Single Fire Event Research Articles

Evaluating Noah‐MP Simulated Runoff and Snowpack in Heavily Burned Pacific‐Northwest Snow‐Dominated Catchments

AbstractTerrestrial hydrology is altered by fires, particularly in snow‐dominated catchments. However, fire impacts on catchment hydrology are often neglected from land surface model (LSM) simulations. Western U.S. wildfire activity has been increasing in recent decades and is projected to continue increasing over at least the next three decades, and thus it is important to evaluate if neglecting fire impacts in operational land surface models (LSMs) is a significant error source that has a noticeable signal among other sources of uncertainty. We evaluate a widely used state‐of‐the‐art LSM (Noah‐MP) in runoff and snowpack simulations at two representative fire‐affected snow‐dominated catchments in the Pacific Northwest: Andrew's Creek in Washington and Johnson Creek in Idaho. These two catchments are selected across all western U.S. fire‐affected catchments because they are snow‐dominated and experienced more than 50% burning in a single fire event with minimal burning outside of this event, which allows analyses of distinct pre‐ and post‐fire periods. There are statistically significant shifts in model skills from pre‐to post‐fire years in simulating runoff and snowpack. At both study catchments, simulations miss enhancements in early‐spring runoff and annual runoff efficiency during post‐fire years, resulting in persistent underestimates of annual runoff anomalies throughout the 12‐year post‐fire analysis periods. Enhanced post‐fire snow accumulation and melt contributes to observed but unmodeled increases of spring runoff and annual runoff efficiency at these catchments. Informing simulations with satellite observed land cover classifications, leaf area index, and green fraction do not consistently improve the model ability to simulate hydrologic responses to fire disturbances.

Practical modeling and quantification of a single-top fire events probabilistic safety assessment model

In general, an internal fire events probabilistic safety assessment (PSA) model is quantified by modifying the pre-existing internal event PSA model. Because many pieces of equipment or cables can be damaged by a fire, a single fire event can lead to multiple internal events PSA initiating events (IEs). Consequently, when the fire events PSA model is quantified, inappropriate minimal cut sets (MCSs), such as duplicate MCSs, may be generated. This paper shows that single quantification of a hypothetical single-top fire event PSA model may generate the following four types of inappropriate MCSs: duplicate MCSs, MCSs subsumed by other MCSs, nonsense MCSs, and MCSs with over-counted fire frequencies. Among the inappropriate MCSs, the nonsense MCSs should be addressed first because they can interfere with the right interpretation of the other MCSs and prevent the resolution of the issues related to the other inappropriate MCSs. In addition, we propose a resolution process for each of the issues caused by these inappropriate MCSs and suggest an overall procedure for resolving them. The results of this study will contribute to the understanding and resolution of the inappropriate MCSs that may appear in the quantification of fire events PSA models.

Too hot, too cold, or just right: Can wildfire restore dry forests of the interior Pacific Northwest?

As contemporary wildfire activity intensifies across the western United States, there is increasing recognition that a variety of forest management activities are necessary to restore ecosystem function and reduce wildfire hazard in dry forests. However, the pace and scale of current, active forest management is insufficient to address restoration needs. Managed wildfire and landscape-scale prescribed burns hold potential to achieve broad-scale goals but may not achieve desired outcomes where fire severity is too high or too low. To explore the potential for fire alone to restore dry forests, we developed a novel method to predict the range of fire severities most likely to restore historical forest basal area, density, and species composition in forests across eastern Oregon. First, we developed probabilistic tree mortality models for 24 species based on tree characteristics and remotely sensed fire severity from burned field plots. We applied these estimates to unburned stands in four national forests to predict post-fire conditions using multi-scale modeling in a Monte Carlo framework. We compared these results to historical reconstructions to identify fire severities with the highest restoration potential. Generally, we found basal area and density targets could be achieved by a relatively narrow range of moderate-severity fire (roughly 365-560 RdNBR). However, single fire events did not restore species composition in forests that were historically maintained by frequent, low-severity fire. Restorative fire severity ranges for stand basal area and density were strikingly similar for ponderosa pine (Pinus ponderosa) and dry mixed-conifer forests across a broad geographic range, in part due to relatively high fire tolerance of large grand (Abies grandis) and white fir (Abies concolor). Our results suggest historical forest conditions created by recurrent fire are not readily restored by single fires and landscapes have likely passed thresholds that preclude the effectiveness of managed wildfire alone as a restoration tool.

Predicting and Mapping Potential Fire Severity for Risk Analysis at Regional Level Using Google Earth Engine

Despite being a natural ecological process, wildfires are dramatic events that, accelerated by global change, could negatively affect ecosystem services depending on their severity level. However, because of data processing constraints, fire severity has been mostly neglected in risk analysis (especially at regional levels). Indeed, previous studies addressing fire severity focused mainly on analyzing single fire events, preventing the projection of the results over large areas. Although, building and projecting robust models of fire severity to integrate into risk analysis is of main importance to best anticipate decisions. Here, taking advantage of free data-processing platforms, such as Google Earth Engine, we use more than 1000 fire records from Western Italy and Southern France in the years 2004–2017, to assess the performance of random forest models predicting the relativized delta normalized burn ratio (rdNBR) used as proxy of fire severity. Furthermore, we explore the explanatory capacity and meaning of several variables related to topography, vegetation, and burning conditions. To show the potentialities of this approach for operational purposes, we projected the model for one of the regions (Sardinia) within the study area. Results showed that machine learning algorithms explain up to 75% of the variability in rdNBR, with variables related to vegetation amount and topography being the most important. These results highlight the potential usefulness of these tools for mapping fire severity in risk assessments.

High-Resolution Smoke Forecasting for the 2018 Camp Fire in California

Abstract Smoke from the 2018 Camp Fire in Northern California blanketed a large part of the region for 2 weeks, creating poor air quality in the “unhealthy” range for millions of people. The NOAA Global System Laboratory’s HRRR-Smoke model was operating experimentally in real time during the Camp Fire. Here, output from the HRRR-Smoke model is compared to surface observations of PM2.5 from AQS and PurpleAir sensors as well as satellite observation data. The HRRR-Smoke model at 3-km resolution successfully simulated the evolution of the plume during the initial phase of the fire (8–10 November 2018). Stereoscopic satellite plume height retrievals were used to compare with model output (for the first time, to the authors’ knowledge), showing that HRRR-Smoke is able to represent the complex 3D distribution of the smoke plume over complex terrain. On 15–16 November, HRRR-Smoke was able to capture the intensification of PM2.5 pollution due to a high pressure system and subsidence that trapped smoke close to the surface; however, HRRR-Smoke later underpredicted PM2.5 levels due to likely underestimates of the fire radiative power (FRP) derived from satellite observations. The intensity of the Camp Fire smoke event and the resulting pollution during the stagnation episodes make it an excellent test case for HRRR-Smoke in predicting PM2.5 levels, which were so high from this single fire event that the usual anthropogenic pollution sources became insignificant. The HRRR-Smoke model was implemented operationally at NOAA/NCEP in December 2020, now providing essential support for smoke forecasting as the impact of U.S. wildfires continues to increase in scope and magnitude.

Fire‐related threats and transformational change in Australian ecosystems

AbstractAimMegafire events generate immediate concern for wildlife and human well‐being, but their broader ecological impacts likely extend beyond individual species and single fire events. In the first mechanistic study of fire effects focussed on ecosystems, we aimed to assess the sensitivity and exposure of ecosystems to multiple fire‐related threats, placing impacts in the context of changing fire regimes and their interactions with other threats.LocationSouthern and eastern Australia.Time period2019–2020.Major species studiedAustralian ecosystems.MethodsWe defined 15 fire‐related threats to ecosystems based on mechanisms associated with: (a) direct effects of fire regime components; (b) interactions between fire and physical environmental processes; (c) effects of fire on biological interactions; and (d) interactions between fire and human activity. We estimated the sensitivity and exposure of a sample of 92 ecosystem types to each threat type based on published relationships and spatial analysis of the 2019–2020 fires.ResultsTwenty‐nine ecosystem types assessed had more than half of their distribution exposed to one or more threat types, and only three of those were listed as nationally threatened. Three fire‐related threat types posed the most severe threats to large numbers of ecosystem types: high frequency fire; pre‐fire drought; and post‐fire invasive predator activity. The ecosystem types most affected ranged from rain forests to peatlands, and included some, such as sclerophyllous eucalypt forests and heathlands, that are traditionally regarded as fire‐prone and fire‐adapted.Main conclusionsMost impacts of the 2019–2020 fires on ecosystems became apparent only when they were placed in the context of the whole fire regime and its interactions with other threatening processes, and were not direct consequences of the megafire event itself. Our mechanistic approach enables ecosystem‐specific management responses for the most threatened ecosystem types to be targeted at underlying causes of degradation and decline.

A novel approach to estimating soil yield risk in fire prone ecosystems

Increasing fire activity in the American west heightens the need for natural resource managers to identify where risk associated with post-fire effects is greatest. This is particularly true for water resources, as many headwater forests are at risk for stand replacing fires. However, current methods to model post-fire erosion often have trade-offs between model area and spatial resolution. We introduce a novel approach to combine a process-based erosion model and state-and-transition simulation modeling to estimate post-fire sediment yield and identify areas of high risk. We demonstrate how this method can be applied at three scales: large watershed, sub-watershed, and single fire event. The combination of the erosion model and state-and-transition simulation model allowed us to identify areas of post-fire high sediment yield potential and increased likelihood of fire occurrence. This method can be used by land managers to prioritize pre-fire restoration practices or post-fire rehabilitation actions.

The effect of fire on ant assemblages does not depend on habitat openness but does select for large, gracile predators

AbstractEcosystems can respond in a variety of ways to the same agent of disturbance. In some contexts, fire causes large and long‐lasting changes to ecological communities. In others, fire has a limited or short‐lived impact on assemblages of animals and plants. Understanding why this occurs is critical if we are to manage these kinds of disturbances across the globe. A recent synthesis proposed that these seemingly idiosyncratic responses to fire can be understood in the context of habitat openness pre‐disturbance. Assemblages in open habitats should respond less to a single fire event that those in closed habitats. We provide a test of this hypothesis by examining the response of ant (Hymenoptera: Formicidae) communities to large‐scale fire events in three habitats of different natural canopy openness on the Peloponnese peninsula in Greece. We also test the hypothesis that assemblage responses to fire are trait dependent. Fire simplifies the physical structure of the environment, increases insolation, and limits opportunities for ants to exploit herbivorous feeding strategies. Consequently, we predict that ants will face a strong environmental filter between unburnt and recently burnt plots, which will be reflected in their functional morphology. Our analysis shows that burnt plots have more individual ants, more species and an almost complete compositional change relative to unburnt plots. These changes do not depend on initial canopy openness. Rather, we suggest that openness must be interpreted relative to the study taxon; for ants, openness should be measured closer to the ground level. In our study, ground‐level openness does not vary across the plots, which may explain the results. Furthermore, ants in burnt plots are significantly larger, have relatively longer legs, relatively longer mandibles, and more elongate heads. This morphotype fits with our prediction of ants that can move and feed successfully in the burnt micro‐landscape. Ultimately, more work is needed to fully explore the relationship between habitat openness and the response to fire. Our results showing a filtered set of ant morphologies in burnt environments suggest that ant traits may offer a further way forward to understand the faunal response to fire and disturbance in general.

Post-fire recruitment and resprouting of a threatened montane eucalypt

Changing climate is predicted to result in increased frequency and size of wildfires in south-eastern Australia. With increasing area burnt there is increased potential for entire species distributions to be burnt in a single fire event. This is particularly the case for range-restricted threatened species. Eucalyptus canobolensis (L.A.S.Johnson & K.D.Hill) J.T.Hunter is restricted to Mount Canobolas, New South Wales, Australia. In 2018, the majority of the E. canobolensis population was burnt by wildfire. One-year post-fire, we measured recruitment, resprouting and mortality of E. canobolensis. At higher fire severities, smaller trees were more likely to resprout from their bases only, as their stems were killed (i.e. ‘top kill’). Seedling regeneration only occurred in burnt plots. Our study demonstrates that E. canobolensis has a fire response typical of many eucalypts, characterised by seedling recruitment and larger trees resprouting epicormically, even after high-severity fire. Nevertheless, E. canobolensis response to repeat and short-interval fire remains unknown, and smaller trees appear to be vulnerable to top kill. Although much of Australia’s flora can respond to fire, this response is likely to be challenged as fire extents increase, especially if this is combined with increasing fire severity and/or frequency. These changes to the fire regime are a particular threat to species with restricted distributions.

Lightning modelling for the research of forest fire ignition in Portugal

The study aims to assess the applicability of the current Meso-NH electrical scheme (CELLS) in the investigation of forest fire ignition. Therefore, the challenge is to diagnose cloud-to-ground (CG) lightning at 1 km spatial resolution and, subsequently, preferred regions where Forest Fire Events (FFE) could be naturally ignited. The afternoon of 17th June 2017 has been considered for the study, since the dry thunderstorm environment configured a perfect scenario for natural ignition and evolution of some fires. The Pedrógão Grande wildfire ignited in this period and was the deadliest single fire event in the Portuguese history, with at least 60 people killed. The available observational data are used to validate the numerical results and to provide a brief characterization of the meteorological environment when jointly analysed with the simulation. In addition, cloud microphysics and cloud electrical structure are explored from the model results. The spatial distribution of the simulated CG lightning showed a good agreement with the lightning strokes obtained from the national lightning detection network. Overall, this paper introduces a possible application of the Meso-NH electrical scheme, namely the study of forest fire ignition by lightning strokes.

A wildfire in an Amazonian canga community maintained important ecosystem properties

Because wildfires alter plant communities, we describe the effects of a single fire event on the composition and diversity of Amazonian ferruginous savannas, locally known as cangas. We installed 20 observation plots in burned and unburned parts of a homogeneous canga site from the Carajás Massif. The single fire event shifted community composition slightly, increased functional richness and the abundance of anemochoric and subshrub species, but did not influence the number of phanerophyte species, highlighting the importance of both seeding and resprouting strategies in the post-fire scenario. In contrast, neither taxonomic nor phylogenetic diversity was affected by the fire event. The absence of differences in the phylogenetic community structure indicated that specific adaptations to fires are widespread within the canga phylogeny, although fires are not an eminent part of these ecosystems, as in other neotropical savannas. As diversity metrics were not negatively affected by a single fire event and only small shifts in species composition were observed, our data indicate maintenance of important ecosystem properties despite an occasional wildfire event in the analysed canga shrubland. Further research should outline how different physiognomies are affected and how different fire regimes influence communities to assist in the design of effective management plans for this ecosystem.

Middle- to late-Holocene fire history and the impact on Mediterranean pine and oak forests according to the core RF93-30, central Adriatic Sea

The high-resolution Adriatic RF93-30 core shows changes in its microcharcoal record, which correlate to terrestrial fires from the last 7000 years. Pollen and microcharcoals were transported by wind and fluvial transport from the sedimentary basin, including the Po River and other rivers flowing into the sea off the Italian east coast. Charcoal particles and pollen were counted in the same samples, and the maximum breadth and length of charcoal particles were measured. Microcharcoals with large dimensions were taken as fire indicators occurring along the near coast, as they probably arrived from short distances, the nearest being in Apulia, in southern Italy. The age–depth model was developed within the multidisciplinary PALICLAS project. Several potential fire activity increases (PFAIs) were visible as peaks in the diagram. The oldest PFAIs occurred at the middle Holocene (approximately dated to c. 6730, 5430, 4150 cal BP), others occurred at the late Holocene ( c. 3760, 2660, 2240, 2030, 1930, 1510 cal BP) and during the last millennium ( c. 900–865, 530, 120–96 cal BP). The two oldest peaks in the diagram, occurring in the 7th–6th millennia, showed the highest contribution of charcoal corresponding to the highest values of arboreal pollen (AP) in the sedimentary record. Although the CHAR peaks did not represent a single fire event, the diagram suggests a good correspondence between paleofire activity and terrestrial vegetation biomass during this early phase. Pollen containing black particles was observed, which suggested some grains were transported in suspension with winds from burned woods. The main unambiguous anthropogenic fire causation would have occurred during the last four millennia. From 4.2 ka, it became hard to disentangle climate and Bronze Age actions. Technology and human activity probably improved the pace of fire events, especially involving oak woods, with evidence of an increase of CHAR during the last millennium.

Data resampling: An approach for improving characterization of complex dynamics from noisy interspike intervals

Extracting dynamics from point processes produced by different models describing spiking phenomena depends on several factors affecting the quality of reconstruction of nonuniformly sampled dynamical systems. Although its ability is verified by embedding theorems analogous to the Takens theorem for uniformly sampled time series, a limited amount of samples, a low firing rate and the presence of noise can provide significant computational errors and incorrect characterization of the analyzed oscillatory regimes. Here, we discuss how to improve the accuracy of the quantitative evaluation of complex oscillations from point processes using data resampling. This approach provides a more stable estimation of Lyapunov exponents for noisy datasets. The advantages of resampling-based reconstruction are confirmed by the analysis of various spiking mechanisms, including the generation of single firing events and chaotic bursts.

Impact of a Historical Fire Event on Pyrogenic Carbon Stocks and Dissolved Pyrogenic Carbon in Spodosols in Northern Michigan

Inventories of fire-derived (pyrogenic) C (PyC) stocks in soils remain incomplete for many parts of the world, yet are critical to reduce uncertainties in global PyC estimates. Additionally, PyC dynamics in soils remain poorly understood. For example, dissolved PyC (DPyC) fluxes from soil horizons, as well as the influence of historical fire events on these fluxes and soil PyC stocks remain poorly quantified. In this study, we examined stock and concentration differences in soil PyC and leached DPyC, respectively, between two forest types in the Great Lakes region (USA): (1) a red pine (Pinus resinosa) forest planted after the site had experienced post-logging slash burning in the late 19th century (100yr-burned site), and (2) a sugar maple (Acer saccharum) forest that showed no evidence of burning in the past 250 years (unburned site). We hypothesized that the 100yr-burned site would have greater PyC stocks and concentrations of DPyC compared to the unburned site. We measured PyC in soil, as well as DPyC in soil water leaching from O and E horizons following a spring snowmelt event in both 100yr-burned and unburned sites. Additionally, we measured DPyC drained from B horizons in 100yr-burned site. In organic horizons, PyC stocks were 1.8 (Oi) and 2.3 (Oe) times greater in the 100yr-burned site than in the unburned site. Contrary to our initial hypothesis, DPyC concentrations did not differ between sites. On average, DPyC leached from all sites contributed 3.11±0.27% of the total dissolved organic carbon pool. In the 100yr-burned site, a significant decline in concentrations of DPyC leaving the B horizon was attributed to the immobilization of this C pool in the Al and Fe oxides-rich subsoil. Even though PyC stock in O horizons was higher in 100yr-burned than in unburned site, our results did not support our initial hypothesis that the 100yr-burned site would have greater DPyC concentrations than the unburned site, suggesting that any differences in DPyC resulting from a single fire event are either not detectable after >100 years post-burn, and/or that the release of DPyC is a continuous, long-term process resulting from the degradation of historically accumulated PyC.

Effect of forest fire on tree diversity and regeneration potential in a tropical dry deciduous forest of Mudumalai Tiger Reserve, Western Ghats, India

IntroductionThe study was conducted in Mudumalai Tiger Reserve, in the Western Ghats to understand the effect of a single fire event on tree diversity and regeneration status. Four forest patches were selected which were unburned, 2-year-old burn, 5-year-old burn, and 15-year-old burn. Three 0.1 ha square plots were laid randomly in all four patches and analyzed for tree diversity, stand structure, and regeneration of tree species.ResultsA total of 4129 individuals of tree species were recorded in field surveys, comprising 3474 seedlings, 121 saplings, and 534 trees. Totally, 40 tree species were recorded in study plots, from which 28 species were seedlings, 16 species were saplings, and 37 species were at tree stages.ConclusionsTree diversity decreased in 2-year-old and 5-year-old burnt plots and was reached to the level of unburnt plots in 15 years of interval. Stems of small size classes started increasing after the fire. Seedling density increased linearly in subsequent years after fire but sapling and tree density recorded less than control in B2 but was higher in B5 and B15. The overall fire affected diversity, but regeneration showed a positive trend.

Fire recurrence and emergency post-fire management influence seedling recruitment and growth by altering plant interactions in fire-prone ecosystems

Projections of future wildfire regimes forecast an increased frequency of large high-severity fires that create very harsh environmental conditions and constitute a challenge to post-fire ecosystem regeneration. Under these new circumstances, better knowledge of the plant interaction mechanisms underlying post-fire seedling establishment success would aid restoration management to achieve the intended targets. We evaluated the combined effect of recurrent large stand-replacing fires and conventional post-fire restoration activities (salvage logging after a single large fire, and direct seeding and linear subsoiling plus seedling planting after two subsequent large fires) on tree seedling recruitment and performance (development, annual growth, and biomass) in the early stages of succession in fire-prone maritime pine (Pinus pinaster Ait.) ecosystems. We quantified plant facilitative/competitive interactions between naturally recruited pine seedlings, neighbouring seedlings and potential nurse shrubs with different post-fire regeneration strategies (obligate seeders vs resprouters), by computing the relative interaction index (RII). The results evidenced that fire recurrence altered plant species composition and conditioned initial pine seedling recruitment and establishment, prevailing over the expected negative impact of salvage logging and positive impact of seeding. Seedling recruitment was sufficient to ensure natural tree regeneration after a single fire event and undermined by repeated fires. Both delaying burned timber removal during salvage logging operations and retaining immature dead trees without commercial value onsite in subsoiled stands enhanced seedling recruitment via facilitative interactions. Higher seedling growth and height under shrubs than in open ground resulted in lower aerial and root biomass, indicating elongation in response to shade, and net competition for resources. Inter-specific competition between naturally regenerated seedlings and shrubs was aggravated by intra-specific competition with neighbouring seedlings and by mechanical site preparation in subsoiled stands. All in all, post-burn increased soil fertility most likely counterbalanced the environmental stress created by fire, shifting the net outcome of plant interactions from positive (facilitation) to negative (competition). We recommend alternative post-fire management actions that decrease plant competition and take advantage of facilitation by residual burned wood, to ultimately accelerate ecosystem recovery after large stand-replacing fires.

Characteristics of lightnings igniting forest fires in Austria

Besides anthropogenic causes, lightning is the major reason for forest fire ignition worldwide. Information on lightning characteristics and impact points is missing or controversial, due to the difficulty of lightning stroke localization and the relation to single forest fire events. Austria as an Alpine country experiences a high number of thunderstorms and lightnings, which ignite more than one third of forest fires from June to August. With data from the “Austrian Lightning Detection and Information System” (ALDIS) it was possible to link single lightnings and their characteristics to the location and attributes of individual forest fires. Three subsets with lightning data were compiled and analyzed regarding their strength (kA), polarity (positive or negative) and multiplicity (number of re-strokes). Additional data on the time of ignition, burned area, sea level, exposition and burned vegetation were investigated. Two fire weather sub-indices (FFMC − Fine Fuel Moisture Code and BUI − Build Up Index) of the Canadian FWI (Fire Weather Index) were calculated for the location of the impact point of each lightning and over a period of twenty days, including the day of ignition. Positive lightnings were significantly more likely to induce a fire. Both the FFMC and BUI showed a significant mean decrease after the day of ignition. Precipitation was significant lower at those impact points where forest fires were ignited. Burned area was larger when lightnings ignited during day hours. Most lightning fires occurred at higher altitudes with southerly or western exposition, mainly in stands of Norway spruce (Picea abies L.). Pine species were four times more often affected than the natural tree species distribution would assume. The study results contribute to the international discussion on lightning fires and will help to provide recommendations for further modelling studies on the forecast of lightning caused forest fires.

Why and How the Sustainable Building Community Should Embrace Fire Safety

Sustainable building construction is one of the fastest-growing industries in the USA. Changes in materials, products, designs, and methodologies are occurring to accommodate this green progression. While these changes have energy and environmental benefits, questions have been raised about impacts on fire safety. There are two major reasons to consider the nexus of fire safety and sustainable design. First is a concern for the environment and how a building fire would cause environmental harm. It is possible that a single fire event can negate several, if not all, elements of green design. Second is a concern that sustainable design features will cause unintended increased fire risk or hazards. Sustainable design is a relatively new market with some unconventional materials, techniques, and features that have not yet been proven with time, which introduces risk of unintentional consequences. Moving forward, it would be valuable to integrate green design with fire safety such that they reinforce rather than undermine each other. This article seeks to examine the relationship between fire safety and sustainability in buildings, discuss the status of the fire and sustainability communities, and recommend avenues for development and implementation to promote fire-safe sustainable designs. Such avenues include incorporating greywater and rainwater reuse systems with fire sprinklers, fire alerts and controls in building automation systems, better safety mechanisms and designs for on-site energy production and storage, and less combustible and more resilient structural elements and insulation.

Resilience of European beech forests (Fagus sylvatica L.) after fire in a global change context

The European beech (Fagus sylvatica L.) is one of the most ecologically and economically important tree species in Europe. Nonetheless, post-fire ecological processes in beech forests have only been marginally studied although they might become more important for forest management in the light of global climate change drought effects. Focusing on the Southern European Alps, where numerous forest fires have affected beech stands, we assessed temporal trends and detected factors that influence beech regeneration in beech forests burnt between 1970 and 2012. Beech regeneration was found to occur abundantly in fire sites of mixed burn severity, and often co-occurred with light-demanding pioneer trees (mostly Betula pendula Roth). These pioneers declined in abundance from 20 years post-fire onwards, whereas beech dominance increased. Beech regeneration density was best explained in regression models by the canopy of remnant trees and the abundance of competing ground vegetation. As fire-injured beech trees slowly die back, the canopy gradually opens, favouring beech recruitment for as long as decades, depending on the light conditions. In contrast, dense layers of early post-fire colonisers may delay beech regeneration for many years. Generally, single fire events favour beech regeneration except in areas where the burn severity is extraordinarily high.

Differences in Ecosystem Carbon Distribution and Nutrient Cycling Linked to Forest Tree Species Composition in a Mid-Successional Boreal Forest

In the boreal forest of Alaska, increased fire severity associated with climate change is expanding deciduous forest cover in areas previously dominated by black spruce (Picea mariana). Needle-leaf conifer and broad-leaf deciduous species are commonly associated with differences in tree growth, carbon (C) and nutrient cycling, and C accumulation in soils. Although this suggests that changes in tree species composition in Alaska could impact C and nutrient pools and fluxes, few studies have measured these linkages. We quantified C, nitrogen, phosphorus, and base cation pools and fluxes in three stands of black spruce and Alaska paper birch (Betula neoalaskana) that established following a single fire event in 1958. Paper birch consistently displayed characteristics of more rapid C and nutrient cycling, including greater aboveground net primary productivity, higher live foliage and litter nutrient concentrations, and larger ammonium and nitrate pools in the soil organic layer (SOL). Ecosystem C stocks (aboveground + SOL + 0–10 cm mineral soil) were similar for the two species; however, in black spruce, 78% of measured C was found in soil pools, primarily in the SOL, whereas aboveground biomass dominated ecosystem C pools in birch forest. Radiocarbon analysis indicated that approximately one-quarter of the black spruce SOL C accumulated prior to the 1958 fire, whereas no pre-fire C was observed in birch soils. Our findings suggest that tree species exert a strong influence over C and nutrient cycling in boreal forest and forest compositional shifts may have long-term implications for ecosystem C and nutrient dynamics.