Indirect Effects Of Fire Research Articles

Effect of abrupt post‐fire ash inputs on water quality and the phytoplankton community in lentic freshwaters

Abstract One of the major threats to biodiversity is changing fire regimes, particularly increasingly frequent fires, especially during the dry season. However, studies on the direct and indirect effects of fire on biotic responses in aquatic ecosystems are still scarce. In this study, we investigated how water quality and phytoplankton community structure were affected by different ash concentrations from burning vegetation of a tropical savanna. We used a microcosm experiment to simulate the aquatic ecosystem with different ash concentration scenarios and evaluated the water quality and the composition, richness and density of phytoplankton over time. We found increased total phosphorus and ammoniacal nitrogen concentrations after ash addition, in addition to changes in electrical conductivity. We identified 242 phytoplankton taxa throughout the experiment and identified changes in species composition among treatments. We identified changes in the taxonomic richness of total phytoplankton, green algae and desmids over time. The density of total phytoplankton, diatoms, green algae, desmids and cyanobacteria also changed over time. Our results suggest that ash from terrestrial fires affects water quality and phytoplankton communities depending on the proportion of ash input. Our results serve as a basis for further investigations of the effects of fire on abiotic conditions in aquatic ecosystems and their communities over long periods of time. Finally, longer‐term experiments are needed to evaluate delayed responses by the phytoplankton community.

Changes in bryophyte functional composition during post-fire succession

Climate and land-use changes are altering fire regimes in many regions around the world. To date, most studies have focused on the effects of altered fire regimes on woody and herbaceous communities, while the mechanisms driving post-fire bryophyte succession remain poorly understood, particularly in Mediterranean-type ecosystems. Here, we examined changes in bryophyte functional composition along a post-fire chronosequence (ranging from 1 to 20+ years) in Pyrenean oak woodlands (northeastern Portugal). To do so, we defined bryophyte functional groups based on seven morphological, reproductive, and life history traits. Then, we fitted linear and structural equation models to disentangle the direct and indirect effects of fire (time since fire and fire intensity), vegetation structure, climate, topography, and edaphic conditions on the abundance of each group. We identified two main functional groups: early colonizers (species with traits associated with strong colonization ability and desiccation tolerance) and perennial stayers (species with high competitive ability, i.e., large perennial mosses). Overall, the abundance of early colonizer species decreased with time since fire and increased with fire intensity, while the opposite was observed for perennial stayers. Thus, successional dynamics reflected a trade-off between species' competitive and colonization abilities, highlighting the role of biotic interactions later in succession. Patterns of functional composition were also consistent with changes in environmental conditions during succession, suggesting that species may experience stressful conditions (i.e., high radiation and low water availability) in early stages of post-fire succession. Our results also indicate that increased fire intensity may alter successional trajectories, leading to long-term changes in bryophyte communities. By understanding the response of bryophyte communities to fire, we were able to identify species with potential use as soil restoration materials.

Direct and indirect effects of fire on parasites in an African savanna

Abstract Fires in grassy ecosystems consume vegetation and initiate high‐quality regrowth, which results in pyric herbivory when mammalian grazers concentrate feeding in recent burns. For environmentally transmitted parasites with transmission mechanisms linked to vegetation structure, fire should exert direct effects on parasites, as well as indirect effects resulting from subsequent enhanced herbivory, which can affect parasite input and exposure to environmental conditions. We combined an experimental manipulation with observational data in the Serengeti National Park to investigate the direct and indirect effects of fire on parasites. We assessed the direct effects of fire by measuring changes in parasitic nematode larvae in the grass layer before and after fire on paired experimental burned and control plots. To investigate indirect effects linked to pyric herbivory, we sampled herbivore dung, grass biomass, ground temperature and larval densities every month for 5 months following fire in seven pairs of burned and unburned monitoring plots. Finally, to assess if fire‐driven changes to larval densities affected host infection burdens, we collected faecal samples from a key host, Grant's gazelle (Nanger granti), each month for 5 months to estimate within‐host parasite burdens. Fire killed all larvae and increased grazer dung inputs by 40% for 2 months following fire. Dung inputs after fire led to larval parasite recolonization of burned patches, but intense herbivory kept grass short and larval densities were associated with changes in ground temperature linked to grass biomass and ambient temperature. Grant's gazelles had lower parasite burdens when sampled in areas with higher compared to lower burned area fraction. Fire and pyric herbivory change the densities of larval parasites in the environment and divide the landscape into burned and unburned regions with distinct infection risks for local herbivores. The indirect effects quantified here represent a novel finding with major implications for all grazing systems impacted by fire.

Direct and indirect effects of fire on germination of shortleaf pine seeds

BackgroundShortleaf pine is a fire-adapted tree species, and prescribed fire is commonly used to increase its regeneration success, improve wildlife habitat, and reach conservation objectives associated with open forest ecosystems. We studied direct effects of heat and smoke on shortleaf pine germination in a greenhouse study and effects of season of burning on the number of new germinants in a field study. Improved understanding of fire effects on shortleaf pine seed and regeneration success can help refine burn prescriptions to better meet specific management objectives.ResultsTemperatures ≥ 120 °C eliminated germination of shortleaf pine seeds in a greenhouse trial, and exposure of seeds to 60 °C resulted in no reduction in germination compared to the unheated control regardless of duration of exposure. At 80 °C, duration of heat exposure mattered, with exposure for 10 min reducing germination compared to unheated controls. Smoke exposure had no effect on germination. A field experiment showed that fall burns (prior to seedfall) resulted in greater initial germinant counts than early spring burns (after seedfall but before germination) or unburned controls, which both resulted in greater initial germinant counts than late spring burns (after germination).ConclusionsSeason of prescribed burning can affect the success of shortleaf pine germination. Late spring burning resulted in high mortality of young germinants. Burning in early spring likely resulted in direct damage to some seeds due to heating but may have also had indirect benefit by exposing mineral soil. Fall burning, before the dispersal of shortleaf pine seed, yielded the highest germinant count and is recommended if improving natural regeneration from seed is the primary objective.

Camera traps link population-level activity patterns with wildfire smoke events for mammals in Eastern Washington State

BackgroundDue to anthropogenic climate change and historic fire suppression, wildfire frequency and severity are increasing across the western United States. Whereas the indirect effects of fire on wildlife via habitat change are well studied, less is known about the impacts of wildfire smoke on animal health and behavior. In this study, we explore the effects of wildfire smoke on the behavior of eight medium- to large-bodied mammalian species in a heterogenous study area in Washington, USA. We linked population-level activity metrics derived from camera trap data to concentrations of fire-specific fine particulate matter (PM2.5). We hypothesized that mammalian activity would decline during smoke events, as animals attempt to reduce potential health impacts of smoke inhalation. We used occupancy models and Poisson regression models to test the effect of fire-specific PM2.5 levels on daily detection probability and the number of detections per day, respectively, for each study species.ResultsWhile we did not observe any significant responses to daily mean concentrations of PM2.5 in the occupancy models, we found three species with significant responses in their rates of detections per day in the Poisson regression. Specifically, for each standard deviation increase in the daily mean concentration of PM2.5, there was a 12.9% decrease in the number of bobcat detections per day, an 11.2% decrease in the number of moose detections per day, and a 5.8% increase in the number of mule deer detections per day. In general, the effects of PM2.5 were small compared to other relevant covariates.ConclusionsWe generally found little evidence to support our hypothesis that animals would reduce their activity in response to wildfire smoke. However, our study demonstrated that mammals exhibited species-specific behavioral responses to smoke, which are possibly adaptive responses to reduce health impacts from smoke inhalation. Though we found only a few immediate behavioral responses to smoke exposure, we note that longer-term health consequences of smoke exposure for wildlife are also likely and generally unknown. Our study shows how camera traps, which are already widely used to study wildlife, can also be used to investigate the impacts of wildfire smoke on animal behavior and provides a step towards developing methods to better understand this increasing source of environmental stress on wildlife.

Impacts of barley (Hordeum vulgare L.) straw mulch on post-fire soil erosion and ground vegetation recovery in a strawberry tree (Arbutus unedo L.) stand

Rural fires are now a major societal concern across the world, especially where fire regimes have (apparently) intensified in terms of burnt area, intensity and recurrency. Among the indirect fire effects, fire-enhanced runoff and erosion have been an important focus of post-fire land and water management, in particular through emergency stabilization of hillslopes using a range of erosion mitigation measures. The most widely applied and – scientifically tested – measure is that of mulching with agricultural straw, in spite of concerns of introducing exogenous organic material and especially seeds of non-native higher plant species, including the straw species it- or themselves. So far, field studies in the present study region of north-central Portugal have preferred using endogenous forest residues but these studies concerned forest types for which such residues are easily available. The latter, however, is not the case for strawberry tree stands, so that straw mulch was selected in this study as a cheaper alternative to eucalypt or pine residues. This - apparently, first – post-fire erosion mitigation study in a strawberry tree (Arbutus unedo L.) stand aimed to compare post-fire sediment and organic matter losses as well as ground vegetation recovery without and with applying barley (Hordeum vulgare L.) straw mulch at a low rate of 2 Mg ha−1. The experimental set-up involved a randomized block design with a total of six geotextile-bounded erosion plots of 2 m by 5 m that were organized in three blocks, were installed and mulched roughly one month after the 17-October-2017 M-fire in inland Central Portugal, and monitored at 12 irregular intervals during the first two post-fire years. The principal findings were that: (i) especially the specific sediment losses without mulching over the first post-fire year were notably higher than those reported by the prior field studies in the region, in eucalypt and maritime pine plantations; and that the - low - mulching rate: (ii) was extremely effective in reducing these first-post-fire-year losses; but (iii) did not result in changes in the cover or floristic composition of the ground vegetation cover that were noteworthy and longer-lived than the first post-fire year.

Fire and Rhizosphere Effects on Bacterial Co-Occurrence Patterns

Fires are common in Mediterranean soils and constitute an important driver of their evolution. Although fire effects on vegetation dynamics are widely studied, their influence on the assembly rules of soil prokaryotes in a small-scale environment has attracted limited attention. In the present study, we reanalyzed the data from Aponte et al. (2022) to test whether the direct and/or indirect effects of fire are reflected in the network of relationships among soil prokaryotes in a Chilean sclerophyllous ecosystem. We focused on bacterial (genus and species level) co-occurrence patterns in the rhizospheres and bulk soils in burned and unburned plots. Four soils were considered: bulk-burnt (BB), bulk-unburnt (BU), rhizosphere-burnt (RB), and rhizosphere-unburnt (RU). The largest differences in network parameters were recorded between RU and BB soils, while RB and BU networks exhibited similar values. The network in the BB soil was the most compact and centralized, while the RU network was the least connected, with no central nodes. The robustness of bacterial communities was enhanced in burnt soils, but this was more pronounced in BB soil. The mechanisms mainly responsible for bacterial community structure were stochastic in all soils, whether burnt or unburnt; however, communities in RB were much more stochastic than in RU.

Interrelationships between fire, habitat, and mammals in a fragmented heathy woodland

Altered fire regimes threaten biodiversity, but there is limited understanding of the mechanisms driving population declines. Relationships between mammal occurrence and time since fire can be unclear because mammals respond directly to changes in habitat structure rather than time since fire per se, and patterns of regeneration can be highly variable. Previous studies have examined how mammals respond to time since fire and habitat structure separately, but rarely considered the three factors together. Furthermore, fires may interact with other threats such as habitat loss and fragmentation, also rarely incorporated into fire studies but known to influence mammal communities. Understanding each of these mechanisms and how they interact is critical for using fire effectively in conservation.We simultaneously related ground-dwelling mammal species activity to habitat structure, habitat structure to post-fire vegetation growth stage, and species activity to growth stage and landscape structure (extent of heathy woodland vegetation) using structural equation models (SEMs). This allowed us to find direct effects of growth stage on mammals, indirect effects mediated by habitat structure, and additional effects of landscape structure.Understorey cover, litter depth, and coarse woody debris responded to growth stage and were important contributors in all SEMs. Four of seven mammal species responded to at least one habitat structure variable. None of the mammal species were related directly to growth stage, but mammals were indirectly related to growth stage through the mediating influence of habitat structure. For example, western grey kangaroos were linked to recently burnt sites, but only through their negative association with litter depth. Extent of heathy woodland vegetation was also an important driver of mammal activity and was related to all but one species; two species showed a positive relationship, and four negative.Important relationships between fire and ground-dwelling mammals may be overlooked unless changes in important habitat resources are also considered. Fire management planning for fauna conservation should incorporate habitat responses as mammal responses to the fire regime may be mediated by fire-driven changes in resources. Knowing how time since fire affects important habitat structures can improve the effectiveness of using fire to manipulate these to support mammal species. Our results will help land managers understand direct and indirect effects of fire in a landscape where multiple drivers threaten biodiversity, and guide the use of prescribed fire to promote aspects of habitat structure that benefit mammals.

Direct and indirect effects of fire on microbial communities in a pyrodiverse dry‐sclerophyll forest

Abstract Fire is one of the predominant drivers of the structural and functional dynamics of forest ecosystems. In recent years, novel fire regimes have posed a major challenge to the management of pyrodiverse forests. While previous research efforts have focused on quantifying the impacts of fire on above‐ground forest biodiversity, how microbial communities respond to fire is less understood, despite their functional significance. Here, we describe the effects of time since fire, fire frequency and their interaction on soil and leaf litter fungal and bacterial communities from the pyrodiverse, Eucalyptus pilularis forests of south‐eastern Australia. Using structural equation models, we also elucidate how fire can influence these communities both directly and indirectly through biotic–abiotic interactions. Our results demonstrate that fire is a key driver of litter and soil bacterial and fungal communities, with effects most pronounced for soil fungal communities. Notably, recently burnt forest hosted lower abundances of symbiotic ectomycorrhizal fungi and Acidobacteria in the soil, and basidiomycetous fungi and Actinobacteriota in the litter. Compared with low fire frequencies, high fire frequency increased soil fungal plant pathogens, but reduced Actinobacteriota. The majority of fire effects on microbial communities were mediated by fire‐induced changes in litter and soil abiotic properties. For instance, recent and more frequent fire was associated with reduced soil sulphur, which led to an increase in soil fungal plant pathogens and saprotrophic fungi in these sites. Pathogenic fungi also increased in recently burnt forests that had a low fire frequency, mediated by a decline in litter carbon and an increase in soil pH in these sites. Synthesis. Our findings indicate that predicted increases in the frequency of fire may select for specific microbial communities directly and indirectly through ecological interactions, which may have functional implications for plants (increase in pathogens, decrease in symbionts), decomposition rates (declines in Actinobacteriota and Acidobacteriota) and carbon storage (decrease in ectomycorrhizal fungi). In the face of predicted shifts in wildfire regimes, which may exacerbate fire‐induced changes in microbial communities, adaptive fire management and monitoring is required to address the potential functional implications of fire‐altered microbial communities.

Fire has short-term negative effects on a super-dominant native fern, Pteridium arachnoideum (Dennstaedtiaceae), in a Brazilian savanna

Although fire occurrence plays a central role in the dominance of the super-dominant bracken fern Pteridium arachnoideum in Neotropical forests, it is unclear whether this applies to the Brazilian savanna (Cerrado), which vegetation is naturally adapted to fire. We assessed fire effects on the aboveground biomass of P. arachnoideum in the Cerrado Ecological Reserve in Central Brazil. We measured frond height, density, standing biomass, and litter biomass before and for two years following a prescribed fire, and also sampled a control site to control for other mortality events and for seasonal variation. The average P. arachnoideum frond height and aboveground biomass decreased over three times in the burnt site 18 months after the fire. The frond density decreased both in the burnt and control site, indicating that this may have been caused in another way than by fire. Conversely, litter biomass decreased shortly after the fire in the burnt site, but returned to pre-fire levels in one year. Possible explanations for the lasting negative effects of fire on the height and biomass of P. arachnoideum include the implementation of the prescribed fire early in the dry season, which likely limited immediate clonal regrowth, and the herbivory by leaf-cutting ants. Nevertheless, the effective clonal growth of P. arachnoideum apparently precluded the fire from having stronger effects and hence this species was not excluded from the site. We conclude that direct and indirect fire effects may cause the decline of P. arachnoideum in Cerrado, so that prescribed fires may be applied as a management strategy in Cerrado sites where this species is super-dominant, ideally in combination with other control measures.

Design of vertical members in large-span steel structures: Can relevance of seismic actions be exceeded on account of indirect fire actions?

Effect of lateral actions evolving from restrained thermal expansions of horizontal structural elements (beams, slabs) on stability of vertical elements (columns, walls) of fire-engulfed buildings remains unaddressed sometimes in engineering practice. Discussion with engineers has revealed that two reasons may contribute most to such design inconsistency. The first is premature assumptions that the effects of these actions can not be sufficient to exceed the effects of other lateral design actions, especially if for the same building considerable seismic influences are also expected. The second reason is the fact that, according to the present version of Eurocodes, these actions need not be addressed specifically if the design is carried out under standard fire curve. This curve, however, is still applied often in practice. For certain vertical members, such as the ones positioned somewhere within the middle of fire compartments, indirect lateral fire actions may indeed be negligible, e.g., due to partial or complete balancation of these actions in fire evolving simultaneously at two opposite sides. However, more pronounced effect might be observed for vertical members at the boundary between a fire-engulfed and a neighbouring cold-side compartment, especially in steel or RC buildings with larger horizontal spans prone to striking lateral thermal elongations. While such structures represent a fair share of existing building stock (they are common, e.g., in prefabricated industrial and commercial buildings), this problem deserves a special attention. In this paper two real one-storey large-span halls are analysed for confirmation of the above hypothesis. Each of them comprises two structurally connected units, i.e. one RC- and the other steel-framed, where fire is assumed to engulf the steel-framed unit. Stability of the ’cold-side’ RC columns at the boundary between both sectors is discussed and for the latter indirect fire actions from the connecting fire-engulfed steel members are found to be of a comparable or a greater size to effect of moderate-size seismic actions. The greatest effects of the observed fire actions are found at average steel temperatures below 400 °C. This is a rather low temperature expected to be achieved (sooner or later) in most fire-affected steel elements with or without fire protection. At the same time, as in this paper also proven by results of exact visco-plastic structural computations, this is also a temperature at which no pronounced creep strains yet evolve in steel within time frames relevant for common structural fire analyses. In addition, the paper also shows that these conclusions would not change for other variations of the discussed two buildings where other possible kinematic boundary conditions were applied at the ends of the steel members or other possible thermal boundary conditions were assumed along their longitudinal surfaces. At most, the observed indirect fire effects would only increase further in these cases. Thus, at least for structures of a similar type (i.e. one-storey frame structures of horizontal spans of similar size and materials), the authors propose that the discussed lateral indirect fire actions are not dismissed from any design procedure regardless of the expected fire scenario as long as steel is allowed to heat to moderate temperatures (around 400 °C). In the last part of the paper the authors also discuss possible change of these findings for multi-storey frame structures and/or frame structures of other spans. However, for these (and other possible) structural types, a more detailed further investigation is proposed.

Untangling the influences of fire, habitat and introduced predators on the endangered heath mouse

AbstractGlobally, species extinctions are driven by multiple interacting factors including altered fire regimes and introduced predators. In flammable ecosystems, there is great potential to use fire for animal conservation, however most fire‐based conservation strategies do not explicitly consider interacting factors. In this study, we sought to understand the interrelationships between the endangered heath mouse Pseudomys shortridgei, fire, resource availability and the introduced fox Vulpes vulpes in southeast Australia. We predicted that heath‐mouse relative abundance would respond indirectly to post‐fire age class (recently burnt; 0–3 years since fire, early; 4–9 years, mid; 10–33 years and late; 34–79 years) via the mediating effects of resources (shrub cover and plant‐group diversity) and fox relative abundance. We used structural equation modelling to determine the strength of hypothesized pathways between variables, and mediation analysis to detect indirect effects. Both the cover of shrubs (0–50 cm from the ground) and fox relative abundance were associated with post‐fire age class. Shrub cover was highest 0–9 years after fire, while fox relative abundance was highest in recently burnt vegetation (0–3 years after fire). Heath mice were positively correlated with shrub cover and plant‐group diversity, and negatively correlated with fox relative abundance. We did not detect a direct relationship between heath mice and post‐fire age class, but they were indirectly associated with age class via its influence on both shrub cover and fox relative abundance. Our findings suggest that heath mice will benefit from a fire regime promoting dense shrub regeneration in combination with predator control. Understanding the indirect effects of fire on animals may help to identify complementary management practices that can be applied concurrently to benefit vulnerable species. Analytical and management frameworks that include multiple drivers of species abundance and explicitly recognize the indirect effects of fire regimes will assist animal conservation.

Litter removal through fire – A key process for wetland vegetation and ecosystem dynamics

Fire is a major driver of global vegetation patterns. It strongly reduces litter and thus alters physical and chemical properties of the environment. Studies investigating the interplay of fire and litter are scarce, and wetland ecosystems are strongly under-represented in research focusing on litter dynamics. We present data on short-term effects of fires in floodplain wetlands along the Amur River in the Russian Far East, an area with a high fire recurrence rate. We analysed vegetation and plant growth patterns as well as soil temperature and nutrient concentrations on recently burnt and unburnt control plots.Directly after fire, litter was reduced by more than 50% on burnt plots. This effect was no longer visible 15 months after fire, probably due to the high productivity of the floodplain ecosystem. Litter was found to act as a key determinant in the net of direct and indirect fire effects, by influencing early plant growth patterns of herbs and grasses. Furthermore, litter removal through fire significantly increased plant species diversity and soil temperature. Contrary, N and P concentrations in living plant biomass of grasses and herbs decreased with decreasing litter cover. Combustion during burning seems to be responsible for the negative direct fire impacts on nutrient concentrations, which were found for N and Mg.Litter removal through fire can strongly affect diversity patterns, dominance structures, and nutrient cycling in wetlands. With increasing fire frequency in the course of global change, significant structural and compositional changes in herbaceous wetland vegetation must be anticipated and the studied ecosystem may shift to reinforced N-limitation.

Direct and Indirect Effects of Fire on Eastern Box Turtles

ABSTRACTPrescribed fire is an increasingly important management tool for eastern deciduous forests, but relativity little is known about the direct effects of fire on the eastern box turtle (Terrapene carolina carolina). We used very high frequency (VHF) transmitters to monitor mortality, movement, and spatial ecology of 118 box turtles in response to 17 prescribed fires across 4 seasons and 3 sites in east Tennessee, USA, during 2016–2018. Annual survival of box turtles that experienced a prescribed fire event was lower (0.87 ± 0.04 [SE]) than turtles that did not (0.98 ± 0.01) and was negatively correlated with fire intensity, fire temperature the turtle experienced, and litter depth. All prescribed fire‐related mortalities occurred during the early (Apr–May,n = 5) or late growing season (Sep–Oct,n = 1). Fourteen percent of box turtles we captured exhibited damage to their carapace from previous fire events. Box turtles that survived prescribed fires were in microsites that did not burn, moved to unburned areas during the fire, or burrowed following ignition. Home range size was similar before and after burns and sinuosity of movements did not differ in burned or unburned areas. Our results indicate that though box turtles are susceptible to prescribed fire during their active season, they have behavioral and physical traits that reduce the direct effects of prescribed fire. Prescribed fire practitioners should be aware of the risks of fire, particularly during the active season. We suggest managers consider altering prescribed fire intensity, seasonality, and firing pattern to minimize risk of direct effects where box turtles are of concern. © 2020 The Wildlife Society.

Fire decline in dry tropical ecosystems enhances decadal land carbon sink

The terrestrial carbon sink has significantly increased in the past decades, but the underlying mechanisms are still unclear. The current synthesis of process-based estimates of land and ocean sinks requires an additional sink of 0.6 PgC yr−1 in the last decade to explain the observed airborne fraction. A concurrent global fire decline was observed in association with tropical agriculture expansion and landscape fragmentation. Here we show that a decline of 0.2 ± 0.1 PgC yr−1 in fire emissions during 2008–2014 relative to 2001–2007 also induced an additional carbon sink enhancement of 0.4 ± 0.2 PgC yr−1 attributable to carbon cycle feedbacks, amounting to a combined sink increase comparable to the 0.6 PgC yr−1 budget imbalance. Our results suggest that the indirect effects of fire, in addition to the direct emissions, is an overlooked mechanism for explaining decadal-scale changes in the land carbon sink and highlight the importance of fire management in climate mitigation.

Species specific effects of prescribed burns on bat occupancy in northwest Arkansas

Due to the recent spread of white nose syndrome, it is imperative that managers understand the effects their management techniques have on bat species. Our research aims to determine the spatial and temporal variation in occupancy of bat species native to the Ozark Highlands and Boston Mountains of northwest Arkansas. Although prescribed burn units in this region are burned on a three-year rotation, it is not currently known how this treatment schedule affects bats. To determine the effects of prescribed burns on bat species including Myotis grisescens, Nycticeius humeralis, and Perimyotis subflavus, acoustic monitors and insect traps were deployed at 20 burned and 20 unburned sites that were visited twice, between April and November of 2017. Bat calls were analyzed for presence/absence data. Single season occupancy modeling was used to determine the effects of environmental covariates on probabilities of detection and occupancy. In total, 132,528 acoustic files were collected. The probability of detection for each bat species was affected by temperature or moon phase. Occupancy models indicated that probability of occupancy for all species was affected by seasonal changes and basal area (m2/Ha), and all but one were affected by prey biomass. These data indicate that although prescribed burns may have not directly affected bats, potential indirect effects of fire, basal area and insect biomass, appear to have significant impacts.

The magnet effect of fire on herbivores affects plant community structure in a forested system

Fire plays an important role in plant community structure in many terrestrial ecosystems. However, most studies assume responses of plant communities to fire are primarily generated by direct effects. That is, studies often assume the net effects of fire on plant communities are primarily driven by fire consuming existing plant biomass, resetting succession, and stimulating new seed germination. Far less attention has been paid to indirect effects of fire on plant communities as mediated by food web interactions. Here we demonstrated in a series of experiments in a loblolly pine (Pinus taeda) forest that the net effects of fire on plant community heterogeneity are indirectly mediated through changes in herbivore behavior. First, we demonstrated that fire causes a magnet effect for herbivores resulting in a 3-fold strengthening of herbivore use. Then in another experiment using a replicated before-after control-impact design with four treatments, we demonstrated that combining fire and herbivory has a non-additive positive effect on plant community heterogeneity. The shifts in the plant community were sustained post-fire through the plant dormancy period. These results highlight the need to conserve the fire-herbivory interaction rather than either force independently.

Fire severity effects on soil carbon and nutrients and microbial processes in a Siberian larch forest.

Fire frequency and severity are increasing in tundra and boreal regions as climate warms, which can directly affect climate feedbacks by increasing carbon (C) emissions from combustion of the large soil C pool and indirectly via changes in vegetation, permafrost thaw, hydrology, and nutrient availability. To better understand the direct and indirect effects of changing fire regimes in northern ecosystems, we examined how differences in soil burn severity (i.e., extent of soil organic matter combustion) affect soil C, nitrogen (N), and phosphorus (P) availability and microbial processes over time. We created experimental burns of three fire severities (low, moderate, and high) in a larch forest in the northeastern Siberian Arctic and analyzed soils at 1, 8days, and 1year postfire. Labile dissolved C and N increased with increasing soil burn severity immediately (1day) postfire by up to an order of magnitude, but declined significantly 1week later; both variables were comparable or lower than unburned soils by 1year postfire. Soil burn severity had no effect on P in the organic layer, but P increased with increasing severity in mineral soil horizons. Most extracellular enzyme activities decreased by up to 70% with increasing soil burn severity. Increasing soil burn severity reduced soil respiration 1year postfire by 50%. However, increasing soil burn severity increased net N mineralization rates 1year postfire, which were 10-fold higher in the highest burn severity. While fires of high severity consumed approximately five times more soil C than those of low severity, soil C pools will also be driven by indirect effects of fire on soil processes. Our data suggest that despite an initial increase in labile C and nutrients with soil burn severity, soil respiration and extracellular activities related to the turnover of organic matter were greatly reduced, which may mitigate future C losses following fire.

Temporal effects of prescribed burning on terpene production in Mediterranean pines.

Prescribed burning is used to reduce fuel hazard but underburning can damage standing trees. The effect of burning on needle terpene storage, a proxy for secondary metabolism, in fire-damaged pines is poorly understood despite the protection terpenes confer against biotic and abiotic stressors. We investigated variation in needle terpene storage after burning in three Mediterranean pine species featuring different adaptations to fire regimes. In two pure-stands of Pinus halepensis Mill. and two mixed-stands of Pinus sylvestris L. and Pinus nigra ssp. salzmanni (Dunal) Franco, we compared 24 h and 1 year post-burning concentrations with pre-burning concentrations in 20 trees per species, and evaluated the relative contribution of tree fire severity and physiological condition (δ13C and N concentration) on temporal terpene dynamics (for mono- sesqui- and diterpenes). Twenty-four hours post-burning, monoterpene concentrations were slightly higher in P. halepensis than at pre-burning, while values were similar in P. sylvestris. Differently, in the more fire-resistant P. nigra monoterpene concentrations were lower at 24 h, compared with pre-burning. One year post-burning, concentrations were always lower compared with pre- or 24 h post-burning, regardless of the terpene group. Mono- and sesquiterpene variations were negatively related to pre-burning δ13C, while diterpene variations were associated with fire-induced changes in needle δ13C and N concentration. At both post-burning times, mono- and diterpene concentrations increased significantly with crown scorch volume in all species. Differences in post-burning terpene contents as a function of the pine species' sensitivity to fire suggest that terpenic metabolites could have adaptive importance in fire-prone ecosystems in terms of flammability or defence against biotic agents post-burning. One year post-burning, our results suggest that in a context of fire-induced resource availability, pines likely prioritize primary rather than secondary metabolism. Overall, this study contributes to the assessment of the direct and indirect effects of fire on pine terpene storage, providing valuable information about their vulnerability to biotic and abiotic stressors throughout time.

Fire indirectly benefits fitness in two invasive species

Ecosystems perturbed from their natural disturbance regimes are more vulnerable to establishment and dominance of exotic plant species. Restoration efforts that reintroduce fire have achieved mixed success in reducing the abundance of exotic plants. The responses of many native species to fire are well known; fire-adapted species respond directly (heat and smoke cue germination) and indirectly (post-fire environment benefits seedling survivorship and growth) to fire. However, the direct and indirect effects of fire are unknown for most exotic plant species. We tested the direct and indirect effects of fire on two exotic invaders of Asian origin, Ailanthus altissima and Lonicera maackii, in North American woodlands. To quantify the direct effects of fire, we compared germination rates of seeds exposed to varying levels of heat and smoke in a laboratory and placed at different soil depths during a prescribed fire in the field. We examined the indirect effects of fire by comparing seedling recruitment in burned and unburned woodland plots. Results indicate that neither A. altissima nor L. maackii have germination cues associated with fire. However, both species have greater seedling recruitment in burned as compared to unburned areas in the field. Although seeds of these invasive species are not specifically adapted to fire, they still benefit from post-fire environments and pose a challenge to restoration of fire-maintained ecosystems. Future studies using our approach will allow land managers to better predict how communities will respond to restoration efforts and to understand variability observed in past restoration projects.