Fire Extent Research Articles

Responses of a forest-dwelling terrestrial turtle, Terrapene carolina, to prescribed fire in a Longleaf Pine ecosystem

Prescribed fire is commonly used as a tool to meet a range of forest management goals. Owing to their limited movement abilities, terrestrial turtles are likely to be at high risk of injury and mortality, and to experience other fitness consequences with population-level implications from fire. Using radiotelemetry, we studied the responses of Eastern Box Turtles, Terrapene carolina carolina, to prescribed fire management in a sandhills Longleaf Pine forest system over a five-year period and compared our results to a nearby population in an unburned coastal plain location. Individual variation in turtle survival was strongly dependent on how frequently and extensively the areas were burned, with annual survival rates of 94.5% in unburned areas decreasing to 45.9% in the most extensively burned areas. Turtles at the fire-maintained sandhills site had annual survival rates 4.9% less than at the unburned coastal plain site, and females had annual survival rates 6.8% less than males. Survival varied seasonally, with greatest mortality rates in winter and spring, especially among females. Growth rates and body condition did not differ between sites, nor did they vary according to fire extent and frequency at the fire-maintained site. Although mortality was greater and spatially variable at the fire- maintained site, annual survival rates across the site (86–90% for females and males, respectively) were comparable to other stable populations of T. carolina. The lesser than expected mortality rate at the fire-maintained site was likely the result of turtles’ strong selection of mesic hardwood forests near bottomlands and streams – habitats that may serve as refugia from fire. In areas where T. carolina conservation is a priority, land managers should integrate maintenance of fire refuge habitats into burn planning to minimize unintended negative impacts to this imperiled species.

Changes in Lightning Fire Incidence in the Tasmanian Wilderness World Heritage Area, 1980–2016

The Tasmanian Wilderness World Heritage Area (TWWHA) has globally significant natural and cultural values, some of which are dependent on the absence of fire or the presence of particular fire regimes. Planned burning is currently used to reduce the risk of loss of world heritage values from unplanned fires, but large and damaging fires still occur, with lightning as the primary ignition source. Lightning-caused fire was rare in the TWWHA before 2000. There has since been an increase in both the number of fires following lightning storms and the area burnt by these fires. In the absence of a direct measurement of lightning strike incidence, we tested whether changes in rainfall, soil dryness and fuel load were responsible for these changes in fire incidence and extent. There were no relationships between these variables and the incidence of fires associated with lightning, but the variability in the Soil Dryness Index and the mean of 25% of driest values did predict both the number and area of fires. Thus, it appears that an increase in the proportion of lightning strikes that occur in dry conditions has increased ignition efficiency. These changes have important implications for the management of the TWWHA’s values, as higher projected fuel loads and drier climates could result in a further increase in the number of fires associated with lightning.

Predicting increasing high severity area burned for three forested regions in the western United States using extreme value theory

More than 70 years of fire suppression by federal land management agencies has interrupted fire regimes in much of the western United States. The result of missed fire cycles is a buildup of both surface and canopy fuels in many forest ecosystems, increasing the risk of severe fire. The frequency and size of fires has increased in recent decades, as has the area burned with high severity in some ecosystems. A number of studies have examined controls on high severity fire occurrence, but none have yet determined what controls the extent of high severity fire. We developed statistical models predicting high severity area burned for the western United States and three sub-regions—the Northern Rocky Mountains, Sierra Nevada Mountains, and Southwest. A simple model with maximum temperature the month of fire, annual normalized moisture deficit and location explains area burned in high severity fire in our west-wide model, with the exception of years with especially large areas burned with high severity fire: 1988, 2002. With respect to mitigation or management of high severity fire, understanding what drives extreme fire years is critical. For the sub-regional models, topography, spring temperature and snowpack condition, and vegetation condition class variables improved our prediction of high severity burned area in extreme fire years. Fire year climate is critical to predicting area burned in high severity fire, especially in extreme fire years. These models can be used for scenario analyses and impact assessments to aid management in mitigating negative impacts of high severity fire.

Historical Drivers and Contemporary Perceptions of Wildfire in a Post-Industrial Rural Landscape

Placed-based fire management planning that considers historical patterns and processes as well as contemporary local knowledge is recognized as an alternative to broad-scale, regional approaches. In this paper, we used dendrochronology and an online survey to assess historical trends and contemporary perceptions of wildfire, respectively, in the fire-prone anthracite coal region of northeastern Pennsylvania. We developed an annual index of fire occurrence and extent from 216 fire-scarred pitch pine (Pinus rigida) distributed across 9 ridgetop study sites for the period 1900–2016. In addition, we collected survey responses from area residents regarding contemporary perceptions of wildfire hazards and management. Our results show that 20th century wildfire activity was not associated with drought, but closely followed fluctuations in the anthracite coal industry, with increased fire occurrence and extent associated with times of severe job losses. Less extensive wildfire continues to occur frequently, with area residents recognizing the need for fuel management (i.e., prescribed fire) and an increase in resources allocated to wildfire prevention and management as well as trash disposal and recycling programs. Our research represents one example of an integrated approach to informing sustainable fire management that considers the link between historical patterns and contemporary perceptions.

Managing mature forest features: The production, accuracy and ecological relevance of a landscape‐scale map

SummaryMature trees and forests contain structural features such as tree hollows, large coarse woody debris and large spreading crowns that provide critical habitat for a wide range of species. These features can take hundreds of years to develop and require careful management to ensure their continued availability. Managing these features requires spatial mapping layers to facilitate landscape‐scale management. This paper outlines how a map of mature forest habitat was developed for Tasmania, Australia. The map was produced using spatial data on vegetation type, mature crown density and senescence, a global layer of forest loss data derived from satellite imagery, a database on timber harvest plans and a spatial layer on the extent of fire. The relationship between mapped mature habitat availability (high, medium, low or negligible) and tree hollow availability in wet forest areas was explored, complementing a similar published study in dry forests. The number of large trees likely to have hollows significantly increased with mapped mature habitat availability, although there was considerable variation and overlap between map categories. Data from a fauna locality database and two radio‐tracking studies showed that three of the vertebrate hollow‐using species examined (Swift Parrot, Common Brushtail Possum and the Tasmanian Long‐eared Bat) and nest records of a species reliant on large tree crowns (the Wedge‐tailed Eagle) were all more likely to occur in areas of higher mapped mature habitat availability. It is concluded that this map reflects the relative availability of tree hollows, is ecologically meaningful and will be useful when managing mature forest habitat at large spatial scales, but the variable accuracy of the map at fine scales needs to be taken into account.

How does forest recovery following moderate-severity fire influence effects of subsequent wildfire in mixed-conifer forests?

BackgroundGiven regional increases in fire activity in western North American forests, understanding how fire influences the extent and effects of subsequent fires is particularly relevant. Remotely sensed estimates of fire effects have allowed for spatial portioning into different severity categories based on the degree of fire-caused vegetation change. Fire effects between minimal overstory tree mortality (< 20%) and complete (or nearly complete) overstory tree mortality (> 95%) are often lumped into a single category referred to as moderate severity. In this paper, we investigated how burned areas in this broad category of moderate-severity fire fared when reburned by a subsequent fire. Specifically, we examined the influence of forest structure, tree species composition, and shrub cover 9–17 yr following moderate-severity fire on the severity of a subsequent large wildfire event. We used plot-based measurements of trees and shrub cover to develop 15 forest structure and composition variables to attempt to explain observed reburn severity.ResultsOnly live Abies Mill. species basal area and dead standing biomass were identified as significant predictors of reburn severity using conditional inference tree analysis, both of which were positively related to reburn severity.ConclusionOur findings emphasize that the wide range of fire effects in the moderate-severity category can contribute to highly variable responses to subsequent wildfire.

The Legacy of a Severe Wildfire on Stream Nitrogen and Carbon in Headwater Catchments

Large, high-severity wildfires alter the physical and biological conditions that determine how catchments retain and release nutrients and regulate streamwater quality. The short-term water quality impacts of severe wildfire are often dramatic, but the longer-term responses may better reflect terrestrial and aquatic ecosystem recovery. We followed streamwater chemistry for 14 years after the largest fire in recorded Colorado history, the 2002 Hayman Fire, to characterize patterns in nitrogen (N) and carbon (C) export. Throughout the post-fire period, stream nitrate and total dissolved N (TDN) remained elevated in 10 burned catchments relative to pre-burn periods and 4 unburned control catchments. Both the extent of fire in a catchment and wildfire severity influenced stream N concentrations. Nitrate was more than an order of magnitude higher in streams draining catchments that burned to a high extent (> 60% of their areas) compared to unburned catchments. Unburned catchments retained more than 95% of atmospheric N inputs, but N retention in burned catchments was less than half of N inputs. Unlike N, stream C was elevated in catchments that burned to a lesser extent (30–60% of their areas burned), compared to either unburned or extensively burned catchments. Remotely sensed estimates of upland and riparian vegetation cover suggest that burned forests could require several more decades before forest cover and nutrient demand return to pre-fire levels. The persistent stream N increases we report are below drinking water thresholds, but exceed ecoregional reference concentrations for healthy stream ecosystems and indicate that extensively burned headwater catchments no longer function as strong sinks for atmospheric N. Combined with increasing trends in wildfire severity and elevated N deposition, our findings demonstrate the potential for substantial post-wildfire changes in ecosystem N retention and have implications for nutrient export to downstream waters.

Human-environmental drivers and impacts of the globally extreme 2017 Chilean fires.

In January 2017, hundreds of fires in Mediterranean Chile burnt more than 5000km2, an area nearly 14 times the 40-year mean. We contextualize these fires in terms of estimates of global fire intensity using MODIS satellite record, and provide an overview of the climatic factors and recent changes in land use that led to the active fire season and estimate the impact of fire emissions to human health. The primary fire activity in late January coincided with extreme fire weather conditions including all-time (1979-2017) daily records for the Fire Weather Index (FWI) and maximum temperature, producing some of the most energetically intense fire events on Earth in the last 15-years. Fire activity was further enabled by a warm moist growing season in 2016 that interrupted an intense drought that started in 2010. The land cover in this region had been extensively modified, with less than 20% of the original native vegetation remaining, and extensive plantations of highly flammable exotic Pinus and Eucalyptus species established since the 1970s. These plantations were disproportionally burnt (44% of the burned area) in 2017, and associated with the highest fire severities, as part of an increasing trend of fire extent in plantations over the past three decades. Smoke from the fires exposed over 9.5 million people to increased concentrations of particulate air pollution, causing an estimated 76 premature deaths and 209 additional admissions to hospital for respiratory and cardiovascular conditions. This study highlights that Mediterranean biogeographic regions with expansive Pinus and Eucalyptus plantations and associated rural depopulation are vulnerable to intense wildfires with wide ranging social, economic, and environmental impacts, which are likely to become more frequent due to longer and more extreme wildfire seasons.

A New Picture of Fire Extent, Variability, and Drought Interaction in Prescribed Fire Landscapes: Insights From Florida Government Records.

Florida, United States, government records provide a new resource for studying fire in landscapes managed with prescribed fire. In Florida, most fire area (92%) is prescribed. Current satellite fire products, which underpin most air pollution emission inventories, detect only 25% of burned area, which alters airborne emissions and environmental impacts. Moreover, these satellite products can misdiagnose spatiotemporal variability of fires. Overall fire area in Florida decreases during drought conditions as prescribed fires are avoided, but satellite data do not reflect this pattern. This pattern is consistent with prescribed fire successfully reducing overall fire risk and damages. Human management of prescribed fires and fuels can, therefore, break the conventional link between drought and wildfire and play an important role in mitigating rising fire risk in a changing climate. These results likely apply in other regions of the world with similar fire regimes.

Mapping future fire probability under climate change: Does vegetation matter?

Understanding where and how fire patterns may change is critical for management and policy decision-making. To map future fire patterns, statistical correlative models are typically developed, which associate observed fire locations with recent climate maps, and are then applied to maps of future climate projections. A potential source of uncertainty is the common omission of static or dynamic vegetation as predictor variables. We therefore assessed the sensitivity of future fire projections to different combinations of vegetation maps used as explanatory variables in a statistically based fire modeling framework. We compared models without vegetation to models that incorporated static vegetation maps and that included output from a dynamic vegetation model that imposed three scenarios of fire and one scenario of land use change. We mapped projected future probability of all and large fires (> = 40 ha) under two climate scenarios in a heterogeneous study area spanning a large elevational gradient in the Sierra Nevada, California, USA. Results showed high model sensitivity to the treatment of vegetation as a predictor variable, particularly for models of large fire probability and for models accounting for wildfire effects on vegetation, which lowered future fire probability. Some scenarios resulted in opposite directional trends in the extent and probability of future fire, which could have serious implications for policy and management resource allocation. Model sensitivity resulted from high relative importance of vegetation variables in the baseline models and from large predicted changes in vegetation, particularly when simulating wildfire. Although statistical fire models often omit vegetation due to uncertainty, model sensitivity demonstrated here suggests a need to account for that uncertainty. Coupling statistical and processed based models may be a promising approach to reflect a more plausible range of scenarios.

Assessing the spatial fidelity of sedimentary charcoal size fractions as fire history proxies with a high-resolution sediment record and historical data

Fire reconstructions provide context for modern rates of burning and inform predictions of fire regimes' responses to climate and/or ecological changes. Charcoal particles preserved in lake sediments are a widely employed fire proxy. Although many studies have calibrated the charcoal proxy, the spatial scales of charcoal dispersal and source area remain disputed. Understanding the spatial fidelity of charcoal accumulation is increasingly important in light of recent efforts to aggregate multiple charcoal records to infer changes in regional, continental- and global-scale fire regimes. Using a high-resolution sediment record from Swamp Lake, California, we compare charcoal accumulation rate (CHAR) variations of three size fractions of sedimentary charcoal (63–150, >150, and >250 μm) to historical area burned data. We find that macroscopic (>250 and >150 μm) and mesoscopic (63–150 μm) charcoal source areas are within 25, 35, and 150 km of Swamp Lake, respectively. We also use a dispersal model to confirm these findings. Our estimates of charcoal source area fall within the large range of estimates for forest fires in the literature. Further, our methodology shows potential for constraining source areas of charcoal in sedimentary records, which is requisite for the reliable inference of the spatial extent of fire in paleorecords.

Significant decline of forest fires in Nilgiri Biosphere Reserve, India

Yet there is considerable uncertainty over management effectiveness of many protected areas around the world. In this regard, long-term monitoring and management of disturbances in the protected areas need to be properly addressed and documented. The present study is aimed to analyze spatial extent, frequency and distribution of forest fires in Nilgiri Biosphere Reserve, Western Ghats, India over four decades (1973–2014). Multi-temporal Landsat and Indian Remote Sensing satellite data were used to quantify forest burnt area. The results showed that the spatial extent of burnt area greatly varied between 1318 km2 (in 1989) to 15.7 km2 (in 2013). The monitoring of fires during the recent decade (2005–2014) was observed to have a gradual decline over the reserve. High frequency of fires has been found in dry deciduous forest followed by moist deciduous forest, scrub, grassland and semi-evergreen forest. Among six protected areas, Bandipur National Park had represented more fire incidents followed by Mudumalai Wildlife Sanctuary, Nagarhole and Mukurthi National Parks. Grid analysis shows that 67% of the grids were affected by forest fires. Large burnt patches have steadily decreased in their size while the other patch classes showed a significant reduction in their size over the study period. This study had revealed the role of climate and accessibility in relation to fire occurrences. Based on historical burnt area mapping outputs, fire hotspots have been modeled to address fire risk zones. Indeed, the Mann-Kendall trend test has indicated that the overall trend of fire incidents have been declining and this indicates the management effectiveness in Nilgiri Biosphere Reserve.

Bat activity before and after a severe wildfire in Pilliga forests: Resilience influenced by fire extent and landscape mobility?

AbstractWildfires are becoming increasingly severe and common in many parts of the world, yet their effects on certain taxa remain poorly studied. In November 2006, a major wildfire occurred in the Pilliga forests of north‐west New South Wales, Australia. This fire was severe and extensive, burning more than 120 000 ha. Prior to the fire, we conducted a study in the affected area assessing bat activity in relation to flyway size and riparian zones, allowing us to opportunistically compare before – and – after effects of wildfire on bats in burnt and unburnt areas. We assessed how bat activity and bat composition changed from 1 year pre‐fire to 1 year post‐fire and 4 years post‐fire, accounting for the effects of flyway size. A BACI analysis showed that there was an effect of time (year) on bat activity, with activity markedly reduced in both burnt and unburnt sites in the year post‐ fire, before recovering 4‐years post‐fire to levels that approached pre‐burn activity. However, there was no treatment or interaction effect, indicating fire alone did not affect bat activity at our sites. Activity was 50% lower at supplementary sites more remote (~5 km) from the fire edge. Multi‐dimensional scaling and permanova described a strong effect of year but no evidence of fire or stream size‐mediated effects on species composition. The drop in activity post‐fire coincided with a period of drought that subsequently broke in the year prior to our survey 4 years post‐fire. Some species‐specific responses to the fire were evident and depended on the proximity to unburnt forest. We suggest the potential for landscape re‐assortment, whereby some species may move from the unburnt landscape into the burnt landscape, possibly in response to a resource pulse of insects. A landscape pattern of movement could obscure the detection of direct fire effects on mobile bats. We suggest fire extent, proximity to unburnt vegetation and severity are key considerations when interpreting the response of bats to wildfire.

Dynamics of forest fires in the southwestern Amazon

The synergism between climatic change and human action has provided conditions for the occurrence of forest fires in the Amazon. We used annual mapping to reconstruct the history of fire in Brazil’s state of Acre to understand the forest-fire regime over a period of 33 years (1984–2016). The burn-scar index (BSI) derived from the fractions of soil and of photosynthetic and non-photosynthetic material was generated by CLASlite© software using Landsat-TM and OLI satellite images. The area of forest-fire scars totaled 525,130 ha in the period analyzed. This total includes forests that fire affected only once (388,350 ha), twice (59,800 ha) and three times (5727 ha). The years 2005 and 2010 represent 90% of the total area of forest fires in Acre, coinciding with severe droughts caused by the anomalous warming of the tropical North Atlantic Ocean. The most heavily impacted portion of Acre was in the eastern part of the state, which has the greatest forest fragmentation, consolidation of agricultural activity and presence of settlement projects. In 2005, the municipalities of Acrelândia, Plácido de Castro and Senador Guiomard accounted for more than 50% of the forest remnants impacted by fire. Of the total extent of forest fires in Acre, 43% occurred in settlement projects administered by the National Institute for Colonization and Agrarian Reform (INCRA) and 16% in conservation units administered by the Ministry of Environment (MMA). The area of forest fires was 36 times greater in the 16 years after 2000, compared to the 16 years before 2000. The frequency of fires increased dramatically from one fire episode roughly every ten years (period from 1984 to 2004), to one fire every five years (period from 2005 to 2016). With the projections of warmer climate and advancing deforestation, the forest fires in Acre will tend be more intense and frequent.

Composition and Structure of Forest Fire Refugia: What Are the Ecosystem Legacies across Burned Landscapes?

Locations within forest fires that remain unburned or burn at low severity—known as fire refugia—are important components of contemporary burn mosaics, but their composition and structure at regional scales are poorly understood. Focusing on recent, large wildfires across the US Pacific Northwest (Oregon and Washington), our research objectives are to (1) classify fire refugia and burn severity based on relativized spectral change in Landsat time series; (2) quantify the pre-fire composition and structure of mapped fire refugia; (3) in forested areas, assess the relative abundance of fire refugia and other burn severity classes across forest composition and structure types. We analyzed a random sample of 99 recent fires in forest-dominated landscapes from 2004 to 2015 that collectively encompassed 612,629 ha. Across the region, fire refugia extent was substantial but variable from year to year, with an annual mean of 38% of fire extent and range of 15–60%. Overall, 85% of total fire extent was forested, with the other 15% being non-forest. In comparison, 31% of fire refugia extent was non-forest prior to the most recent fire, highlighting that mapped refugia do not necessarily contain tree-based ecosystem legacies. The most prevalent non-forest cover types in refugia were vegetated: shrub (40%), herbaceous (33%), and crops (18%). In forested areas, the relative abundance of fire refugia varied widely among pre-fire forest types (20–70%) and structural conditions (23–55%). Consistent with fire regime theory, fire refugia and high burn severity areas were inversely proportional. Our findings underscore that researchers, managers, and other stakeholders should interpret burn severity maps through the lens of pre-fire land cover, especially given the increasing importance of fire and fire refugia under global change.

Ecological legacies of fire detected using plot-level measurements and LiDAR in an old growth coastal temperate rainforest

Vegetation succession following fire disturbances has long been of interest in ecology, but the evolution of landscape pattern and structure following low-severity ground fires is poorly understood. In coastal temperate rainforest ecosystems historic fire disturbances are not well documented and time since the most recent fire is largely unknown. We sampled 6000 tree cores from 27 forest plots that burned 124 years ago and 11 plots with no recent history of fire (within the last 1000 years) to understand the legacies of fire on forest stand structure in a British Columbia high-latitude coastal temperate rainforest. We assessed the timing and spatial extent of historic fires with a 700 year fire history reconstruction built from fire scars, and applied light detection and ranging (LiDAR) to ground-truth plot-level measurements. We sampled an additional 32 plots with known fire histories to validate the ability of LiDAR to detect and characterize historic fire legacies. In total, we sampled 70 plots for stem density, stand structure, and stand composition. Trees in burned plots were significantly taller, and the mean stem density was less than half that of unburned plots despite 124 years since the most recent fire. LiDAR analyses had similar results and also showed that burned plots had lower canopy cover and greater canopy complexity. Field-based measurements are still required to resolve differences in community structure and composition in our temperate rainforest study area. However, LiDAR may be an important tool to bridge the spatial information offered by plot-level measurements to larger area characterizations in the future. Our comparative analyses provide an improved understanding of fire legacies and temperate rainforest structure, which increases our ability to detect fire disturbances in heterogeneous forests and is important for forest resource management and conservation.

Use of imaging spectroscopy and LIDAR to characterize fuels for fire behavior prediction

To protect ecosystem services and the increasing wildland urban interface in a world with fire, comprehensive maps of wildland fuels are needed to predict fire behavior and effects. Traditionally, fuels have been categorized into a classification scheme whereby a single metric represents vegetation composition and structure, which can then be parameterized based on variable vegetation amount and condition. Remote sensing has been used to extrapolate between known field plots across the landscape, however until recently, those technologies have had limited ability to characterize fuels (e.g., composition, horizontal and vertical connectivity). Using new technologies (imaging spectroscopy and LIDAR), the objectives of this study are to assess: 1) how fuel characteristics observed from remote sensing affect categorical fuel classifications, and 2) how fuel characteristics affect landscape-scale fire behavior (spread rate, areal extent and perimeter). The analysis was conducted over the 2014 California King Fire that burned ~40,000 ha over lands with varying use and history and has unique remote sensing observations from before and after the fire. This analysis compares fuel classifications from a synergistic field, model, and Landsat approach (LANDFIRE) and products derived from the Airborne Visible/Infrared Imaging Spectrometer and LIDAR (MapFUELS). Each classification focuses on different fuel characteristics, which were then used to compare differences in a fire simulation model (CAWFE) and actual fire behavior. The results show that fuel characteristic inputs such as horizontal connectivity or fuel type and vertical structure affect fire spread rate and final fire extent (respectively). These results present the opportunity for future integration of fuel characteristics observed at coarser resolutions (900 m2) into predictions of fire behavior a similar spatial resolutions (as opposed to the current standard based on empirical relationships between fuel and fire behavior at ~12 m2 resolution).

A native C3 grass alters fuels and fire spread in montane grassland of South Africa

Although most fire research in plant ecology focuses on vegetation responses to burning, shifts in plant community composition wrought by climate change can change wildland fuelbeds and affect fire behaviour such that the nature of fire in these systems is altered. Changes that introduce substantially different fuel types can alter the spatial extent of fire, with potential impacts on community succession and biodiversity. Montane grasslands of sub-Saharan Africa are threatened by climate change because species distributions can shift with climatically determined ranges. We studied the impact of patches of the temperate C3 grass Festuca costata in C4-dominated grassland at the transition between their subalpine ranges in South Africa’s Drakensberg. We used empirical data on fuel moisture and fuel load across F. costata-dominated patches in a C4-dominated matrix in fire spread models to predict the effect of larger, higher-moisture F. costata patches on the spatial extent of fire. Results indicate F. costata reduces fire spread and burn probability in F. costata patches, and the effect increases as live fuel moisture increases and patches get larger. However, as a native species, F. costata does not appear to have the extreme, fire-suppressing effect of non-native C3 grasses in other C4 grasslands. Instead, F. costata patches likely increase variability in the spatial extent of fire in this C4-dominated grassland, which likely translates to spatial variability on vegetation succession.

Ecosystem size and flooding drive trophic dynamics of riparian spiders in a fire-prone Sierra Nevada river system

Disturbance can play an important role in structuring stream food webs. Although floods have received the greatest attention as a disturbance agent in rivers, wildfire — which can strongly influence fluvial ecosystem structure and function — may also drive consumer trophic dynamics. We measured the relative effects of wildfire, hydrologic disturbance, ecosystem size, and canopy openness (as a proxy for in-stream productivity) on trophic position and reliance on aquatically-derived nutritional subsidies of riparian spiders of the family Tetragnathidae along two rivers on the west slope of the Sierra Nevada in California, USA. Ecosystem size received strong support as an environmental determinant of both trophic measures, with variability in flood magnitude emerging as an important mechanism linking ecosystem size and trophic responses. Piecewise linear regression revealed significant breakpoints in spider trophic position and reliance on aquatically-derived nutritional subsidies that were related to thresholds in fire extent within the catchment. These nonlinear relationships with wildfire may lend additional insight into the potential interactions among ecosystem size, productivity, and disturbance that determine stream–riparian food-web architecture.

A Model-Based Framework to Evaluate Alternative Wildfire Suppression Strategies

The complexity and demands of wildland firefighting in the western U.S. have increased over recent decades due to factors including the expansion of the wildland-urban interface, lengthening fire seasons associated with climate change, and changes in vegetation due to past fire suppression and timber harvest. In light of these changes, the use of more wildland fire on the landscape could reduce fuels and form barriers to the spread of future fires while performing forest restoration in some areas. However, the risks, costs and benefits of changing fire response strategy have not been quantified. Here, we identify gaps regarding the ability to simulate alternative wildfire suppression strategies, due to a number of factors including limited data collected on fireline construction, as well as synergies between firefighting resources and resource effectiveness. We present a fire management continuum: at one end lies full suppression of all fires under all circumstances, and at the opposite end lies no suppression of any fires regardless of location or time in season, with a wide array of managed fire options falling in between. Next, we demonstrate the proof-of-concept using a stochastic fire simulation model, FSim, to simulate two alternative fire suppression strategies close to opposite ends of this continuum for the Sierra National Forest of California: (1) business-as-usual, which equates to nearly full fire suppression; and (2) full suppression of human-caused fires and no suppression actions on lightning-caused fires. Results indicate that fire management strategy can substantially affect the number of large fires and landscape burn probabilities, both of which were shown to increase under the second scenario. However, temporal feedbacks are expected to play an important role: we show that increases in burned area substantially limit ignition potential and the extent of subsequent fires within the first five to ten years, especially under the second scenario. While subject to current data gaps and limitations in fire modeling, the methodology presented here can be used to simulate a number of alternative fire suppression strategies, including decisions to suppress or not suppress fires based on location, time of season or other factors. This method also provides basic inputs needed to estimate risks, costs and benefits of various alternative suppression strategies in future work. In future work, uncertainties resulting from current limitations in knowledge can be addressed using techniques such as scenario planning in order to provide land managers with a set of possible fire outcomes.