Patch‐burn grazing increases habitat heterogeneity and biodiversity of small mammals in managed rangelands

Heterogeneity-Based Management Restores Diversity and Alters Vegetation Structure without Decreasing Invasive Grasses in Working Mixed-Grass Prairie

Non-native plants can reduce grassland biodiversity, degrade wildlife habitat, and threaten rural livelihoods. Management can be costly, and the successful eradication of undesirable species does not guarantee the restoration of ecosystem service delivery. An alternative to the eradication of invasive species in rangelands is to target the restoration of diversity and heterogeneous plant structure, which have direct links to ecosystem function. In this study, we evaluate patch-burn grazing (PBG) with one and two fires per year and variably stocked rotational grazing in Poa pratensis- and Bromus inermis-invaded grasslands using traditional (cover) and process-based (diversity and vegetation structural heterogeneity) frameworks in central North Dakota, USA. Within 3–4 years of initiating management, we found little evidence of decreased Poa pratensis and Bromus inermis cover compared to continuous grazing (Poa pratensis F3,12 = 0.662, p = 0.59; Bromus inermis F3,12 = 0.13, p = 0.13). However, beta diversity increased over time in all treatments compared to continuous grazing (tPBG1 = 2.71, tPBG2 = 3.45, tRotational = 3.72), and variably stocked rotational treatments had greater increases in spatial heterogeneity in litter depth and vegetation structure than continuously grazed pastures (tvisual obstruction= 2.42, p = 0.03; tlitter depth = 2.59, p = 0.02) over the same time period. Alternative frameworks that promote grassland diversity and heterogeneity support the restoration of ecological services and processes in invaded grasslands.

Evaluating the Cumulative Effects of Livestock Grazing on Wildlife With an Integrated Population Model

Livestock grazing can shape temperate grassland ecosystems, with both positive and negative effects on wildlife documented depending on a variety of grazing and site factors. Historically, research investigating the impacts of livestock grazing on wildlife has been limited by a narrow focus on simple “grazed” vs. “ungrazed” treatments or examining how grazing affects only a single vital rate in isolation. To overcome these limitations, we used a two-stage class, female-based integrated population model (IPM) to examine whether three grazing management regimes (season-long, rest-rotation, and summer rotation) differentially impacted population growth rates of sharp-tailed grouse (Tympanachus phasianellus) in eastern Montana and western North Dakota. We estimated 14 vital rates related to survival and fecundity and examined whether subtle cumulative effects of livestock grazing were present but not detected in prior analyses focused on single vital rates. While the management regimes did not differentially impact survival or fecundity of female grouse in our study system, we found evidence for significant cumulative impacts of grazing regime on population growth rates that were only apparent when all vital rates were evaluated concurrently. Population growth rates were higher in areas managed with season-long livestock grazing. The IPM framework encourages comprehensive investigations into the influence of covariates on critical components of species life histories and can assist in guiding management decisions in a world of limited resources. This integrated approach allowed us to more efficiently use multiple data types to provide a more complete picture of the effects of management on an important indicator species.

Terrestrial ecosystem restoration increases biodiversity and reduces its variability, but not to reference levels: A global meta-analysis

Ecological restoration projects often have variable and unpredictable outcomes, and these can limit the overall impact on biodiversity. Previous syntheses have investigated restoration effectiveness by comparing average restored conditions to average conditions in unrestored or reference systems. Here, we provide the first quantification of the extent to which restoration affects both the mean and variability of biodiversity outcomes, through a global meta-analysis of 83 terrestrial restoration studies. We found that, relative to unrestored (degraded) sites, restoration actions increased biodiversity by an average of 20%, while decreasing the variability of biodiversity (quantified by the coefficient of variation) by an average of 14%. As restorations aged, mean biodiversity increased and variability decreased relative to unrestored sites. However, restoration sites remained, on average, 13% below the biodiversity of reference (target) ecosystems, and were characterised by higher (20%) variability. The lower mean and higher variability in biodiversity at restored sites relative to reference sites remained consistent over time, suggesting that sources of variation (e.g. prior land use, restoration practices) have an enduring influence on restoration outcomes. Our results point to the need for new research confronting the causes of variability in restoration outcomes, and close variability and biodiversity gaps between restored and reference conditions.

Fire-driven landscape heterogeneity shapes habitat selection of bighorn sheep

Patterns in disturbance severity and time since fire can drive landscape heterogeneity that is critical to conservation; however, there is limited understanding of how wildlife interact with the spatial–temporal complexities of disturbance outcomes and at what scales. We conducted multiscale modeling of habitat selection for male and female Rocky Mountain bighorn sheep (Ovis canadensis canadensis) over an 8-year period. We aimed to identify the spatial scales at which bighorn sheep responded to various habitat features and determine how fire severity and time since fire can shape habitat selection by bighorn sheep over different seasons and between sexes. With the exception of litter cover, spatial scales that extended beyond the finest spatial grain (i.e., a 30-m pixel) to include the surrounding landscape were better at predicting habitat selection. Escape terrain, elevation, fire severity, year, perennial and annual forb and grass cover, and shrub cover occurred in every best-supported model. Associations with escape terrain, elevation, and perennial and annual forb and grass cover varied by sex and season. In contrast, bighorn sheep were consistently positively associated with low- and high-severity fire. Females increased use of low- and high-severity burned areas with greater time since fire, while males tended to decrease use of areas that burned at high severity with greater time since fire. Our results support the importance of landscape heterogeneity created by fire severity and time since fire for Rocky Mountain bighorn sheep and reinforces calls to integrate disturbance-driven heterogeneity into our assessments and management of wildlife.

Reintroduced grazers and prescribed fire effects on beetle assemblage structure and function in restored grasslands

Ecological restoration seeks to reestablish functioning ecosystems, but planning and evaluation often focus on taxonomic community structure and neglect consumers and their functional roles. The functional trait composition of insect assemblages, which make up the majority of animal diversity in many systems, can reveal how they are affected by restoration management and the consequences for ecosystem function. We sampled ground beetle (Coleoptera: Carabidae) assemblages in restored tallgrass prairies varying in management with prescribed fire and reintroduced American bison (Bison bison) to describe their taxonomic and functional trait structure. We also measured seed and arthropod predation to relate management, beetle assemblage characteristics, and function, and to test if function is maximized by trait diversity, dominant trait values, or beetle abundance. Beetle assemblages primarily varied with restoration age, declining over time in richness and both taxonomic and functional diversity, but bison presence also influenced taxonomic composition. Prescribed fire reduced seed predation in summer and arthropod predation in fall. Although seed predation was unrelated to beetle assemblages, arthropod predation was greater in sites with higher abundances of carnivorous ground beetles. The relatively weak impacts of fire and bison on functional assemblage structure is a promising sign that these management disturbances, aimed at supporting a diverse native plant community, are not detrimental to beetle assemblages. The significance of reduced predator function following prescribed fire will depend on the restoration context and whether seed or arthropod predation relates to management goals.

Virginia opossum distributions are influenced by human-modified landscapes and water availability in tallgrass prairies

The Flint Hills represent the largest tract of tallgrass prairie in North America and is located near the western edge of the native range of the Virginia opossum (Didelphis virginiana). This region is undergoing rapid landscape changes (e.g., urbanization, agriculture, woody encroachment) that are negatively affecting mammal communities. Although previous research has revealed northward distributional expansions of Virginia opossums facilitated by urban development, no studies have assessed how landscape change affects distribution patterns along the western edge of their geographic range. During 2016–2018, we monitored site (n = 74) occupancy along urban–rural transects in the Flint Hills to assess the influence of landscape change (i.e., urban, grassland, agriculture, woody encroachment) and water availability on the distribution of Virginia opossums. Sites surrounded by urban land cover had greater initial occupancy probabilities and lower extinction rates. Sites closer to permanent water sources experienced greater colonization rates and lower extinction rates. In addition, site extinction rates were lower in areas surrounded by woody encroachment. Our results concur with other studies suggesting that growing urban areas may expand opossum distributions along the edges of their geographic range. Our study also suggests that woody encroachment into tallgrass prairies may provide an alternative pathway for future distributional expansions. Future research must consider the potential for landscape change, along with dynamic water availability, in models predicting the distribution of Virginia opossums.

Reproductive plasticity and landscape heterogeneity benefit a ground-nesting bird in a fire-prone ecosystem

Disturbance is critical for the conservation of rangeland ecosystems worldwide and many of these systems are fire dependent. Although it is well established that restoring fire as an ecological process can lead to increased biodiversity in grasslands and shrublands, the underlying mechanisms driving community patterns are poorly understood for fauna in fire-prone landscapes. Much of this uncertainty stems from the paucity of studies that examine the effects of fire at scales relevant to organism life histories. We assessed the response of a non-migratory ground-dwelling bird to disturbance (i.e., prescribed fire) and environmental stochasticity over the course of a 4-yr period, which spanned years of historic drought and record rainfall. Specifically, we investigated the nesting ecology of Northern Bobwhite (Colinus virginianus; hereafter Bobwhite) to illuminate possible avenues by which individuals respond to dynamic landscape patterns during a critical reproductive stage (i.e., nesting) in a mixed-grass shrubland in western Oklahoma, USA. We found that Bobwhites exhibited extreme plasticity in nest substrate use among time since fire categories (TSF) and subsequently maintained high nest survival (e.g., 57-70%). Bobwhites were opportunistic in nest substrate use among TSF categories (i.e., 72% of nest sites in shrubs in 0-12 months post fire compared to 71% in herbaceous vegetation in >36 months post fire), yet nesting decisions were first filtered by similar structural components (i.e., vertical and horizontal cover) within the vicinity of nest sites regardless of TSF category. Despite being a non-migratory and comparatively less mobile ground-nesting bird species, Bobwhites adjusted to dynamic vegetation mosaics on a fire-prone landscape under stochastic climatic conditions that culminated in stable and high nest survival. Broadly, our findings provide a unique depiction of organism response strategies to fire at scales relevant to a critical life-stage, a topic that has been previously understudied and poorly understood. We also demonstrate how doing so can better inform conservation practices aimed at restoring fire regimes on grassland and shrubland landscapes.

Pyric-carnivory: Raptor use of prescribed fires

Fire is a process that shaped and maintained most terrestrial ecosystems worldwide. Changes in land use and patterns of human settlement have altered fire regimes and led to fire suppression resulting in numerous undesirable consequences spanning individual species and entire ecosystems. Many obvious and direct consequences of fire suppression have been well studied, but several, albeit less obvious, costs of alteration to fire regimes on wildlife are unknown. One such phenomenon is the response of carnivores to fire events-something we refer to as pyric-carnivory. To investigate the prevalence of pyric-carnivory in raptors, we monitored 25 prescribed fires occurring during two different seasons and across two different locations in tallgrass prairie of the central United States. We used paired point counts occurring before and during prescribed fires to quantify the use of fires by raptors. We found a strong attraction to fires with average maximum abundance nearly seven times greater during fires than prior to ignitions (before: x¯ = 2.90, SE = 0.42; during: x¯ = 20.20; SE = 3.29) and an average difference between fire events and immediately before fires of 15.2 (±2.69) raptors. This result was driven by Swainson's hawks (Buteo swainsoni), which were the most abundant (n = 346) of the nine species we observed using fires. Our results illustrate the importance of fire as integral disturbance process that effects wildlife behavior through multiple mechanisms that are often overshadowed by the predominant view of fire as a tool used for vegetation management.