contact fire regime — a role that is largely concealed in the pre-European strata because of the overriding effects of anthropogenic burning.

Historic Fire Regime of an Upland Oak Forest in South-Central North America

Prescribed burning is used in upland oak forests of south-central North America to improve wildlife habitat, reduce fire hazard, restore ecosystem integrity, and maintain biological diversity. However, little is known about the frequency, seasonality, and ignition source of historic fires that shaped these forests. In general, it is believed that fire frequency in upland oak forests of south-central North America was influenced by climate and humans, and decreased since Euro-American settlement; yet there is a dearth of scientific evidence to support this conclusion. The objective of this study was to link the fire history of an upland oak forest in east-central Oklahoma with factors controlling the fire regime. We removed cross-sections from 69 dead post oak (Quercus stellata Wangenh.) trees in a 1 km2 area of old-growth post oak and blackjack oak (Q. marilandica Münchh.) forest, and determined the tree-ring record and exact dates of fire scars from 1750 to 2005, using standard dendrochronological methods. An increase in fire from the eighteenth to early twenty-first centuries appeared to be associated with changes in human occupation, and there was little evidence linking the frequency, severity, or extent of fires to climate factors including drought, lightning, and late-spring frosts. These findings appeared to contradict the belief that fire decreased from the eighteenth to early twenty-first centuries and appeared to emphasize the importance of anthropogenic ignition to the local fire regime.

The Role of Fire in the Establishment and Spread of Nonnative Plants in Arizona Ponderosa Pine Forests: A Review

Arizona ponderosa pine (Pinus ponderosa) forests have undergone dramatic changes since the late nineteenth century. Management practices such as fire exclusion have resulted in increased surface and tree crown fuel loads. Consequently, large and severe wildfires have been occurring more frequently in the ponderosa pine forests of Arizona. Furthermore, prescribed fire, both with and without tree thinning, is being applied to ponderosa pine forests to mitigate the risk of wildfire. Increasingly, normative plant species are spreading into burned forests regardless of fire type. In this article, we review recent literature on normative establishment in the post-fire plant community. Current research suggests an increasing risk of nonnative establishment is associated with increasing fire severity. Furthermore, wildfires seem more likely to promote nonnative species establishment than prescribed fires. The results are inconsistent, however, with some high-severity fires having few normatives and some prescribed fires strongly promoting invasion. Further research is needed to understand the mechanisms of invasion. In the 23 studies we examined, a total of 43 nonnative plant species were reported in post-fire communities. Of these, only three species were listed as noxious in Arizona: field bindweed (Convolvulus arvensis), Dalmatian toadflax (Linaria dalmatica), and Scotch cottonthistle (Onopordum acantium). Cheatgrass (Bromus tectorum), Kentucky bluegrass (Poa pratensis), and common mullein (Verbascum thapsus) were the most commonly observed species in burned areas, regardless of natural or anthropogenic ignition. Generally, nonnative presence increased after fire, but abundance of these species remained low (< 10% cover). Changes in nonnative populations reported in Arizona are consistent with those seen in ponderosa pine forests of other regions, with normatives tending to increase with increasing fire severity.