Increased Fire Activity Research Articles

Does burn severity affect plant community diversity and composition in mixed conifer forests of the United States Intermountain West one decade post fire?

BackgroundWildfire is an important ecological process in mixed conifer forests of the Intermountain West region of the USA. However, researchers and managers are concerned because climate warming has led to increased fire activity in recent decades. More area burned will result in larger land areas in early successional stages and will potentially limit tree establishment; therefore, evaluating long-term forest understory response to fire is important. We evaluate the impact of burn severity, overstory canopy cover, topography, and climate on understory plant community diversity and composition in seven wildfires, 9 to 12 years post fire, along a broad climate gradient from dry to moist mixed conifer forests in Idaho, Montana, and Washington, USA.ResultsClimate was the most important driver for species diversity and composition, but a burn severity gradient was detectable in the species data one decade post fire. A strong overlap in species composition between burn severity levels was documented, but dispersion was lower for high burn severity sites, indicating that those sites are still recovering. Local species richness and diversity had a nonlinear relationship with the burn severity index dNBR, with a maximum at low to moderate burn severity; the relationship was stronger in moist climates. Functional trait analysis revealed higher grass and forb cover in high-severity burns, higher cover of tree seedlings, residual and off-site colonizers in burned areas, and more shade-tolerant species in unburned areas. Of the 270 species recorded, 10% were introduced; however, only three were of noxious status and two were invasive annual grasses, generally occurring on dry sites.ConclusionsThe understory plant community was not fundamentally altered by these fires and fire contributed to increased species diversity both locally and regionally, suggesting that low to moderate burn severity fire is a treatment that contributes to long-term maintenance of a diverse and productive understory. Individual species traits were significant drivers of understory species assemblages and, as future change in climate and fire regimes leads to shifts in species composition, anticipation of consequences will be important. Although invasive species occurred at low cover levels, noxious weeds and invasive annual grasses will continue to be management challenges, particularly in dry regions of mixed conifer forests.

Hippocampal Ripple Communicates with Retrosplenial Inhibitory Neurons During Slow-Wave Sleep

The hippocampus and retrosplenial cortex (RSC) both play indispensable roles in memory formation, and, importantly, a hippocampal oscillation known as ripple is key to the consolidation of new memory. However, it remains unclear how the hippocampus and RSC communicate and the role of ripple oscillation in coordinating information exchange between these two brain regions. Here we recorded from the dorsal hippocampus and RSC simultaneously in freely-behaving mice during sleep and revealed that the RSC displayed a shift of fast-to-slow oscillations preceding hippocampal ripples. Immediately after ripples, a group of RSC putative inhibitory neurons increased firing activity, while most RSC putative excitatory neurons decreased activity. Consistently, optogenetic activation of this hippocampus-to-RSC pathway activates and suppresses RSC putative inhibitory and excitatory neurons, respectively. These results suggest that the dorsal hippocampus mainly inhibits RSC activity via its direct innervation of RSC inhibitory neurons, which overshadows the RSC in supporting learning and memory functions.

Peatland Hydrological Dynamics as A Driver of Landscape Connectivity and Fire Activity in the Boreal Plain of Canada

Drought is usually the precursor to large wildfires in northwestern boreal Canada, a region with both large wildfire potential and extensive peatland cover. Fire is a contagious process, and given weather conducive to burning, wildfires may be naturally limited by the connectivity of fuels and the connectivity of landscapes such as peatlands. Boreal peatlands fragment landscapes when wet and connect them when dry. The aim of this paper is to construct a framework by which the hydrological dynamics of boreal peatlands can be incorporated into standard wildfire likelihood models, in this case the Canadian Burn-P3 model. We computed hydrologically dynamic vegetation cover for peatlands (37% of the study area) on a real landscape in the Canadian boreal plain, corresponding to varying water table levels representing wet, moderate, and severely dry fuel moisture and hydrological conditions. Despite constant atmospheric drivers of fire spread (air temperature, humidity, and wind speed) between drought scenarios, fire activity increased 6-fold in moderate drought relative to a low drought baseline; severe (1 in 40 years) drought scenarios drove fires into previously fire-restrictive environments. Fire size increased 5-fold during moderate drought conditions and a further 20%–25% during severe drought. Future climate change is projected to lead to an increase in the incidence of severe drought in boreal forests, leading to increases in burned area due to increasing fire frequency and size where peatlands are most abundant. Future climate change in regions where peatlands have historically acted as important barriers to fire spread may amplify ongoing increases in fire activity already observed in Western North American forests.

CO2-induced climate forcing on the fire record during the initiation of Cretaceous oceanic anoxic event 2

Abstract Cretaceous oceanic anoxic event 2 (OAE2) is thought to have been contemporary with extensive volcanism and the release of large quantities of volcanic CO2 capable of triggering marine anoxia through a series of biogeochemical feedbacks. High-resolution reconstructions of atmospheric CO2 concentrations across the initiation of OAE2 suggest that there were also two distinct pulses of CO2 drawdown coeval with increased organic carbon burial. These fluctuations in CO2 likely led to significant climatic changes, including fluctuations in temperatures and the hydrological cycle. Paleofire proxy records suggest that wildfire was a common occurrence throughout the Cretaceous Period, likely fueled by the estimated high atmospheric O2 concentrations at this time. However, over geological time scales, the likelihood and behavior of fire are also controlled by other factors such as climate, implying that CO2-driven climate changes should also be observable in the fossil charcoal record. We tested this hypothesis and present a high-resolution study of fire history through the use of fossil charcoal abundances across the OAE2 onset, and we compared our records to the estimated CO2 fluctuations published from the same study sites. Our study illustrates that inferred wildfire activity appears to relate to changes in CO2 occurring across the onset of OAE2, where periods of CO2 drawdown may have enabled an increase in fire activity through suppression of the hydrological cycle. Our study provides further insight into the relationships between rapid changes in the carbon cycle, climate, and wildfire activity, illustrating that CO2 and climate changes related to inferred wildfire activity can be detected despite the estimated high Cretaceous atmospheric O2 concentrations.

Late Holocene (Meghalayan) palaeoenvironmental evolution inferred from multi-proxy-studies of lacustrine sediments from the Dayan Nuur region of Mongolia

The ‘Altai Tavan Bogd’ National Park, located between 2000 m and 4000 m a.s.l. in the north-western part of the Mongolian Altai, is a forest-steppe ecosystem in Central Asia which is noticeable because of its extreme continental and high-altitude conditions. Its vegetation is very sensitive to environmental changes and impact by nomadic people. To reconstruct the dynamics of this forest-steppe ecosystem, a broad approach was taken employing multi-proxy analyses including the analysis of pollen, spores, non-pollen palynomorphs, charcoal and diatoms, as well as XRF scanning of a lacustrine sediment core of a small and shallow lake located south of Dayan Nuur. Five radiocarbon dates indicate a record spanning the last 4375 years.Between 4310 and 1040 cal yr BP, the vegetation was characterized by a mixture of alpine meadow and moist true steppe communities as well as forested areas with Larix sibirica, Pinus sibirica and Picea obovata stands. Starting around 2350 cal yr BP, a substantially greater and/or denser forest occurrence can be inferred. A marked forest decline after 1040 cal yr BP and the loss of Pinus sibirica and Picea obovata near the study area proceeded in accordance with a significantly higher abundance of large herbivores and a strong indication of nomadic people in the area as inferred from coprophilous fungi. One period of markedly increased fire activity is found from 640 to 550 cal yr BP. For the latest Holocene period, the records of non-pollen palynomorphs and diatoms suggest a rise of the lake water level. These contrasting trends of forest decline despite higher water availability may reflect the considerable human impact of the nomadic population and their cattle on the ecosystem in the ‘Altai Tavan Bogd’ National Park and Central Asia in general.

Turning Down the Heat: Vegetation Feedbacks Limit Fire Regime Responses to Global Warming

Climate change is projected to dramatically increase boreal wildfire activity, with broad ecological and socioeconomic consequences. As global temperatures rise, periods with elevated fire weather are expected to increase in frequency and duration, which would be expected to increase the number and size of fires. Statistical forecasts or simulations of future fire activity often account for direct climatic effects only, neglecting other controls of importance, such as biotic feedbacks. This could result in overestimating the effects of climate change on fire activity, if the future distribution of vegetation or fuels were to change. We incorporated sensitivity to climate or fire weather and vegetation in a fire simulation model and represented explicitly two key biotic feedbacks linked to succession and regeneration processes. We used this model to forecast annual fire activity from 2011 to 2099 over a large region of boreal forest in Quebec, Canada, dominated by balsam fir (Abies balsamea (L.) Mill) and yellow birch (Betula alleghaniensis Britt.) or paper birch (Betula papyrifera Marsh.), with and without the biotic feedbacks. Our simulations show that vegetation changes triggered by fire disturbance altered future fire activity and may even be as important a driver as climate change itself. Indeed, over the course of the century, vegetation changes were projected to offset much of the increase in fire activity that would be expected due to global warming as such. It follows that if biotic feedbacks are not included in statistical or simulation-based forecasts, the resultant projections of future fire activity could be biased upward to a very considerable degree. For the case of end-of-century mean annual burn rate, we estimated this positive bias to be as high as 400%. Accounting for biotic feedbacks in simulation models is therefore necessary for accurate projection of future wildfire activity and associated vegetation changes. Purely statistical forecasts based on current vegetation cannot be relied upon, in the presence of biotic feedbacks. Our results further suggest that vegetation management could reduce fire risk in some systems by altering the abundance and distribution of the most highly flammable fuels and thus mitigate the impact of climate change on fire activity.

Frequent and intense fires in the final coals of the Paleozoic indicate elevated atmospheric oxygen levels at the onset of the End-Permian Mass Extinction Event

During the End-Permian mass extinction event (EPME) there is extensive evidence for depletion of oxygen in the marine realm. Atmospheric models based upon biogeochemical cycling predict a comparable decline leading up to this event and have been postulated as a possible driver for marine depletion. However, these models contrast with broadly contemporaneous empirical evidence from charcoal in coals. New charcoal data from the temporally well-constrained late Permian Xuanwei Formation coals of eastern Yunnan Province, China, deposited just prior to the onset of the Permian-Triassic Transitional Beds, supports the coarser analysis and further challenges these biogeochemical models. Inertinite group macerals, comprising fusinite, semifusinite, macrinite, inertodetrinite, secretinite, all funginite with elevated reflectance, and some micrinite, are proxies for wildfire activity, and indicate abundant evidence for this phenomenon in the latest Permian and preclude low levels of atmospheric oxygen concentration coevally. Henceforward, we will employ the term ‘inertinite group macerals sensu amplo’ to refer to just these precise macerals, though these encompass what are the overwhelming preponderance of inertinites in most coals. Both inertinite abundance and reflectance indicate an increase in fire activity and intensity towards the End-Permian faunal crisis. Quantitatively, these inertinite data indicate atmospheric oxygen concentration was high and at the close of the Paleozoic was probably elevated to levels well above those of the present-day. The elevated fire activity at this time may have functioned as a causal link to explain some localized oxygen depletion in the marine realm as a result of post-fire increased run-off and erosion. However, globally depressed atmospheric oxygen concentration at the End-Permian was not a driver of extensive marine anoxia at that time.

The relative importance of biotic and abiotic factors influencing aspen recruitment in Arizona

Poor recruitment in some quaking aspen (Populus tremuloides) stands has led to debate over which factors play the largest role in aspen forest persistence. Understanding the relative importance of the many relevant factors over a large landscape could inform management strategies regarding aspen recruitment by focusing efforts on the most important factors. Therefore, between 2011 and 2016 we collected data on 29 biotic and abiotic factors thought to affect aspen recruitment from 92 randomly-selected aspen stands growing along the southwestern limit of its distribution in Arizona, USA. We assessed the condition of selected aspen stands by quantifying the number of recently recruited aspen stems (saplings >2 m tall and <5 cm dbh) in each sampling plot. We used negative binomial regression to estimate the relationship between aspen recruitment and the measured covariates. We fit a balanced set of models, calculated AIC weights for those models, and summed the weights of the models containing each covariate as a measure of covariate relative importance. Six covariates had relative importance values that were significantly greater than random: fire severity in 2011, conifer encroachment, rust presence, fire severity in 2015, blight presence, and the standardized precipitation-evapotranspiration index. There were no significant differences in the ranking of these six covariates by relative importance. Although we estimated that cattle and elk had a significant negative impact on aspen recruitment, these factors were relatively unimportant. This seemingly counter-intuitive result arose because many sites lacked ungulates, but still failed to recruit aspen, indicating that other factors were more important for aspen recruitment. Our results indicate that conifer removal and increased fire activity could be among the most effective management tools to help promote aspen recruitment.

Comparison of organic and palynological proxies for biomass burning and vegetation in a lacustrine sediment record (Lake Allom, Fraser Island, Australia)

Continental fire and vegetation history have been studied in sedimentary archives using palynological proxies (i.e. charcoal abundance and the pollen assemblage) and organic proxies (i.e. the anhydrosugars levoglucosan and it isomers, and plant-wax n-alkanes), but rarely in concert. Here, we compared palynological and organic proxies to reconstruct fire and vegetation history in a sediment core from Lake Allom on Fraser Island, Australia, covering the last 5.4 kyrs. We found that anhydrosugar and microscopic charcoal accumulation rates had similar trends, while trends in macroscopic charcoal accumulation rates were different. This was attributed to the short distance over which macroscopic charcoal is transported compared to microscopic charcoal and anhydrosugars. Furthermore, differences in fire regime and combusted types of vegetation may also explain the differences in levoglucosan and charcoal accumulation rates in lacustrine sediments. Moreover, we found that the ratios between anhydrosugars seem to be governed by combustion conditions, or by type of burned vegetation. Long chain n-alkane accumulation rates and stable isotope compositions showed similar patterns to the pollen assemblage throughout the last 5.4 kyrs, with both representing the local vegetation history. Collectively, our results showed that in the period between 5.4 and 4 ka, biomass burning was low on Fraser Island, while at 4 ka, fire occurrence started to increase, slightly earlier than changes in vegetation and hydrology. Therefore, we suggest that increased fire activity on Fraser Island around 4 ka might have been caused by human-lit biomass burning, since aboriginals settled on Fraser Island around this time.

Risks to carbon dynamics in semi-arid woodlands of eastern Australia under current and future climates

Extreme disturbance events, such as wildfire and drought, have large impacts on carbon storage and sequestration of forests and woodlands globally. Here, we present a modelling approach that assesses the relative impact of disturbances on carbon storage and sequestration, and how this will alter under climate change. Our case study is semi-arid Australia where large areas of land are managed to offset over 122 million tonnes of anthropogenic carbon emissions over a 100-year period. These carbon offsets include mature vegetation that has been protected from clearing and regenerating vegetation on degraded agricultural land. We use a Bayesian Network model to combine multiple probabilistic models of the risk posed by fire, drought, grazing and recruitment failure to carbon dynamics. The model is parameterised from a review of relevant literature and additional quantitative analyses presented here. We found that the risk of vegetation becoming a net source of carbon due to a mortality event, or failing to realise maximum sequestration potential, through recruitment failure in regenerating vegetation, was primarily a function of rainfall in this semi-arid environment. However, the relative size of an emissions event varied across vegetation communities depending on plant attributes, specifically resprouting capacity. Modelled climate change effects were variable, depending on the climate change projection used. Under ‘best-case’ or ‘most-likely’ climate scenarios for 2050, similar or increased projections of mean annual precipitation, associated with a build-up of fuel, were expected to drive an increase in fire activity (a 40–160% increase), but a decrease in drought (a 20–35% decrease). Under a ‘worst-case’ climate scenario, fire activity was expected to decline (a 37% decrease), but drought conditions remain similar (a 5% decrease). These projected changes to the frequency of drought and fire increase the risk that vegetation used for carbon offsetting will fail to provide anticipated amounts of carbon abatement over their lifetime.

Examining forest resilience to changing fire frequency in a fire-prone region of boreal forest.

Future changes in climate are widely anticipated to increase fire frequency, particularly in boreal forests where extreme warming is expected to occur. Feedbacks between vegetation and fire may modify the direct effects of warming on fire activity and shape ecological responses to changing fire frequency. We investigate these interactions using extensive field data from the Boreal Shield of Saskatchewan, Canada, a region where >40% of the forest has burned in the past 30years. We use geospatial and field data to assess the resistance and resilience of eight common vegetation states to frequent fire by quantifying the occurrence of short-interval fires and their effect on recovery to a similar vegetation state. These empirical relationships are combined with data from published literature to parameterize a spatially explicit, state-and-transition simulation model of fire and forest succession. We use this model to ask if and how: (a) feedbacks between vegetation and wildfire may modify fire activity on the landscape, and (b) more frequent fire may affect landscape forest composition and age structure. Both field and GIS data suggest the probability of fire is low in the initial decades after fire, supporting the hypothesis that fuel accumulation may exert a negative feedback on fire frequency. Field observations of pre- and postfire composition indicate that switches in forest state are more likely in conifer stands that burn at a young age, supporting the hypothesis that resilience is lower in immature stands. Stands dominated by deciduous trees or jack pine were generally resilient to fire, while mixed conifer and well-drained spruce forests were less resilient. However, simulation modeling suggests increased fire activity may result in large changes in forest age structure and composition, despite the feedbacks between vegetation-fire likely to occur with increased fire activity.

Machine learning to predict final fire size at the time of ignition.

Fires in boreal forests of Alaska are changing, threatening human health and ecosystems. Given expected increases in fire activity with climate warming, insight into the controls on fire size from the time of ignition is necessary. Such insight may be increasingly useful for fire management, especially in cases where many ignitions occur in a short time period. Here we investigated the controls and predictability of final fire size at the time of ignition. Using decision trees, we show that ignitions can be classified as leading to small, medium or large fires with 50.4 ± 5.2% accuracy. This was accomplished using two variables: vapour pressure deficit and the fraction of spruce cover near the ignition point. The model predicted that 40% of ignitions would lead to large fires, and those ultimately accounted for 75% of the total burned area. Other machine learning classification algorithms, including random forests and multi-layer perceptrons, were tested but did not outperform the simpler decision tree model. Applying the model to areas with intensive human management resulted in overprediction of large fires, as expected. This type of simple classification system could offer insight into optimal resource allocation, helping to maintain a historical fire regime and protect Alaskan ecosystems.

Mecp2 Disruption in Rats Causes Reshaping in Firing Activity and Patterns of Brainstem Respiratory Neurons

People with Rett Syndrome (RTT), a neurodevelopmental disorder caused by mutations in the MECP2 gene, have breathing abnormalities manifested as periodical hypoventilation with compensatory hyperventilation, which are attributable to a high incidence of sudden death. Similar breathing abnormalities have been found in animal models with Mecp2 disruptions. Although RTT-type hypoventilation is believed to be due to depressed central inspiratory activity, whether this is true remains unknown. Here we show evidence for reshaping in firing activity and patterns of medullary respiratory neurons in RTT-type hypoventilation without evident depression in inspiratory neuronal activity. Experiments were performed in decerebrate rats in vivo. In Mecp2-null rats, abnormalities in breathing patterns were apparent in both decerebrate rats and awake animals, suggesting that RTT-type breathing abnormalities take place in the brainstem without forebrain input. In comparison to their wild-type counterparts, both inspiratory and expiratory neurons in Mecp2-null rats extended their firing duration, and fired more action potentials during each burst. No changes in inspiratory or expiratory neuronal distributions were found. Most inspiratory neurons started firing in the middle of expiration and changed their firing pattern to a phase-spanning type. The proportion of post-inspiratory neurons was reduced in the Mecp2-null rats. With the increased firing activity of both inspiratory and expiratory neurons in null rats, phrenic discharges shifted to a slow and deep breathing pattern. Thus, the RTT-type hypoventilation appears to result from reshaping of firing activity of both inspiratory and expiratory neurons without evident depression in central inspiratory activity.

Holocene fire activity during low-natural flammability periods reveals scale-dependent cultural human-fire relationships in Europe

Fire is a natural component of global biogeochemical cycles and closely related to changes in human land use. Whereas climate-fuel relationships seem to drive both global and subcontinental fire regimes, human-induced fires are prominent mainly on a local scale. Furthermore, the basic assumption that relates humans and fire regimes in terms of population densities, suggesting that few human-induced fires should occur in periods and areas of low population density, is currently debated. Here, we analyze human-fire relationships throughout the Holocene and discuss how and to what extent human-driven fires affected the landscape transformation in the Central European Lowlands (CEL). We present sedimentary charcoal composites on three spatial scales and compare them with climate model output and land cover reconstructions from pollen records. Our findings indicate that widespread natural fires only occurred during the early Holocene. Natural conditions (climate and vegetation) limited the extent of wildfires beginning 8500 cal. BP, and diverging subregional charcoal composites suggest that Mesolithic hunter-gatherers maintained a culturally diverse use of fire. Divergence in regional charcoal composites marks the spread of sedentary cultures in the western and eastern CEL. The intensification of human land use during the last millennium drove an increase in fire activity to early-Holocene levels across the CEL. Hence, humans have significantly affected natural fire regimes beyond the local scale – even in periods of low population densities – depending on diverse cultural land-use strategies. We find that humans have strongly affected land-cover- and biogeochemical cycles since Mesolithic times.

How does forest recovery following moderate-severity fire influence effects of subsequent wildfire in mixed-conifer forests?

BackgroundGiven regional increases in fire activity in western North American forests, understanding how fire influences the extent and effects of subsequent fires is particularly relevant. Remotely sensed estimates of fire effects have allowed for spatial portioning into different severity categories based on the degree of fire-caused vegetation change. Fire effects between minimal overstory tree mortality (< 20%) and complete (or nearly complete) overstory tree mortality (> 95%) are often lumped into a single category referred to as moderate severity. In this paper, we investigated how burned areas in this broad category of moderate-severity fire fared when reburned by a subsequent fire. Specifically, we examined the influence of forest structure, tree species composition, and shrub cover 9–17 yr following moderate-severity fire on the severity of a subsequent large wildfire event. We used plot-based measurements of trees and shrub cover to develop 15 forest structure and composition variables to attempt to explain observed reburn severity.ResultsOnly live Abies Mill. species basal area and dead standing biomass were identified as significant predictors of reburn severity using conditional inference tree analysis, both of which were positively related to reburn severity.ConclusionOur findings emphasize that the wide range of fire effects in the moderate-severity category can contribute to highly variable responses to subsequent wildfire.

High-latitude Southern Hemisphere fire history during the mid- to late Holocene (6000–750 BP)

Abstract. We determined the specific biomass burning biomarker levoglucosan in an ice core from the TALos Dome Ice CorE drilling project (TALDICE) during the mid- to late Holocene (6000–750 BP). The levoglucosan record is characterized by a long-term increase with higher rates starting at ∼ 4000 BP and peaks between 2500 and 1500 BP. The anomalous increase in levoglucosan centered at ∼ 2000 BP is consistent with other Antarctic biomass burning records. Multiple atmospheric phenomena affect the coastal Antarctic Talos Dome drilling site, where the Southern Annular Mode (SAM) is the most prominent as the Southern Annular Mode Index (SAMA) correlates with stable isotopes in precipitation throughout the most recent 1000 years of the ice core. If this connection remains throughout the mid- to late Holocene, then our results demonstrate that changes in biomass burning, rather than changes in atmospheric transport, are the major influence on the TALDICE levoglucosan record. Comparisons with charcoal syntheses help evaluate fire sources, showing a greater contribution from southern South American fires than from Australian biomass burning. The levoglucosan peak centered at ∼ 2000 BP occurs during a cool period throughout the Southern Hemisphere, yet during a time of increased fire activity in both northern and southern Patagonia. This peak in biomass burning is influenced by increased vegetation in southern South America from a preceding humid period, in which the vegetation desiccated during the following cool, dry period. The Talos Dome ice core record from 6000 to ∼ 750 BP currently does not provide clear evidence that the fire record may be strongly affected by anthropogenic activities during the mid- to late Holocene, although we cannot exclude at least a partial influence.

Disequilibrium of fire-prone forests sets the stage for a rapid decline in conifer dominance during the 21st century

The impacts of climatic changes on forests may appear gradually on time scales of years to centuries due to the long generation times of trees. Consequently, current forest extent may not reflect current climatic patterns. In contrast with these lagged responses, abrupt transitions in forests under climate change may occur in environments where alternative vegetation states are influenced by disturbances, such as fire. The Klamath forest landscape (northern California and southwest Oregon, USA) is currently dominated by high biomass, biodiverse temperate coniferous forests, but climate change could disrupt the mechanisms promoting forest stability (e.g. growth, regeneration and fire tolerance). Using a landscape simulation model, we estimate that about one-third of the Klamath forest landscape (500,000 ha) could transition from conifer-dominated forest to shrub/hardwood chaparral, triggered by increased fire activity coupled with lower post-fire conifer establishment. Such shifts were widespread under the warmer climate change scenarios (RCP 8.5) but were surprisingly prevalent under the climate of 1949–2010, reflecting the joint influences of recent warming trends and the legacy of fire suppression that may have enhanced conifer dominance. Our results demonstrate that major forest ecosystem shifts should be expected when climate change disrupts key stabilizing feedbacks that maintain the dominance of long-lived, slowly regenerating trees.

Simulating vegetation response to climate change in the Blue Mountains with MC2 dynamic global vegetation model

Warming temperatures are projected to greatly alter many forests in the Pacific Northwest. MC2 is a dynamic global vegetation model, a climate-aware, process-based, and gridded vegetation model. We calibrated and ran MC2 simulations for the Blue Mountains Ecoregion, Oregon, USA, at 30 arc-second spatial resolution. We calibrated MC2 using the best available spatial datasets from land managers. We ran future simulations using climate projections from four global circulation models (GCM) under representative concentration pathway 8.5. Under this scenario, forest productivity is projected to increase as the growing season lengthens, and fire occurrence is projected to increase steeply throughout the century, with burned area peaking early- to mid-century. Subalpine forests are projected to disappear, and the coniferous forests to contract by 32.8%. Large portions of the dry and mesic forests are projected to convert to woodlands, unless precipitation were to increase. Low levels of change are projected for the Umatilla National Forest consistently across the four GCM’s. For the Wallowa-Whitman and the Malheur National Forest, forest conversions are projected to vary more across the four GCM-based simulations, reflecting high levels of uncertainty arising from climate. For simulations based on three of the four GCMs, sharply increased fire activity results in decreases in forest carbon stocks by the mid-century, and the fire activity catalyzes widespread biome shift across the study area. We document the full cycle of a structured approach to calibrating and running MC2 for transparency and to serve as a template for applications of MC2.

Topoedaphic and Forest Controls on Post-Fire Vegetation Assemblies Are Modified by Fire History and Burn Severity in the Northwestern Canadian Boreal Forest

Wildfires, which constitute the most extensive natural disturbance of the boreal biome, produce a broad range of ecological impacts to vegetation and soils that may influence post-fire vegetation assemblies and seedling recruitment. We inventoried post-fire understory vascular plant communities and tree seedling recruitment in the northwestern Canadian boreal forest and characterized the relative importance of fire effects and fire history, as well as non-fire drivers (i.e., the topoedaphic context and climate), to post-fire vegetation assemblies. Topoedaphic context, pre-fire forest structure and composition, and climate primarily controlled the understory plant communities and shifts in the ranked dominance of tree species (***8% and **13% of variance explained, respectively); however, fire and fire-affected soils were significant secondary drivers of post-fire vegetation. Wildfire had a significant indirect effect on understory vegetation communities through post-fire soil properties (**5%), and fire history and burn severity explained the dominance shifts of tree species (*7%). Fire-related variables were important explanatory variables in classification and regression tree models explaining the dominance shifts of four tree species (R2 = 0.43–0.65). The dominance of jack pine (Pinus banksiana Lamb.) and trembling aspen (Populus tremuloides Michx.) increased following fires, whereas that of black spruce (Picea mariana (Mill.) BSP.) and white spruce (Picea glauca (Moench) Voss) declined. The overriding importance of site and climate to post-fire vegetation assemblies may confer some resilience to disturbed forests; however, if projected increases in fire activity in the northwestern boreal forest are borne out, secondary pathways of burn severity, fire frequency, and fire effects on soils are likely to accelerate ongoing climate-driven shifts in species compositions.

A spatio-temporal analysis of fires in the Southern African Development Community region

Wildfires are considered one of the most common disasters in southern Africa resulting in a high number of human fatalities and financial loss on an annual basis. It is believed that increased population growth, as well as more concentrated settlement planning, is likely to result in increased fire disasters and increased human fatalities as a direct result of wildfires. To better understand the spatial and temporal variations and characteristics of wildfires in the Southern African Development Community (SADC), an 11-year dataset of satellite-derived Active Fire Hotspots was analysed using an open source geographic information system. Results indicate that annual fire frequency for most SADC countries is highly variable. Increasing trends in annual fire frequency were observed in five out of 13 SADC countries with a decrease in annual fire frequency observed in four countries. An additional four countries displayed a somewhat stable trend in fire frequency. Temporally, fires have been observed in all months for the SADC region although distinct fire seasons were observed, largely driven by uni-modal rainfall seasons. The timing, location and strength of rainfall seasons have a marked influence on fire activity depending on the seasonal wet and dry (growing and desiccation) periods. Fire activity in vegetation eco-regions can be attributed to both natural and anthropogenic sources of ignition. However, increased anthropogenic agroforestry activities have resulted in increased fire activity in numerous SADC eco-regions with woodlands, savannahs and montane grassland eco-regions being most prone to wildfires.