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a Expected fire return interval (FRI) by relative gradient position. b Proportion of plots (n = 489) burned per relative gradient position. The dashed line represents the FRI for gradients with a shrub-dominant (shrubby) wetland and the solid line represents those with an herbaceous wetland

a Expected fire return interval (FRI) by relative gradient position. b Proportion of plots (n = 489) burned per relative gradient position. The dashed line represents the FRI for gradients with a shrub-dominant (shrubby) wetland and the solid line represents those with an herbaceous wetland

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Positive feedbacks influenced by direct and indirect interactions between fire, vegetation, and microclimate can allow pyrophilic and pyrophobic ecosystems to co-occur in the same landscape, resulting in the juxtaposition of flammable and non-flammable vegetation. To quantify the drivers of these feedbacks, we combined measurements of vegetation, f...

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... We investigated distribution-limiting factors in two ecotypes of an endemic bunchgrass. Wiregrass (Aristida beyrichiana) is a dominant understory species in pine savannas of the southeastern U.S., growing along xeric to mesic hydrologic gradients that span slight elevational differences (~30 cm to 10 m; Wells and Shunk 1931;Christensen 2000;Orzell and Bridges 2006;Crandall and Platt 2012;Just et al. 2016). Wiregrass is often used to restore longleaf (Pinus palustris) understories, but ecotypic responses to conspecific plant-soil feedbacks and different soil conditions may affect restoration outcomes. ...
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Purpose Previous research alludes to two wiregrass (Aristida beyrichiana) ecotypes from mesic and xeric environments. It is unknown whether these ecotypes are restricted by conspecific plant-soil feedbacks or specific components of mesic and xeric soils. We investigated whether biomass production of wiregrass ecotypes grown in mesic and xeric soil was affected by conspecific plant-soil feedbacks, and whether wiregrass ecotypes responded differently to the soil biota and nutrients that characterize each of the two soil types. Methods We established a greenhouse experiment to compare the biomass production of mesic and xeric wiregrass ecotypes in mesic and xeric soil. To establish the effects of conspecific soil conditioning, each soil type was either conditioned or unconditioned by wiregrass. To to isolate the effects of soil biota and nutrients, each combination of soil type and conditioning was replicated in three soil manipulations (i.e., whole, inoculated, and sterile soil) where each wiregrass ecotype was grown. Results Biomass of the xeric ecotype was marginally greater in xeric soil than in mesic soil. The mesic ecotype tended to grow more in mesic than xeric soil, but it was not significant. Soil conditioning did not affect biomass production of either ecotype. Soil biota coupled with nutrients affected biomass production of both ecotypes when not growing in their own soil. Conclusions We found some evidence for wiregrass ecotypes that have increased growth in their own soil type, but not for conspecific plant-soil feedbacks. Ecotypes were affected by negative interactions with soil biota when growing in a different type. Thus, the soil environment should be considered when sourcing seeds for restoration.
... Nevertheless, there has been increased attention given to the subject world-widely [55,66]. The factors behind fire spread behaviour depend heavily on local physical, environmental and meteorological variables [78,71,50], such as vegetation density distribution, landscape slope, fuel continuity and wind dynamics. For reasons including high dimensionality and the lack of historical data, among others, current fire modelling systems, for instance, those based on Rothermel equation [67], NWP(numerical weather prediction)-driven forecasting and Cellular Automation (CA) [2], remain highly empirical [58]. ...
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The large and catastrophic wildfires have been increasing across the globe in the recent decade, highlighting the importance of simulating and forecasting fire dynamics in near real-time. This is extremely challenging due to the complexities of physical models and geographical features. Running physics-based simulations for large wildfire events in near real-time is computationally expensive, if not infeasible. In this work, we develop and test a novel data-model integration scheme for fire progression forecasting, that combines Reduced-order modelling, recurrent neural networks (Long-Short-Term Memory), data assimilation, and error covariance tuning. The Reduced-order modelling and the machine learning surrogate model ensure the efficiency of the proposed approach while the data assimilation enables the system to adjust the simulation with observations. We applied this algorithm to simulate and forecast three recent large wildfire events in California from 2017 to 2020. The deep-learning-based surrogate model runs around 1000 times faster than the Cellular Automata simulation which is used to generate training data-sets. The daily fire perimeters derived from satellite observation are used as observation data in Latent Assimilation to adjust the fire forecasting in near real-time. An error covariance tuning algorithm is also performed in the reduced space to estimate prior simulation and observation errors. The evolution of the averaged relative root mean square error (R-RMSE) shows that data assimilation and covariance tuning reduce the RMSE by about 50% and considerably improves the forecasting accuracy. As a first attempt at a reduced order wildfire spread forecasting, our exploratory work showed the potential of data-driven machine learning models to speed up fire forecasting for various applications.
... The ecotone between these two vegetation types is of particular interest as this is where vegetation properties will intergrade and where fire is most likely to cross-over from shrubland and enter woodland ecosystems (Gartner et al., 2012). Ecotones between fire-prone and fire sensitive vegetation can be dynamic, changing with fire history, and can be challenging to manage (Nicholas et al., 2011;Just et al., 2016). However, they also provide opportunities to protect fire sensitive vegetation through active fuel management or clearing of fire breaks located near edges (Parks et al., 2015). ...
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... Populations of L. subcoriacea have been observed in four vegetation communities in North Carolina (Schafale 2012;Wall et al. 2013 Fort Bragg is divided into over 1200 burn units that are burned on a roughly 3-year rotation. In general, there is complete burning of the understory in upland communities, but the wetland areas experience intermittent burning (Sorrie et al. 2006;Just et al. 2016). This leads to varied fire return intervals within burn units and within L. subcoriacea populations located in the four vegetation communities. ...
... Rather, the fire return interval at these specific locations may have previously been more frequent, maintaining a different vegetation community than the current that allowed L. subcoriacea recruitment sometime in the past. Dynamic changes in local vegetation communities due to changes in fire frequency are anticipated (Sorrie et al. 2006;Schafale 2012;Gray et al. 2016); Streamhead Pocosins and the ecotones between pocosins and xeric uplands are particularly susceptible to short-term reductions in fire frequency and can quickly become dominated by evergreen shrubs due to feedbacks between vegetation and fire behavior (Just et al. 2016). ...
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Understanding demographic vital rates and the factors that affect those rates are key components of successful conservation strategies for many threatened and endangered rare plant species. Lindera subcoriacea is a rare dioecious shrub that occupies isolated wetland habitats in a small number of locations in the southeastern United States. The species faces a number of threats to its continued persistence, including habitat destruction, invasive species, and population isolation. From 2011 to 2019, we collected demographic information from 290 L. subcoriacea individuals within 28 populations on Fort Bragg, North Carolina and used the data to estimate demographic vital rates in unburned populations and after being exposed to prescribed fire. We then constructed population matrices and estimated population growth rates under a 3-, 5-, and 10-year return interval. Results indicated that L. subcoriacea individuals have high survivorship in both burned and unburned populations, seed production was reduced 1- and 2-year post-fire, seed production was highly uneven across individuals, seedling recruitment was extremely low, and simulated population growth rates were only above 1.0 under the 10-year fire return interval. Taken together, these results indicate that (1) L. subcoriacea populations are persisting with population growth rates close to one, (2) the short-term impacts of fire on the overall population growth rate of L. subcoriacea, while only 2–3% may determine long-term population viability, and (3) extremely uneven seed production and limited recruitment of seedlings into larger size classes make L. subcoriacea populations vulnerable to stochastic demographic processes.
... Fire-sensitive hardwood species were more abundant on sandy loam soils and at lower elevations due to the better growing conditions and how local fire behavior is affected by edaphic conditions. On Fort Bragg, lower elevations and sandy loam soils typically were associated with mesic ecotones adjacent to riparian corridors (Sorrie et al., 2006;Just et al., 2016), and the conditions in these mesic ecotones interact with fire behavior to drive FSH abundance. For example, riparian zones act as natural firebreaks (Just et al., 2016), creating heterogeneity in fire behavior (e.g., patchiness and intensity) that may positively affect FSH abundance. ...
... On Fort Bragg, lower elevations and sandy loam soils typically were associated with mesic ecotones adjacent to riparian corridors (Sorrie et al., 2006;Just et al., 2016), and the conditions in these mesic ecotones interact with fire behavior to drive FSH abundance. For example, riparian zones act as natural firebreaks (Just et al., 2016), creating heterogeneity in fire behavior (e.g., patchiness and intensity) that may positively affect FSH abundance. Although we did not document support for fire return interval as predictor of FSH abundance, the number of growing-season fires was an important predictor. ...
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The longleaf pine (Pinus palustris) ecosystem has been reduced to a fraction of its original extent, and where this ecosystem does occur, it is often degraded by hardwood encroachment. The reduction of hardwood tree cover is often a desirable longleaf pine community restoration outcome, though hardwood midstory and overstory trees have been recognized as an important natural component of the communities. Moreover, the appropriate amount of hardwood tree cover in a restored longleaf pine community is debated, as more hardwood tree cover can benefit mixed forest and mast-dependent wildlife (e.g., fox squirrels [Sciurus niger], white-tailed deer [Odocoileus virginianus]), and less hardwood tree cover is critical to the federally endangered red-cockaded woodpecker (Leuconotopicus borealis). To inform the debate, we assessed the environmental (e.g., topography, edaphic conditions, and pine basal area) and management (e.g., distance to firebreaks, prescribed fire history) factors that influenced abundance of upland hardwood trees in xeric longleaf pine communities on a site where frequent growing-season fire has been ongoing since 1991. We counted upland hardwoods ≥5 cm diameter at breast height (DBH) at 307 random field plots (0.04 ha) and categorized all hardwood trees as belonging to either a guild of fire-tolerant oaks or a guild of fire-sensitive hardwood species. We used generalized linear models (GLM) to determine the most important predictors of abundance for both guilds. The predictors of abundance differed between the two guilds, with fire-tolerant oak abundance increasing with greater slope and proximity to ignition sources and decreasing with greater pine basal area. Fire-sensitive hardwood abundance increased with mesic site conditions and decreased with the number of growing-season fires and greater pine basal area. Although seasonality in fire history was an important predictor of fire-sensitive hardwood abundance, variables related to long-term fire-history were not important predictors of fire-tolerant oak abundance in longleaf pine communities. However, with limited variation in fire return interval across the study area, our ability to draw inferences regarding the role of fire return interval was limited. Where hardwood encroachment is not a problem, and hardwood levels are below desired, balanced target levels, hardwood abundance in longleaf pine communities can be increased by reducing pine basal area and reducing prescribed fire intensity.
... Depending upon the seasonality and fuel conditions, midstory vegetation can increase wind drag lowering wind speeds or increase fuel moisture, which each can slow fire spread or reduce intensity. Thus, to evaluate the efficacy of fuel treatments, fuel structure alone is insufficient to understand how treatments will alter future wildfire spread and suppression success 18,[27][28][29][30][31][32][33][34][35][36][37][38][39] . To this effect, Bessie and Johnson 40 determined that local weather conditions, especially factors governing fuel moisture and wind speed are stronger indicators to determine fire behavior in vegetative fuel beds compared to stand age or species composition 41,42 . ...
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Abstract Increasing trends in wildfire severity can partly be attributed to fire exclusion in the past century which led to higher fuel accumulation. Mechanical thinning and prescribed burns are effective techniques to manage fuel loads and to establish a higher degree of control over future fire risk, while restoring fire prone landscapes to their natural states of succession. However, given the complexity of interactions between fine scale fuel heterogeneity and wind, it is difficult to assess the success of thinning operations and prescribed burns. The present work addresses this issue systematically by simulating a simple fire line and propagating through a vegetative environment where the midstory has been cleared in different degrees, leading to a canopy with almost no midstory, another with a sparse midstory and another with a dense midstory. The simulations are conducted for these three canopies under two different conditions, where the fuel moisture is high and where it is low. These six sets of simulations show widely different fire behavior, in terms of fire intensity, spread rate and consumption. To understand the physical mechanisms that lead to these differences, detailed analyses are conducted to look at wind patterns, mean flow and turbulent fluxes of momentum and energy. The analyses also lead to improved understanding of processes leading to high intensity crowning behavior in presence of a dense midstory. Moreover, this work highlights the importance of considering fine scale fuel heterogeneity, seasonality, wind effects and the associated fire-canopy-atmosphere interactions while considering prescribed burns and forest management operations.
... Prescribed burning at this site is done using low-intensity backing fires to maximize control of the fires and prevent them from escaping into the tree crowns. As a result, low-lying wet areas burn infrequently despite prescribed burning (Weakley and Schafale, 1991;Just et al., 2016). ...
... site) but do not provide detailed burn maps. Because of this, and the fact that areas deep in lowland areas burn infrequently (Weakley and Schafale, 1991;Just et al., 2016), we restricted our analyses to open-canopy plots located where understorey burning is generally complete, for a total of 88 plots. For each monitoring plot, we quantified its elevation above the stream head in centimetres as described in Ames et al. (2016). ...
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Background and Aims Understanding impacts of altered disturbance regimes on community structure and function is a key goal for community ecology. Functional traits link species composition to ecosystem functioning. Changes in the distribution of functional traits at community scales in response to disturbance can be driven not only by shifts in species composition, but also by shifts in intraspecific trait values. Understanding the relative importance of these two processes has important implications for predicting community responses to altered disturbance regimes. Methods We experimentally manipulated fire return intervals in replicated blocks of a fire-adapted, long leaf pine (Pinus palustris) ecosystem in North Carolina, USA and measured specific leaf area (SLA), leaf dry matter content (LDMC) and compositional responses along a lowland to upland gradient over a four-year period. Plots were burned between zero and four times. Using a trait-based approach, we simulate hypothetical scenarios which allow species presence, abundance or trait values to vary over time and compare these to observed traits to understand the relative contributions of each of these three processes to observed trait patterns at the study site. We addressed the following questions: 1) How do changes in the fire regime affect community composition, structure, and community-level trait responses? 2) Are these effects consistent across a gradient of fire intensity? and, 3) What are the relative contributions of species turnover, changes in abundance, and changes in intraspecific trait values to observed changes in community weighted mean (CWM) traits in response to altered fire regime? Key Results We found strong evidence that altered fire return interval impacted understory plant communities. The number of fires a plot experienced significantly affected the magnitude of its compositional change and shifted the ecotone boundary separating shrub-dominated lowland areas from grass-dominated upland areas, with suppression sites (0 burns) experiencing an upland shift and annual burn sites a lowland shift. We found significant effects of burn regimes on the CWM of specific leaf area (SLA), and that observed shifts in both SLA and LDMC were driven primarily by intraspecific changes in trait values. Conclusions In a fire-adapted ecosystem, increased fire frequency altered community composition and structure of the ecosystem through changes in the position of the shrub line. We also found that plant traits responded directionally to increased fire frequency, with SLA decreasing in response to fire frequency across the environmental gradient. For both SLA and LDMC, nearly all of the observed changes in CWM traits were driven by intraspecific variation.
... The feedbacks that govern savanna-forest dynamics are highly dependent upon the negative relationship between tree cover and flammability (D'Odorico et al., 2006), but surprisingly few generalizations can be confidently drawn from the literature about this relationship. One point of general agreement is that the relationship between tree cover and flammability is largely controlled by C 4 grasses (Bond, 2008;Hoffmann et al., 2012b;Silverio et al., 2013;Just et al., 2016;Prior et al., 2017;Cardoso et al., 2018;D'Onofrio et al., 2018;Kahiu & Hanan, 2018;Hempson et al., 2019). Specifically, as tree density increases, highly flammable C 4 grasses decline, and the fuel bed becomes increasingly dominated by leaf litter, which is less flammable than grass (Prior et al., 2017). ...
... The relationship between tree cover and flammability often is presumed to exhibit a threshold at which flammability declines abruptly once a particular tree cover is reached (Staver & Levin, 2012;Hoffmann et al., 2012a,b;Li et al., 2019) owing to the disappearance of grass. Some evidence supports a threshold response to woody cover (Archibald et al., 2009;Cardoso et al., 2018), but other evidence suggests a gradual transition (D'Odorico et al., 2006;Just et al., 2016). Fire often is observed to stop reliably at sharp savanna-forest boundaries (Hennenberg et al., 2006;Ibanez et al., 2013;Cardoso et al., 2018), but this behavior may offer little information about the shape of the relationship between tree cover and flammability because intermediate tree covers are absent at sharp boundaries. ...
... Conditions that prevent ignition, as studied here, may differ quantitatively from those that cause landscape-scale fires to stop. Arguably, the latter would be the most informative for understanding savanna-forest dynamics (Just et al., 2016), so further research is needed to confirm our results for landscape fires. ...
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Vegetation‐fire feedbacks are important for determining the distribution of forest and savanna. To understand how vegetation structure controls these feedbacks, we quantified flammability across gradients of tree density from grassland to forest in the Brazilian Cerrado. We experimentally burned 102 plots, for which we measured vegetation structure, fuels, microclimate, ignition success, and fire behavior. Tree density had strong negative effects on ignition success, rate of spread, fire‐line intensity, and flame height. Declining grass biomass was the principal cause of this decline in flammability as tree density increased, but increasing fuel moisture contributed. Although the response of flammability to tree cover is often portrayed as an abrupt, largely invariant threshold, we found the response to be gradual, with considerable variability driven largely by temporal changes in atmospheric humidity. Even when accounting for humidity, flammability at intermediate tree densities cannot be reliably predicted. Fire spread in savanna‐forest mosaics is not as deterministic as often assumed, though may appear deterministic where vegetation boundaries are already sharp. Where transitions are diffuse, fire spread is difficult to predict, but should become increasingly predictable over multiple fire cycles, as boundaries are progressively sharpened until flammability appears to respond in a threshold‐like manner.
... These prescribed burns are applied primarily early in the growing season using low-intensity backing fires. The upland savanna matrix consistently burns when exposed to prescribed fire, but wetland communities have a longer fire return interval due to vegetation and microclimatic controls (Sorrie et al. 2006, Just et al. 2016). ...
Article
Rare species reintroductions are an increasingly common conservation strategy, but often result in poor survival of reintroduced individuals. Reintroduction sites are chosen primarily based on historical occupancy and/or abiotic properties of the site, with much less consideration given to properties of the larger biotic community. However, ecological niche theory suggests that the ability to coexist with other species is determined in part by the degree of functional similarity between species. The degree to which functional similarity affects the survival of reintroduced plants is poorly understood, but has important implications for the allocation of limited conservation resources. We collected a suite of abiotic, biotic and functional trait variables centered on outplanted individuals from four reintroduced rare plant species and used logistic regression and model selection to assess their influence on individual survival. We show that higher functional similarity between reintroduced individuals and the local community, measured by differences between their multivariate functional traits and the community weighted mean traits of their immediate neighbors, increases survival and is a stronger predictor of survival than local variation in abiotic factors, suggesting that the functional composition of the biotic community should be incorporated into site selection to improve reintroduction success.
... Firstly, spatial and temporal variations in fire activity and ash and charcoal products within the wetlands are important because they generate an uneven distribution of charcoal in these wetland systems. Wetlands that experience fires do not burn uniformly and this is due to the local environmental conditions (e.g., ignition mechanism, flammability, vegetation type, and fuel production) and climatic and weather controls (e.g., rainfall, water balance, wind, temperature) that influence the ignition and spread of fires [118][119][120]. For example, research has shown fires were absent from some permanent wetlands in semi-arid north-eastern South Africa [120]. ...
... Conversely, fire is a common occurrence in some seasonal wetlands, as they are more susceptible to fire activity due to the drying of vegetation during the winter months and the hydrological regime [120]. Research examining the spread of fires (following a prescribed burn) across savanna-wetland ecotones also showed different burning patterns between herbaceous and ligneous vegetation types [118]. Herbaceous plants (i.e., non-woody) tend to undergo full combustion leaving no residual macro-charcoal, whereas their ligneous counterparts (i.e., woody) produce a majority of macro-charcoal in the sedimentary record [121][122][123]. ...
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Floodplain wetland ecosystems respond dynamically to flooding, fire and geomorphological processes. We employed a combined geomorphological and environmental proxy approach to assess allochthonous and autochthonous macro-charcoal accumulation in the Macquarie Marshes, Australia, with implications for the reconstruction of fire regimes and environmental conditions in large, open-system wetlands. After accounting for fluvial macro-charcoal flux (1.05 ± 0.32 no. cm⁻² a⁻¹), autochthonous macro-charcoal in ~1 m deep sediment profiles spanning ~1.7 ka were highly variable and inconsistent between cores and wetlands (concentrations from 0 to 438 no. cm⁻³, mean accumulation rates from 0 to 3.86 no. cm⁻² a⁻¹). A positive correlation existed between the number of recent fires, satellite-observed ignition points, and macro-charcoal concentrations at the surface of the wetlands. Sedimentology, geochemistry, and carbon stable isotopes (δ¹³C range -15 to -25 ‰) were similar in all cores from both wetlands and varied little with depth. Application of macro-charcoal and other environmental proxy techniques is inherently difficult in large, dynamic wetland systems due to variations in charcoal sources, sediment and charcoal deposition rates, and taphonomic processes. Major problems facing fire history reconstruction using macro-charcoal records in these wetlands include: (1) spatial and temporal variations in fire activity and ash and charcoal products within the wetlands, (2) variations in allochthonous inputs of charcoal from upstream sources, (3) tendency for geomorphic dynamism to affect flow dispersal and sediment and charcoal accumulation, and (4) propensity for post-depositional modification and/or destruction of macro-charcoal by flooding and taphonomic processes. Recognition of complex fire-climate-hydrology-vegetation interactions is essential. High-resolution, multifaceted approaches with reliable geochronologies are required to assess spatial and temporal patterns of fire and to reconstruct in order to interpret wetland fire regimes.