Land cover influences boreal-forest fire responses to climate change: geospatial analysis of historical records from Alaska

Context

Wildfire activity in boreal forests is projected to increase dramatically in response to anthropogenic climate change. By altering the spatial arrangement of fuels, land-cover configuration may interact with climate change to influence fire-regime dynamics at landscape and regional scales.

Objectives

We evaluate how land cover interacts with weather conditions to influence boreal-forest burning from 2012 to 2014 in Alaska.

Methods

Using geospatial fire and land-cover data, we quantify relationships between area burned and land cover, and test whether observed patterns of burning differ from random under varying weather conditions and fire sizes.

Results

Mean summer moisture index was correlated with annual area burned (ρ = ?0.78, p < 0.01), the total number of fires (ρ = ?0.68, p = 0.01), and the number of large fires (>500 km²; ρ = ?0.58, p = 0.04). Area burned was related positively to percent cover of coniferous forest and woody wetlands, and negatively to percent cover of shrub scrub, dwarf scrub, and open water and barren areas. Fires preferentially burned coniferous forest, which represented 50.1 % of the area burned in warmer/drier summers and 40.3 % of area burned in cooler/wetter summers, compared to the 34.5 % (±4.2 %) expected by random selection of land-cover classes. Overall vegetation tended to burn more similarly to random in warmer/drier than cooler/wetter years.

Conclusions

Land cover exerted greater influences on boreal fire regimes when weather conditions were less favorable for forest burning. Reliable projections of boreal fire-regime change thus require consideration of the interactions between climate and land cover, as well as feedbacks from land-cover change.

     

Characterizing combined fire and insect outbreak disturbance regimes in British Columbia,Canada

Context

Fires and insect outbreaks are important agents of forest landscape change, but the classification and distribution of these combined processes remain unstudied aspects of forest disturbance regimes.

Objectives

We sought to map areas of land characterized by homogenous fire regime (HFR) attributes and by distinctive combinations of fire, bark beetles and defoliating insect outbreaks, and how their distribution might change should current climatic trends continue.

Methods

We used a 41-year history of mapped fires and forest insect outbreaks to classify HFRs and combined fire and insect disturbance regimes (HDRs). Spatially constrained cluster analysis of 2524 20-km grid cells used mean annual area burned, ignition Julian date, fire size and fire frequency to delineate HFR zones. Mean annual areas burned, affected by bark beetles, and affected by defoliators were used to delineate HDR zones. Random forests classification used climate associations of HDRs to project likely changes in their distribution.

Results

Eighteen HFR zones accounted for 30% of variance, compared to 27 HDR zones accounting for 59% of variance. Fire regime designation had low predictive power in explaining 23 homogenous insect outbreak regimes or the 27 HDRs. Climate change projections indicate a northward migration of current HDR zones. Conditions suitable for defoliator outbreaks are projected to increase, resulting in a projected increase in the total rate of forest disturbance.

Conclusions

When describing forest disturbance regimes, it is important to consider the combined and possibly interacting agents of tree mortality, which can result in emergent properties not predictable from any single agent.

     

Bending the carbon curve: fire management for carbon resilience under climate change

Context

Forest landscapes are increasingly managed for fire resilience, particularly in the western US which has recently experienced drought and widespread, high-severity wildfires. Fuel reduction treatments have been effective where fires coincide with treated areas. Fuel treatments also have the potential to reduce drought-mortality if tree density is uncharacteristically high, and to increase long-term carbon storage by reducing high-severity fire probability.

Objective

Assess whether fuel treatments reduce fire intensity and spread and increase carbon storage under climate change.

Methods

We used a simulation modeling approach that couples a landscape model of forest disturbance and succession with an ecosystem model of carbon dynamics (Century), to quantify the interacting effects of climate change, fuel treatments and wildfire for carbon storage potential in a mixed-conifer forest in the western USA.

Results

Our results suggest that fuel treatments have the potential to ‘bend the C curve’, maintaining carbon resilience despite climate change and climate-related changes to the fire regime. Simulated fuel treatments resulted in reduced fire spread and severity. There was partial compensation of C lost during fuel treatments with increased growth of residual stock due to greater available soil water, as well as a shift in species composition to more drought- and fire-tolerant Pinus jeffreyi at the expense of shade-tolerant, fire-susceptible Abies concolor.

Conclusions

Forest resilience to global change can be achieved through management that reduces drought stress and supports the establishment and dominance of tree species that are more fire- and drought-resistant, however, achieving a net C gain from fuel treatments may take decades.

     

Drivers and trends in landscape patterns of stand-replacing fire in forests of the US Northern Rocky Mountains (1984–2010)

Context

Resilience in fire-prone forests is strongly affected by landscape burn-severity patterns, in part by governing propagule availability around stand-replacing patches in which all or most vegetation is killed. However, little is known about drivers of landscape patterns of stand-replacing fire, or whether such patterns are changing during an era of increased wildfire activity.

Objectives

(a) Identify key direct/indirect drivers of landscape patterns of stand-replacing fire (e.g., size, shape of patches), (b) test for temporal trends in these patterns, and (c) anticipate thresholds beyond which landscape patterns of burn severity may change fundamentally.

Methods

We applied structural equation modeling to satellite burn-severity maps of fires in the US Northern Rocky Mountains (1984–2010) to test for direct and indirect (via influence on fire size and proportion stand-replacing) effects of climate/weather, vegetation, and topography on landscape patterns of stand-replacing fire. We also tested for temporal trends in landscape patterns.

Results

Landscape patterns of stand-replacing fire were strongly controlled by fire size and proportion stand-replacing, which were, in turn, controlled by climate/weather and vegetation/topography, respectively. From 1984 to 2010, the proportion of stand-replacing fire within burn perimeters increased from 0.22 to 0.27. Trends for other landscape metrics were not significant, but may respond to further increases proportion stand-replacing fire.

Conclusions

Fires from 1984 to 2010 exhibited tremendous heterogeneity in landscape patterns of stand-replacing fire, likely promoting resilience in burned areas. If trends continue on the current trajectory, however, fires may produce larger and simpler shaped patches of stand-replacing fire with more burned area far from seed sources.

     

Normalized burn ratios link fire severity with patterns of avian occurrence

Context

Remotely sensed differenced normalized burn ratios (DNBR) provide an index of fire severity across the footprint of a fire. We asked whether this index was useful for explaining patterns of bird occurrence within fire adapted xeric pine-oak forests of the southern Appalachian Mountains.

Objectives

We evaluated the use of DNBR indices for linking ecosystem process with patterns of bird occurrence. We compared field-based and remotely sensed fire severity indices and used each to develop occupancy models for six bird species to identify patterns of bird occurrence following fire.

Methods

We identified and sampled 228 points within fires that recently burned within Great Smoky Mountains National Park. We performed avian point counts and field-assessed fire severity at each bird census point. We also used Landsat? imagery acquired before and after each fire to quantify fire severity using DNBR. We used non-parametric methods to quantify agreement between fire severity indices, and evaluated single season occupancy models incorporating fire severity summarized at different spatial scales.

Results

Agreement between field-derived and remotely sensed measures of fire severity was influenced by vegetation type. Although occurrence models using field-derived indices of fire severity outperformed those using DNBR, summarizing DNBR at multiple spatial scales provided additional insights into patterns of occurrence associated with different sized patches of high severity fire.

Conclusions

DNBR is useful for linking the effects of fire severity to patterns of bird occurrence, and informing how high severity fire shapes patterns of bird species occurrence on the landscape.

     

Applying fire connectivity and centrality measures to mitigate the cheatgrass-fire cycle in the arid West,USA

Context

Strategic placement of fuel treatments across large landscapes is an important step to mitigate the collective effects of fires interacting over broad spatial and temporal extents. On landscapes where highly invasive cheatgrass (Bromus tectorum) is increasing fire activity, such an approach could help maintain landscape resilience.

Objectives

Our objectives are to 1) model and map fire connectivity on a cheatgrass-invaded landscape, as well as the centrality of large cheatgrass patches, in order to inform a landscape fuel treatment (i.e., a network of greenstrips); and 2) evaluate the modeled greenstrip network based on changes to cheatgrass patch centrality.

Methods

Our analysis covers 485-km² on the Kaibab National Forest in Northern Arizona. We apply a circuit-theoretic model of fire connectivity between all pairs of large cheatgrass patches. Based on these results, we calculate a measure of centrality for each patch to inform fuel treatment placement. We evaluate the modeled greenstrip network by comparing the pre- and post-treatment centrality of each patch.

Results

After modeling fire connectivity across the landscape, we identify 25 of 68 large cheatgrass patches with relatively high centrality. When we simulate greenstrips around these focal patches, model results suggest that they are effective in reducing the centrality for at least 19 of the 25 patches.

Conclusions

Fire connectivity models provide robust network centrality measures, which can help generate multiple, landscape fuel treatment alternatives and facilitate on-the-ground decisions. The extension of these methods is well suited for landscape fuels management in other vegetation communities and ecosystems.

     

Influence of landscape structure,topography, and forest type on spatial variation in historical fire regimes,Central Oregon,USA

Context

In the interior Northwest, debate over restoring mixed-conifer forests after a century of fire exclusion is hampered by poor understanding of the pattern and causes of spatial variation in historical fire regimes.

Objectives

To identify the roles of topography, landscape structure, and forest type in driving spatial variation in historical fire regimes in mixed-conifer forests of central Oregon.

Methods

We used tree rings to reconstruct multicentury fire and forest histories at 105 plots over 10,393 ha. We classified fire regimes into four types and assessed whether they varied with topography, the location of fuel-limited pumice basins that inhibit fire spread, and an updated classification of forest type.

Results

We identified four fire-regime types and six forest types. Although surface fires were frequent and often extensive, severe fires were rare in all four types. Fire regimes varied with some aspects of topography (elevation), but not others (slope or aspect) and with the distribution of pumice basins. Fire regimes did not strictly co-vary with mixed-conifer forest types.

Conclusions

Our work reveals the persistent influence of landscape structure on spatial variation in historical fire regimes and can help inform discussions about appropriate restoration of fire-excluded forests in the interior Northwest. Where the goal is to restore historical fire regimes at landscape scales, managers may want to consider the influence of topoedaphic and vegetation patch types that could affect fire spread and ignition frequency.

     

Dryness thresholds for fire occurrence vary by forest type along an aridity gradient: evidence from Southern Australia

Context

Wildfires are common in localities where there is sufficient productivity to allow the accumulation of biomass combined with seasonality that allows this to dry and transition to a flammable state. An understanding of the conditions under which vegetated landscapes become flammable is valuable for assessing fire risk and determining how fire regimes may alter with climate change.

Objectives

Weather based metrics of dryness are a standard approach for estimating the potential for fires to occur in the near term. However, such approaches do not consider the contribution of vegetation communities. We aim to evaluate differences in weather-based dryness thresholds for fire occurrence between vegetation communities and test whether these are a function of landscape aridity.

Methods

We analysed dryness thresholds (using Drought Factor) for fire occurrence in six vegetation communities using historic fires events that occurred in South-eastern Australia using logistic regression. These thresholds were compared to the landscape aridity for where the communities persist.

Results

We found that dryness thresholds differed between vegetation communities, and this effect could in part be explained by landscape aridity. Dryness thresholds for fire occurrence were lower in vegetation communities that occur in arid environments. These communities were also exposed to dry conditions for a greater proportion of the year.

Conclusions

Our findings suggest that vegetation driven feedbacks may be an important driver of landscape flammability. Increased consideration of vegetation properties in fire danger indices may provide for better estimates of landscape fire risk and allow changes to fire regimes to be anticipated.

     

Microhabitat conditions and landscape pattern explain nocturnal rodent activity,but not seed removal,in burned and unburned lodgepole pine forests

Context

Disturbances create spatial variation in environments that may influence animal foraging. Granivory by rodents can influence seed supply and thus plant establishment. However, effects of disturbance patterns on rodent seed removal in western North American conifer forests are generally unknown.

Objectives

We conducted a study in lodgepole pine (Pinus contorta var. latifolia) forests of Greater Yellowstone (Wyoming, USA) to answer: (1) How do seed removal and rodent activity vary between recently burned and adjacent unburned forests and with distance from fire perimeter? (2) Which microhabitat conditions explain variability in seed removal and rodent activity?

Methods

One or two years after wildfires, we established transects (n = 23) with four stations each: at 10 and 40 m from the fire perimeter in both burned and unburned forest. At stations, we deployed trays with lodgepole pine seeds and cameras pointed at trays for 28 days and quantified habitat structure and seed abundance.

Results

Seed removal, which averaged 85%, and diurnal rodent activity did not differ between burned and unburned forests or with distance from the fire perimeter; however, nocturnal rodent activity was lower in burned forests. Seed removal and diurnal rodent activity were not associated with any microhabitat conditions we measured. However, nocturnal rodent activity was associated with microhabitat in both burned and unburned forests.

Conclusions

High seed removal rates suggested that rodent foraging was not reduced by high-severity wildfire. If observed seed removal represents natural conditions, post-dispersal seed predation could influence post-fire recruitment of a widespread foundation tree species.

     

Biophysical influences on the spatial distribution of fire in the desert grassland region of the southwestern USA

Context

Fire is an important driver of ecological processes in semiarid systems and serves a vital role in shrub-grass interactions. In desert grasslands of the southwestern US, the loss of fire has been implicated as a primary cause of shrub encroachment. Where fires can currently be re-introduced given past state changes and recent restoration actions, however, is unknown and controversial.

Objectives

Our objective was to evaluate the interactive effects of climate, urban development, and topo-edaphic properties on fire distribution in the desert grassland region of the southwestern United States.

Methods

We characterized the spatial distribution of fire in the Chihuahuan Desert and Madrean Archipelago ecoregions and investigated the influence of soil properties and ecological site groups compared to other commonly used biophysical variables using multi-model inference.

Results

Soil-landscape properties significantly influenced the spatial distribution of fire ignitions. Fine-textured bottomland ecological site classes experienced more fires than expected in contrast to upland sites with coarse soil textures and high fragment content that experienced fewer fire ignitions than expected. Influences of mean annual precipitation, distance to road/rail, soil available water holding capacity (AWHC) and topographic variables varied between ecoregions and political jurisdictions and by fire season. AWHC explained more variability of fire ignitions in the Madrean Archipelago compared to the Chihuahuan Desert.

Conclusions

Understanding the spatiotemporal distribution of recent fires in desert grasslands is needed to manage fire and predict responses to climate change. The use of landscape units such as ecological sites presents an opportunity to improve predictions at management scales.

     

Landscape,fire and habitat: which features of recently burned heathland influence site occupancy of an early successional specialist?

Context

Multiple ecological drivers generate spatial patterns in species’ distributions. Changes to natural disturbance regimes can place early successional habitat specialists at an increased risk of extinction by altering landscape patterns of habitat suitability.

Objectives

We developed a series of hypotheses to evaluate the effects of landscape structure, fire history, and site-level habitat quality on site occupancy by an early successional specialist, the eastern chestnut mouse (Pseudomys gracilicaudatus).

Methods

We obtained eight years of monitoring data from 26 sites in recently burned heathland in southeast Australia. We used generalised linear models to determine which explanatory variables were related to occupancy. We also explored predictability in patterns of small mammal species co-occurrence.

Results

Landscape structure (patch area, landscape heterogeneity) was strongly related to site occupancy. Site occupancy was associated with dead shrubs in the understory and rock cover on ground layer, but was not directly influenced by recent or historical fire. Contrary to contemporary ecological theory, we found no predictable species associations in our early successional community.

Conclusions

We recommend surveys take account of landscape configuration and proximity to suitable habitat for optimal results. Fire regimes expected to promote eastern chestnut mouse population growth should encourage the retention of critical habitat features rather than be based on temporal rates of successional stages. For management to adequately account for post-disturbance patterns in early successional communities, a species-by-species, multi-scaled approach to research is necessary.

     

The changing landscape of wildfire: burn pattern trends and implications for California’s yellow pine and mixed conifer forests

Purpose

Wildfire spatial patterns drive ecological processes including vegetation succession and wildlife community dynamics. Such patterns may be changing due to fire suppression policies and climate change, making characterization of trends in post-fire mosaics important for understanding and managing fire-prone ecosystems.

Methods

For wildfires in California’s yellow pine and mixed-conifer forests, spatial pattern trends of two components of the post-fire severity matrix were assessed for 1984–2015: (1) unchanged or very low-severity and (2) high-severity, which represent remnant forest and stand-replacing fire, respectively. Trends were evaluated for metrics of total and proportional burned area, shape complexity, aggregation, and core area. Additionally, comparisons were made between management units where fire suppression is commonly practiced and those with a history of managing wildfire for ecological/resource benefits.

Results

Unchanged or very low-severity area per fire decreased proportionally through time, and became increasingly fragmented. High-severity area and core area increased on average across most of California, with the high-severity component also becoming simpler in shape in the Sierra Nevada. Compared to suppression units, managed wildfire units lack an increase in high-severity area, have less aggregated post-fire mosaics, and more high-severity spatial complexity.

Conclusions

Documented changes in severity patterns have cascading ecological effects including increased vegetation type conversion risk, habitat availability shifts, and remnant forest fragmentation. These changes likely benefit early-seral-associated species at the expense of mature closed-canopy forest-associated species. Managed wildfire appears to moderate some effects of fire suppression, and may help buy time for ecosystems and managers to respond to a changing climate.

     

Holding the line: three decades of prescribed fires halt but do not reverse woody encroachment in grasslands

Context

Encroachment of woody vegetation represents a significant global threat to biodiversity in grasslands, but practices used to reverse encroachment are rarely evaluated comprehensively. Several factors may drive encroachment, such as land use history, alteration of disturbance regimes, and local environment, but their relative importance is poorly understood. Another complicating factor is that encroachment may proceed via positive feedbacks that result in thresholds, beyond which its reversal is difficult.

Objectives

We ask what impact reintroducing frequent fire has on encroachment relative to the influences of landscape context and historical vegetation. We investigate whether woody cover frequency distributions suggest that feedbacks reinforce encroachment after a threshold of woody cover is surpassed.

Methods

We analyze aerial photos in glade grasslands in Missouri, USA, to assess encroachment patterns over a 75-year period. Fire was excluded from this landscape for the first 45 years, and then reintroduced at varying frequencies in the last 30 years.

Results

Woody vegetation cover increased sevenfold from 1939 to 2014 overall. After the reintroduction of prescribed fire, woody cover stayed approximately constant in burned glades, but continued increasing in unburned glades. Woody cover followed bimodal frequency distributions in burned areas. Fire-tolerant vegetation tended to encroach near historically wooded areas, while fire-sensitive vegetation responded more to fire history.

Conclusions

Altered disturbance regimes, in addition to numerous recognized drivers, can cause ecosystem state changes associated with losses to biodiversity. Conducting management early in the encroachment process and restoring grasslands at broad landscape scales may help counteract local feedbacks that promote encroachment.

     

Interactions of landscape disturbances and climate change dictate ecological pattern and process: spatial modeling of wildfire,insect, and disease dynamics under future climates

Context

Interactions among disturbances, climate, and vegetation influence landscape patterns and ecosystem processes. Climate changes, exotic invasions, beetle outbreaks, altered fire regimes, and human activities may interact to produce landscapes that appear and function beyond historical analogs.

Objectives

We used the mechanistic ecosystem-fire process model FireBGCv2 to model interactions of wildland fire, mountain pine beetle (Dendroctonus ponderosae), and white pine blister rust (Cronartium ribicola) under current and future climates, across three diverse study areas.

Methods

We assessed changes in tree basal area as a measure of landscape response over a 300-year simulation period for the Crown of the Continent in north-central Montana, East Fork of the Bitterroot River in western Montana, and Yellowstone Central Plateau in western Wyoming, USA.

Results

Interacting disturbances reduced overall basal area via increased tree mortality of host species. Wildfire decreased basal area more than beetles or rust, and disturbance interactions modeled under future climate significantly altered landscape basal area as compared with no-disturbance and current climate scenarios. Responses varied among landscapes depending on species composition, sensitivity to fire, and pathogen and beetle suitability and susceptibility.

Conclusions

Understanding disturbance interactions is critical for managing landscapes because forest responses to wildfires, pathogens, and beetle attacks may offset or exacerbate climate influences, with consequences for wildlife, carbon, and biodiversity.

     

Fire legacies impact conifer regeneration across environmental gradients in the U.S. northern Rockies

Context

An increase in the incidence of large wildfires worldwide has prompted concerns about the resilience of forest ecosystems, particularly in the western U.S., where recent changes are linked with climate warming and 20th-century land management practices.

Objectives

To study forest resilience to recent wildfires, we examined relationships among fire legacies, landscape features, ecological conditions, and patterns of post-fire conifer regeneration.

Methods

We quantified regeneration across 182 sites in 21 recent large fires in dry mixed-conifer forests of the U.S. northern Rockies. We used logistic and negative binomial regression to predict the probability of establishment and abundance of conifers 5–13 years post-fire.

Results

Seedling densities varied widely across all sites (0–127,500 seedlings ha^?1) and were best explained by variability in distance to live seed sources (β = ?0.014, p = 0.002) and pre-fire tree basal area (β = 0.072, p = 0.008). Beyond 95 m from the nearest live seed source, the probability of seedling establishment was low. Across all the fires we studied, 75 % of the burned area with high tree mortality was within this 95-m threshold, suggesting the presence of live seed trees to facilitate natural regeneration.  

Conclusions

Combined with the mix of species present within the burn mosaic, dry mixed-conifer forests will be resilient to large fires across our study region, provided that seedlings survive, fire do not become more frequent, high-severity patches do not get significantly larger, and post-fire climate conditions remain suitable for seedling establishment and survival.

     

Wildfire and exotic grass invasion alter plant productivity in response to climate variability in the Mojave Desert

Context

Annual grass invasions often increase the frequency and extent of wildfire. Climate variability and fire history may have modifying effects on invasion success and its link to changing fire regimes.

Objective

Characterize the role of climate variability and fire history in vegetation shifts of an invaded desert landscape.

Method

Pre- and post-fire landscape vegetation greenness were assessed on multiple, independent wildfires in Mojave Desert shrublands using a 34 year record of normalized difference vegetation index (NDVI) derived from 1685 Landsat images and matched with a record of precipitation using linear regression.

Results

Annual maximum NDVI, and its annual variance of monthly maximum values, were significantly higher on post-fire than pre-fire landscapes. Additionally, post-fire landscapes showed greater sensitivity to antecedent precipitation received the previous 4 months than pre-fire and unburned landscapes. Ground surveys of vegetation indicate that post-fire landscapes show little indication of recovery of native shrub cover and density but instead are dominated by the exotic grass red brome (Bromus rubens L.). Increased NDVI sensitivity to precipitation is likely related to the growth of red brome, which dominates burned landscapes. Record precipitation in the fall of 2004 contributed to the record NDVI values in 2005 likely driven by high density of red brome.

Conclusions

The heightened response of post-fire vegetation to extreme and more variable precipitation events appears to be contributing to the emergence of an invasive grass-fire cycle that constrains the re-establishment of fire sensitive native shrubs while reinforcing the dominance of exotic grasses.

     

Diversity–disturbance relationship in forest landscapes

Context

Despite decades of research, there is an intense debate about the consistency of the hump-shaped pattern describing the relationship between diversity and disturbance as predicted by the intermediate disturbance hypothesis (IDH). Previous meta-analyses have not explicitly considered interactive effects of disturbance frequency and intensity of disturbance on plant species diversity in terrestrial landscapes.

Objective

We conducted meta-analyses to test the applicability of IDH by simultaneously examining the relationship between species richness, disturbance frequency (quantified as time since last disturbance as originally proposed) and intensity of disturbance in forest landscapes.

Methods

The effects of disturbance frequency, intensity, and their interaction on species richness was evaluated using a mixed-effects model.

Results

We found that species richness peaks at intermediate frequency after both high and intermediate disturbance intensities, but the richness-frequency relationship differed between intensity classes.

Conclusions

Our study highlights the need to measure multiple disturbance components that could help reconcile conflicting empirical results on the effect of disturbance on plant species diversity.

     

Drivers of forest fire occurrence in the cultural landscape of Central Europe

Context

Wildfires in temperate Central Europe have traditionally been perceived as a mere consequence of human activity without any relevance to natural forest development, despite their documented frequent occurrence. As a result, knowledge about local fire ecology and patterns of wildfire occurrence in the landscape is lacking.

Objectives

We aimed to reveal the factors influencing the spatial distribution of forest fires in the Czech Republic as a model area for the broader region. Specifically, we aimed to (1) find out which factors influence the occurrence and frequency of the forest fires at the country scale and in a selected fire-prone region; (2) examine the relationship of lightning strikes and their polarity with wildfire incidence; (3) identify the conditions determining areas with naturally driven fire-prone conditions.

Methods

We took data on 15,985 wildfire records and explored their spatial distribution using GIS layers of human, topographic, climatic and vegetation composition factors. We analysed the data using GLM and hierarchical partitioning methods.

Results

Wildfire occurrence was controlled mostly by environmental factors whereas wildfire frequency was strongly driven by human factors. In the selected fire-prone region, the effect of environmental factors was even more pronounced and wildfire frequency was also driven, albeit marginally, by lightning strikes of positive polarity.

Conclusion

The pattern of wildfire occurrence in the Czech Republic was similar also to those from regions where wildfire is considered a natural part of local ecosystems. We identified the areas with natural fire-prone conditions which probably led to the development of local fire-adapted ecosystems.

     

Accounting for spatial autocorrelation improves the estimation of climate,physical environment and vegetation’s effects on boreal forest’s burn rates

Context

Wildfires play a crucial role in maintaining ecological and societal functions of North American boreal forests. Because of their contagious way of spreading, using statistical methods dealing with spatial autocorrelation has become a major challenge in fire studies analyzing how environmental factors affect their spatial variability.

Objectives

We aimed to demonstrate the performance of a spatially explicit method accounting for spatial autocorrelation in burn rates modelling, and to use this method to determine the relative contribution of climate, physical environment and vegetation to the spatial variability of burn rates between 1972 and 2015.

Methods

Using a 482,000 km² territory located in the coniferous boreal forest of eastern Canada, we built and compared burn rates models with and without accounting for spatial autocorrelation. The relative contribution of climate, physical environment and vegetation to the burn rates variability was identified with variance partitioning.

Results

Accounting for spatial autocorrelation improved the models’ performance by a factor of 1.5. Our method allowed the unadulterated extraction of the contribution of climate, physical environment and vegetation to the spatial variability of burn rates. This contribution was similar for the three groups of factors. The spatial autocorrelation extent was linked to the fire size distribution.

Conclusions

Accounting for spatial autocorrelation can highly improve models and avoids biased results and misinterpretation. Considering climate, physical environment and vegetation altogether is essential, especially when attempting to predict future area burned. In addition to the direct effect of climate, changes in vegetation could have important impacts on future burn rates.