Fire-prone Ecosystems Research Articles

Adaptation Strategies and Approaches for Managing Fire in a Changing Climate

As the effects of climate change accumulate and intensify, resource managers juggle existing goals and new mandates to operationalize adaptation. Fire managers contend with the direct effects of climate change on resources in addition to climate-induced disruptions to fire regimes and subsequent ecosystem effects. In systems stressed by warming and drying, increased fire activity amplifies the pace of change and scale of severe disturbance events, heightening the urgency for management action. Fire managers are asked to integrate information on climate impacts with their professional expertise to determine how to achieve management objectives in a changing climate with altered fire regimes. This is a difficult task, and managers need support as they incorporate climate adaptation into planning and operations. We present a list of adaptation strategies and approaches specific to fire and climate based on co-produced knowledge from a science–management partnership and pilot-tested in a two-day workshop with natural resource managers and regional stakeholders. This “menu” is a flexible and useful tool for fire managers who need to connect the dots between fire ecology, climate science, adaptation intent, and management implementation. It was created and tested as part of an adaptation framework used widely across the United States and should be applicable and useful in many fire-prone forest ecosystems.

Fire-released seed dormancy - a global synthesis.

ABSTRACTSeed dormancy varies greatly between species, clades, communities, and regions. We propose that fireprone ecosystems create ideal conditions for the selection of seed dormancy as fire provides a mechanism for dormancy release and postfire conditions are optimal for germination. Thus, fire‐released seed dormancy should vary in type and abundance under different fire regimes. To test these predictions, we compiled data from a wide range of fire‐related germination experiments for species in different ecosystems across the globe. We identified four dormancy syndromes: heat‐released (physical) dormancy, smoke‐released (physiological) dormancy, non‐fire‐released dormancy, and non‐dormancy. In fireprone ecosystems, fire, in the form of heat and/or chemical by‐products (collectively termed ‘smoke’), are the predominant stimuli for dormancy release and subsequent germination, with climate (cold or warm stratification) and light sometimes playing important secondary roles. Fire (heat or smoke)‐released dormancy is best expressed where woody vegetation is dense and fires are intense, i.e. in crown‐fire ecosystems. In such environments, seed dormancy allows shade‐intolerant species to take advantage of vegetation gaps created by fire and synchronize germination with optimal recruitment conditions. In grassy fireprone ecosystems (e.g. savannas), where fires are less intense but more frequent, seed dormancy is less common and dormancy release is often not directly related to fire (non‐fire‐released dormancy). Rates of germination, whether controls or postfire, are twice as fast in savannas than in mediterranean ecosystems. Fire‐released dormancy is rare to absent in arid ecosystems and rainforests. The seeds of many species with fire‐released dormancy also possess elaiosomes that promote ant dispersal. Burial by ants increases insulation of seeds from fires and places them in a suitable location for fire‐released dormancy. The distribution of these dormancy syndromes across seed plants is not random – certain dormancy types are associated with particular lineages (phylogenetic conservatism). Heat‐released dormancy can be traced back to fireprone floras in the ‘fiery’ mid‐Cretaceous, followed by smoke‐released dormancy, with loss of fire‐related dormancy among recent events associated with the advent of open savannas and non‐fireprone habitats. Anthropogenic influences are now modifying dormancy‐release mechanisms, usually decreasing the role of fire as exaptive effects. We conclude that contrasting fire regimes are a key driver of the evolution and maintenance of diverse seed dormancy types in many of the world's natural ecosystems.

Fire-prone Rhamnaceae with South African affinities in Cretaceous Myanmar amber.

The rapid Cretaceous diversification of flowering plants remains Darwin's 'abominable mystery' despite numerous fossil flowers discovered in recent years. Wildfires were frequent in the Cretaceous and many such early flower fossils are represented by charcoalified fragments, lacking complete delicate structures and surface textures, making their similarity to living forms difficult to discern. Furthermore, scarcity of information about the ecology of early angiosperms makes it difficult to test hypotheses about the drivers of their diversification, including the role of fire in shaping flowering plant evolution. We report the discovery of two exquisitely preserved fossil flower species, one identical to the inflorescences of the extant crown-eudicot genus Phylica and the other recovered as a sister group to Phylica, both preserved as inclusions together with burned plant remains in Cretaceous amber from northern Myanmar (~99 million years ago). These specialized flower species, named Phylica piloburmensis sp. nov. and Eophylica priscastellata gen. et sp. nov., exhibit traits identical to those of modern taxa in fire-prone ecosystems such as the fynbos of South Africa, and provide evidence of fire adaptation in angiosperms.

Do bird communities differ with post-fire age in

Prescribed fire is a widespread management practice in fire-prone ecosystems that can have significant effects on fauna. To inform the development of appropriate prescribed burning regimes, we explored bird responses to time since fire in threatened Banksia woodlands in south-western Australia. We used area searches to estimate bird densities on 20 plots ranging from 1 to 26 years post fire. Fire had no significant effect on the overall bird community or any foraging guilds and there was no clear post-fire succession. Of the 26 frequently occurring species analysed, only two showed responses to fire, with yellow-rumped thornbills more abundant in early and late post-fire sites and scarlet robins more abundant in either early, or early and late post-fire habitats. Our study suggested that bird communities in Banksia woodlands are quite adaptable to a range of prescribed burning regimes. However, owing to late-successional reptiles, Carnaby’s black cockatoo and mammals in Banksia woodlands, we recommend prescribed burning regimes that reduce early and increase late successional habitat. Phytophthora dieback, urbanisation and associated habitat fragmentation and a drying climate may have important synergistic effects and the role of these in structuring bird communities needs to be further considered in developing appropriate fire regimes.

Rainforest bird communities threatened by extreme fire

Fire occurs naturally in many ecosystems and is predicted to increase in frequency and severity with climate change. The 2019–2020 Australian bushfire season was extreme, unprecedented in scale and severity, burning almost 19 million ha. This included half of the Gondwanan rainforests in eastern Australia, an ecosystem with no documented record of fire. We investigated the recovery of rainforest bird communities one-year post fire, using 80 bird and vegetation surveys within and adjacent to Gondwanan rainforests. We compared bird communities in burnt and unburnt non-fire prone rainforests and burnt and unburnt fire prone dry sclerophyll forests. Bird diversity was lower in burnt rainforests than unburnt rainforests, but the inverse was true for dry sclerophyll forests. 12 functional groups responded to differences in forest type and fire history, including frugivores, folivores, and insectivores which may be more vulnerable in burnt rainforest. We identified a further 10 functional groups where variation related to vegetation structure, reflecting forest types and fire histories. Finally, we estimated that four species were more common in unburnt rainforest than burnt rainforest, while three species were more common in burnt rainforests than unburnt rainforests. In dry sclerophyll forests, one species was more common in burnt and one more common in unburnt. The responses of bird communities to the extreme 2019–2020 fires highlighted the vulnerability of rainforests to fire compared with more fire-prone ecosystems. To protect species and functional diversity of rainforests from the growing risk of fire with climate change, local fire mitigation management may be needed.

Modifying regeneration strategies classification to enhance the understanding of dominant species growth in fire-prone forest in Southwest China

In fire-prone ecosystems, plant species having different post-fire regeneration strategies (PFRS) coexist at the local scale while showing different growth dynamics. To evaluate the effect of PFRS on species regeneration, we investigated the plant communities burned in different years in the central Yunnan Province, Southwest China. Several indicators describing plant growth and population importance were measured to compare the regeneration of four dominant tree species, including one facultative seeders (FS) and three obligate resprouters (OR). Partial correlation and mixed linear effect modeling were applied to disentangle the contribution of intrinsic and environmental factors to the interspecific variation in post-fire regeneration. We identified two subtypes of plant growth strategy in the early post-fire stage for OR species; i.e., number growth (OR ​+ ​N) priority and height growth (OR ​+ ​H) priority for sprouting stems. Generally, the FS and OR species varied in height growth rate with different temporal dynamics. The OR ​+ ​N species occupied post-fire space horizontally with more resprouts and larger coverage than OR ​+ ​H and FS species at the earlier stage. In contrast, the OR ​+ ​H species generally had far less resprouts per clump, more variations in stem height and basal diameter. Factor analysis showed that the variation of post-fire plant regeneration was not effectively explained by environmental factors (R2 ​< ​20%); however, the linear mixed models with the modified PFRS as a random effect substantially increased the explanation. The differentiated regeneration dynamics and growth priorities in the four dominant tree species indicated a critical dichotomy of habitat occupation strategy for the resprouter species during the early stage of post-fire forest restoration. Our study uncovered a trade-off between height versus number growth priority in the post-fire tree growth strategy and provides a novel perspective in understanding the living space occupying (niche partitioning) process and species coexistence in post-fire forest community assembly.

The role of decomposer communities in managing surface fuels: a neglected ecosystem service

Surface fuel loads are a key driver of forest fires and the target of hazard reduction burns to reduce fire risk. However, the role of biota in decomposition, or feedbacks between fire and decomposer communities are rarely considered. We review the evidence that decomposer organisms play an important role in surface fuel regulation and how this role is affected by fire. First, we outline the contribution of decomposer organisms to the breakdown of surface fuels. Next, we consider the three distinct phases through which fire regulates decomposer communities and how this may affect decomposition and future fire regimes. Finally, we consider interactions between global change and decomposer–fire feedbacks and the implications for fire management. Evidence indicates that decomposer organisms are important in regulating surface fuels and we propose that the biological basis and dynamic nature of fuel load control require greater attention. This includes better understanding of functional redundancy among decomposer organisms, the impacts of global change on the biota that drive decomposition and the factors that limit decomposer persistence and recolonisation following fires. By filling these knowledge gaps, we will be better armed to conserve and manage these functionally critical taxa in fire-prone ecosystems in a changing world.

Pre-fire aboveground biomass, estimated from LiDAR, spectral and field inventory data, as a major driver of burn severity in maritime pine (Pinus pinaster) ecosystems

The characterization of surface and canopy fuel loadings in fire-prone pine ecosystems is critical for understanding fire behavior and anticipating the most harmful ecological effects of fire. Nevertheless, the joint consideration of both overstory and understory strata in burn severity assessments is often dismissed. The aim of this work was to assess the role of total, overstory and understory pre-fire aboveground biomass (AGB), estimated by means of airborne Light Detection and Ranging (LiDAR) and Landsat data, as drivers of burn severity in a megafire occurred in a pine ecosystem dominated by Pinus pinaster Ait. in the western Mediterranean Basin. Total and overstory AGB were more accurately estimated ( R 2 equal to 0.72 and 0.68, respectively) from LiDAR and spectral data than understory AGB ( R 2 ​= ​0.26). Density and height percentile LiDAR metrics for several strata were found to be important predictors of AGB. Burn severity responded markedly and non-linearly to total ( R 2 ​= ​0.60) and overstory ( R 2 ​= ​0.53) AGB, whereas the relationship with understory AGB was weaker ( R 2 ​= ​0.21). Nevertheless, the overstory plus understory AGB contribution led to the highest ability to predict burn severity (RMSE ​= ​122.46 in dNBR scale), instead of the joint consideration as total AGB (RMSE ​= ​158.41). This study novelty evaluated the potential of pre-fire AGB, as a vegetation biophysical property derived from LiDAR, spectral and field plot inventory data, for predicting burn severity, separating the contribution of the fuel loads in the understory and overstory strata in Pinus pinaster stands. The evidenced relationships between burn severity and pre-fire AGB distribution in Pinus pinaster stands would allow the implementation of threshold criteria to support decision making in fuel treatments designed to minimize crown fire hazard.

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.

Fire-Related Cues Significantly Promote Seed Germination of Some Salt-Tolerant Species from Non-Fire-Prone Saline-Alkaline Grasslands in Northeast China.

Seed germination in response to fire-related cues has been widely studied in species from fire-prone ecosystems. However, the germination characteristics of species from non-fire-prone ecosystems, such as the saline-alkaline grassland, where fire occasionally occurs accidentally or is used as a management tool, have been less studied. Here, we investigate the effects of different types of fire cues (i.e., heat and smoke water) and their combined effect on the seed germination of 12 species from the saline-alkaline grassland. The results demonstrated that heat shock significantly increased the germination percentage of Suaeda glauca and Kochia scoparia var. sieversiana seeds. Smoke water significantly increased the germination percentage of Setaria viridis and K. scoparia seeds. However, compared with single fire cue treatments, the combined treatment neither promoted nor inhibited seed germination significantly in most species. These results suggest that fire cues can be used as germination enhancement tools for vegetation restoration and biodiversity protection of the saline-alkaline grassland.

An improved drought-fire assessment for managing fire risks in tropical peatlands

Peatlands transformation in Indonesia has caused immense ecological and environmental degradation. Land use conversion has changed this natural carbon sink to a drought- and fire-prone ecosystem. Public awareness to tackle the drought and fire risk in peatlands has led to the development of drought-fire index. Current knowledge states that both climate and hydrology have a strong influence on drought-induced fire in tropical peatlands, yet the role of soil hydraulic properties in controlling the drying of peats remains unclear. This study develops an improved drought-fire index for tropical peatlands, called the Peat Fire Vulnerability Index, by incorporating groundwater and soil water retention information. We tested the new index on two peatland regions in Kubu Raya and Batanghari, Indonesia, to assess fire danger. We monitored daily rainfall, groundwater tables, and soil moisture from 2018 to 2019 on eight stations in the peatlands. Our model was calibrated against the observed drought index of two stations, and the results were verified with actual fire events through daily fire hotspots and fire burned areas in the other six stations. Results showed that soil-hydrological properties influenced the moistening and drying of peats through capillarity. Our model showed good performance in assessing fire danger during the calibration period, as indicated by three employed statistical metrics: the RMSE-standard deviation ratio (RSR = 0.57), Kling-Gupta Efficiency (KGE = 0.81), and percent bias (PBIAS = 1%). For verification, all observed fire events fell in high and extreme fire danger classes predicted by PFVI. Further, our findings revealed the importance of the groundwater table as a threshold of fire events. The high fire danger class was mostly found when groundwater table dropped below 40 cm, and burned areas only occurred when the groundwater table was below 60 cm. These findings suggest that our drought-fire index can be used as a peat fire risk management tool, and its application may minimize fire risks in tropical peatlands.

Structural resilience and high interaction dissimilarity of plant-pollinator interaction networks in fire-prone grasslands.

Fire is a frequent disturbance in most grasslands around the world, being key for the structure and dynamics of the biodiversity in such ecosystems. While grassland species may be resilient, little is known on how plant-pollinator networks reassemble after fire. Here, we investigate the structure and dynamics of plant-pollinator networks and the variation in species roles over a 2-year post-fire chronosequence on grassland communities in Southern Brazil. We found that both network specialization and modularity were similar over the chronosequence of time-since-fire, but in freshly burnt areas, there were more species acting as network hubs. Species roles exhibited high variation, with plant and pollinator species shifting roles along the post-disturbance chronosequence. Interaction dissimilarity was remarkably high in networks irrespective of times-since-fire. Interaction dissimilarity was associated more with rewiring than with species turnover, indicating that grassland plant and pollinator species are highly capable of switching partners. Time-since-fire had little influence on network structure but influenced the identity and diversity of pollinators playing key roles in the networks. These findings suggest that pollination networks in naturally fire-prone ecosystems are highly dynamic and resilient to fire with both plants and pollinators being highly capable of adjusting their interactions and network structure after disturbance.

Evidence for widespread changes in the structure, composition, and fire regimes of western North American forests.

Implementation of wildfire‐ and climate‐adaptation strategies in seasonally dry forests of western North America is impeded by numerous constraints and uncertainties. After more than a century of resource and land use change, some question the need for proactive management, particularly given novel social, ecological, and climatic conditions. To address this question, we first provide a framework for assessing changes in landscape conditions and fire regimes. Using this framework, we then evaluate evidence of change in contemporary conditions relative to those maintained by active fire regimes, i.e., those uninterrupted by a century or more of human‐induced fire exclusion. The cumulative results of more than a century of research document a persistent and substantial fire deficit and widespread alterations to ecological structures and functions. These changes are not necessarily apparent at all spatial scales or in all dimensions of fire regimes and forest and nonforest conditions. Nonetheless, loss of the once abundant influence of low‐ and moderate‐severity fires suggests that even the least fire‐prone ecosystems may be affected by alteration of the surrounding landscape and, consequently, ecosystem functions. Vegetation spatial patterns in fire‐excluded forested landscapes no longer reflect the heterogeneity maintained by interacting fires of active fire regimes. Live and dead vegetation (surface and canopy fuels) is generally more abundant and continuous than before European colonization. As a result, current conditions are more vulnerable to the direct and indirect effects of seasonal and episodic increases in drought and fire, especially under a rapidly warming climate. Long‐term fire exclusion and contemporaneous social‐ecological influences continue to extensively modify seasonally dry forested landscapes. Management that realigns or adapts fire‐excluded conditions to seasonal and episodic increases in drought and fire can moderate ecosystem transitions as forests and human communities adapt to changing climatic and disturbance regimes. As adaptation strategies are developed, evaluated, and implemented, objective scientific evaluation of ongoing research and monitoring can aid differentiation of warranted and unwarranted uncertainties.

Litter Flammability of 50 Southeastern North American Tree Species: Evidence for Mesophication Gradients Across Multiple Ecosystems

Widespread fire exclusion and land-use activities across many southeastern United States forested ecosystems have resulted in altered species composition and structure. These changes in composition and structure have been implicated in positive fire-vegetation feedbacks termed “mesophication” where fire spread and intensity are diminished. In forests and woodlands, inherent flammability of different species is the mechanistic driver of mesophication. To date, there has been limited work on documenting the high diversity of flammability among species in the region, limiting the ability to differentiate among species to restore fuels that sustain fire regimes. Here, we coalesce disparate flammability data and add missing species across the spectrum from species that facilitate fire (so called “pyrophytes”) to those that dampen fire (so called “mesophytes”). We present data on 50 important tree species from across the southeast, all burned using identical laboratory methods. We divide our results for four dominant ecosystems: Coastal Plain uplands, oak-hickory woodlands, Appalachian forests, and bottomland forests. Across ecosystems, the most flammable species were American chestnut (Castanea dentata), a suite of pines (Pinus palustris, P. elliottii, P. serotina, and P. rigida), several oaks (Q. laevis, Q. falcata, Q. margaretta, and Q. alba), and sourwood (Oxydendrum arboreum). At the mesophytic end, the least flammable species were Tsuga canadensis, Acer rubrum, and several other hardwoods previously implicated in mesophication. Each of the four ecosystems we studied contained species that spanned the pyrophytic to mesophytic gradient. These data fill in some key holes in our understanding of southeastern fire adaptations, but also provide context for restoration decisions and fire management prioritization efforts to restore and sustain fire-prone ecosystems of the region.

Different post-fire stages encompass different plant community compositions in fire-prone grasslands from Southern Brazil

Fire is among the major forces shaping patterns in nature. Although sometimes it is only acknowledged for its destructive power, it was one of the evolutionary drivers that produced present-day species and biome distributions, being inextricably linked to fire-prone ecosystems such as grasslands. Knowing how fire influences grassland biodiversity is therefore fundamental to conserve it. Here we analyzed the taxonomic and functional structure of grassland plant communities from Southern Brazil under different post-fire successional stages. We sampled 12 sites that were fire-suppressed for varying amounts of time (3 to 300 months), categorized in three post-fire stages: freshly-burnt (FB), intermediate-burnt (IB), and old-burnt (OB). We compared these stages regarding taxonomic composition, species richness, diversity (partitioned in different spatial components), and functional composition (based on plant life forms and metabolism). We sampled 307 plant species from 52 families. Species richness was lower in the OB stage, and did not differ between FB and IB stages. Species composition was markedly different between stages. Forty-five percent of the sampled species were exclusive to one post-fire stage, and only 23% were shared among them. Old-burnt sites share only up to 5% species with other stages and concentrated most of the trees and tussocks. Because long-term fire suppression allowed for the entry of different floristic elements in the community, taxonomic diversity (beta and gamma levels) was higher in old-burnt sites. Our results provide empirical evidence that fire suppression is likely to shift the fire-prone grasslands from Southern Brazil towards different ecosystem states. However, whether this process is leading towards a closed forest system or to a different system with coexisting grassland and forest elements, remains an open question. The sharp floristic differences and exclusive species in the different post-fire stages reinforce the need to include fire in the conservation framework for fire-prone grasslands.

Prescribed Burning Reduces Large, High-Intensity Wildfires and Emissions in the Brazilian Savanna

Brazil has recently (2014) changed from a zero-fire policy to an Integrated Fire Management (IFM) program with the active use of prescribed burning (PB) in federal Protected Areas (PA) and Indigenous Territories (IT) of the Brazilian savanna (Cerrado). PB is commonly applied in the management of fire-prone ecosystems to mitigate large, high-intensity wildfires, the associated emissions, and high fire suppression costs. However, the effectiveness of such fire management in reducing large wildfires and emissions over Brazil remains mostly unevaluated. Here, we aim to fill the gap in the scientific evidence of the PB benefits by relying on the most up-to-date, satellite-derived fire datasets of burned area (BA), fire size, duration, emissions, and intensity from 2003 to 2018. We focused on two Cerrado ITs with different sizes and hydrological regimes, Xerente and Araguaia, where IFM has been in place since 2015. To understand fire regime dynamics, we divided the study period into three phases according to the prevalent fire policy and the individual fire scars into four size classes. We considered two fire seasons: management fire season (MFS, which goes from rainy to mid-dry season, when PBs are undertaken) and wildfires season (WFS, when PBs are not performed and fires tend to grow out of control). Our results show that the implementation of the IFM program was responsible for a decrease of the areas affected by high fire recurrence in Xerente and Araguaia, when compared with the Zero Fire Phase (2008–2013). In both regions, PB effectively reduced the large wildfires occurrence, the number of medium and large scars, fire intensity, and emissions, changing the prevalent fire season from the WFS to the MFS. Such reductions are significant since WFS causes higher negative impacts on biodiversity conservation and higher greenhouse gas emissions. We conclude that the effect on wildfires can still be reduced if effective fire management policies, including PB, continue to be implemented during the coming decades.

Fire does not change sprouting nor flowering, but affects fruiting phenology in a Neotropical savanna community

In fire-prone ecosystems, such as savannas, fire has been a common event for thousands of years. In these biomes, phenology is a functional trait characterizing the responses of plant communities to fire. In this study, we aimed to evaluate the effects of fire on the period of occurrence, seasonality, and number of species expressing vegetative and reproductive phenophases (sprouting, flowering, and fruiting) in a South American savanna community. We burned experimental plots in 2013, and during the subsequent year, we performed monthly evaluations of the presence and absence of vegetative and reproductive structures in 44 species of angiosperms in the control and burned plots. We described plant phenology at two levels: (i) considering all sampled plant species together (community); and (ii) separately considering the species found in the herbaceous-subshrub and shrub-tree layers (vegetation strata). We analyzed the data using circular statistics and generalized linear mixed models. At the community level, fire did not alter the mean period of occurrence of vegetative and reproductive phenophases; however, we observed changes in fruiting seasonality, which were mainly caused by the changes occurring in the shrub-tree layer. Except for those found in the shrub-tree layer, more species expressed the analyzed phenophases after fire compared to the “control” treatment. This study provides information regarding the responses of plants to burning at the end of the dry season, when most anthropogenic fires occur. Additionally, according to climate change predictions, the Southern Hemisphere is expected to experience longer dry seasons, which may contribute to an increased frequency of anthropogenic fires. Therefore, this phenological information can motivate subsidies that are important for the conservation of this biome and management plans related to the prescription of fires.

Climate change induced declines in fuel moisture may turn currently fire-free Pyrenean mountain forests into fire-prone ecosystems

Fuel moisture limits the availability of fuel to wildfires in many forest areas worldwide, but the effects of climate change on moisture constraints remain largely unknown. Here we addressed how climate affects fuel moisture in pine stands from Catalonia, NE Spain, and the potential effects of increasing climate aridity on burned area in the Pyrenees, a mesic mountainous area where fire is currently rare. We first quantified variation in fuel moisture in six sites distributed across an altitudinal gradient where the long-term mean annual temperature and precipitation vary by 6–15 °C and 395–933 mm, respectively. We observed significant spatial variation in live (78–162%) and dead (10–15%) fuel moisture across sites. The pattern of variation was negatively linked (r = |0.6|–|0.9|) to increases in vapor pressure deficit (VPD) and in the Aridity Index. Using seasonal fire records over 2006–2020, we observed that summer burned area in the Mediterranean forests of Northeast Spain and Southern France was strongly dependent on VPD (r = 0.93), the major driver (and predictor) of dead fuel moisture content (DFMC) at our sites. Based on the difference between VPD thresholds associated with large wildfire seasons in the Mediterranean (3.6 kPa) and the maximum VPD observed in surrounding Pyrenean mountains (3.1 kPa), we quantified the “safety margin” for Pyrenean forests (difference between actual VPD and that associated with large wildfires) at 0.5 kPa. The effects of live fuel moisture content (LFMC) on burned area were not significant under current conditions, a situation that may change with projected increases in climate aridity. Overall, our results indicate that DFMC in currently fire-free areas in Europe, like the Pyrenees, with vast amounts of fuel in many forest stands, may reach critical dryness thresholds beyond the safety margin and experience large wildfires after only mild increases in VPD, although LFMC can modulate the response.

Allelopathic Mechanisms in Fire-Prone Ecosystems

Understanding the fire-prone arid-zone pine species and maquis vegetation's response to fire is very important to reveal the ecology and evolution of these species. During the succession of vegetation, there are complex relationships between allelopathic metabolites and fires. Many plant communities such as pines, maquis, savannas and woodlands are known to play a critical role in the development of succession. However, studies revealing the relationship between succession processes and allelopathic mechanisms in fire-prone ecosystems are quite limited. Most evergreen maquis vegetations are one of the most studied fire ecosystems. In maquis vegetation, fire causes the formation of plant communities that continue with allelochemicals produced by plants, as well as shaping the climate of the region. The event of a living species inhibiting another species by secreting toxic compounds is expressed as allelopathy. These toxic compounds are generally referred to as allelochemicals. Many maquis species that grow in fire-prone ecosystems excrete their allelochemicals, preventing the development of herbaceous species around them and invade their habitats. These chemicals, which accumulate in the soil during the dry season, affect the succession processes in vegetation in the event of a fire and determine which species will follow each other. Considering these relationships, it can be said that allelopathic plants have the potential to change plant diversity in vegetation by changing their functional plant characteristics. The purpose of this review is to determine the relationship between allelochemicals and fire of plant species in fire-prone ecosystems, and to reveal how this affects the succession processes.

Putting fire on the map of Brazilian savanna ecoregions

The Brazilian savanna (Cerrado) is considered the most floristically diverse savanna in the world, home to more than seven thousand species. The region is a mosaic of savannas, grasslands and forests whose unique biophysical and landscape attributes are on the basis of a recent ecoregional map, paving the way to improved region-based strategies for land management actions. However, as a fire-prone ecosystem, Cerrado owes much of its distribution and ecological properties to the fire regime and contributes to an important parcel of South America burned area. Accordingly, any attempt to use ecoregion geography as a guide for management strategies should take fire into account, as an essential variable. The main aim of this study is to complement the ecoregional map of the Cerrado with information related to the fire component. Using remotely sensed information, we identify patterns and trends of fire frequency, intensity, seasonality, extent and scar size, and combine this information for each ecoregion, relying on a simple classification that summarizes the main fire characteristics over the last two decades. Results show a marked north-south fire activity gradient, with increased contributions from MATOPIBA, the latest agricultural frontier. Five ecoregions alone account for two thirds of yearly burned area. More intense fires are found in the Arc of Deforestation and eastern ecoregions, while ecoregions in MATOPIBA display decreasing fire intensity. An innovative analysis of fire scars stratified by size class shows that infrequent large fires are responsible for the majority of burned area. These large fires display positive trends over many ecoregions, whereas smaller fires, albeit more frequent, have been decreasing in number. The final fire classification scheme shows well defined spatially-aggregated groups, where trends are found to be the key factor to evaluate fire within their regional contexts. Results presented here provide new insights to improve fire management strategies under a changing climate.