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At least 181 records · Page 10Linked to original sources
USGS2001

Interactions between fire and invasive plants in temperate grasslands of North America

A substantial number of invasive grasses, forbs and woody plants have invaded temperate grasslands in North America. Among the invading species are winter annuals, biennials, cool-season perennials, warm-season perennials, vines, shrubs, and trees. Many of these species have been deliberately introduced and widely planted; some are still used for range improvement, pastures, lawns, and as ornamentals, though many are listed as state or federal noxious weeds. Others have been greatly facilitated by widespread land disturbance. Historically, fire has been a major selective force in the evolution of temperate grasslands. Further, prescribed fire is commonly used as a method of ecological management for native grassland communities as well as in conjunction with restoration efforts. Within this context, it is important to understand how invasive species will interact with natural and prescribed fire regimes. In this paper, we consider what is known about how exotic species that invade temperate grasslands relate to fire. The primary issues addressed for each species are (1) Does fire appear to enhance colonization? (2) To what degree does fire affect the survival of plants? (3) Are plants that are burned able to regrow following fire and, if so, how rapidly can they recover? (4) How important is competition with native species to the response to fire? and (5) What effect does an invasive species have on the characteristics of the fire regime? For many species, results are preliminary, incomplete, or inconsistent among studies. For this reason, many of the conclusions drawn for individual species must be considered preliminary. Based on analyses of individual species, a conceptual framework is presented for considering how invasive plants may interact with fire when they invade an ecosystem. The major categories of influences are the native community, the fire regime, growth conditions for both invasive and native species, and influences that disturbances, human impacts, and landscape characteristics have had in the past and will have in the future. The examples considered in this paper provide support for a few, tentative generalizations. First, among our current worst invaders of temperate grasslands, adaptation to fire is quite variable. Some species are not well adapted to burning and can be easily eliminated; other species are better adapted but can still be eliminated if fire occurs during periods of particular vulnerability and/or at high frequency. There is a set of species that is extremely well adapted to fire and will not be eliminated through burning alone. Second, competitive interactions with native species play a crucial role in the success of nonnative invaders. In cases where differential burn responses between invasive and native species can be exploited, and adequate populations of native dominant species are present, fire can sometimes tip the competitive balance away from invasives. Third, there are a few invasive species that have exceptional attributes and for which there are no easy solutions. The ability of cheatgrass ( Bromus tectorum ) to enhance fire, the ability of Chinese tallow ( Triadica sebifera ) to suppress fire, and the ability of leafy spurge ( Euphorbia esula ) to resprout from repeated injury make these species exceptional threats to native diversity. Finally, the available information for many invasive species is very incomplete, partic- ularly with regard to how fire affects competitive interactions with the native community. There is much more we need to know if we are to consistently predict how invasive species will respond to fire and how burning can best be used to manage for natural diversity.

Conference Paper↗
USGS2021

Fire frequency impacts soil properties and processes in sagebrush steppe ecosystems of the Columbia Basin

Increased fire frequency in semi-arid ecosystems can alter biochemical soil properties and soil processes that underpin ecosystem structure and functioning, thus threatening native plant communities and the species that rely on them. However, there is much uncertainty about the magnitude of change as soils are exposed to more fires, because soil recovery and changes in fire severity following a first fire mediate the impact of successive fires on soil properties. With this study we aim to evaluate how increased fire frequency affects soil biochemical properties (i.e. soil pH, soil organic matter (SOM), soil organic carbon (SOC), soil structure and mineral N) and processes (i.e. microbial and enzymatic activity) in a sagebrush-steppe ecosystem located in the Columbia Plateau Ecoregion, Washington, USA. During 2016, we collected soils from once (2012), twice (2003 and 2012), and thrice (2003, 2007, and 2012) burned areas, enabling us to test the hypothesis that increasing fire frequency will exacerbate the impact of fire on soil properties and processes. Our study yielded three main results: (1) fire reduced the total soil C concentration and soil C in aggregates relative to unburned soil, but only when soil was exposed to fire once (i.e. the most recent fire), (2) compared to the unburned soils, SOM contents, enzyme activity and microbial CO 2 respiration were suppressed in the once and thrice burned soils, but not in the twice burned soils, and (3) fire increased NO 3 − -N contents across the once and twice burned sites, and reduced enzyme activity associated with N cycling in the thrice burned sites. Taken together, our findings suggest that a one-time fire in this shrub dominated semi-arid ecosystem significantly changes soil biochemical attributes and microbially driven processes. With sufficient time between fires, these structural and functional properties can partially recover, and this may persist even after a second fire, but recovery is limited when a third fire creates an additional disturbance at a shorter time interval. Furthermore, while soil C pools and microbial decomposition processes were able to recover with sufficient time, greater soil resource availability prevailed in soil across all fire frequencies, indicating that fire is likely to promote invasion and reduce ecosystem stability, even when other soil properties recover.

Washington↗
USGS2011

A comparison of effects from prescribed fires and wildfires managed for resource objectives in Sequoia and Kings Canyon National Parks

Current goals for prescription burning are focused on measures of fuel consumption and changes in forest density. These benchmarks, however, do not address the extent to which prescription burning meets perceived ecosystem needs of heterogeneity in burning, both for overstory trees and understory herbs and shrubs. There are still questions about how closely prescribed fires mimic these patterns compared to natural wildfires. This study compared burn patterns of prescribed fires and managed unplanned wildfires to understand how the differing burning regimes affect ecosystem properties. Measures of forest structure and fire severity were sampled in three recent prescribed fires and three wildfires managed for resource objectives in Sequoia and Kings Canyon National Parks. Fine scale patterns of fire severity and heterogeneity were compared between fire types using ground-based measures of fire effects on fuels and overstory and understory vegetation. Prescribed fires and wildfires managed for resource objectives displayed similar patterns of overstory and understory fire severity, heterogeneity, and seedling and sapling survival. Variation among plots within the same fire was always greater than between fire types. Prescribed fires can provide burned landscapes that approximate natural fires in many ways. It is recognized that constraints placed on when wildfires managed for resource objectives are allowed to burn freely may bias the range of conditions that might have been experienced under more natural conditions. Therefore they may not exactly mimic natural wildfires. Overall, the similarity in fire effects that we observed between prescribed fires and managed wildfires indicate that despite the restrictions that are often placed on prescribed fires, they appear to be creating post-fire conditions that approximate natural fires when assessed on a fine spatial scale.

California↗
USGS2016

Historical dominance of low-severity fire in dry and wet mixed-conifer forest habitats of the endangered terrestrial Jemez Mountains salamander ( Plethodon neomexicanus )

Anthropogenic alteration of ecosystem processes confounds forest management and conservation of rare, declining species. Restoration of forest structure and fire hazard reduction are central goals of forest management policy in the western United States, but restoration priorities and treatments have become increasingly contentious. Numerous studies have documented changes in fire regimes, forest stand structure and species composition following a century of fire exclusion in dry, frequent-fire forests of the western U.S. (e.g., ponderosa pine and dry mixed-conifer). In contrast, wet mixed-conifer forests are thought to have historically burned infrequently with mixed- or high-severity fire—resulting in reduced impacts from fire exclusion and low restoration need—but data are limited. In this study we quantified the current forest habitat of the federally endangered, terrestrial Jemez Mountains salamander (Plethodon neomexicanus) and compared it to dendroecological reconstructions of historical habitat (e.g., stand structure and composition), and fire regime parameters along a gradient from upper ponderosa pine to wet mixed-conifer forests. We found that current fire-free intervals in Jemez Mountains salamander habitat (116–165 years) are significantly longer than historical intervals, even in wet mixed-conifer forests. Historical mean fire intervals ranged from 10 to 42 years along the forest gradient. Low-severity fires were historically dominant across all forest types (92 of 102 fires). Although some mixed- or highseverity fire historically occurred at 67% of the plots over the last four centuries, complete mortality within 1.0 ha plots was rare, and asynchronous within and among sites. Climate was an important driver of temporal variability in fire severity, such that mixed- and high-severity fires were associated with more extreme drought than low-severity fires. Tree density in dry conifer forests historically ranged from open (90 trees/ha) to moderately dense (400 trees/ha), but has doubled on average since fire exclusion. Infill of fire-sensitive tree species has contributed to the conversion of historically dry mixedconifer to wet mixed-conifer forest. We conclude that low-severity fire, which has been absent for over a century, was a critical ecosystem process across the forest gradient in Jemez Mountains salamander habitat, and thus is an important element of ecosystem restoration, resilience, and rare species recovery.

Forest Ecology and Management↗
USGS2005

Factors affecting plant diversity during post-fire recovery and succession of mediterranean-climate shrublands in California, USA

Plant community diversity, measured as species richness, is typically highest in the early post-fire years in California shrublands. However, this generalization is overly simplistic and the present study demonstrates that diversity is determined by a complex of temporal and spatial effects. Ninety sites distributed across southern California were studied for 5 years after a series of fires. Characteristics of the disturbance event, in this case fire severity, can alter post-fire diversity, both decreasing and increasing diversity, depending on life form. Spatial variability in resource availability is an important factor explaining patterns of diversity, and there is a complex interaction between landscape features and life form. Temporal variability in resource availability affects diversity, and the diversity peak in the immediate post-fire year (or two) appears to be driven by factors different from subsequent diversity peaks. Early post-fire diversity is influenced by life-history specialization, illustrated by species that spend the bulk of their life cycle as a dormant seed bank, which is then triggered to germinate by fire. Resource fluctuations, precipitation in particular, may be associated with subsequent post-fire diversity peaks. These later peaks in diversity comprise a flora that is compositionally different from the immediate post-fire flora, and their presence may be due to mass effects from population expansion of local populations in adjacent burned areas. ?? 2005 Blackwell Publishing Ltd.

Diversity and Distributions↗
USGS2013

Human and biophysical influences on fire occurrence in the United States

National-scale analyses of fire occurrence are needed to prioritize fire policy and management activities across the United States. However, the drivers of national-scale patterns of fire occurrence are not well understood, and how the relative importance of human or biophysical factors varies across the country is unclear. Our research goal was to model the drivers of fire occurrence within ecoregions across the conterminous United States. We used generalized linear models to compare the relative influence of human, vegetation, climate, and topographic variables on fire occurrence in the United States, as measured by MODIS active fire detections collected between 2000 and 2006. We constructed models for all fires and for large fires only and generated predictive maps to quantify fire occurrence probabilities. Areas with high fire occurrence probabilities were widespread in the Southeast, and localized in the Mountain West, particularly in southern California, Arizona, and New Mexico. Probabilities for large-fire occurrence were generally lower, but hot spots existed in the western and south-central United States The probability of fire occurrence is a critical component of fire risk assessments, in addition to vegetation type, fire behavior, and the values at risk. Many of the hot spots we identified have extensive development in the wildland–urban interface and are near large metropolitan areas. Our results demonstrated that human variables were important predictors of both all fires and large fires and frequently exhibited nonlinear relationships. However, vegetation, climate, and topography were also significant variables in most ecoregions. If recent housing growth trends and fire occurrence patterns continue, these areas will continue to challenge policies and management efforts seeking to balance the risks generated by wildfires with the ecological benefits of fire.

Ecological Applications↗
USGS2020

Mapping fire regime ecoregions in California

The fire regime is a central framing concept in wildfire science and ecology and describes how a range of wildfire characteristics vary geographically over time. Understanding and mapping fire regimes is important for guiding appropriate management and risk reduction strategies and for informing research on drivers of global change and altered fire patterns. Most efforts to spatially delineate fire regimes have been conducted by identifying natural groupings of fire parameters based on available historical fire data. This can result in classes with similar fire characteristics but wide differences in ecosystem types. We took a different approach and defined fire regime ecoregions for California to better align with ecosystem types, without using fire as part of the definition. We used an unsupervised classification algorithm to segregate the state into spatial clusters based on distinctive biophysical and anthropogenic attributes that drive fire regimes – and then used historical fire data to evaluate the ecoregions. The fire regime ecoregion map corresponded well with the major land cover types of the state and provided clear separation of historical patterns in fire frequency and size, with lower variability in fire severity. This methodology could be used for mapping fire regimes in other regions with limited historical fire data or forecasting future fire regimes based on expected changes in biophysical characteristics.

California↗
USGS2023

Predicting burn severity for integration with post-fire debris-flow hazard assessment: A case study from the Upper Colorado River Basin, USA

Background: Burn severity significantly increases the likelihood and volume of post-wildfire debris flows. Pre-fire severity predictions can expedite mitigation efforts because precipitation contributing to these hazards often occurs shortly after wildfires, leaving little time for post-fire planning and management. Aim: The aim of this study was to predict burn severity using pre-fire conditions of individual wildfire events and estimate potential post-fire debris flow to unburned areas. Methods: We used random forests to model dNBR from pre-fire weather, fuels, topography, and remotely sensed data. We validated our model predictions against post-fire observations and potential post-fire debris-flow hazard estimates. Key results: Fuels, pre-fire weather, and topography were important predictors of burn severity, although predictor importance varied between fires. Post-fire debris-flow hazard rankings from predicted burn severity (pre-fire) were similar to hazard assessments based on observed burn severity (post-fire). Conclusion: Predicted burn severity can serve as an input to post-fire debris-flow models before wildfires occur, antecedent to standard post-fire burn severity products. Assessing a larger set of fires under disparate conditions and landscapes will be needed to refine predictive models. Implications: Burn severity models based on pre-fire conditions enable the prediction of fire effects and identification of potential hazards to prioritise response and mitigation.

Arizona, Colorado, New Mexico, Utah, Wyoming↗
USGS2018

Quantifying variance across spatial scales as part of fire regime classifications

The emergence of large‐scale fire classifications and products informed by remote sensing data has enabled opportunities to include variability or heterogeneity as part of modern fire regime classifications. Currently, basic fire metrics such as mean fire return intervals are calculated without considering spatial variance in a management context. Fire return intervals are also only applicable at a particular grain size (defined as the spatial unit of interest) even though they are typically applied homogeneously. In this study, we utilized a 29‐yr fire occurrence database to show how spatial variance changes with respect to grain as postulated by Wiens ( 1989 ) when reporting fire patterns within the Great Plains, USA. We utilized data from the Monitoring Trends in Burn Severity database of fire occurrence for the years 1984–2012. We analyzed median numbers of fire along with their variance at four spatial grains ranging from small units (e.g., plots at 3 × 3 km resolution) to large units (e.g., landscapes at 1500 × 2700 km resolution). Median number of fire occurrences was consistently low, irrespective of grain. Despite the consistency in low median numbers of fires across grain, variance in the numbers of fires between units decreased. Variance within units, however, did not change as grain increased indicating fire‐pattern‐scale inconsistencies. Fire pattern interpretations depended entirely on the scale at which it is calculated. Given that the Great Plains region has a large disparity in fire patterns (i.e., some regions burn often, while others may never burn), fire regime classifications will benefit from including scale‐specific variance estimates as a foundation for understanding changes in fire regimes and corresponding social–ecological and policy responses.

Ecosphere↗
USGS2019

Spatio-temporal variability of human-fire interactions on the Navajo Nation

Unraveling the effects of climate and land-use on historical fire regimes provides important insights into broader human-fire-climate dynamics, which are necessary for ecologically-based forest management. We developed a spatial human land-use model for Navajo Nation forests across which we sampled a network of tree-ring fire history sites to reflect contrasting historical land-use intensity: high human use, primarily in the Chuska Mountains, and low human use, primarily on the central Defiance Plateau. We tested for and compared human- and climate-driven changes in the fire regimes by applying change point detection, regression, and superposed epoch analyses. The historical fire regimes and fire-climate relationships reflect those of similar forests regionally, and are similar between the two Navajo landscapes until the early 1800s. We then determined that a previously identified, localized, early (1830s) decline in fire activity was geographically widespread across higher human use sites. In contrast, fires continued to burn uninterrupted through this period at the lower use sites. Though the 1830s included significantly wet and cold periods that could have contributed to fire regime decline, human factors pose a more spatio-temporally consistent explanation. A rise in Navajo pastoralism in the 1820s-1830s was concentrated seasonally in the heavy use sites. By the 1880s, livestock numbers more than doubled, grazing became far more spatially widespread, and frequent fire regimes of Navajo forests collapsed. The last widespread fire recorded on either landscape was in 1886. In the Chuska Mountains, livestock and fire co-existed for over 50 years between the initial 1832 fire decline and the end of frequent fires after 1886, an exceptional pattern in the western US. Though unique in its timing, character, and spatial dynamics, the collapse of historical fire regimes in Navajo forests contributed to now over a century without frequent surface fire, leaving Navajo forests at risk for large, uncharacteristic high-severity fires.

Arizona, New Mexico↗
USGS2018

Effects of prescribed fire on San Francisco gartersnake survival and movement

The application of fire is prescribed for management of habitats for many plant and animal communities, but its effects on herpetofauna are diverse and remain poorly understood. To date no studies have examined the effects of prescribed fire on endangered San Francisco gartersnake ( Thamnophis sirtalis tetrataenia ) populations, despite a call for prescribed fire in the recovery plan for the species. We used multi‐state capture‐mark‐recapture models to assess whether effects of prescribed fire were ephemeral, occurring only during the year of the fire, or persisted for 3 years following the fire, and to estimate the effects of prescribed fire on demographic parameters of San Francisco gartersnakes inhabiting California coastal prairie. Ephemeral fire effects were better supported for transitions (movement) between burned and unburned areas, but persistent fire effects were better supported for apparent survival and recapture probabilities. Movement between burned and unburned areas decreased during the year of the fire, but transition rates from burned to unburned areas decreased less than transition rates from unburned to burned areas in the year of the fire. Apparent survival probabilities increased in the unburned areas following the fire but were largely unchanged, though more uncertain, in burned areas following the fire. Recapture probabilities decreased site‐wide following the fire, though the decrease was greater in burned areas than in unburned areas. Although imprecise, our estimates of the effects of prescribed fire suggest that under the conditions of this fire (low‐intensity fall burn applied to a small area within a robust population and followed by wet weather), prescribed fire is a viable management tool for maintaining open habitats where San Francisco gartersnakes occur.

California↗
USGS2002

Fire management of California shrubland landscapes

Fire management of California shrublands has been heavily influenced by policies designed for coniferous forests, however, fire suppression has not effectively excluded fire from chaparral and coastal sage scrub landscapes and catastrophic wildfires are not the result of unnatural fuel accumulation. There is no evidence that prescribed burning in these shrublands provides any resource benefit and in some areas may negatively impact shrublands by increasing fire frequency. Therefore, fire hazard reduction is the primary justification for prescription burning, but it is doubtful that rotational burning to create landscape age mosaics is a cost effective method of controlling catastrophic wildfires. There are problems with prescription burning in this crown-fire ecosystem that are not shared by forests with a natural surface-fire regime. Prescription weather conditions preclude burning at rotation intervals sufficient to effect the control of fires ignited under severe weather conditions. Fire management should focus on strategic placement of prescription burns to both insure the most efficient fire hazard reduction and to minimize the amount of landscape exposed to unnaturally high fire frequency. A major contributor to increased fire suppression costs and increased loss of property and lives is the continued urban sprawl into wildlands naturally subjected to high intensity crown fires. Differences in shrubland fire history suggest there may be a need for different fire management tactics between central coastal and southern California. Much less is known about shrubland fire history in the Sierra Nevada foothills and interior North Coast Ranges, and thus it would be prudent to not transfer these ideas too broadly across the range of chaparral until we have a clearer understanding of the extent of regional variation in shrubland fire regimes.

Environmental Management↗
USGS2020

Simulated increases in fire activity reinforce shrub conversion in a southwestern US forest

Fire exclusion in historically frequent-fire forests of the southwestern United States has altered forest structure and increased the probability of high-severity fire. Warmer and drier conditions, coupled with dispersal distance limitations, are impeding tree seedling establishment and survival following high-severity fire. High-severity patches are commonly dominated by non-forest vegetation, a state that can be reinforced by subsequent fire events. We sought to determine the influence of fire probability on post-fire vegetation development in a severely burned landscape in New Mexico, USA. We used LANDIS-II to simulate three fire probability scenarios—historical fire probability, contemporary fire probability, and the mean of the two—with contemporary climate. As fire probability increased, the mean size of the largest fires and the mean landscape fire severity increased. These changes in fire characteristics resulted in decreased total aboveground biomass and photosynthetic capacity on the landscape after 50 years. Additionally, the distribution of individual species biomass shifted, with early successional species, especially those that resprout after fire, increasing as a fraction of total biomass with increasing fire occurrence. Counter to empirical data, our simulations did not show a conifer establishment limitation, suggesting a source of uncertainty that will need to be addressed to improve projections of forest dynamics under future climate. Even without limited conifer regeneration, continued increases in fire frequency are likely to favor resprouting species and result in a loss of forest biomass and ecosystem productivity in this southwestern forest landscape.

New Mexico↗
USGS2009

Calibration and validation of the relative differenced Normalized Burn Ratio (RdNBR) to three measures of fire severity in the Sierra Nevada and Klamath Mountains, California, USA

Multispectral satellite data have become a common tool used in the mapping of wildland fire effects. Fire severity, defined as the degree to which a site has been altered, is often the variable mapped. The Normalized Burn Ratio (NBR) used in an absolute difference change detection protocol (dNBR), has become the remote sensing method of choice for US Federal land management agencies to map fire severity due to wildland fire. However, absolute differenced vegetation indices are correlated to the pre-fire chlorophyll content of the vegetation occurring within the fire perimeter. Normalizing dNBR to produce a relativized dNBR (RdNBR) removes the biasing effect of the pre-fire condition. Employing RdNBR hypothetically allows creating categorical classifications using the same thresholds for fires occurring in similar vegetation types without acquiring additional calibration field data on each fire. In this paper we tested this hypothesis by developing thresholds on random training datasets, and then comparing accuracies for (1) fires that occurred within the same geographic region as the training dataset and in similar vegetation, and (2) fires from a different geographic region that is climatically and floristically similar to the training dataset region but supports more complex vegetation structure. We additionally compared map accuracies for three measures of fire severity: the composite burn index (CBI), percent change in tree canopy cover, and percent change in tree basal area. User's and producer's accuracies were highest for the most severe categories, ranging from 70.7% to 89.1%. Accuracies of the moderate fire severity category for measures describing effects only to trees (percent change in canopy cover and basal area) indicated that the classifications were generally not much better than random. Accuracies of the moderate category for the CBI classifications were somewhat better, averaging in the 50%-60% range. These results underscore the difficulty in isolating fire effects to individual vegetation strata when fire effects are mixed. We conclude that the models presented here and in Miller and Thode ([Miller, J.D. & Thode, A.E., (2007). Quantifying burn severity in a heterogeneous landscape with a relative version of the delta Normalized Burn Ratio (dNBR). Remote Sensing of Environment, 109, 66-80.]) can produce fire severity classifications (using either CBI, or percent change in canopy cover or basal area) that are of similar accuracy in fires not used in the original calibration process, at least in conifer dominated vegetation types in Mediterranean-climate California.

Remote Sensing of Environment↗
USGS2011

Fire management of Mediterranean landscapes

The hazardous mediterranean climate, highly flammable vegetation, and rugged terrain, all important elements of fire behavior, become problems only in the presence of people. People recreate and build homes in the mediterranean wildlands because of the delightful climate and will continue to do so as long as space is available. People start most fires, and their mere presence tends to warp fire suppression strategies because fire agencies must protect lives and property threatened by fires rather than “back off” and build fire lines around fire perimeters . Carl C. Wilson (1979a), Chief of Division of Forest and Fire Research, USFS/Pacific Southwest Forest and Range Experiment Station Human presence in mediterranean-type climate (MTC) regions has differed markedly in the length of human occupation; however, there are remarkable similarities in how early inhabitants altered fire regimes and how modern societies deal with the fire hazard. Here we draw on the history of human impacts outlined in the regional reviews (see Chapters 4–8), the problems created by nineteenth and twentieth century management practices, and conclude with twenty-first century problems and future options. As discussed throughout this book, MTC ecosystems are highly fire adapted but, as illustrated here, contemporary societies have not fully adapted to balancing fire hazard risk and resource needs on these landscapes. Early Human Fire Use and Impacts Fire has been a widely utilized management tool throughout the history of humankind (Pyne 1995). Early hunter–gatherers utilized fire to manage for plant and animal resources. Fire also played an important role in early domestication of crops as clearing off woody or other perennial vegetation would have required fire on many landscapes. With domestication of livestock it was an important tool for increasing forage.

Book chapter↗
USGS2020

Contemporary fire regimes provide a critical perspective on restoration needs in the Mexico-United States borderlands

The relationship between people and wildfire has always been paradoxical: fire is an essential ecological process and management tool, but can also be detrimental to life and property. Consequently, fire regimes have been modified throughout history through both intentional burning to promote benefits and active suppression to reduce risks. Reintroducing fire and its benefits back into the Sky Island mountains of the United States-Mexico borderlands has the potential to reduce adverse effects of altered fire regimes and build resilient ecosystems and human communities. To help guide regional fire restoration, we describe the frequency and severity of recent fires over a 32-year period (1985-2017) across a vast binational region in the United States-Mexico borderlands and assess variation in fire frequency and severity across climate gradients and in relation to vegetation and land tenure classes. We synthesize relevant literature on historical fire regimes within 9 major vegetation types and assess how observed contemporary fire characteristics vary from expectations based on historical patterns. Less than 28% of the study area burned during the observation period, excluding vegetation types in warmer climates that are not adapted to fire (eg, Desertscrub and Thornscrub). Average severity of recent fires was low despite some extreme outliers in cooler, wetter environments. Midway along regional temperature and precipitation gradients, approximately 64% of Pine-Oak Forests burned at least once, with fire frequencies that mainly corresponded to historical expectations on private lands in Mexico but less so on communal lands, suggesting the influence of land management. Fire frequency was higher than historical expectations in extremely cool and wet environments that support forest types such as Spruce-Fir, indicating threats to these systems possibly attributable to drought and other factors. In contrast, fires were absent or infrequent across large areas of Woodlands (~73% unburned) and Grasslands (~88% unburned) due possibly to overgrazing, which reduces abundance and continuity of fine fuels needed to carry fire. Our findings provide a new depiction of fire regimes in the Sky Islands that can help inform fire management, restoration, and regional conservation planning, fostered by local and traditional knowledge and collaboration among landowners and managers.

Arizona, Sonora↗
USGS1986

Interpretation and compendium of historical fire accounts in the Northern Great Plains

This interpretation and compendium of historical fire accounts in the northern Great Plains provides resource managers with background information to justify the study or use of fire in management and provides a reference of historic fire accounts for those without ready access to major library collections. Historical accounts of fire are critiqued to aid interpreting the compendium accounts. An interpretation is included by the author.Lightning-set fires were recorded in the literature far less frequently than were Indian-set fires. The kinds of fire most frequently reported were scattered, single events of short duration and small extent. Although fires occurred in wetlands, wetlands as well as sandy soil sites usually were good areas for escape from the effects of fire. Both Indians and wild animals were reportedly injured or killed during prairie fires. The frequency of historic fires was less evident in the literature than the descriptions of fire distribution in time and space. Indian-set fires were reported in every month except January. Fires occurred mainly in two periods, March through May with a peak in April, and July to early November with a peak in October. Grassland fuels burned readily within a few hours or days after rain and even during light snowfall.I agree with arguments that support the concept that Indians of the northern Great Plains generally did not subscribe to annual wholesale or promiscuous burning practices, but that they did purposely use fire as a tool to aid hunting and gathering of food and materials. Apparently, the northern plains Indians did not pattern their use of fire with the seasonal patterns of lightning fires. More likely they developed seasonal patterns of burning the prairies in harmony with bison (Bison bison) herd movements because the hunter-gatherer economy of these nomadic tribes was centrally focused and largely dependent on bison and bison ecology.

Resource Publication↗
USGS2005

Effects of fire intensity on vital rates of an endemic herb of the Florida keys, USA

Fire intensity is one of the important components of a fire regime. However, relatively few studies have linked fire intensity with post-fire population vital rates. In this study, we explored the effects of fire intensity on population vital rates of Chamaecrista keyensis Pennell (Fabaceae) up to two years post-fire. C. keyensis is an endemic understory plant of pine rockland, a fire-dependent ecosystem of the Lower Florida Keys. We measured one fire intensity indicator, fire temperature reached by steel plates on the ground, during three prescribed fires at different sites. We followed marked individuals up to two years post-fire to derive annual survival, annual growth rate, percentage of fruiting plants, mean number of fruits per reproductive plant, and number of seedlings per census plot (1 m2) of C. keyensis. We found fire intensity had significant effects on reproduction in the first year post-fire only. More specifically, mean number of fruits and percentage of fruiting plants increased as fire intensity increased. Results from this study suggest that extremely low fire intensity caused by very short fire return intervals (e.g., less than three years) may not provide sufficient stimulation to reproduction to achieve the best post-fire recovery for C. keyensis.

Florida↗