Exotic Annual Grasses Research Articles

Multiple plant-community traits improve predictions of later-stage outcomes of restoration drill seedings: Implications for metrics of success

Success of ecological restoration is often only knowable if treatments meet criteria defined by biotic thresholds, but analytical frameworks to determine metrics of success and their underlying thresholds are needed. Early indicators of longer-term recovery trajectories are particularly critical where re-treatments may be required, such as in harsh climates or where repeated disturbances or invasive pressures prevail. We developed a framework for identifying which biotic traits would provide the best initial indication of longer-term target restoration goals and applied the framework to restoration drill-seedings of deep-rooted perennial bunchgrasses (DRPBGs) used to rehabilitate and restore semiarid rangelands threatened by exotic annual grasses (EAGs, e.g. cheatgrass) and the recurrent wildfire that EAGs cause. Initial traits measured included cover, basal diameter, height, and density (#plants/area) of DRPBGs and cover of EAGs and Sandberg bluegrass (Poa secunda, POSE, a disturbance-adapted perennial). The longer-term target objective was ≥25 % DRPBG cover and ≤13 % EAG cover by the 5th year following drill-seedings. Measurements were made on 112 plots spanning 113,000 ha in sagebrush steppe on the Soda wildfire scar, in the Northern Great Basin, USA. Traits of DRPBGs tended to be uncorrelated with one another, thus each was informative in describing vegetation condition. Where DRPBG cover was initially >17 %, it tended to become >25 % by the 5th-year post-seeding. In plots that overcame an initial risk of not meeting the target objective (i.e. <17 % initial DRPBG cover), DRPBG tended be large DRPBGs (>22.8 cm height) and plots also had >7 % cover of POSE. Additional “sets” of initial vegetation traits were also predictive of longer-term restoration success or failure. Restoration drill-seeding of DRPBGs is a key but varied-outcome tool for breaking the exotic grass-fire cycle, and, contrary to a conventional tendency to rely on a limited number of mean traits such as % cover, a suite of biotic traits appears necessary to monitor to reliably know if trials are likely to yield success.

Modeling cheatgrass distribution, abundance, and response to climate change as a function of soil microclimate.

Exotic annual grass invasions in water-limited systems cause degradation of native plant and animal communities and increased fire risk. The life history of invasive annual grasses allows for high sensitivity to interannual variability in weather. Current distribution and abundance models derived from remote sensing, however, provide only a coarse understanding of how species respond to weather, making it difficult to anticipate how climate change will affect vulnerability to invasion. Here, we derived germination covariates (rate sums) from mechanistic germination and soil microclimate models to quantify the favorability of soil microclimate for cheatgrass (Bromus tectorum L.) establishment and growth across 30 years at 2662 sites across the sagebrush steppe system in the western United States. Our approach, using four bioclimatic covariates alone, predicted cheatgrass distribution with accuracy comparable to previous models fit using many years of remotely-sensed imagery. Accuracy metrics from our out-of-sample testing dataset indicate that our model predicted distribution well (72% overall accuracy) but explained patterns of abundance poorly (R2 = 0.22). Climatic suitability for cheatgrass presence depended on both spatial (mean) and temporal (annual anomaly) variation of fall and spring rate sums. Sites that on average have warm and wet fall soils and warm and wet spring soils (high rate sums during these periods) were predicted to have a high abundance of cheatgrass. Interannual variation in fall soil conditions had a greater impact on cheatgrass presence and abundance than spring conditions. Our model predicts that climate change has already affected cheatgrass distribution with suitable microclimatic conditions expanding 10%-17% from 1989 to 2019 across all aspects at low- to mid-elevation sites, while high- elevation sites (>2100 m) remain unfavorable for cheatgrass due to cold spring and fall soils.

Prescribed fire and exotic plant responses in phreatophytic Sarcobatus vermiculatus rangelands with contrasting degradation

The effects of fire seasonality and prescribed burning on exotic species invasion are poorly understood in black greasewood (Sarcobatus vermiculatus) plant communities of North America. The impacts of reintroducing fire in the fall and spring on community composition and current-year biomass were evaluated at two such sites, one dominated by exotic annual C3 grasses in Miles City, Montana, USA, and one dominated by native perennial C4 grasses in Laramie, Wyoming, USA. Study sites were assessed based on existing Ecological Site Description (ESD) and State-and-Transition Models (STMs) and the Montana site was determined to be more degraded than the Wyoming site. Experimental design was a randomized complete block design with burns conducted in the fall of 2020 and spring of 2021. Exotic species such as Bromus arvensis were reduced by 56% in spring burned plots the following year and by 25% in the fall burned plots over the course of the study in Montana (58.3–43.5%) and Bromus tectorum did not increase in spring or fall burned plots in Wyoming. Accordingly, the proportion of native species in both plant communities remained constant and native perennial C4 grasses such as Sporobolus airoides were resilient to fire. Moreover, burn treatment had no negative effects on plant species richness, evenness, or diversity in either location. Fire treatments had variable effects on current-year biomass with variable influences of drought and season of burn. Prescribed fire, regardless of season, did not exacerbate exotic plant species spread or reduce native species dominance in either location – suggesting that phreatophytic S. vermiculatus rangelands near the eastern terminus of their range are resilient to anthropogenic burning. Future research should investigate the use of prescribed fire with other methods such as revegetation and herbicide application for reducing exotic plant dominance and increasing native plant species.

Vegetation, fuels, and fire-behavior responses to linear fuel-break treatments in and around burned sagebrush steppe: are we breaking the grass-fire cycle?

BackgroundLinear fuel breaks are being implemented to moderate fire behavior and improve wildfire containment in semiarid landscapes such as the sagebrush steppe of North America, where extensive losses in perennial vegetation and ecosystem functioning are resulting from invasion by exotic annual grasses (EAGs) that foster large and recurrent wildfires. However, fuel-break construction can also pose EAG invasion risks, which must be weighed against the intended fire-moderation benefits of the treatments. We investigated how shrub reductions (mowing, cutting), pre-emergent EAG-herbicides, and/or drill seedings of fire-resistant perennial bunchgrasses (PBGs) recently applied to create a large fuel-break system affected native and exotic plant abundances and their associated fuel loading and predicted fire behavior.ResultsIn heavily EAG-invaded areas, herbicides reduced EAG and total herbaceous cover without affecting PBGs for 2–3 years and reduced predicted fire behavior for 1 year (from the Fuel Characteristic Classification System). However, surviving post-herbicide EAG cover was still > 30%, which was sufficient fuel to exceed the conventional 1.2-m-flame length (FL) threshold for attempting wildfire suppression with hand tools. In less invaded shrubland, shrub reduction treatments largely reduced shrub cover and height by ~ half without increasing EAGs, but then redistributed the wood to ground level and increased total herbaceous cover. Herbicides and/or drill seeding after shrub reductions did not affect EAG cover, although drill seedings increased PBG cover and exotic forbs (e.g., Russian thistle). Fire behavior was predicted to be moderated in only one of the many yearly observations of the various shrub-reduction treatment combinations. Over all treatments and years, FLs were predicted to exceed 1.2 m in 13% of simulations under average (11 km h−1) or high (47 km h−1) wind speed conditions and exceed the 3.4-m threshold for uncontrollable fire in 11% of simulations under high-wind speeds only.ConclusionsPredicted fire-moderation benefits over the first 4 years of fuel break implementation were modest and variable, but, generally, increases in EAGs and their associated fire risks were not observed. Nonetheless, ancillary evidence from shrublands would suggest that treatment-induced shifts from shrub to herbaceous fuel dominance are expected to improve conditions for active fire suppression in ways not readily represented in available fire models.

Nontarget effects of pre‐emergent herbicides and a bioherbicide on soil resources, processes, and communities

Community‐type conversions, such as replacement of perennials by exotic annual grasses in semiarid desert communities, are occurring due to plant invasions that often create positive plant–soil feedbacks, which favor invaders and make restoration of native perennials difficult. Exotic annual grass control measures, such as pre‐emergent herbicides, can also alter soil ecosystems directly or indirectly (i.e. via the plant community), yet there are few studies on the topic in natural, non‐cropped landscapes. We asked how spray treatments applied to soil post‐fire with the intention of inhibiting invasive annual grasses (such as Bromus tectorum L.) and releasing existing native perennial grasses affected soil resources, a microbial process, and invertebrates in three climatically varied sagebrush steppe sites. Spray treatments included chemical herbicides (imazapic and rimsulfuron) that strongly affected plant communities and a bioherbicide (Pseudomonas fluorescens strain D7) that did not. Chemical herbicides increased soil mineral nitrogen in proportion to their negative effects on plant cover for 2 years after treatments in all sites and increased soil water and net N mineralization (measured at one site) but did not affect total carbon, nitrogen, or organic matter. Invertebrate responses to herbicides varied by site, and invertebrates increased with chemical herbicides at the highest, wettest site. We show that herbicide treatments can exacerbate pulses of mineral nutrients, which previous studies have shown can weaken ecosystem resistance to invasion. Thus, restoration strategies that increase the likelihood that desired plants can capture mineralized nutrients after herbicide application will likely be more successful.

Cross-scale analysis reveals interacting predictors of annual and perennial cover in Northern Great Basin rangelands.

Exotic annual grass invasion is a widespread threat to the integrity of sagebrush ecosystems in Western North America. Although many predictors of annual grass prevalence and native perennial vegetation have been identified, there remains substantial uncertainty about how regional-scale and local-scale predictors interact to determine vegetation heterogeneity, and how associations between vegetation and cattle grazing vary with environmental context. Here, we conducted a regionally extensive, one-season field survey across burned and unburned, grazed, public lands in Oregon and Idaho, with plots stratified by aspect and distance to water within pastures to capture variation in environmental context and grazing intensity. We analyzed regional-scale and local-scale patterns of annual grass, perennial grass, and shrub cover, and examined to what extent plot-level variation was contingent on pasture-level predictions of site favorability. Annual grasses were widespread at burned and unburned sites alike, contrary to assumptions of annual grasses depending on fire, and more common at lower elevations and higher temperatures regionally, as well as on warmer slopes locally. Pasture-level grazing pressure interacted with temperature such that annual grass cover was associated positively with grazing pressure at higher temperatures but associated negatively with grazing pressure at lower temperatures. This suggests that pasture-level temperature and grazing relationships with annual grass abundance are complex and context dependent, although the causality of this relationship deserves further examination. At the plot-level within pastures, annual grass cover did not vary with grazing metrics, but perennial cover did; perennial grasses, for example, had lower cover closer to water sources, but higher cover at higher dung counts within a pasture, suggesting contrasting interpretations of these two grazing proxies. Importantly for predictions of ecosystem response to temperature change, we found that pasture-level and plot-level favorability interacted: perennial grasses had a higher plot-level cover on cooler slopes, and this difference across topography was starkest in pastures that were less favorable for perennial grasses regionally. Understanding the mechanisms behind cross-scale interactions and contingent responses of vegetation to grazing in these increasingly invaded ecosystems will be critical to land management in a changing world.

Analysis adapted from text mining quantitively reveals abrupt and gradual plant-community transitions after fire in sagebrush steppe

ContextPlant communities vary both abruptly and gradually over time but differentiating between types of change can be difficult with existing classification and ordination methods. Structural topic modeling (STRUTMO), a text mining analysis, offers a flexible methodology for analyzing both types of temporal trends.ObjectivesOur objectives were to (1) identify post-fire dominant sagebrush steppe plant association types and ask how they vary with time at a landscape (multi-fire) scale and (2) ask how often major association changes are apparent at the plot-level scale.MethodsWe used STRUTMO and plant species cover collected between 2002–2022 across six large burn areas (1941 plots) in the Great Basin, USA to characterize landscape change in dominant plant association up to 14 years post-fire. In a case study, we assessed frequency of large annual changes (≥ 10% increase in one association and decrease in another) between associations at the plot-level scale.ResultsSTRUTMO revealed 10 association types dominated by either perennial bunchgrasses, mixed perennial or annual grasses and forbs, or exotic annual grasses. Across all study fires, associations dominated by large-statured perennial bunchgrasses increased then stabilized, replacing the Sandberg bluegrass (Poa secunda)-dominated association. The cheatgrass (Bromus tectorum)-dominant association decreased and then increased. At the plot-level, bidirectional changes among associations occurred in ~ 75% of observations, and transitions from annual invaded to perennial associations were more common than the reverse.ConclusionsThe analysis revealed that associations dominated by some species (i.e. crested wheatgrass, Agropyron cristatum, Siberian wheatgrass, Agropyron fridgida, or medusahead, Taeniatherum caput-medusae) were more stable than associations dominated by others (i.e. Sandberg bluegrass or cheatgrass). Strong threshold-like transitions were not observed at the multi-fire scale, despite frequent ephemeral plot-level changes.

Long-term biocrust responses to wildfires in Washington, USA.

Dryland ecosystems in the western United States are affected by invasive species, wildfires, livestock grazing, and climate change in ways that are difficult to distinguish. Biocrusts perform important ecological roles in these systems and are sensitive to all of these pressures. We revisited a Washington, USA, site sampled for biocrusts in 1999 to focus on effects of exotic annual grass invasion and wildfires in the absence of livestock grazing. We examined changes between 1999 and 2020 using a Bayesian directed acyclic graph (DAG) to interpret direct and indirect causal impacts of wildfire on perennial bunchgrasses, exotic annual grasses, and biocrusts. Between 1999 and 2020, exotic annual grass cover increased in all plots and in unburned plots by 16% and 18%, respectively, bunchgrass cover decreased by 21% and 25%, and biocrust cover decreased by 8.9% and 9.8%. Our DAG suggested that decreases in bunchgrass increased exotic annual grass, which reduced biocrust cover. Wildfires did not directly influence changes in bunchgrass, exotic annual grass, or biocrust cover. Areas dominated by exotic annual grass had less abundant and diverse biocrusts than areas with less exotic annual grass. Biocrust community changes were more strongly related to increasing exotic annual grasses than to wildfires. Changes may relate to other soil disturbances or broad-scale changes in climate or air quality. The minimal influence of wildfire on exotic annual grass and biocrusts suggests that apparent negative impacts of wildfire at other sites may be due to exacerbation by livestock grazing or other surface disturbance.

Forage Quality of Ventenata dubia in a Southeastern Oregon Meadow System

Ventenata (Ventenata dubia L.) is an exotic annual grass gaining attention for its environmental and economic impacts across the western United States. Since cattle reportedly avoid grazing it, there is speculation regarding why it is rejected, though little is known about its forage quality and digestibility. We examined the seasonal and annual forage dynamics of ventenata in a southeastern Oregon meadow system by analyzing the forage quality (crude protein, acid detergent fiber, lignin); silica content; in vitro digestibility (IVDMD); and macrominerals (phosphorous, calcium, magnesium, potassium, and sulfur) of ventenata over the growing season (May, June, and July) for 2 yr. We did not find that ventenata is low in forage quality, macrominerals, or digestibility. Overall, the forage quality of ventenata, especially in early spring (May and June), appears to pose little issue nutritionally. In fact, the crude protein of ventenata stayed above the crude protein minimum requirement for maintenance in grazing cattle through June. However, we did find that silica content as acid insoluble ash content (AIA%) of ventenata at our sites increased throughout the growing season and ranged between 4.3% and 12.1%, nearly 4× the amount previously reported. We also found variability in digestibility and nutrient profile from year to year that can be related to annual precipitation. For example, digestibility decreased by June in the wetter year but did not decrease in the dryer year until into July. Our results have implications for the management of ventenata and are especially relevant for the consideration of targeted grazing as a control method. Forage quality and digestibility of ventenata are best in early spring but, due to the height of the annual grass during this time, there is only a brief window for a targeted grazing strategy because its quality and digestibility declines and silica content increases over the growing season.

A nontarget, disturbance‐resilient native species influences post‐fire recovery and multiphasic herbicide‐seeding outcomes in drylands threatened by exotic annual grasses

Native species that are abundant and persistent across disturbance‐succession cycles can affect recovery and restoration of plant communities, especially in drylands. In the sagebrush‐steppe deserts of North America, restoring deep‐rooted perennial bunchgrasses (DRPBGs) is key to the strategy for breaking an increasingly problematic cycle of wildfire promoted by exotic annual grasses (EAGs) and displacement of perennials by post‐fire increases in EAGs. We asked how Sandberg bluegrass (Poa secunda, POSE)—a common native grass that shares traits with EAGs such as resilience to disturbance and rapid, shallow‐rooted, early season growth—(1) recovered after wildfire, (2) responded to different combinations of native‐plant seedings of DRPBGs and EAG‐targeting herbicides; and (3) in turn, related to DRPBG recovery. In repeated sampling of up to approximately 2,000 plots spanning 113,000 burned hectares, POSE was initially more abundant than DRPBGs until POSE began to decline 5 years post‐fire, and POSE was marginally affected or unaffected by restoration treatments targeting DRPBGs or EAGs. In comparison, EAG cover decreased 8–16% where preemergent herbicide was sprayed and DRPBG cover increased 3–9% where they were drill‐seeded, and the greatest EAG reductions and DRPBG increases were seen where seeding and herbicides were combined in a time‐staggered fashion. Treatments had less target effects where POSE cover was high (&gt;18%), which is also where EAG cover was scarcer and DRPBG cover greater, regardless of post‐fire interventions. Consideration of the ecological role of disturbance‐resilient species with ruderal characteristics that match traits of key invaders may improve the efficiency and effectiveness of restoration interventions.

Predicting Exotic Annual Grass Abundance in Rangelands of the Western United States Using Various Precipitation Scenarios

Expansion of exotic annual grass (EAG), such as cheatgrass (Bromus tectorum L.) and medusahead (Taeniatherum caput-medusae [L.] Nevski), could cause irreversible changes to arid and semiarid rangeland ecosystems in the western United States. The distribution and abundance of EAG species are highly affected by weather variables such as temperature and precipitation. The study's goal is to understand how different precipitation scenarios affect EAG abundance estimates and dynamics, and we develop a machine learning modeling approach to predict how changes in annual and immediate past precipitation patterns could affect the abundance of EAG. The machine learning predictive model used seed source from previous years, weather variables, and soil profiles to drive its predictions. We achieved excellent training accuracy (r = 0.95 and median absolute error [MdAE] = 2.36% cover) and strong test accuracy (r = 0.79 and MdAE = 4.54% cover). We developed five versions of EAG abundance maps for 2022 with different precipitation scenarios: 9 yr of average precipitation, half of the average, three-fourths of the average, one and one-half times the average, and two times the average. The approach presented can be replicated to new study domains and easily modified for use with other precipitation scenarios. Developing multiple versions of a year's EAG spatially explicit abundance dataset predictions from multiple weather-based scenarios can provide important information to land managers as they prepare for variable EAG dynamics each year. Informed annual predictions based on weather scenario−driven models have the potential to improve fire preparation decisions.

Influence of directional side of sagebrush canopies and interspaces on microhabitats

Shrubs can contribute to spatial heterogeneity in plant communities by creating distinct microsites under their canopies compared to between their canopies (interspaces). This results in distinct microhabitats that differ in understory vegetation characteristics and ground cover. However, microhabitats may also differ under the north and south side of canopies because of differences in shading and other microsite characteristics. We investigated if microhabitats varied among north and south sides of sagebrush canopies, and interspaces in 16 plant communities. Several understory vegetation characteristics and most ground cover variables varied among north sides, south sides, and interspaces. Moss and litter cover were greatest and bare ground was lowest in north sides. Moss and litter cover decreased and bare ground increased from north to south sides and from south sides to interspaces. Exotic annual grass cover and abundance was less in north side microsites compared to south side and interspace microsites, implying that sagebrush creates heterogeneity in resistance to invasion. This may be critical in allowing native herbaceous vegetation to persist under annual grass invasion pressure. Our results provide evidence that sagebrush creates distinct microhabitats. This highlights the pivotal role of shrubs in creating heterogeneity in shrub steppe communities and indicates that preventing the loss of shrubs in these communities should be a management priority. This also suggests that it is critical to restore sagebrush, and potentially other shrubs in similar ecosystems, after they are lost to maintain differences in microhabitats that promote diversity and coexistence.

Is Crested Wheatgrass Invasive in Sagebrush Steppe with Intact Understories in the Great Basin?

Seeding crested wheatgrass (Agropyron desertorum [Fisch.] Schult.) in the sagebrush steppe is a controversial management action. There are concerns that crested wheatgrass may invade new areas and exclude native vegetation because many former crested wheatgrass seedings are near monocultures. However, crested wheatgrass is often seeded to prevent exotic annual grass invasion and stabilize soils after disturbances in areas where native vegetation is unlikely to establish. These areas can be difficult to identify and, consequentially, crested wheatgrass may be seeded in areas it is not needed, such as sagebrush steppe with understories dominated by native perennial grasses and forbs (intact understories). Thus, land managers need to know the potential effects of seeding crested wheatgrass, especially if it can invade and exclude native vegetation in sagebrush steppe with intact understories. We investigated the ability of crested wheatgrass to invade and exclude native vegetation by drill seeding crested wheatgrass into intact sagebrush steppe understories at five sites. To be invasive, crested wheatgrass would need to increase in abundance beyond initial establishment from drill seeding, causing decreases in native vegetation. We measured vegetation cover and density for 7 yr after seeding to evaluate the effects of seeding crested wheatgrass. Crested wheatgrass established with drill seeding but did not increase from its original density. Cover of crested wheatgrass increased with time but was < 2% seven yr after seeding. We found no evidence that seeding crested wheatgrass decreased the cover or abundance of native vegetation. These results suggest that intact sagebrush steppe understories are competitive with crested wheatgrass and, thereby, limit its recruitment and growth. Though crested wheatgrass did not show indications of being invasive in intact sagebrush steppe understories, longer-term evaluations with the inclusion of disturbances that might open safe sites in these communities would be prudent to fully understand its potential effects.

Extracting exotic annual grass phenology and climate relations in western U.S. rangeland ecoregions

This research builds upon the extensive body of work to model exotic annual grass (EAG) characteristics and invasion. EAGs increase wildland fire risk and intensifies wildland fire behavior in western U.S. rangelands. Therefore, understanding characteristics of EAG growth increases understanding of its dynamics and can inform rangeland management decisions. To better understand EAG phenology and spatial distribution, monthly weather (precipitation, minimum and maximum temperature) variables were analyzed for 24 level III ecoregions. This research characterizes EAGs’ phenology identified by a normalized difference vegetation index (NDVI) threshold-based interpolation technique. An EAG phenology metric model was used to estimate a growing season dynamic for the years 2017–2021 for shrub and herbaceous land cover types in the western conterminous United States (66% of the area). The EAG phenology metrics include six growing season metrics such as start of season time, end of season time, and time of maximum NDVI during the growing season. The models’ cross validation results for Pearson’s r ranged from 0.88 to 0.95. Increased understanding of the effects that weather conditions have on EAG growth and spatial distribution can help land managers develop time-sensitive plans to protect entities deemed valuable to society like native habitat, wildlife, recreational areas, and air quality.

Estimates of fine fuel litter biomass in the northern Great Basin reveal increases during short fire-free intervals associated with invasive annual grasses

Exotic annual grasses invasion across northern Great Basin rangelands has promoted a grass-fire cycle that threatens the sagebrush (Artemisia spp.) steppe ecosystem. In this sense, high accumulation rates and persistence of litter from annual species largely increase the amount and continuity of fine fuels. Here, we highlight the potential use and transferability of remote sensing-derived products to estimate litter biomass on sagebrush rangelands in southeastern Oregon, and link fire regime attributes (fire-free period) with litter biomass spatial patterns at the landscape scale. Every June, from 2018 to 2021, we measured litter biomass in 24 field plots (60 m × 60 m). Two remote sensing-derived datasets were used to predict litter biomass measured in the field plots. The first dataset used was the 30-m annual net primary production (NPP) product partitioned into plant functional traits (annual grass, perennial grass, shrub, and tree) from the Rangeland Analysis Platform (RAP). The second dataset included topographic variables (heat load index -HLI- and site exposure index -SEI-) computed from the USGS 30-m National Elevation Dataset. Through a frequentist model averaging approach (FMA), we determined that the NPP of annual and perennial grasses, as well as HLI and SEI, were important predictors of field-measured litter biomass in 2018, with the model featuring a high overall fit (R2 = 0.61). Model transferability based on extrapolating the FMA predictive relationships from 2018 to the following years provided similar overall fits (R2 ≈ 0.5). The fire-free period had a significant effect on the litter biomass accumulation on rangelands within the study site, with greater litter biomass in areas where the fire-free period was <10 years. Our findings suggest that the proposed remote sensing-derived products could be a key instrument to equip rangeland managers with additional information towards fuel management, fire management, and restoration efforts.

Plant community trajectories following livestock exclusion for conservation vary and hinge on initial invasion and soil‐biocrust conditions in shrub steppe

AbstractAdjustments or complete withdrawal of livestock grazing are among the most common conservation actions in semiarid uplands, but outcomes can vary considerably with ecological context. Invasion by exotic annual grasses and the excessive wildfire they promote are increasing threats to semiarid shrub‐steppe, and plant‐community response to livestock exclusion in these areas may be complicated by the rapid colonization ability of invaders. We evaluated vegetation‐community changes over 14‐year interval (2007–2021) in a shrub‐steppe landscape where a &gt;100‐year history of livestock grazing had been terminated in 1996. Field surveys revealed that bare‐soil exposure decreased &gt;20% over the 14 years owing to biomass accumulation, but this was primarily due to large increases in exotic annual “cheatgrass” (Bromus tectorum, +1.8‐fold) and the litter it produces (+1.5‐fold). Soil biocrusts increased 11.9% and perennial bunchgrasses increased 3% over the 14 years. These community changes varied at the patch scale and entailed inverse relationships of (1) both cheatgrass and biocrusts to plant‐community basal cover, (2) cheatgrass to both biocrusts and perennial grasses, and (3) biocrusts to cheatgrass and litter. The spatiotemporal variability in vegetation constituted changes in plant‐community states, according to cluster analysis. The modeled probability of a community transitioning to a cheatgrass state was (1) strongly and positively related to the initial (2007) cover of cheatgrass in hotspots where initial cheatgrass cover was &gt;20%, and (2) negatively related to biocrust cover where initial biocrust cover was &gt;4% of ground area. The decision space for this landscape can be framed as a shifting from acceptance towards resisting further degradation by removing livestock and their trampling of soil surfaces and utilization of perennial herbs. However, cheatgrass appears to be the most impactful agent of change and continued invasion appears imminent. Active restoration may help resist further degradation and direct change towards tolerable conditions.

Relationship of greater sage‐grouse to natural and assisted recovery of key vegetation types following wildfire: insights from scat

Megafires are creating severe conservation problems worldwide for wildlife that have obligate dependencies on plant species that are foundational but fire‐intolerant. Wildfire‐induced loss of native perennials and increases in exotic annual grasses threaten greater sage‐grouse (GRSG, Centrocercus urophasianus) in its sagebrush steppe habitat in western North America. Post‐fire restoration using herbicides, seeding, and planting of native perennials such as sagebrush are common, but there are few assessments of GRSG response to the treatments. We measured the presence of GRSG scat and modeled the probability of GRSG presence (PrGRSG‐scat) in relation to variation in plot‐level and landscape‐level predictors, and land treatments, in an intensive, repeat sampling from 2017 to 2020 of 113,000 ha area burned in 2015 in the Soda Megafire (Oregon and Idaho, U.S.A.). GRSG scat was present in less than 200 of more than 8,000 observations, as would be expected for a philopatric species (i.e. high fidelity to home site) returning to degraded habitat. PrGRSG‐scat was positively associated with sagebrush presence at the plot level and was positively related to elevation, lower‐angle slopes, and proximity to sagebrush seedling outplant islands. The statistical significance of relationships of PrGRSG‐scat to restoration treatments was marginal at best, with the largest effect being a positive response of PrGRSG‐scat to pre‐emergent herbicide sprayed to reduce exotic annual grasses. More time may be required for restored sagebrush steppe to meet GRSG needs or for GRSG to “adopt” the restored vegetation. Moreover, whereas scat is a convenient and non‐invasive method to monitor GRSG, its post‐fire scarcity weakens the strength of statistical inference on GRSG recovery patterns and response to restoration.

Grazing Effects on Fuels Vary by Community State in Wyoming Big Sagebrush Steppe

Limiting fire in Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis [Beetle & A. Young] S.L. Welsh) steppe is often a management priority as fires threatens its ecological integrity and rural economies that depend on it. However, the Wyoming big sagebrush steppe is vast and occurs in different community states from intact (sagebrush-bunchgrass dominated) to exotic annual grass dominated. Grazing has been suggested as the only tool that is likely feasible to apply across such large landscapes to manage fine fuels, but there is concern that over time grazing may induce undesirable shifts in plant community composition (e.g., increases in exotic annuals) that increase fire risk. Therefore, we evaluated the longer-term (+10 yr) effects of contemporary, moderate grazing by cattle compared with grazing exclusion on fuel characteristics in three community states: intact, degraded, and exotic annual grass states. We accomplished this by measuring fuel characteristics in five grazed and ungrazed areas in each community state in 2020 and 2021. Grazing generally decreased fine fuel continuity and biomass and increased the live-to-dead ratio. These fuel alterations are consistent with decreasing the probability of fire ignition and, if ignited, producing a slower spreading fire with shorter flame lengths. The response of several fine fuel characteristics to grazing varied by community state. Fine fuel characteristics also commonly varied among community states and between years. These results suggest that fuel management plans need to recognize that grazing effects will vary by community state and be flexible because fuel characteristics vary spatially and temporally. Overall, our results suggest that contemporary grazing in the Wyoming big sagebrush steppe reduces the probability of wildfire and likely increases the effectiveness and safety of fire suppression. Consequently, grazing exclusion in these communities increases the probability of frequent, large wildfires that are difficult and dangerous to suppress.

Reducing Exotic Annual Grass Competition did not Improve Shrub Restoration Success During a Drought

Restoration of native shrub species is challenging but direly needed in arid and semiarid rangelands globally as native shrubs provide critical habitat for wildlife and livestock forage. Restoration of antelope bitterbrush (Purshia tridentata Pursh DC), a wildlife-important shrub, is often a priority on western US rangelands. One challenge to bitterbrush restoration is competitive exotic annual grasses. Exotic annual grasses can be successfully controlled with pre-emergent herbicides, but the effects of controlling exotic annual grasses with pre-emergent herbicides on bitterbrush survival and growth are unknown. We evaluated the effects of applying a pre-emergent herbicide, imazapic, to control exotic annual grasses on planted bitterbrush seedlings and existing vegetation for 2 yr post treatment at five sites in southeastern Oregon. Imazapic application reduced exotic annual grass cover and density but did not improve bitterbrush establishment. Exotic annual grass control did lead to an increase in native perennial bunchgrass cover. We suspect the lack of treatment effect was caused by high mortality of bitterbrush seedlings from drought in the first year. By the second year, bitterbrush was largely lost across the study sites with only four individuals surviving. The high bitterbrush seedling mortality observed in this study highlights that multiple barriers to restoration success likely exist in arid and semiarid rangelands. For successful restoration, land managers and restoration practitioners need to have a plan and resources for overcoming multiple barriers, which may require several restoration attempts should initial attempts be unsuccessful.

Predictive Models of Selective Cattle Use of Large, Burned Landscapes in Semiarid Sagebrush-steppe

The fire-exotic annual grass cycle is a severe threat to shrub-steppe rangelands, and a greater understanding of how livestock grazing relates to the problem is needed to guide effective management interventions. Grazing effects vary throughout shrub-steppe rangelands because livestock are selective in their use within pastures. Thus, knowing where cattle are located and concentrate their use in a postfire landscape is important for enhancing plant community resiliency to disturbance and resistance to exotic annual grass invasion. We asked how the distribution and intensity of cattle use varied across 113 000 ha of recently burned, environmentally varied shrub-steppe. Generalized linear mixed effects models were used to determine the relationship of cattle dung (presence/absence and counts), which was recorded during the third to fifth postfire year (after grazing deferment) on 1166 (531-m2) plots, to water sources, burn severity, grass cover, and topographic predictors. Our distribution and intensity of use models revealed similar relationships between cattle use and landscape predictors. Cattle use was greater in areas that were flatter and closer to water and that had moderate burn severity and less heat load and ruggedness. Slope had the strongest effect on cattle use of the predictors. The probability of cattle being present decreased by 10% for every 5° increase in slope until slope exceeded 15°, and then the effect of slope weakened. Despite moderate slopes (χ¯ = 14°), cattle use was greater in areas of moderate burn severity, presumably because these areas provided greater perennial grass production. While there was much unexplained variation, these models suggest that cooler climate, water access, topographic factors, and burn severity affect maneuverability to create greater livestock use of certain areas within grazing pastures. Restoration investment planning or assessments and expectations of restoration success could be improved by considering that these livestock hotspots may recover differently from the surrounding landscape.