Anthropogenic Ignitions Research Articles

Characterizing a Poacher-Driven Fire Regime in Low-Nutrient Coastal Grasslands of Pondoland, South Africa

Understanding fire regimes in the coastal region of the Pondoland center of plant endemism, (Eastern Cape, South Africa) is of critical importance, especially in areas where anthropogenic ignitions influence the fire regime. We characterized the fire regime (2007 to 2016) of Mkambati Nature Reserve (9200 ha) in terms of fire season, seasonality of fire-prone weather conditions, fire return interval (FRI), and influence of poaching-related ignitions. Fires were concentrated in winter when monthly fire danger weather index was highest. The mean FRI at Mkambati was <3 years, but varied according to vegetation type, and whether censoring (for open-ended FRIs) was applied. Mean estimated FRIs were 2.6 yr to 3.1 yr in the majority of grassland types, 5.6 yr to 8.0 yr in forests, and 9.0 yr to 44.4 yr in Themeda triandra Forssk. grasslands. Poachers, with the intention of attracting ungulates, are an important source of ignitions at Mkambati. Accordingly, FRIs were shorter (1.99 yr to 2.08 yr) in areas within 3 km of likely poacher entry points than in areas farther away (2.56 yr to 2.88 yr). Although all fires recorded at Mkambati during the study period were of anthropogenic origin, mean FRI still fell within the natural range reported for interior grasslands in South Africa.

Cheatgrass (Bromus tectorum) distribution in the intermountain Western United States and its relationship to fire frequency, seasonality, and ignitions

Cheatgrass (Bromus tectorum) is an invasive grass pervasive across the Intermountain Western US and linked to major increases in fire frequency. Despite widespread ecological impacts associated with cheatgrass, we lack a spatially extensive model of cheatgrass invasion in the Intermountain West. Here, we leverage satellite phenology predictors and thousands of field surveys of cheatgrass abundance to create regional models of cheatgrass distribution and percent cover. We compare cheatgrass presence to fire probability, fire seasonality and ignition source. Regional models of percent cover had low predictive power (34% of variance explained), but distribution models based on a threshold of 15% cover to differentiate high abundance from low abundance had an overall accuracy of 74%. Cheatgrass achieves ≥ 15% cover over 210,000 km2 (31%) of the Intermountain West. These lands were twice as likely to burn as those with low abundance, and four times more likely to burn multiple times between 2000 and 2015. Fire probability increased rapidly at low cheatgrass cover (1–5%) but remained similar at higher cover, suggesting that even small amounts of cheatgrass in an ecosystem can increase fire risk. Abundant cheatgrass was also associated with a 10 days earlier fire seasonality and interacted strongly with anthropogenic ignitions. Fire in cheatgrass was particularly associated with human activity, suggesting that increased awareness of fire danger in invaded areas could reduce risk. This study suggests that cheatgrass is much more spatially extensive and abundant than previously documented and that invasion greatly increases fire frequency, even at low percent cover.

The influence of lightning activity and anthropogenic factors on large-scale characteristics of natural fires

A module for simulating of natural fires (NFs) in the climate model of the A.M. Obukhov Institute of Atmospheric Physics, Russian Academy of Sciences (IAP RAS CM), is extended with respect to the influence of lightning activity and population density on the ignition frequency and fire suppression. The IAP RAS CM is used to perform numerical experiments in accordance with the conditions of the project that intercompares climate models, CMIP5 (Coupled Models Intercomparison Project, phase 5). The frequency of lightning flashes was assigned in accordance with the LIS/OTD satellite data. In the calculations performed, anthropogenic ignitions play an important role in NF occurrences, except for regions at subpolar latitudes and, to a lesser degree, tropical and subtropical regions. Taking into account the dependence of fire frequency on lightning activity and population density intensifies the influence of characteristics of natural fires on the climate changes in tropics and subtropics as compared to the version of the IAP RAS CM that does not take the influence of ignition sources on the large-scale characteristics of NFs into consideration.

Aboriginal impacts on fire and vegetation on a Tasmanian island

AbstractAimTo evaluate the influence of climate and Aboriginal landscape management on Holocene vegetation and fire activity.LocationFlinders Island, Bass Strait, Tasmania where archaeological data document extended periods of human presence and absence over the past 12,000 years.MethodsWe evaluated climate–human–fire interactions through high‐resolution pollen, charcoal and geochemical analyses of sediment cores from two wetland sites. Proxies for environmental change are qualitatively compared with archaeological data documenting Aboriginal occupation and later abandonment during the mid‐Holocene.ResultsWarm and dry conditions of the early Holocene combined with anthropogenic ignitions promoted frequent fires that sustained highly fire‐tolerant Eucalyptus savanna. During the mid‐Holocene, when both temperatures and precipitation reached Holocene maxima, archaeological data suggest Aboriginal populations abandoned Flinders Island. At this time, Eucalyptus savanna was replaced by Casuarinaceae and broadleaf forests and fire activity decreased. The late Holocene was marked by a transition to increased incidence of intense fires that was associated with a shift from Casuarinaceae forests to xerophytic scrub dominated by Callitris rhomboidea, a conifer that is sensitive to frequent fires but regenerates well following infrequent fires.Main conclusionsPalaeoenvironmental analyses from Flinders Island document significant shifts in fire regimes and vegetation types through the Holocene. In the early Holocene, Aboriginal landscape management played a key role in maintaining open Eucalyptus savanna, a prime habitat for marsupial prey species. Increasing aridity and strengthening of the El Niño Southern Oscillation climate mode during the mid to late Holocene contributed to the cessation of permanent human occupation and concomitant reduction of ignitions. Infrequent fire activity led to the dominance of xerophytes, especially Callitris, a genus adapted to drought and infrequent high‐severity fires. This study highlights how climate change affects the persistence of human populations on islands and the capacity of human‐set fires to create savanna habitats.

Analysis of recent spatial–temporal evolution of human driving factors of wildfires in Spain

Fire regimes are strongly dependent on human activities. Understanding the relative influence of human factors on wildfire is an important ongoing task especially in human-dominated landscapes such as the Mediterranean, where anthropogenic ignitions greatly surpass natural ignitions and human activities are modifying historical fire regimes. Most human drivers of wildfires have a temporal dimension, far beyond the appearance of change, and it is for this reason that we require an historical/temporal analytical perspective coupled to the spatial dimension. In this paper, we investigate and analyze spatial–temporal changes in the contribution of major human factors influencing forest fire occurrence, using Spanish historical statistical fire data from 1988 to 2012. We hypothesize that the influence of socioeconomic drivers on wildfires has changed over this period. Our method is based on fitting yearly explanatory regression models—testing several scenarios of wildfire data aggregation—using logit and Poisson generalized linear models to determine the significance thresholds of the covariates. We then conduct a trend analysis using the Mann–Kendall test to calculate and analyze possible trends in the explanatory power of human driving factors of wildfires. Finally, Geographically Weighted Regression Models are explored to examine potential spatial–temporal patterns. Our results suggest that some of the explanatory factors of logistic models do vary over time and that new explanatory factors might be considered (such as arson-related variables or climate factors), since some of the traditional ones seem to be losing significance in the presence–absence models, opposite to fire frequency models. In particular, the wildland–agricultural interface and wildland–urban interface appear to be losing explanatory power regarding ignition probability, and protected areas are becoming less significant in fire frequency models. GWR models revealed that this temporal behavior is not stationary neither over space nor time.

Sources of anthropogenic fire ignitions on the peat-swamp landscape in Kalimantan, Indonesia

Abstract Fire disturbance in many tropical forests, including peat swamps, has become more frequent and extensive in recent decades. These fires compromise a variety of ecosystem services, among which mitigating global climate change through carbon storage is particularly important for peat swamps. Indonesia holds the largest amount of tropical peat carbon globally, and mean annual CO 2 emissions from decomposition of deforested and drained peatlands and associated fires in Southeast Asia have been estimated at ∼2000 Mt y-1. A key component to understanding and therefore managing fire in the region is identifying the land use/land cover classes associated with fire ignitions. We assess the oft-asserted claim that escaped fires from oil palm concessions and smallholder farms near settlements are the primary sources of fire in a peat-swamp forest area in Central Kalimantan, Indonesia, equivalent to around a third of Kalimantan's total peat area. We use the MODIS Active Fire product from 2000 to 2010 to evaluate the fire origin and spread on the land use/land cover classes of legal, industrial oil palm concessions (the only type of legal concession in the study area), non-forest, and forest, as well as in relation to settlement proximity. We find that most fires (68–71%) originate in non-forest, compared to oil palm concessions (17%–19%), and relatively few (6–9%) are within 5 km of settlements. Moreover, most fires started within oil palm concessions and in close proximity to settlements stay within those boundaries (90% and 88%, respectively), and fires that do escape constitute only a small proportion of all fires on the landscape (2% and 1%, respectively). Similarly, a small proportion of fire detections in forest originate from oil palm concessions (2%) and within close proximity to settlements (2%). However, fire ignition density in oil palm (0.055 ignitions km −2 ) is comparable to that in non-forest (0.060 km-2 ignitions km- 2 ), which is approximately ten times that in forest (0.006 ignitions km −2 ). Ignition density within 5 km of settlements is the highest at 0.125 ignitions km −2 . Furthermore, increased anthropogenic activity in close proximity to oil palm concessions and settlements produces a detectable pattern of fire activity. The number of ignitions decreases exponentially with distance from concessions; the number of ignitions initially increases with distance from settlements, and, around from 7.2 km, then decreases with distance from settlements. These results refute the claim that most fires originate in oil palm concessions, and that fires escaping from oil palm concessions and settlements constitute a major proportion of fires in this study region. However, there is a potential for these land use types to contribute substantially to the fire landscape if their area expands. Effective fire management in this area should therefore target not just oil palm concessions, but also non-forested, degraded areas where ignitions and fires escaping into forest are most likely to occur.

Modelling the spatial patterns of ignition causes and fire regime features in southern France: implications for fire prevention policy

A good knowledge of the spatiotemporal patterns of the causes of wildfire ignition is crucial to an effective fire policy. However, little is known about the situation in south-eastern France because the fire database contains unreliable data. We used data for cases with well-established causes from 1973–2013 to determine the location of spatial hotspots, the seasonal distribution, the underlying anthropogenic and environmental drivers and the tendency of five main causes to generate large fires. Anthropogenic ignitions were predominant (88%) near human settlements and infrastructures in the lowlands, whilst lightning-induced fires were more common in the coastal mountains. In densely populated urban areas, small summer fires were predominating, due to the negligence of private individuals around their homes or accidental ignitions near infrastructures. In rural hinterlands, ignitions due to negligence by professionals generate many medium-sized fires from autumn to spring. Intentional and accidental ignitions contribute the most to the total burned area and to large fires. We conclude that socioeconomic factors partially control the fire regime, influencing the timing, spatial distribution and potential size of fires. This improved understanding of why, where and when ignitions occur provides the opportunity for controlling certain causes of ignitions and adapting French policy to global changes.

Wildland fire deficit and surplus in the western United States, 1984–2012

Wildland fire is an important disturbance agent in the western US and globally. However, the natural role of fire has been disrupted in many regions due to the influence of human activities, which have the potential to either exclude or promote fire, resulting in a “fire deficit” or “fire surplus”, respectively. In this study, we developed a model of expected area burned for the western US as a function of climate from 1984 to 2012. We then quantified departures from expected area burned to identify geographic regions with fire deficit or surplus. We developed our model of area burned as a function of several climatic variables from reference areas with low human influence; the relationship between climate and fire is strong in these areas. We then quantified the degree of fire deficit or surplus for all areas of the western US as the difference between expected (as predicted with the model) and observed area burned from 1984 to 2012. Results indicate that many forested areas in the western US experienced a fire deficit from 1984 to 2012, likely due to fire exclusion by human activities. We also found that large expanses of non‐forested regions experienced a fire surplus, presumably due to introduced annual grasses and the prevalence of anthropogenic ignitions. The heterogeneity in patterns of fire deficit and surplus among ecoregions emphasizes fundamentally different ecosystem sensitivities to human influences and suggests that large‐scale adaptation and mitigation strategies will be necessary in order to restore and maintain resilient, healthy, and naturally functioning ecosystems.

Sensitivity of global wildfire occurrences to various factors in the context of global change

The occurrence of wildfires is very sensitive to fire meteorology, vegetation type and coverage. We investigate the potential impacts of global change (including changes in climate, land use/land cover, and population density) on wildfire frequencies over the period of 2000–2050. We account for the impacts associated with the changes in fire meteorology (such as temperature, precipitation, and relative humidity), vegetation density, as well as lightning and anthropogenic ignitions. Fire frequencies under the 2050 conditions are projected to increase by approximately 27% globally relative to the 2000 levels. Significant increases in fire occurrence are calculated over the Amazon area, Australia and Central Russia, while Southeast Africa shows a large decreasing trend due to significant increases in land use and population. Changes in fire meteorology driven by 2000–2050 climate change are found to increase the global annual total fires by around 19%. Modest increases (∼4%) in fire frequency at tropical regions are calculated in response to climate-driven changes in lightning activities, relative to the present-day levels. Changes in land cover by 2050 driven by climate change and increasing CO2 fertilization are expected to increase the global wildfire occurrences by 15% relative to the 2000 conditions while the 2000–2050 anthropogenic land use changes show little effects on global wildfire frequency. The 2000–2050 changes in global population are projected to reduce the total wildfires by about 7%. In general, changes in future fire meteorology plays the most important role in enhancing the future global wildfires, followed by land cover, lightning activities and land use while changes in population density exhibits the opposite effects during the period of 2000–2050.

Controls on fire activity over the Holocene

Abstract. Changes in fire activity over the last 8000 years are simulated with a global fire model driven by changes in climate and vegetation cover. The changes were separated into those caused through variations in fuel availability, fuel moisture or wind speed, which react differently to changes in climate. Disentangling these controlling factors helps in understanding the overall climate control on fire activity over the Holocene. Globally the burned area is simulated to increase by 2.5% between 8000 and 200 cal yr BP, with larger regional changes compensating nearly evening out on a global scale. Despite the absence of anthropogenic fire ignitions, the simulated trends in fire activity agree reasonably well with continental-scale reconstructions from charcoal records, with the exception of Europe. For some regions the change in fire activity is predominantly controlled through changes in fuel availability (Australia monsoon, Central America tropics/subtropics). For other regions changes in fuel moisture are more important for the overall trend in fire activity (North America, Sub-Saharan Africa, Europe, Asia monsoon). In Sub-Saharan Africa, for example, changes in fuel moisture alone lead to an increase in fire activity between 8000 and 200 cal yr BP, while changes in fuel availability lead to a decrease. Overall, the fuel moisture control is dominating the simulated fire activity for Sub-Saharan Africa. The simulations clearly demonstrate that both changes in fuel availability and changes in fuel moisture are important drivers for the fire activity over the Holocene. Fuel availability and fuel moisture do, however, have different climate controls. As such, observed changes in fire activity cannot be related to single climate parameters such as precipitation or temperature alone. Fire models, as applied in this study, in combination with observational records can help in understanding the climate control on fire activity, which is essential to project future fire activity.

Effects of high-frequency understorey fires on woody plant regeneration in southeastern Amazonian forests

Anthropogenic understorey fires affect large areas of tropical forest, yet their effects on woody plant regeneration post-fire remain poorly understood. We examined the effects of repeated experimental fires on woody stem (less than 1 cm at base) mortality, recruitment, species diversity, community similarity and regeneration mode (seed versus sprout) in Mato Grosso, Brazil. From 2004 to 2010, forest plots (50 ha) were burned twice (B2) or five times (B5), and compared with an unburned control (B0). Stem density recovered within a year after the first burn (initial density: 12.4-13.2 stems m(-2)), but after 6 years, increased mortality and decreased regeneration--primarily of seedlings--led to a 63 per cent and 85 per cent reduction in stem density in B2 and B5, respectively. Seedlings and sprouts across plots in 2010 displayed remarkable community similarity owing to shared abundant species. Although the dominant surviving species were similar across plots, a major increase in sprouting occurred--almost three- and fourfold greater in B2 and B5 than in B0. In B5, 29 species disappeared and were replaced by 11 new species often present along fragmented forest edges. By 2010, the annual burn regime created substantial divergence between the seedling community and the initial adult tree community (greater than or equal to 20 cm dbh). Increased droughts and continued anthropogenic ignitions associated with frontier land uses may promote high-frequency fire regimes that may substantially alter regeneration and therefore successional processes.

A model for global biomass burning in preindustrial time: LPJ-LMfire (v1.0)

Abstract. Fire is the primary disturbance factor in many terrestrial ecosystems. Wildfire alters vegetation structure and composition, affects carbon storage and biogeochemical cycling, and results in the release of climatically relevant trace gases including CO2, CO, CH4, NOx, and aerosols. One way of assessing the impacts of global wildfire on centennial to multi-millennial timescales is to use process-based fire models linked to dynamic global vegetation models (DGVMs). Here we present an update to the LPJ-DGVM and a new fire module based on SPITFIRE that includes several improvements to the way in which fire occurrence, behaviour, and the effects of fire on vegetation are simulated. The new LPJ-LMfire model includes explicit calculation of natural ignitions, the representation of multi-day burning and coalescence of fires, and the calculation of rates of spread in different vegetation types. We describe a new representation of anthropogenic biomass burning under preindustrial conditions that distinguishes the different relationships between humans and fire among hunter-gatherers, pastoralists, and farmers. We evaluate our model simulations against remote-sensing-based estimates of burned area at regional and global scale. While wildfire in much of the modern world is largely influenced by anthropogenic suppression and ignitions, in those parts of the world where natural fire is still the dominant process (e.g. in remote areas of the boreal forest and subarctic), our results demonstrate a significant improvement in simulated burned area over the original SPITFIRE. The new fire model we present here is particularly suited for the investigation of climate–human–fire relationships on multi-millennial timescales prior to the Industrial Revolution.

Environmental drivers and spatial dependency in wildfire ignition patterns of northwestern Patagonia

Fire management requires an understanding of the spatial characteristics of fire ignition patterns and how anthropogenic and natural factors influence ignition patterns across space. In this study we take advantage of a recent fire ignition database (855 points) to conduct a comprehensive analysis of the spatial pattern of fire ignitions in the western area of Neuquén province (57,649 km2), Argentina, for the 1992–2008 period. The objectives of our study were to better understand the spatial pattern and the environmental drivers of the fire ignitions, with the ultimate aim of supporting fire management. We conducted our analyses on three different levels: statistical “habitat” modelling of fire ignition (natural, anthropogenic, and all causes) based on an information theoretic approach to test several competing hypotheses on environmental drivers (i.e. topographic, climatic, anthropogenic, land cover, and their combinations); spatial point pattern analysis to quantify additional spatial autocorrelation in the ignition patterns; and quantification of potential spatial associations between fires of different causes relative to towns using a novel implementation of the independence null model. Anthropogenic fire ignitions were best predicted by the most complex habitat model including all groups of variables, whereas natural ignitions were best predicted by topographic, climatic and land-cover variables. The spatial pattern of all ignitions showed considerable clustering at intermediate distances (<40 km) not captured by the probability of fire ignitions predicted by the habitat model. There was a strong (linear) and highly significant increase in the density of fire ignitions with decreasing distance to towns (<5 km), but fire ignitions of natural and anthropogenic causes were statistically independent. A two-dimensional habitat model that quantifies differences between ignition probabilities of natural and anthropogenic causes allows fire managers to delineate target areas for consideration of major preventive treatments, strategic placement of fuel treatments, and forecasting of fire ignition. The techniques presented here can be widely applied to situations where a spatial point pattern is jointly influenced by extrinsic environmental factors and intrinsic point interactions.

Quantifying the role of fire in the Earth system – Part 1: Improved global fire modeling in the Community Earth System Model (CESM1)

Abstract. Modeling fire as an integral part of an Earth system model (ESM) is vital for quantifying and understanding fire–climate–vegetation interactions on a global scale and from an Earth system perspective. In this study, we introduce to the Community Earth System Model (CESM) the new global fire parameterization proposed by Li et al. (2012a, b), now with a more realistic representation of the anthropogenic impacts on fires, with a parameterization of peat fires, and with other minor modifications. The improved representation of the anthropogenic dimension includes the first attempt to parameterize agricultural fires, the economic influence on fire occurrence, and the socioeconomic influence on fire spread in a global fire model – also an alternative scheme for deforestation fires. The global fire parameterization has been tested in CESM1's land component model CLM4 in a 1850–2004 transient simulation, and evaluated against the satellite-based Global Fire Emission Database version 3 (GFED3) for 1997–2004. The simulated 1997–2004 average global totals for the burned area and fire carbon emissions in the new fire scheme are 338 Mha yr−1 and 2.1 Pg C yr−1. Its simulations on multi-year average burned area, fire seasonality, fire interannual variability, and fire carbon emissions are reasonable, and show better agreement with GFED3 than the current fire scheme in CESM1 and modified CTEM-FIRE. Moreover, the new fire scheme also estimates the contributions of global fire carbon emissions from different sources. During 1997–2004, the contributions are 8% from agricultural biomass burning, 24% from tropical deforestation and degradation fires, 6% from global peat fires (3.8% from tropical peat fires), and 62% from other fires, which are close to previous assessments based on satellite data, government statistics, or other information sources. In addition, we investigate the importance of direct anthropogenic influence (anthropogenic ignitions and fire suppression) on global fire regimes during 1850–2004, using CESM1 with the new fire scheme. Results show that the direct anthropogenic impact is the main driver for the long-term trend of global burned area, but hardly contributes to the long-term trend of the global total of fire carbon emissions.

Wildfire Exposure Analysis on the National Forests in the Pacific Northwest, USA

We analyzed wildfire exposure for key social and ecological features on the national forests in Oregon and Washington. The forests contain numerous urban interfaces, old growth forests, recreational sites, and habitat for rare and endangered species. Many of these resources are threatened by wildfire, especially in the east Cascade Mountains fire-prone forests. The study illustrates the application of wildfire simulation for risk assessment where the major threat is from large and rare naturally ignited fires, versus many previous studies that have focused on risk driven by frequent and small fires from anthropogenic ignitions. Wildfire simulation modeling was used to characterize potential wildfire behavior in terms of annual burn probability and flame length. Spatial data on selected social and ecological features were obtained from Forest Service GIS databases and elsewhere. The potential wildfire behavior was then summarized for each spatial location of each resource. The analysis suggested strong spatial variation in both burn probability and conditional flame length for many of the features examined, including biodiversity, urban interfaces, and infrastructure. We propose that the spatial patterns in modeled wildfire behavior could be used to improve existing prioritization of fuel management and wildfire preparedness activities within the Pacific Northwest region.

The reproductive response of an endemic bunchgrass indicates historical timing of a keystone process

Restoration of the Pinus palustris (longleaf pine)‐wiregrass ecosystem of the southeastern United States requires information on reference conditions such as the historical fire regime. Aristida beyrichiana (wiregrass), a keystone perennial bunchgrass, was historically widespread throughout the southeast, but its dependence upon growing season fires for sexual reproduction hastened its decline in the face of decades of human fire suppression. The reproductive response of wiregrass is described by patterns of meristem allocation between competing life history strategies (i.e., vegetative growth vs. sexual reproduction). The temporal link between fire and flowering indicates this allocation was optimized to the historical fire regime through selection. In this study, we used the observed allocation of wiregrass reproductive effort to sexual reproduction as the response variable to examine reproductive response to fire season, using plant size as a covariate. Sexual reproduction was positively associated with plant size. Plants burned during early summer (May–June) produced a greater proportion of inflorescences than did those burned in early spring (March–April) or in late summer (August). Using state records of natural (lightning‐ignited) and anthropogenic (human‐ignited) fires from historical (1933–1946) and contemporary (1998–2010) periods we found that the distribution of maximum wiregrass reproductive output most closely reflected the distribution of historical fires with natural ignition sources. Moreover, while the monthly distributions of historical and contemporary fires were different for anthropogenic ignitions, they did not differ for fires with natural ignitions. Our predictions of peak allocation based upon the biology of wiregrass provide strong support for the use of wiregrass as an indicator of the historical fire season (early summer). Efforts to restore the longleaf pine ecosystem should therefore consider the biological response of wiregrass in planning prescribed fires.

Recent climate change: Long-term trends in meteorological forest fire danger in the Alps

Climate change is one of the key issues in current scientific research. In this paper we investigate the impacts of rising temperatures and changing precipitation patterns on meteorological forest fire danger in the Alps. Our analysis is based on daily meteorological observations from 25 long-term stations in six Alpine countries. The selected stations are distributed more or less uniformly over the whole Alpine area and represent the different climate regions in this complex terrain. Stations with similar climatological conditions were grouped into regions. These were: Western Alps, Northern Alps, inner Alpine area and Southern Alps. The meteorological forest fire danger in the time period 1951–2010 was assessed on the basis of different forest fire danger indices (FWI, Nesterov, Baumgartner, etc.) calculated on a daily basis. A statistical percentile analysis revealed different impacts of recent climate change in the four regions. A significant increase in forest fire danger occurred at the stations in the Western Alps and even more strongly in the Southern Alps. Here, the yearly averaged fire danger increased during the past six decades. Additionally, in recent years the number of days with elevated forest fire danger (indices above a pre-defined threshold) has also increased. A comparatively weak increase was observed in the Northern Alps and no clear signal was evident at the stations in the inner Alpine valleys. In order to analyze extreme events (highest index value per year and region) extreme values statistics was applied. It was shown that the return period of extraordinarily high index values has decreased significantly over the past decades, especially in the Western and Southern Alps.For three pilot areas (Valais in the Western Alps, Bavaria in the Northern Alpine region and Ticino in the Southern Alps) a comparison with observed historical fire data is shown. In Valais, a region in the Western Alps with a generally low fire hazard, a weak trend toward more forest fires and more area burned could be found. The correlation between calculated indices and observed fires was quite low in this region. In Bavaria (Northern Alps) this correlation was higher, but while the trend of forest fires in Bavaria was decreasing in terms of number and burned area, the meteorological fire danger in contrast increased. Reasons for this contrasting trend may be related to altered anthropogenic factors such as less military activities, technical progress, and higher awareness. The correlation between indices and forest fires south of the Alps (Ticino) was considerably lower because here most forest fires occurred in winter when the meteorological fire danger is usually lower than in summer. In this region a positive trend in meteorological fire danger over recent decades was also counterbalanced by decreasing anthropogenic ignitions.

Decreases in Fire Spread Probability with Forest Age Promotes Alternative Community States, Reduced Resilience to Climate Variability and Large Fire Regime Shifts

The generalization that plant communities increase in flammability as they age and invariably lead to resilient self-organized landscape mosaics is being increasingly challenged. Plant communities often exhibit rapidly saturating or even hump-shaped age-flammability trajectories and landscapes often display strong non-linear behaviors, abrupt shifts, and self-reinforcing alternative community states. This plethora of fire-landscape interactions calls for a more general model that considers alternative age-flammability rules. We simulated landscape dynamics assuming communities that (1) increase in flammability with age and (2) gain flammability up to a certain age followed by a slight and moderate loss to a constant value. Simulations were run under combinations of ignition frequency and interannual climatic variability. Age-increasing fire probability promoted high resilience to changes in ignition frequency and climatic variability whereas humpbacked-shaped age-flammability led to strong non-linear behaviors. Moderate (20%) reductions in mature compared to peak flammability produced the least resilient behaviors. The relatively non-flammable mature forest matrix intersected by young flammable patches is prone to break up and disintegrate with slight increases in ignition/climate variability causing large-scale shifts in the fire regime because large fires were able to sweep through the more continuous young/flammable landscape. Contrary to the dominant perception, fire suppression in landscapes with positive feedbacks may effectively reduce fire occurrence by allowing less flammable later stage communities composed of longer lived, obligate seeders to replace earlier stages of light demanding, often more flammable resprouters. Conversely, increases in anthropogenic ignitions, a common global trend of many forested regions may, in synergism with increased climate variability, induce abrupt shifts, and large-scale forest degradation.

Fire and vegetation shifts in the Americas at the vanguard of Paleoindian migration

Across North and South America, the final millennia of the Pleistocene saw dramatic changes in climate, vegetation, fauna, fire regime, and other local and regional paleo-environmental characteristics. Rapid climate shifts following the Last Glacial Maximum (LGM) exerted a first-order influence, but abrupt post-glacial shifts in vegetation composition, vegetation structure, and fire regime also coincided with human arrival and transformative faunal extinctions in the Americas. We propose a model of post-glacial vegetation change in response to climatic drivers, punctuated by local fire regime shifts in response to megaherbivore-driven fuel changes and anthropogenic ignitions. The abrupt appearance of humans, disappearance of megaherbivores, and resulting changes in New World fire systems were transformative events that should not be dismissed in favor of climate-only interpretations of post-glacial paleo-environmental shifts in the Americas. Fire is a mechanism by which small human populations can have broad impacts, and growing evidence suggests that early anthropogenic influences on regional, even global, paleo-environments should be tested alongside other potential causal mechanisms.

Fire in the American South: Vegetation Impacts, History, and Climatic Relations

AbstractFire plays a key role in many ecosystems of the southeastern U.S. Longleaf pine (Pinus palustris) and Table Mountain pine‐pitch pine (P. pungens–P. rigida) forests along with other ecosystems – including oak (Quercus) forests, grasslands, and spruce‐fir (Picea‐Abies) forests – illustrate the range of fire effects and plant persistence strategies in the American South. Fire history research reveals that fires and fire‐associated vegetation were common before the fire exclusion of the past century. Both lightning and anthropogenic ignitions (caused by American Indians or European settlers) contributed to burning, but their relative importance is debated. The humid climate constrains burning, especially by lightning‐ignited fires, which often occur during moist conditions. Studies of fire climatology indicate the importance of dry conditions (e.g. drought years and relatively dry areas) for widespread burning in this humid region. Landscape fragmentation also influences burning. In the past some fires also likely grew much larger than today because they were unimpeded by roads, farms, and other barriers.