Keywords

1 Introduction

Aldo Leopold famously laid out the tools for wildlife management including the axe, plow, cow, fire, and gun (Leopold 1949). Contemporary wildlife managers still use a variety of these basic tools for directly manipulating habitats, including fire. Fire plays a foundational role in shaping rangeland ecosystem structure and function and thus, wildlife habitat. For instance, fire can drive the stimulation of aspen (Populus tremuloides) resprouts that provide browse and fawning cover (Pojar and Bowden 2004; Margolis and Farris 2014; Krasnow and Stephens 2015; Walker et al. 2015), as well as maintain open grasslands for gallinaceous and other ground-nesting birds (Briggs et al. 2002; Hagen et al. 2004; Hovick et al. 2014; Lautenbach et al. 2017). While fire is used for both livestock and wildlife management in rangelands, objectives often differ. For example, a rancher in the eastern Great Plains ecoregion might burn the same pasture every year in the early spring in order to stimulate perennial grass dominance and production (Anderson et al. 1970). In contrast, a wildlife manager in the same region might burn different portions of a pasture at different times of the year for a variety of objectives, such as burning some patches in the fall to stimulate forbs for quail, burning some patches in the spring for forage and browse production for herbivores, and leaving some unburned patches as refugia for other species (Weir and Scasta 2017). Manipulation of fire at different times and at different spatial scales alters the structure and function of an ecosystem by, for instance, variably depressing or enhancing certain plant species or manipulating the balance and availability of plant species (Towne and Craine 2016). An understanding of the complex interactions between different components of fire regimes (the pattern of fires over space and time, including fire frequency, intensity, severity, and seasonality; see Table 6.1) and rangeland abiotic and biotic components is needed to inform decisions by wildlife managers in how to integrate fire into a management plan (Limb et al. 2016). For a historical review of the fire regime concept see Krebs et al. (2010).

Table 6.1 Key terms and definitions for metrics of a fire regime
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Perspectives on fire management in North America is ever evolving, having shifted from a tool historically used for survival and land-stewardship activities, to a force that must be suppressed, to a contemporary tool for ecosystem manipulation. These shifting fire management perspectives have had lasting legacies on rangeland systems. Indigenous use of fire by Native American and First Nation tribes historically included applications for survival, including hunting, warfare, and agriculture, and survival (Roos et al. 2018; Nikolakis et al. 2020) and today include applications for land stewardship. Fire as a survival tool was supplanted by the Euro-American settlers’ approach of fire suppression, an idea reinforced by federal suppression policies (Busenberg 2004; Roos et al. 2018). For example, educational campaigns such as Smokey Bear’s iconic “only you can prevent forest fires” slogan set the precedent of United States fire management with implications for wildlife for over half a century (Donovan and Brown 2007). This “pyropolitical” campaign started in 1944 and has influenced the notion that fire needed to be eliminated from the landscape (Minor and Boyce 2018), creating a paradigm ingrained in post-European North American culture that there was no “good” fire. In contemporary times, however, wildlife managers have come to recognize the facilitating nature of fire and have begun to integrate fire disturbances into wildlife management plans. Ultimately, the shifting social perception of fire to allowances for useful applications has begun to transform fuel loads, wildlife habitats, and ecosystems. Future management of wildfires and prescribed fires must embrace the social perspectives of fire in order to optimize impacts on wildlife.

Both wildfires and prescribed fires shape the context of wildlife management today. Wildfires are unplanned and often burn outside of human control. As such, they may burn under drier and windier weather conditions than prescribed fires, generating fires that are hotter (often > 1000 °C) and thus burn with greater intensity, and with higher levels of fuel consumption. In contrast, prescribed fires are planned fires conducted to achieve targeted management objectives. Due to safety concerns, prescribed fires are generally conducted during more mild weather conditions that are moister and less windy. Thus, prescribed fires tend to burn cooler (often between 400 and 700 °C), with lower intensity, and with a lower level of fuel consumption. However, there are some instances where prescribed fires have been safely implemented during drier conditions or with added fuel loads to generate higher fire intensities (> 1000 °C) in order to achieve rangeland and wildlife management objectives, such as to restore rangelands that are experiencing woody encroachment (e.g., Twidwell et al. 2016). In both cases, prescribed fires require substantial preparation, including developing a written plan, acquiring necessary approvals, installing sufficient fire guards, maintaining functioning equipment, and having a trained crew (Weir 2009). The spatial and temporal patterns of wildfire and prescribed fire events combined make up the fire regime that shapes rangeland habitat.

In this chapter, we use Twidwell et al. (2021) Cultural Fire Eras in rangelands to provide a historical overview of how shifts in people’s relationship with fire are associated with major changes in rangeland fire regimes. We then describe how fire regime components can shape wildlife habitats. Finally, we discuss the potential for future fire management ideologies to emerge, the implications of competing ideologies for wildlife, and the challenges of creating critical ranges of complexity and spatiotemporal heterogeneity (defined as variation of landscape features and in the context of wildlife it is habitat features that vary relative to fire variation) necessary for rangeland wildlife persistence.

2 Cultural Fire Eras on North American Rangelands

2.1 The ‘Coexistence Era’ of Fire Management

Historically, people coexisted and thrived with fire across many of the Earth’s flammable biomes (Bond and Keeley 2005). Prior to Euro-American settlement of North American rangelands (~ 20,000–200 years ago), Indigenous people’s land stewardship using fire helped to promote dynamic rangeland systems that spanned much of North America. Human fire ignitions promoted frequent fire in areas like the Great Plains ecoregion, making it one of the most pyrogenic systems on Earth. Here, there was a high level of heterogeneity in applications of fire characteristics of occurrence, intensity, spatial arrangement, severity, and seasonality. The shifting spatial arrangement of burned and unburned areas followed by spatially heterogeneous grazing created by roaming herds of American bison (Bison bison) and other mammals, created a diversity of rangeland habitats that, in turn, harbored a diversity of wildlife populations and plant communities.

The occurrence of fire is often described in terms of the fire regime and specifically the frequency of fire (Table 6.1). Fire frequency, or fire return intervals, varied greatly depending on location. In the Great Plains ecoregion, the average fire return interval ranged from 1 to 3 years in eastern tallgrass prairies to 3–8 years in shortgrass and mixed-grass prairies (Guyette et al. 2012). In contrast, rangelands of the Great Basin (i.e., the Western Deserts, Grasslands, Shrublands, and Woodlands ecoregion) had average fire return intervals that, in some places, could exceed 100 years (Guyette et al. 2012; Mensing et al. 2006). Fire intensities ranged from low to extreme, both within and among fire events. High-intensity fires were used by indigenous people for hunting and warfare (Stewart 2002, 1951), whereas lower-intensity fires were used for clearing vegetation, attracting game species, and for agricultural purposes (Higgins 1986). Fires ranged from very small for clearing around camp to very large (> 500,000 ha) with great variation in size. Given the variation in fire size and intensity there was also variation in severity of the effects of the fire in terms of plant mortality, vegetation structure, botanical composition. Thus it is important to understand the variation of fire effects and ecological processes generated by these practices that have been shown to be important for plant and wildlife populations because certain species prefer different scales and relative time since the fire disturbance (Hutto et al. 2016; Roberts et al. 2020). Moreover, the concept of pyrodiversity (considered the variation or heterogeneity in fire frequency, seasons, spatial arrangement, fire type, severity, and intensity) has been suggested to be important for biodiversity and may serve as a framework for conservation (Fuhlendorf et al. 2006; Kelly et al. 2017).

2.2 The ‘Suppression and Wildfire Eras’ of Fire Management

Following Euro-American settlement and the displacement of indigenous Indigenous people from their lands, fire patterns in North American rangelands underwent a drastic shift (Twidwell et al. 2021). Sharp declines in human ignitions due to the differing land management practices of invading European settlers, along with the later introduction of extensive fire suppression efforts, led to a massive decrease in the number of fires across North American rangelands (Fuhlendorf et al. 2018). This change was not necessarily immediate nor uniform as some native fire cultures persisted longer than others and some Euro-American fire cultures established such as the Celtic descendants in the southeastern U.S. (Doolittle and Lightsey 1979; Putz 2003; Stambaugh et al. 2013); yet such changes were detectable in the landscape through charcoal analysis and tree scars (Brown and Sieg 1999; Scasta et al. 2016b). Grazing became static and constrained to fenced pastures while fire was de-coupled from human land management, eliminating the shifting mosaic of fire and grazing interactions. The Great Plains ecoregion, once one of the most burned biomes in the world, became an area with a low probability of fire occurrence (Donovan et al. 2017).

The era of fire suppression is recognized as one of unrealistic expectations underpinning a failure in ecosystem management. Briefly, the generally applied policy of suppressing all fires resulted a ubiquitous fuel load increase and subsequent wildfire risk escalation across numerous ecosystems (Calkin et al. 2015; Pyne 2007; Twidwell et al. 2013b). As a result, wildfires, rather than the purposeful human ignitions used in land stewardship activities to manipulate ecosystems during the Coexistence Era, now dominate North American rangelands. As human populations have expanded and the climate has changed in North America, there has been a surge in total area burned by wildfire in rangeland and forested ecosystems, despite increases in suppression costs over time (Fig. 6.1; Donovan et al. 2017; Hanes et al. 2019). The Great Basin has seen a shift, with some areas changing from 100-year fire return intervals to fires occurring every 5–10 years (D’Antonio and Vitousek 1992). This increase in fire frequency outside of historical fire return intervals can degrade wildlife habitat, for example through the loss of sagebrush shrubs, and drive local wildlife extirpation (e.g., Pedersen et al. 2003). Wildfires have surged in the Great Plains ecoregion, associated in part with woody species that have been able to proliferate through grasslands due to a lack of fire activity (Donovan et al. 2017, 2020). While contemporary fire frequency is still lower than historical frequency in the region, the change in frequency represents stochastic disturbances that can pose a greater risk to human populations than the fires stewarded by humans in the past (Twidwell et al. 2013b). Of particular concern is the significant increases in wildfire size and the greater prevalence of very large wildfires (> 20,234 ha) in western regions (Stavros et al. 2014). Exacerbating this trend is the warming global climate and enhanced aridity (Williams and Abatzoglou 2016) and increasing wildfire season length due to earlier warming in the spring (Westerling 2016; Westerling et al. 2006). For example, wildfire seasons and the duration of burns have increased in length—from 2003 to 2012 seasons were 84 days longer than those from 1973 to 1982 (Westerling et al. 2006), with an increase of average wildfire burn time from 6 days (1973–1982), to 20 days (1983–1992), to 37 days (1993–2002), to > 50 days (2003–2012). In 2020, many very large wildfires occurred, such as the Mullen Fire along the border of Colorado and Wyoming that engulfed more than 70,000 ha (Fig. 6.2). As climate changes and novel shifts in drought conditions occur, these wildfires are likely to further increase in intensity, severity and extent (e.g., Scasta et al. 2016b).

Fig. 6.1
4 illustrations. Left. 2 line graphs present the area of wildfire in acres and the wildfire impression cost from the years 1985 to 2020. Right. 2 photographs display the wildfires in Wyoming and Oklahoma. The fire safety workers are suppressing the wildfire.

Annual wildland fire statistics from the National Interagency Fire Center covering all 50 U.S. states for a total wildland fire acres and b federal firefighting costs for suppression only. Data are publicly available at https://www.nifc.gov/fire-information/statistics. c In 2020, total wildland fire acres in the U.S. exceeded 4 million hectares and included large conflagrations such as the Mullen Fire along the border of Colorado and Wyoming. In this photo taken at 6:15 pm on September 24, 2020, crews were attempting to slow the fire and prevent its jumping the road by lighting a smaller and controlled fire, but the fire was moving too quickly and crews were pulled to safety. Photo credit to Josh Shroyer (Operations Section Chief Type 2, Flaming Tree Solutions LLC, Riverton, WY). d Lighting a prescribed fire in the southern Great Plains. Photo credit to John Derek Scasta

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Fig. 6.2
4 photographs display the Aspen regeneration after a fire, Elk foraging in a recently burned area, a prescribed fire to reduce juniper trees, and training future fire managers.

a Example of the diversity of plant species and regeneration strategies 15 years after a wildfire on the Bridger-Teton National Forest of Wyoming. Aspen (Populus tremuloides) has a resprouting strategy (note the recruitment of new resprouts around adult trees), whereas sagebrush (Artemisia tridentata) has a reseeding strategy. Photo credit to John Derek Scasta. b Elk (Cervus canadensis) foraging in a recent prescribed fire in southern Wyoming. The burned area was dominated by aspen and serviceberry (Amelanchier species). Photo credit to John Derek Scasta. c Example of prescribed fire employed to reduce juniper (Juniperus species) encroachment in the Great Plains. Photo credit to Caleb Roberts. d Training future fire managers requires hands-on opportunities and collaborations to develop the social license (i.e., the approval within a local community and group of stakeholders such that an activity can start or continue) to burn. Photo credit to John Derek Scasta

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2.3 The ‘Contemporary Era’ of Fire Management

Today, fire regimes in North American rangeland systems are overwhelmingly driven by wildfire occurrences rather than fires used for land stewardship (Fig. 6.3). Only one rangeland-dominated ecoregion in the central and western U.S.—the Flint Hills of Kansas—has a fire regime dominated by prescribed fire rather than wildfire (Fig. 6.3). Prescribed fires throughout the rest of the U.S. Great Plains typically occur on < 1% of the land area. In cases where contemporary prescribed fires are applied in rangelands, they represent a greatly dampened range of variability in the size, frequency, intensity, severity, and seasonality of the fire regimes stewarded by Indigenous people before Euro-American settlement. Prescribed fires are small, typically ranging from 10 to 160 ha (Weir et al. 2016, 2015). Restrictions tied to ‘safe fire conditions’ limit the weather conditions under which prescribed fires can burn, leading to low and homogenous fire intensities and generating highly restricted prescribed fire seasonality. Thus, while prescribed fires are discussed commonly as the backbone of fire management, prescribed fires impact minimal land area, and their functional variability has been reduced to a shadow of its role during the Coexistence Era.

Fig. 6.3
A map presents the non-Rangeland, wildfire-driven Rangeland, and prescribed fire-driven Rangeland in the western and central U.S.

Rangeland ecosystems driven by wildfire versus prescribed fire in the western and central U.S. (figure developed by the authors)

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At the turn of the twenty-first century, diverse stakeholders have created Prescribed Burn Associations (PBAs) and Prescribed Fire Councils (PFCs) to create cultural and attitudinal change towards the willingness to utilize prescribed fire as a management tool and apply prescribed fires on their landholdings. For example, over 60 PBAs have now been created throughout the Great Plains ecoregion—from southern Texas to South Dakota, pooling equipment, funds, experience, and training on how to safely apply prescribed fire (Weir et al. 2016). PFC organizations also have spread nationally to provide educational outlets to private landowners to better understand the benefits of prescribed fire (Wilbur and Scasta 2021). Whereas PBAs and PFCs strive to instill confidence and share resources in prescribed burning, Rangeland Fire Protection Associations (RFPAs) and Good Neighbor Authority (GNAs) projects foster collaborative efforts between federal, state, local, and tribal agencies to suppress the spread of wildfire and to facilitate restoration projects (i.e., hazardous fuel reduction) (Taylor 2005; Twidwell et al. 2013b; Abrams et al. 2017; Stasiewicz and Paveglio 2017; Bertone-Riggs et al. 2018). This grass-roots rise in privatized fire management organizations represents the largest restoration of prescribed fire within North America’s rangelands, but still mostly operate within a landscape where purposeful human ignitions for fire management have been extirpated (Twidwell et al. 2013b).

3 Influence of Fire on Wildlife Habitat

Human-driven shifts in fire regimes have imposed novel pressures on wildlife habitat. In North American rangelands, wildlife and biodiversity are dependent on the extent to which fire shaped ecological complexity historically (Fuhlendorf and Engle 2001; Pyne 2001). Many rangeland songbirds, for example, rely on prescribed fire to curtail the encroachment of woody species and to maintain grasslands of varying plant heights and litter denseness to provide breeding habitat for a diverse avian assemblage (reviewed in Chaps. 8–26). Biodiversity in grassland birds, for instance, is highly dependent on heterogeneity created by patterns in fire regime characteristics like fire frequency and fire seasonality (Hovick et al. 2015a). Species often select for fire outcomes tied to fire severity, like the black-backed woodpecker (Picoides arcticus), which is dependent on severely burned areas (Hutto 2008). It is the fire regime that is most important to understand for wildlife management, not the impacts of a single fire event. Ecological complexity owed to fire, both historically and today, is the aggregate result of multiple fire events that vary in terms of their intensity, severity, spatial pattern and extent, thereby leading to a temporal signature of fire’s role in a given region. Even the rare occurrence of fire can leave legacies that impart unique niche space that can last for decades after the event (Roberts et al. 2019). This is what drove cross-scale variation that occurs within and among patches, landscapes, and biomes that created sufficient diversity in habitats to host the entire suite of rangeland biota (Fuhlendorf et al. 2012; Fuhlendorf and Engle 2001; Roberts et al. 2020). Changes in these fire regime components have therefore been linked to losses in grassland biodiversity and abundances of grassland biota, which have declined at a greater rate than in any other ecosystem type (Brennan and Kuvlesky 2005; Newbold et al. 2016; Rosenberg et al. 2019). Similar effects have been noted in open forested ecosystems such as ponderosa pine. To advance our understanding of fire relative to wildlife management, we briefly overview the direct effects of a single fire event, which are described in terms of first-order and second-order fire effects and shape the immediate response of vegetation to fire occurrence, and then contrast perspectives that will impact future fire regimes and future wildlife management efforts.

3.1 Understanding First-Order and Second-Order Fire Effects

The effects of fire on ecosystem properties, and thus wildlife habitat, are characterized often as first-order and second-order fire effects. First-order fire effects are the direct or immediate consequences of fire, and include biomass consumption, tree crown scorch, soil heating, and smoke production. These occur during the fire. Second-order fire effects include interactions with many other non-fire factors that influence post-fire ecosystem responses. Whereas first-order fire effects are owed to immediate consequences of fire, second-order fire effects characterize responses over longer time periods, from days to months to years or longer. Examples of second-order fire effects include vegetation succession, changes in vegetation productivity, and forest regeneration. The concept of ordered effects on plants has also been applied to animals (Whelan et al. 2002; Engstrom 2010). The direct impacts of heat transfer or first-order effects can cause injury or mortality heat exposure, toxic effects of smoke, and oxygen depletion. The processes that occur after the fire, particularly soil, water, and plant responses, can influence starvation, predation, or immigration ultimately influencing population viability.

Second-order fire effects are complex. For rangeland soils, the amount of heating is generally less than 5% which is radiated into the soil profile (i.e., the vertical section of the soil from the surface of the ground downward to where soil meets the underlying rock layer) and this radiating heat interacts with non-fire factors to influence soil organic matter, soil microbiology, nutrient cycling, and erosion potential. For plants, second-order effects can be categorized relative to life history strategies associated with post-fire recovery (i.e., recovery from fire damage or mortality). Some plants persist and regenerate on-site from established plants; these use asexual ‘resprouting’ life strategies relying on below-ground and/or above-ground plant parts (Bond and Midgley 2003). Other plants are colonizers or reseeders and rely on recruitment to regenerate from seed. Residual colonizers regenerate on-site from seedbank present at the time of the burn, whereas off-site colonizers regenerate from seed brought in by animals or other sources from unburned areas in the surrounding landscape. See Table 6.2 for important rangeland plant species and the associated life history strategy (Midgley 1996).

Table 6.2 Common plants in western North America and associated strategy for responding to fire disturbance
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Highly specialized regeneration strategies for both life history strategies have developed, including conifers with serotinous cones that open and release seeds following fire (Pinus contorta in the Rocky Mountains ecoregion; Knapp and Anderson 1980) and layering, which occurs via asexual reproduction when vertical stems droop and root upon contact with the soil (Symphoricarpos orbiculatus; Scasta et al. 2014). All of these affect forage availability and habitat characteristics that in turn affect wildlife. For instance, species such as aspen (Populus tremuloides) can be stimulated by fire to resprout, often quite aggressively (Krasnow and Stephens 2015; Fig. 6.2), and this provides high quality browse and fawning habitat for ungulates like mule deer (Odocoileus hemionus) and nesting cover for ruffed grouse (Bonasa umbellus) (Pojar and Bowden 2004; Rusch and Keith 1971).

Powerful models of first-order fire effects rely on complex, physics-based models of fire behavior coupled with knowledge of key factors that affect first-order fire effects. To model first-order effects, these models most commonly assume homogeneous or spatially constant conditions relevant to scales of individual plants or homogeneous landscape patches (Reinhardt and Dickinson 2010). Second-order effects are dependent on first-order effects, so knowledge of second-order effects is dependent on understanding first-order effects and interactions with additional non-fire drivers. Existing assumptions of homogeneous conditions limit applicability for many wildlife studies, so it is rare for investigations to link second-order effects to first-order impacts. Even the leading fire models do not sufficiently capture the complexity owed to describing their interdependencies and instead model one or the other (e.g., First Order Fire Effects Model; FOFEM). This is one reason that the fire regime concept has been useful in simplifying key aspects of these complex relationships to characterize major departures in key landscape-scale fire metrics and corresponding fire effects important to wildlife such as escalation of fire frequency in the Great Basin.

3.2 Control of Invasive Plants with Prescribed Burning

The first- and second-order effects of prescribed fire are the primary points of consideration used to strategically manage invasive species and structure habitat features for wildlife (DiTomaso et al. 2006). For the control of annual plants, the strategic application of fire to kill plants before seeds become viable or before they disperse may be effective. Because the majority of fire-associated heat radiates upward, seeds in the soil bank are not usually exposed to lethal temperatures and thus seeds still in the canopy would be most susceptible. For example, early summer burning has been shown to reduce barb goatgrass (Aegilops triuncialis) in California when flames kill exposed seeds (Marty et al. 2015). Fire also may alter the soil-litter environment; for example, fall burning may lead to reductions of litter and subsequently of annual bromes (Bromus species) in the northern mixed-grass prairie and along such ecotones transitioning to sagebrush steppe (Whisenant 1990; Estep 2020; Symstad et al. 2021). Similarly, annual forbs such as yellow starthistle (Centaurea solstitialis), which is widespread throughout California, Oregon, Washington, and Idaho, can be controlled with repeated early summer burns (DiTomaso et al. 1999). Perennial forbs such as leafy spurge (Euphorbia esula) present a more difficult challenge and may require the integration with fire of other methods, such as herbicide applications (DiTomaso et al. 2006). Cool-season perennial grasses such as Kentucky bluegrass (Poa pratensis) and smooth brome (Bromus inermis) may be controlled with fire if applied when tillers are elongating on the target species but concurrently when the desirable native warm-season grasses are still dormant (DiTomaso et al. 2006). Obligate-seeding woody species that rely solely on recruitment of seeds for regeneration (such as eastern red cedar [Juniperus virginiana] and Wyoming big sagebrush [Artemisia tridentata]) are very susceptible to fire (Beck et al. 2009, 2012; Twidwell et al. 2013a), whereas woody species that use asexual regeneration strategies such as resprouting may be difficult to control or may be stimulated by fire (such as mesquite (Prosopis glandulosa; in the Tamaulipan Vegetation ecoregion, southern Great Plains ecoregion, and the Western Deserts, Grasslands, Shrublands, and Woodlands ecoregion) and roughleaf dogwood (Cornus drummondii; in the Great Plains ecoregion) (Drewa 2003; Heisler et al. 2004; Starns et al. 2021) unless fires are conducted in more extreme conditions that overcome plant species persistence (Twidwell et al. 2016). The timing of fire, fuel load, topographic position, and post-fire moisture conditions of fire applications also must be considered because such features can influence the flammability and response of a species (Keeley and McGinnis 2007; Weir and Scasta 2014).

First order and second-order fire effects always result in both positive and negative responses for wildlife (Table 6.3). This is critical to understand to avoid oversimplifications of complex fire-plant-wildlife interactions. Some species will respond positively to the immediate post-fire environment and preferentially select recently burned areas, whereas others avoid it and move to later successional habitat stages. For instance, greater prairie chickens (Tympanuchus cupido) in the Great Plains ecoregion have been shown to move lek locations in response to dynamic fire patterns so that leks fall near the edges of recently burned patches providing recently disturbed habitat and nearby unburned refugia habitat (Hovick et al. 2015b). In a heterogeneous landscape, an array of patches facilitate a shifting mosaic of vegetation structure that varies spatially and temporally with the temporal pattern of fire in the region. In a homogeneous landscape, there may only be short vegetation across the landscape (if fire is applied homogeneously) or only tall vegetation (if fire is suppressed homogeneously).

Table 6.3 First-order and second-order fire effects lead to plant-wildlife-fire interactions and directional positive (+) and/or negative (−) ecological outcomes for different taxa
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Positive and negative effects of fire often are associated with human values or conservation goals rather than natural biological outcomes. Some examples of positive effects include enhanced forage quality, reduced parasite and disease exposure, altered animal distribution, reduced dominance by invasive plants, and greater diversity of habitat and food resources (Fig. 6.2). In tallgrass prairie, forage crude protein may be 4 times higher in recently burned areas, resulting in a strong attraction for large herbivores such as American bison (Allred et al. 2011). This type of focal grazing and intense disturbance of plants may alter plant primary nutrients as well as secondary compounds and rate of plant defoliation compared to unburned areas (Scasta et al. 2021). The reduction by fire of ecto-parasites such as ticks, which reduces all life stages, may consequently reduce risk of Lyme disease transmission (Scifres et al. 1988; Mather et al. 1993; Stafford et al. 1998; Cully 1999). Similar positive effects are noteworthy for endo-parasites. For example, native sheep (Ovis dalli stonei) in western Canada that were able to access recent burns had up to 10 × lower lungworm (Protostrongylus spp.) loads (Seip and Bunnell 1985); in the southeastern US, fire is thought to disrupt microhabitat of gastropod hosts of the meningeal brain worm (Parelaphostrongylus tenuis) which has negatively affected elk (Cervus canadensis) and deer (Weir 2009); and for amphibians, internal nematodes with free-living terrestrial stages are reduced (Hossack et al. 2013b).

Some examples of negative effects include direct mortality, loss of habitat structure, and/or loss of food resources. These vary with fire intensity, spatial extent, and post-fire moisture availability. Direct mortalities are thought to be relatively rare for both prescribed fires and wildfires (Lyon et al. 1978; Means and Campbell 1981; Russell et al. 1999; Smith 2000) but do occur, with slow-moving species at greatest risk. However, even slow-moving species, such as amphibians and reptiles, have strategies for escaping fire morality by finding refugia, such as going underground in tunnels or new burrows; these species may even respond positively to fire due to changes in the thermal environment (Hossack and Corn 2007; Hossack et al. 2009, 2013a). The post-fire moisture and subsequent recovery of vegetation for food and cover is also critical. For example, Clapp and Beck (2016) reported that translocated sheep in Wyoming had a 30% reduction in survival after wildfires and droughts, suggesting that interactions with other abiotic features can influence outcomes. However, these same sheep were shown to select low- and high-severity fire areas after the fire and drought events (Donovan et al. 2021a), with female use of low- and high-severity burned areas increasing with greater time since fire, while males tended to decrease use of areas that burned at high severity with greater time since fire. The loss of habitat structure and food resources also can impose long-term effects such as the case for Wyoming big sagebrush and sage-grouse (Centrocercus urophasianus; a sagebrush obligate species) that can take decades to centuries to recover to pre-fire levels (Beck et al. 2012).

It is also important to note how animals immediately respond to fires. Some animals flee while others may hide below ground. Pausas (2019) suggests four mechanisms of animal responses to fire including resistance (by using thick cover or having physiological tolerance), refugia (by detecting fire and being able to quickly react and hide), avoidance (by selecting habitat with reduced flammability generally), and crypsis (by altering feeding and or hiding capacity after fire such as a darker cryptic color in neonates or adults or entering torpor). Such responses are initiated by olfactory, auditory, and visual cues of fire (Nimmo et al. 2021). For more information on refugia see Meddens et al. (2018).

Ultimately, the placement of human values onto fire effects for flora and fauna—whether positive or negative—are often short-term, sometimes biased, and usually oversimplify fire to a binary (positive or negative) outcome. In reality, fire’s role in nature is more complex. A comprehensive understanding of fire is difficult, if not impossible, without looking beyond individual fire events and considering how fire regime characteristics have changed in terms of their spatial pattern and extent, frequency of occurrence over time, critical ranges of variation in fire function, and the relative contribution of these factors to the degree of vegetation heterogeneity that occurs on landscapes (Twidwell et al. 2021).

3.3 Spatial Scales of Fire–Akin to Wildlife Home Range Size

Fire effects cannot be deeply understood, or applied in wildlife management, without careful consideration of scale. Scientists and managers are becoming increasingly aware of the importance of scale in solving academic and managerial debates about how to best apply and manage fire for a variety of outcomes for plants and animals following fire. Scale refers to the spatial and temporal dimensions used to study phenomena in ecology such as migration at large landscape scales or habitat attributes for nesting. Scale also refers to the analytical and quantitative dimensions that might differ between observers or independent studies. Spatial scale is described analytically in terms of both grain (the resolution of the data) and extent (the size of the landscape encompassed for observation). A single fire event is often described in terms of its extent (the perimeter of the burned area) but vegetation is never 100% consumed in a fire event. Plant parts, whole plants, or entire patches in the landscape escape fire and remain unburned and the scale at which these are measured represents the grain. Both the minimum resolution associated with variability in burned/unburned patterns at fine scales and the total size, or spatial extent, of the fire are important to wildlife. Fire regimes, like other disturbance regimes, operate across a sufficient range of scales (through both space and time), and changes in its scale of function represent some of the greatest challenges to wildlife managers.

One way to better understand the context of animal responses to the scale of fire is to think of it relative to a species’ home range size. Home range is the spatial extent at which an animal operates; it can fluctuate with an animal’s size, seasonal needs, age, and sex as well as the spatial distribution of hiding and nesting cover, brood-rearing habitat, thermal regulation resources, food, and water (Burt 1943; Hayne 1949; Powell and Mitchell 2012). The scale and distribution of fire can affect all these drivers of home range size and core use areas differentially in a wildlife community. For example, ornate box turtles (Terrapene carolina) have a home range of < 10 ha, indicating that its resource needs are fulfilled within that spatial extent but also suggesting that larger fires could alter habitat resources at a spatial scale much larger than a single individual. In contrast, the more expansive seasonal home ranges of mule deer (Odocoileus hemionus; > 2878 ha (Kie et al. 2002)) and seasonal migrations of more than 110 km (Sawyer et al. 2019) suggest that mule deer are capable of shifting use areas in relation to fire. While identifying important seasonal use is important, defining home ranges solely by seasonality fails to recognize the spatial extent over which species may operate during the annual cycle and how the timing of a fire may affect a species. Moreover, the patchiness of burn severity in a burned area can also influence animal home range because the distribution of fire-altered resources can significantly influence home range sizes for wildlife in nearly every North American ecosystem (e.g., Gullion 1984; Kie et al. 2002; Patten et al. 2011; Fuhlendorf et al. 2017b). Because home range considerations differ among wildlife species, every ecosystem type exhibits unique and complex spatial signatures of fire on wildlife communities. The same complexities needed to understand the spatial context of a species’ home range are also necessary to understand fire, the occurrence of variable fire effects within and across ecosystem types, and then how wildlife are likely to respond.

4 Competing Ideologies for Future Fire Management

Future fire management has the potential to alter outcomes for wildlife and wildlife management in rangelands depending on the ideologies that are embraced (Twidwell et al. 2021; Fuhlendorf et al. 2012). Perceptions tied to fire as a management tool, the range of variability in fire regimes utilized for management, the spatial and temporal scales of fire, and the spatial scales of fire management planning all have impacts on how we manage rangeland wildlife in the future. Following Twidwell et al.’s (2021) framework we present five ideologies that currently exist or that could further emerge, and that may shape or constrain wildlife management. These ideologies reflect competing sociopolitical values, potentially further changing the fire regimes that wildlife evolved with during the Coexistence Era from the changes imposed during the Wildfire and Suppression Era that dominates today. These five ideologies acknowledge that some form of disturbance is necessary to maintain rangeland wildlife diversity, but they differ by (1) how/if they utilize fire as a key disturbance, (2) how much they seek to control fire’s range of variability, (3) the spatial and temporal scales at which they allow fire to function, and (4) the spatial scales of management planning (Fig. 6.4).

Fig. 6.4
5 circular diagrams present the fire management ideologies, Rangeland zoos, managed ecosystem and homogeneity paradigms, managed ecosystem and heterogeneity paradigms, wilderness area protectionist paradigms, and living landscapes.

Five fire management ideologies that compare the range of variation in fire regime characteristics, outcomes, and management area, applicable to North American rangelands (figure developed by the authors)

Full size image

4.1 Ideology 1: ‘Rangeland Zoos’

Given anthropogenic pressures this century, wildlife are being more intensively managed to safeguard iconic species in ecosystems with extensive land use conversion through such measures such as translocations to support viable populations of species vulnerable to extinctions or extirpations (IUCN 2013) and vaccination programs for endangered species (Haydon et al. 2006). As these types of intensive management efforts continue, a network of small, zoo-like “ghosts of rangelands past” are expected. Unlike typical classical zoos, these areas may be very small remnants of habitat that will still mirror habitat requirements through intensive management that tailors vegetation structure and composition to rangeland wildlife species’ needs. Maintaining these zoo-like systems to support a small portion of their endemic biodiversity will require intensive and expensive management to coerce the system into an idealized state while reinforcing fire and fuel feedbacks are absent. Fire, if used at all, will occur only under the tightest range of variation and likely only as a demonstration of its occurrence as a historically relevant process. Thus, unlike other future fire ideologies, rangeland zoos will largely avoid the use of fire, focusing on very small spatial scales for management.

Species that require large expanses of heterogeneous rangelands may be locally extirpated or require intensive management. Even for species that require smaller-scale rangeland habitat features, the limited size of rangeland zoos will be unlikely to support even a minimum viable population without human intervention (With et al. 2008). Species will require assisted dispersal, colonization, and migration. Pressure will mount from threats in the surrounding habitat matrix. Outside of the boundaries of rangeland zoos, ecosystems will continue to undergo conversion and collapse to alternative, undesirable vegetative states (e.g., woodlands, nonnative annual grasslands) or to be developed for alternative land uses. Examples of the latter occur today in the last remaining (small) remnants of tallgrass prairie, where intensive management with a suite of regularly applied chemical and mechanical treatments are needed to preserve a semblance of the region’s past biodiversity.

4.2 Ideology 2: ‘Managed Ecosystem—Homogeneity Paradigm’

The Managed Ecosystem—Homogeneity Paradigm shares many similarities to Rangeland Zoos but operates at larger scales and has livestock production as a secondary concern. The Homogeneity Paradigm is the classical rangeland approach used to create uniform vegetation utilization and is based on the utilitarian perspective of benefiting livestock production while limiting tradeoffs to other ecosystem services (e.g., wildlife; Fuhlendorf et al. 2012). As a result, fire management is used to create specific vegetation conditions that are relatively homogenous in terms of vegetation composition and structure. Fire regime characteristics are constrained to low intensities, strict spatial scales, strict seasonality, and single property or jurisdictional boundaries. Under the Homogeneity Paradigm, wildlife abundance and diversity may be reduced due to homogeneity of the vegetation, creating a narrower range of habitat conditions that benefit only that select suite of species that prefers conditions associated with a heavily grazed and burned land use (Fuhlendorf et al. 2012). Species that require expansive, more heterogeneous vegetation characteristics may experience range contractions and therefore require translocations or assisted dispersal. Species that require vegetation structure from high-intensity fires may be locally extirpated (Hutto 2008; Hutto et al. 2016). Without the full range of variability, positive feedbacks that lead to undesirable vegetation state transitions can emerge (i.e., transition from a grassland or shrubland to a woodland; Twidwell et al. 2016, 2019). By constraining variation, rangeland management production predictability in the short-term and local scales for unpredictability in the long-term and at broad scales. This can lead to the need for the Rangeland Zoos ideology if fire management is delayed or slowed during, for example, drought years or if surrounding rangelands are experiencing state transitions.

The homogeneity paradigm has been the predominant approach used to manage rangelands and its wildlife over the past several decades. The hallmark of the Homogeneity Paradigm for ecosystem management is the assumption that rangelands can be maintained without cross-scale heterogeneity. The idea implicit in this assumption is that rangelands can be held in a static state with a precise amount of human-directed disturbance per the succession-retrogression theory of rangeland management. Importantly, fire may or may not be part of management strategies; when used, it is a tool to maintain stasis. Much of North America’s current rangelands have been managed as static, fire-excluded systems for decades while maintaining their identities and many wildlife species. For example, the Nebraska Sandhills excluded fire for decades and remain one of the most intact grasslands in North America—although there are early warnings of vegetation state transitions to woodlands (Donovan et al. 2018; Fogarty et al. 2020). Once external factors like climate change or woody plant encroachment appear, managing for static systems becomes infeasible except at small scales at specific locations. This is due to the increasingly intensive management required to counteract the positive feedbacks of the surrounding collapsed rangeland state. Such practices can also have inadvertent negative outcomes relative to fire. For instance, throughout the Great Plains ecoregion, this static view of management that utilizes fire suppression is a major reason that woody encroachment is a primary management concern across the region (Briggs et al. 2005; Twidwell et al. 2013b), which in turn has been linked to increasing wildfire (Donovan et al. 2020).

4.3 Ideology 3: ‘Managed Ecosystems—Heterogeneity Paradigm’

Counter to the utilitarian perspective of classical rangeland management that stresses uniform forage production for livestock use, the Heterogeneity Paradigm of ecosystem management recognizes that critical ranges of vegetation variability (or heterogeneity) are the foundation for biological diversity (Fuhlendorf et al. 2012, 2017a). The Heterogeneity Paradigm acknowledges that fire played a role, whether frequent or infrequent, in shaping the vegetation heterogeneity upon which wildlife diversity depends. To date, however, the application of the Heterogeneity Paradigm has been applied primarily in ecosystems that burned more frequently in the past and where fire was the primary driver of spatial heterogeneity (e.g., grasslands of the Great Plains). This has been accomplished within managed areas by embracing ‘pyric herbivory,’ which refers to herbivory driven by fire and that creates a shifting mosaic of fire, grazing, and vegetation structure through space and time (Fuhlendorf et al. 2009).

The Heterogeneity Paradigm has increased coexistence of livestock and wildlife in many managed rangelands and removed the perspective that they are competing interests (Fuhlendorf et al. 2017a). Fire results in high-quality forage for livestock while also maintaining a greater range of vegetation structures that promote wildlife diversity (Fuhlendorf and Engle 2001; Hovick et al. 2014; Scasta et al. 2016a). Elapsed time-since-fire is an integral consideration of management; however, other characteristics associated with fire regimes are tightly restricted or not considered as part of fire management objectives, such as fire intensity, seasonality, and the spatial scales at which fires are applied, nor is the vegetation heterogeneity that might derive from these characteristics (Donovan et al. 2021b; Hutto et al. 2016; Roberts et al. 2020). For example, fire is generally avoided in sage-brush dominated systems due to negative effects on sage obligate wildlife species.

The application of the Heterogeneity Paradigm is much lower than application of the Homogeneity Paradigm, so its outcomes are limited to the extent of heterogeneity created within geographically expansive homogeneous rangelands or converted ecosystems. As a result, wildlife species that range over expansive areas and require large-scale heterogeneity will still likely experience range contractions and may require assisted dispersal. The landscape heterogeneity promoted by pyric herbivory will better enhance rangeland stability (Holling and Meffe 1996), however, it may be unable to promote high levels of rangeland ecosystem resilience to large-scale global change drivers without greater adoption and geographic influence.

4.4 Ideology 4: ‘Wilderness Area—Protectionist Paradigm’

Like the Homogeneity Paradigm of rangeland management, the Protectionist Paradigm used in wilderness areas has been the prevailing focus of large-scale wildlife management efforts on public lands. Wilderness areas often focus on a protectionist viewpoint with a fixed endpoint at large scales. Disturbances are generally minimized in order to maintain an idealized habitat configuration based on a historical reference condition (or an idealized climax community). Major disturbances, like wildfire, are usually suppressed before they can ‘damage’ too much of the idealized community configuration. Charismatic species are often the main focus of conservation (Brambilla et al. 2013; Colléony et al. 2017) and may require more intensive habitat and population management to create the conditions necessary for their persistence. While the larger size of wilderness areas enhances the conservation of far-ranging wildlife species, management efforts generally favor habitat generalists and the few species that are adapted to persist in the climax community. Less charismatic species reliant on fire and its interaction with other disturbance processes are less abundant or extirpated. In an effort to offset tradeoffs to fire-dependent species, management tactics like prescribed fire are utilized under a limited range of conditions and at small scales.

4.5 Ideology 5: ‘Living Landscape’

Rangeland management under the Living Landscapes Paradigm builds off of the Heterogeneity Paradigm and, of all the ideologies, places the fewest restrictions on fire. Fire and its full range of variability are treated as an integral system process in rangelands, rather than something that degrades or destroys habitat under more ‘extreme’ conditions. This management style shifts away from applying wildlife management principles to the advantage of a few charismatic species, to applying principles on maintaining the integrity of ecosystems and ecosystem processes. Large expanses of rangelands are maintained by allowing fire variability to play out across their full range of variability (temperatures, seasons, humidity, wind speeds, sizes, frequencies, intensities) and interact with dynamic patterns in variables like grazing, topography, and climate, with fire only be restricted in the wildland-urban interface. This creates heterogeneous conditions across multiple scales, allowing for landscapes that are heterogeneous at local, regional, and biome levels and that can support a wide range of rangeland plant and wildlife species.

The Living Landscapes and Heterogeneity Paradigm are the two ideologies that embrace variability in fire as a critical driver of wildlife habitat and they are closest to the ideologies embraced during the Coexistence Era. Expanding on these ideologies in fire management will require large-scale landowner collaborations and land planning to allow for fires to burn across multiple property boundaries to avoid small, fragmented burn patterns of limited utility in rangeland management objectives. Corridors for fire spread, along with other ecological processes like wildlife migration and dispersal, could help facilitate large-scale interactions and connectivity unhindered by roads and other human development. In terms of fire, these corridors could help to reduce the impacts of fragmentation on fire size and intensity (Brudvig et al. 2012). Regional planning could emphasize fire districts to assist in planning of prescribed fires to develop alternative fuel break types, like existing crops or agriculture, to protect human developments from wildfires (Donovan et al. 2020). Further expansion of prescribed fires within the wildland-urban interface would need to consider risks to anthropogenic developments (Radeloff et al. 2018; Theobald and Romme 2007), and land-use planning would instead need to operate under the assumption that fires, whether planned or unplanned, will inevitably occur. The focus here is to identify areas with the potential to foster coexistence of rangelands, wildlife, fire, and people once again. While examples of re-creating critical ranges of variability in fire regime functioning for wildlife management is exceedingly rare, particularly given novel global change threats mounting today, recent applications have led to increased biodiversity and enhanced conservation outcomes (e.g., Twidwell et al. 2021).

4.6 Practical Applications of Competing Ideologies

To maintain the full suite of the habitat needs of rangeland wildlife and also to meet society’s needs in the face of global climate change, critical ranges of variability in fire function need to be understood—and managed accordingly—across North America (Bowman and Legge 2016; Hutto et al. 2016; Roberts et al. 2020). Only two existing ideologies focus on that perspective and attempt to manage for complexity by understanding fire’s contribution to it (the Managed Ecosystems—Heterogeneity Paradigm and Living Landscapes ideologies). However, all five ideologies will likely be necessary given the rate and prevalence of state transitions and rapid global change impacting North American rangelands (Garmestani et al. 2020; McWethy et al. 2019). For example, the Rangeland Zoos ideology may be necessary where rangelands have already succumbed or are completely surrounded by alternative regimes (e.g., Attwater’s prairie chicken conservation in coastal prairie, TX). Nevertheless, investments in those areas should not be replicated at large-scales where greater complexity in wildlife habitat management is possible. Rangelands were forged by fire functioning across spatial and temporal scales, and many species evolved to be highly dependent on specific fire dynamics (Pausas and Parr 2018; Twidwell et al. 2021). Although we may never return to these historical fire dynamics in all North American rangelands, restoring large-scale fire dynamics in as many locations as possible is the best and most economical approach to maintaining rangeland wildlife diversity and resilience (Fuhlendorf et al. 2012).

5 Conclusions

In order to acquire a modern understanding of fire and wildlife, it is necessary to understand how fire historically functioned and how that function is changing across spatial and temporal scales. Cultural perspectives about wildfire and prescribed fire have dictated the policies, regulations, management, and resources dedicated to fire management in the past and will continue to do so into the future (Calkin et al. 2005; Canton-Thompson et al. 2008; Ryan et al. 2013). These decisions affect how wildlife function within rapidly changing ecosystems and the potential to mitigate impacts from invasive species or a changing climate. Public views of fire take on multiple lenses that are influenced by news media, liability, knowledge, personal experience, collective attitudes, and cultural norms (Paveglio et al. 2011; Toledo et al. 2013; Joshi et al. 2019; Bendel et al. 2020). Prescribed fire application requires cultural and attitudinal acceptability, along with resources and planning assistance to foster prescribed fire as a management tool to reduce hazardous fuels and invasive species (Kreuter et al. 2008; Weir 2010; Toledo et al. 2013). Considering the effects fire can have on a landscape, there are also concerns about the impacts prescribed fire may have on wildlife species because of a lack of literacy on the complexity of how fire interacts with non-fire factors (Bowker et al. 2008; Elmore et al. 2009; Coon et al. 2018). Legacies of fire can generate unique and more diverse wildlife communities that can persist for decades (Roberts et al. 2019; Donovan et al. 2021b), and there is great opportunity for wildlife managers to incorporate knowledge of how fire regimes have been altered in recent decades to set unique conservation priorities and improve wildlife outcomes.