The stoichiometric signature of high‐frequency fire in forest floor food webs

The focus of the study is to investigate regional and local past, present and future changes in fire regimes of tropical and subtropical Queensland and shifts in vegetation composition and structure. Fire has been shown to be a significant driver of ecosystem evolution, composition and distribution through its impact on biota. Within Australia fire has long played a role in shaping the landscape, with increased fire frequency, associated with heightened aridity, over the last five million years promoting the expansion of fire adapted sclerophyll vegetation across the continent. Evidence of anthropogenic fires date back to approximately 50 ka (thousand years ago) with the advent of Aboriginal occupation and fire-stick practices, however with the arrival of Europeans there was a decline in fire frequencies, related to fire exclusion that observes an increase in fire intensity and severity.A review of the introduction of tropical African perennial grasses to improve grazing in tropical and semi-arid regions of northern Australia was also undertaken. This introduction has resulted in some exotic grass species such as Gamba grass (Andropogon gayanus), Mission grass (Cenchrus polystachios syn. Pennisetum polystachion) and Guinea grass (Megathyrsus maximus syn. Panicum maximum Jacq. var. trichoglume) becoming invasive pests. Invasion by these exotic grasses has serious implications for ecosystem function, altering fire regime dynamics through increasing the distribution and abundance of fine fuels. With increased fine fuels there is a serious danger that there will be an increase in fire frequency and intensity resulting in higher severity burns and higher vegetation mortality, with possible local species extinctions and habitat modification or change.Macro charcoal and pollen records were used from Fraser Island, subtropical eastern Australia to identify fire and vegetation histories, which show substantial temporal and spatial changes in past fire frequencies and vegetation composition for the last 24,000 years. Pollen records show pyrophobic rainforest taxa dominated and then declined while pyrogenic sclerophyll arboreal taxa increased correlating with an increase in fire frequencies, and a dryer climate. This was followed by a dramatic increase in Restionaceae values at the beginning of the Holocene (~10,000 years ago) that dropped off as a marked peak in mangroves, primarily the Rhizophoraceae and Melaleuca occurred, possibly linked with sea level rise approximately 6000 to 5000 years ago, which was also associated with lower fire frequencies. Restionaceae then recovered from around 2 ka to the European settlement period, when a dramatic change in fire frequency occurred linked to fire suppression and was followed by vegetation thickening (i.e. increase in arboreal taxa) in the mid to late 20th century.Vegetation thickening was investigated on Fraser Island through land change analysis of aerial photographs and survey data between 1958 and 2016 of a wetland system at Moon Point. This was undertaken using the Land Change Modeller (IDRISI TerrSet), with results showing that forest and woodland communities have invaded the fringes of a restiad dominated wetland. Pollen results from adjacent sediment cores support the occurrence of vegetation thickening that appears to be linked to marked changes in fire regimes on the island associated with European management since the 19th century. A projection of further landscape change was made to 2066 and this suggested a 30% loss in wetland extent by this time under present fire frequencies (i.e. with a mean of approximately one fire every plus/minus 12 years).Identifying past and present fire regimes and vegetation composition are important for fire modelling as this provides possible scenario based probabilities for changes in fire frequency and intensity. Modelling is useful in that it provides managers with a tool to ascertain possible scenario based outcomes depending on the input values. Here the FireBGCv2 fire simulation model has been applied to an Australian context to provide a research simulation platform for exploring fire, vegetation, and climate dynamics that can be directly applied to fire management applications.Fire has played an integral role in shaping the Australian landscape, with fire regimes driven by both climatic and anthropogenic factors during the late Quaternary period. Evidence of shifts in vegetation and fire regimes for the subtropics of Australia can be seen from pollen and charcoal analysis, with dramatic changes occurring over the past 24,000 years on Fraser Island. With the arrival and settlement of Europeans in the mid19th century, fire regimes were once again changed that resulted in further vegetation shifts due to a fire exclusion policy. Further shifts in fire regimes can be seen in tropical northern Australia through the introduction on invasive grasses increasing fuel loads and fire frequency, resulting in a transformed landscape, perpetuating a fire grass cycle. However in the subtropics alterations in fire management have seen a reduction in fire frequency with a thickening of vegetation along the ecotone of E. minus wetlands and sclerophyllous forests at Moon Point on Fraser Island. The complexities of fire regimes for managers is obvious, therefore there is a need for a dynamic mechanistic fire simulation model that managers can use as a tool to project present and future fire events.

Climate change is predicted to result in a warmer and drier climate in many parts of the world, including south-central British Columbia. With a shift in climate, a change in fire regimes is likely to occur. In this study, a statistically significant increase in mean fire size was predicted to occur along with an increase maximum fire size and decrease in the mean fire interval. A change in these fire regime characteristics suggests a climate-change driven shift in fire regimes may occur by the 2020s. The shift in fire regime suggests the proportion of the landscape burning every 50 years or less will increase from 34 % to 93 % by the 2080s. Change in fire regimes will have direct implications for ecosystem management as the combination of large, flammable fuel types and fire-prone climatic conditions will increase the risk of larger more frequent fires and increase the costs and dangers involved in managing fire-prone forests in the Cordilleran region of south-central British Columbia. The climate change-driven shift in fire regime questions the use of historic fire regime characteristics for determining landscape-level conservation targets within the study area.

Fire regime shifts as a consequence of fire policy and socio-economic development: An analysis based on the change point approach

Fire regime changes are considered a major threat to future biodiversity in the Mediterranean Basin. Such predictions remain uncertain, given that fire regime changes and their ecological impacts occur over timescales that are too long for direct observation. Here we analyse centennial- and millennial-scale shifts in fire regimes and compositional turnover to track the consequences of fire regime shifts on Mediterranean vegetation diversity. We estimated rate-of-change, richness and compositional turnover (beta diversity) in 13 selected high-resolution palaeoecological records from Mediterranean Iberia and compared these with charcoal-inferred fire regime changes. Event sequence analysis showed fire regime shifts to be significantly temporally associated with compositional turnover, particularly during the last three millennia. We find that the timing and direction of fire and diversity change in Mediterranean Iberia are best explained by long-term human–environment interactions dating back perhaps 7500 years. Evidence suggests that Neolithic burning propagated a first wave of increasing vegetation openness and promoted woodland diversity around early farming settlements. Landscape transformation intensified around 5500 to 5000 cal. yr BP and accelerated during the last two millennia, as fire led to permanent transitions in ecosystem state. These fire episodes increased open vegetation diversity, decreased woodland diversity and significantly altered richness on a regional scale. Our study suggests that anthropogenic fires played a primary role in diversity changes in Mediterranean Iberia. Their millennia-long legacy in today’s vegetation should be considered for biodiversity conservation and landscape management.

Climate change is causing fire regime shifts in ecosystems worldwide. Plant species with regeneration strategies strongly linked to a fire regime, such as obligate seeders, may be particularly threatened by these changes. It is unclear whether changes in fire regimes or the direct effects of climate change will be the dominant threats to obligate seeders in future. We investigated the relative importance of fire-related variables (fire return interval and fire severity) and environmental factors (climate and topography) on seedling establishment in the world’s tallest angiosperm, an obligate seeder, Eucalyptus regnans. Throughout its range, this species dominates the wet montane forests of south-eastern Australia and plays a keystone role in forest structure. Following major wildfires, we investigated seedling establishment in E. regnans within 1 year of fire as this is a critical stage in the regeneration niche of obligate seeders. Seedling presence and abundance were strongly related to the occurrence of fire but not to variation in fire severity (moderate vs. high severity). Seedling abundance increased with increasing fire return interval (range 26–300 years). First-year seedling establishment was also strongly associated with low temperatures and with high elevations, high precipitation and persistent soil water availability. Our results show that both climate and fire regimes are strong drivers of E. regnans seedling establishment. The predicted warming and drying of the climate might reduce the regeneration potential for some obligate seeders in future and these threats are likely to be compounded by changes in fire regimes, particularly increases in fire frequency.

Wildfires are an integral part of Mediterranean ecosystems; humans impact on landscapes imply changes in fuel amount and continuity, and thus in fire regime. We tested the hypothesis that fire regime changed in western Mediterranean Basin during the last century using time series techniques. We first compiled a 130-year fire history for the Valencia province (Spain, Eastern Iberian Peninsula, Western Mediterranean Basin) from contemporary statistics plus old forest administration dossiers and newspapers. We also compiled census on rural population and climatic data for the same period in order to evaluate the role of climate and human-driven fuel changes on the fire regime change. The result suggested that there was a major fire regime shift around the early 1970s in such a way that fires increased in annual frequency (doubled) and area burned (by about an order of magnitude). The main driver of this shift was the increase in fuel amount and continuity due to rural depopulation (vegetation and fuel build-up after farm abandonment) suggesting that fires were fuel-limited during the pre-1970s period. Climatic conditions were poorly related to pre-1970s fires and strongly related to post-1970s fires, suggesting that fire are currently less fuel limited and more drought-driven than before the 1970s. Thus, the fire regime shift implies also a shift in the main driver for fire activity, and this has consequences in the global change agenda.

Acidification can have broad effects on forest ecosystems, ranging from consequences for individual organisms to alterations in trophic dynamics. While the effects of acidification on certain aspects of forest ecosystems have been well studied, less is known about the influence of soil acidification on the forest floor food web that includes amphibians and invertebrates. We investigated the effects of acidification on the American Toad (Anaxyrus americanus) and its interaction with the forest floor invertebrate community. We evaluated survival, growth, and diet of newly metamorphosed toads placed in terrestrial enclosures in forest plots with either experimentally elevated soil pH or untreated, acidified soils. We also conducted invertebrate pitfall sampling in these two soil pH types to evaluate the trophic interactions between toads and invertebrates. Toad mass after 90 days tended to be larger in plots with elevated soil pH, although survival and diet did not differ between soil pH types. We found no effect of soil pH on invertebrate abundances nor overall invertebrate diversity. We also found no evidence that toads exhibited top-down control of the invertebrate community. Collectively, our results indicate that acidified soils did not affect forest floor trophic dynamics. The presence of temporary enclosures we constructed, however, significantly reduced invertebrate abundances and overall diversity. Thus, the strong effect these structures can have on invertebrate communities should be considered when used in future studies.

Due to the spatial heterogeneity of the disturbance regimes and community assemblages along topoclimatic gradients, the response of forest ecosystem to climate change varies at the landscape scale. Our objective was to quantify the possible changes in forest ecosystems and the relative effects of climate warming and fire regime changes in different topographic positions. We used a spatially explicit model (LANDIS PRO) combined with a gap model (LINKAGES) to predict the possible response of boreal larch forests to climate and fire regime changes, and examined how this response would vary in different topographic positions. The result showed that the proportion of landscape occupied by broadleaf species increased under warming climate and frequent fires scenarios. Shifts in species composition were strongly influenced by both climate warming and more frequent fires, while changes in age structure were mainly controlled by shifts in fire regime. These responses varied in the different topographic positions, with forests in valley bottoms being most resilient to climate-fire changes and forests in uplands being more likely to shift their composition from larch-dominant to mixed forests. Such variation in the topographic response may be induced by the heterogeneities of the environmental conditions and fire regime. Fire disturbance could alter the equilibrium of ecosystems and accelerate the response of forests to climate warming. These effects are largely modulated by topographic variations. Our findings suggest that it is imperative to consider topographic complexities when developing appropriate fire management policies for mitigating the effects of climate change.

Fire regimes during the Last Glacial

Paleoecological records of past fire events and forest composition provide long‐term ecological context for modern changes in fire regimes and forest dynamics. Here, we use pollen and contiguous macroscopic charcoal analyses of lake sediments from Pender Island, British Columbia, Canada to reconstruct changes in fire regimes over the last 10,000 years and investigate how these interact with changes in climate and forest composition with a focus on fire‐related plant functional types. The relatively warm and dry early Holocene was characterized by high charcoal accumulation rates, fire episodes of moderate severity, and a mean fire return interval of 100 ± 27 years. Forests at the time were open‐canopy Pseudotsuga menziesii forests with abundant fire endurer taxa (e.g., Pteridium aquilinum) that have a competitive advantage in regimes of frequent fire. Fire continued to occur every ~100 years, on average, during the establishment of Quercus garryana savanna communities; however, a decrease in charcoal peak magnitudes suggests the fire regime shifted to one characterized by smaller and/or lower intensity surface fires. As temperature and moisture deficits decreased in the mid‐ and late Holocene (i.e., after ~6000 calendar years before present), mean fire return intervals lengthened to 176 ± 54 years and increased variability in charcoal peak magnitudes suggests a mixed fire regime of low‐moderate‐intensity fires combined with infrequent crown or stand‐replacing fires. Relatively stable and moderate climate, longer fire return intervals, and mixed‐severity fires allowed P. menziesii (a fire resister) to dominate closed‐canopy forests and for fire avoiders to gradually become more common forest constituents. Millennial‐scale climate change has acted as the dominant driver of changes in both fire regimes and forest composition over the last 10,000 years; however, changes in fire‐related plant functional types highlight the important role that interactions between vegetation and fire play in long‐term fire regimes and forest dynamics.

Fire regimes are changing around the world raising important questions about the risks to biodiversity. Fire seasons are lengthening, high-severity fires are occurring more often and in unexpected places. Extensive research examines some of the fire related risks to life and property. However, in the fire risk research space there is often limited or simplified inclusion of ecological values. Future fire regimes, alongside climatic change, could have profound impacts on biodiversity conservation and ecosystem function. For example, plant population trajectories can be influenced by demographic traits, disturbance regimes and environmental variables such as climate. Climate change can affect all three and is likely to impact on plant populations through altering natural fire regimes as well as influencing species demographic traits. These changes are unlikely to be unidirectional with some plant types benefiting and others being disadvantaged. Here, we examine the impacts of climate change both on the shifts in fire regimes alone and combined with predicted climate-induced demographic shifts. We use two functional plant types (obligate seeder, facultative resprouter) in a number of case-study areas representing woodland-dominated landscapes of south-eastern Australia. We link a fire regime simulation tool with a spatially explicit population viability analysis model. We simulate fire regimes under six different future climates representing different temperature and precipitation shifts, and 16 demographic change scenarios, characterised by changes to individual or multiple plant demographic processes. Obligate seeder species were predicted to be less resilient to changes in demographic parameters. However, both resprouter and seeder species were found to be negatively affected by the combined impacts of changes to multiple demographic parameters or to a combination of a shifting fire regime and changes to demographic traits, particularly through simulated reductions in adult survival. To our knowledge this is the first study to integrate fire regime simulations with spatially explicit population viability analyses. Such an approach significantly increases our ability to identify which functional types are most at risk of population extinction under predicted fire regime and demographic changes. This flexible framework is an important first step in exploring the complex interactions that determine plant viability under a changing climate and will increase our ability to prioritise research and fire management for biodiversity into the future.

Shifts in fire regimes can trigger rapid changes in ecosystem functioning and biodiversity. We synthesize evidence for patterns, causes and consequences of recent change in fire regimes across the Eurasian steppes, a neglected global fire hotspot. Political and economic turmoil following the break-up of the Soviet Union in 1991 triggered abrupt land abandonment over millions of hectares and a collapse of livestock populations. The build-up of vegetation as fuel, rural depopulation and deteriorating fire control led to a rapid increase in fire size, area burned and fire frequency. Fire regimes were also driven by drought, but likely only after fuel had accumulated. Increased fire disturbance resulted in grass encroachment, vegetation homogenization and decreasing plant species diversity. Feedback loops due to the high grass flammability were likely. Direct and carry-on effects on birds, keystone small mammals and insects were largely negative. Nutrient cycling and carbon balance changed, but these changes have yet to be quantified. The regime of large and frequent fires persisted until ca 2010 but shifted back to a more grazing-controlled regime as livestock populations recovered, reinforced by increasing precipitation. Key future research topics include the effects of future climate change, changing pyrodiversity and pyric herbivory on ecosystem resilience. Ongoing steppe restoration and rewilding efforts, and integrated fire management will benefit from a better understanding of fire regimes.This article is part of the theme issue ‘Novel fire regimes under climate changes and human influences: impacts, ecosystem responses and feedbacks’.

Recent years have seen rapid climatic changes in Central Asia, particularly Mongolia. An increase in the thickness of the active layer above permafrost and considerable changes to the vegetation structure are likely outcomes of the long-term temperature rise and precipitation changes. The management of future habitats or the biodiversity of northern Mongolia faces significant difficulties from rising temperatures, prolonged and frequent droughts, and gradual permafrost degradation. Our knowledge of the historical processes involved in permafrost degradation and the ensuing ecological effects is still mostly incomplete. These connections may be used to explain changes in the fire regime, permafrost melting, and plant distribution in the Khentii mountains region. Therefore, based on a multiproxy study of peat archive data, we provide the first high-resolution fire history from northeastern Mongolia over the last 1000 years (micro- and macroscopic charcoals, charcoal size classes and morphotypes, peat geochemistry). We examined microscopic and macroscopic charcoal particles as a proxy for fire activity. We also tracked changes in regional and local plant composition using pollen data. To investigate how changes in fire regimes and the climate affect the functioning of the peatland ecosystem, we also conducted a geochemical analysis.Additionally, to better comprehend the changes in earlier fire regimes and fire-vegetation connections, we employed the morphotypes of macrocharcoal to pinpoint vegetation burning. This study's primary objective is to evaluate the impact of human behavior, vegetation, and prolonged droughts on the incidence of fire regime transitions during the past 1000 years in Central Asia permafrost marginal zone (Mongolia). The findings showed that most of the fires in the area were probably started by natural causes, presumably connected to heatwaves that resulted in prolonged droughts. We have established a connection between increased fires and the local weather phenomena known as "dzud", a catastrophic confluence of winter snowfall and droughts that impacts fire intensity.The study is the result of research project No. 2017/01/X/ST10/01216 and 2018/31/B/ST10/02498 funded by the Polish National Science Centre.

In high latitudes, changes in climate impact fire regimes and snow cover duration, altering the surface albedo and the heating of the regional atmosphere. In the western Arctic, under four scenarios of future climate change and future fire regimes (2003–2100), we examined changes in surface albedo and the related changes in regional atmospheric heating due to: (1) vegetation changes following a changing fire regime, and (2) changes in snow cover duration. We used a spatially explicit dynamic vegetation model (Alaskan Frame‐based Ecosystem Code) to simulate changes in successional dynamics associated with fire under the future climate scenarios, and the Terrestrial Ecosystem Model to simulate changes in snow cover. Changes in summer heating due to the changes in the forest stand age distributions under future fire regimes showed a slight cooling effect due to increases in summer albedo (mean across climates of −0.9 W m−2 decade−1). Over this same time period, decreases in snow cover (mean reduction in the snow season of 4.5 d decade−1) caused a reduction in albedo, and a heating effect (mean across climates of 4.3 W m−2 decade−1). Adding both the summer negative change in atmospheric heating due to changes in fire regimes to the positive changes in atmospheric heating due to changes in the length of the snow season resulted in a 3.4 W m−2 decade−1 increase in atmospheric heating. These findings highlight the importance of gaining a better understanding of the influences of changes in surface albedo on atmospheric heating due to both changes in the fire regime and changes in snow cover duration.

Wildfire occurrence and severity are projected to increase in response to anthropogenic climate change, leading to fire regimes that may exceed the limits of tolerance for some species. Plants capable of regenerating from aerial shoots following high intensity fires, termed ‘epicormic resprouters’, are assumed to be resilient to changes in fire regimes. However, empirical tests of the response of epicormic resprouters to extreme fire regimes, such as repeated canopy fires at short intervals, are currently lacking. This study examined the effect of combinations of understorey fire and canopy fire across two successive wildfires (2007, 2013) on the resilience of eucalypts that resprout epicormically. The study took place in a temperate eucalypt forest in south eastern Australia. Measures used to infer community resilience included stem topkill and damage, and seedling recruitment. It was predicted that: (a) stems will exhibit lower resistance (i.e. increased topkill and damage) to canopy fire than understorey fire; (b) recruitment will be higher following canopy fire than understorey fire; (c) prior exposure to canopy fire will reduce stem resistance and recruitment in response to subsequent wildfires; and (d) stem resistance will vary depending on bark traits. Topkill of saplings and small stems (<30 cm diameter at breast height) was higher in sites that recently (i.e. 2013) experienced canopy fire as opposed to understorey fire. Recent fire severity had no effect on topkill of large trees. Tree species with dense bark on the main stem and larger branches were less prone to topkill or partial stem and branch mortality than species with fibrous bark or exposed branches. Seedling recruitment was greater following canopy fire than understorey fire. Exposure to past canopy fire (i.e. in 2007) did not decrease stem resistance or recruitment. Synthesis. The results of this study suggest that communities of eucalypts that can resprout epicormically following fire will experience demographic shifts following repeated canopy fires. However, given the high resistance of large trees and rapid post‐fire recovery of the seedbank, ecosystem conversion appears unlikely. The findings support the presumption that forest communities of epicormic resprouters are highly resilient to shifts in fire regimes.