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Precipitation pulses and interpulse dry periods are major drivers of dryland ecosystem function globally, yet how the patterning and timing of precipitation inputs and dry periods influence seedling recruitment in these systems is poorly understood. We conducted two experiments to understand how limited and variable patterns of precipitation inputs may influence recruitment of bluebunch wheatgrass (Pseudoroegneria spicata [Pursh] A. Love). In the first experiment, we evaluated how precipitation magnitude and dry-d interval during spring influenced recruitment. Ambient precipitation was excluded during spring, and we experimentally applied 5 levels of water (25, 35, 45, 55, and 65 mm) and 5-dry-d durations (1, 2, 4, 6, or 8 dry d between waterings) to plots sown with P. spicata. In the second experiment, we evaluated how the seasonal timing and duration of dry d influenced recruitment. All ambient precipitation was excluded through late winter and spring, and we experimentally applied three levels of dry-d duration (10, 20, and 30 d) four times during the growing season (February, March, April, and May) to plots sown with P. spicata. We observed strong, nonlinear interactive effects of precipitation amount and dry-d interval on recruitment where the midpoint dry-d treatment (4 d) interacted with low water availability to drive a major decline in recruitment. We also found strong evidence that recruitment was limited by dry periods occurring in late winter as opposed to dry periods occurring through spring, with recruitment decreasing over 40% during February dry periods compared with dry periods in March, April, or May. By understanding how precipitation pulses and interpulse dry periods interact to drive recruitment, we can refine efforts to develop weather-centric restoration frameworks, as well as hone ongoing efforts to identify plant materials and seed enhancement technologies that may buffer effects of variable precipitation on recruitment.

Rangelands in the western United States exhibit extremely high temporal variability in seedbed microclimate, and this variability contributes to poor establishment of revegetation species that are typically planted in the fall. We conducted long-term simulations of cumulative germination as a function of planting date and identified alternative germination syndromes based on population-level responses to environmental variability. These germination syndromes reveal ecologically significant differences but also noteworthy similarities in species and seed lot response that can inform rangeland restoration planning and management. Seed germination may occur much sooner than assumed under the traditional paradigm of fall-planting/spring-emergence in the intermountain western United States, and seed germination per se does not appear to be a bottleneck for successful establishment in most years. Instead, simulations of germination response support recent hypotheses that postgermination/preemergent mortality may be the larger contributor to poor seedling establishment. Our data support two general strategies to improve the likelihood of seedling survival into the spring: seeding as late as possible in the fall and active diversification of germination syndromes within a given seed mix. Consistent application of these strategies could increase the probability that some seeds are always available to take advantage of any pulse of seedbed favorability in the late fall, winter, or early spring.

Restoration of dryland ecosystems is often limited by low seedling establishment and survival. Defoliation caused by insects and small mammals could be an overlooked cause of seedling mortality. In the sagebrush steppe, we examined the effect of seedling defoliation on the survival of perennial grasses commonly used as restoration materials. Under field conditions, seedlings of three perennial bunchgrass species (non-native Agropyron cristatum, and native grasses Poa secunda and Pseudoroegneria spicata) were defoliated at two intensities (30 % and 70 % leaf length removal) and frequencies (one or two clippings) and compared to a non-defoliated control. Following emergence the first year, clippings occurred at the two-leaf stage; a second clipping occurred 1 month later for repeated defoliation treatments. We monitored seedling survival and tillering for 2 years. We expected higher defoliation intensity and frequency to reduce survival for all species, but only a few treatments reduced Po. secunda survival. Conversely, larger-statured Triticeae (wheatgrasses) benefited from some defoliation treatments. In both years, A. cristatum survival increased with repeated defoliation at both intensities. Defoliation did not affect Ps. spicata survival in the first year, but a single defoliation in the second year resulted in increased survival. In both A. cristatum and Ps. spicata, higher-intensity defoliation reduced the boost to survival resulting from defoliation frequency. Seedlings with more tillers had greater survival probabilities, but tiller number was unaffected by defoliation. Further research may elucidate mechanisms seedlings use to compensate for or benefit from defoliation. In the meantime, managers should aim to select defoliation-tolerant species if they anticipate herbivory will be problematic for restoration sites.

Restoration of dryland ecosystems is often limited by low seedling establishment and survival. Defoliation caused by insects and small mammals could be an overlooked cause of seedling mortality. In the sagebrush steppe, we examined the effect of seedling defoliation on the survival of perennial grasses commonly used as restoration materials. Under field conditions, seedlings of three perennial bunchgrass species (non-native Agropyron cristatum, and native grasses Poa secunda and Pseudoroegneria spicata) were defoliated at two intensities (30 % and 70 % leaf length removal) and frequencies (one or two clippings) and compared to a non-defoliated control. Following emergence the first year, clippings occurred at the two-leaf stage; a second clipping occurred 1 month later for repeated defoliation treatments. We monitored seedling survival and tillering for 2 years. We expected higher defoliation intensity and frequency to reduce survival for all species, but only a few treatments reduced Po. secunda survival. Conversely, larger-statured Triticeae (wheatgrasses) benefited from some defoliation treatments. In both years, A. cristatum survival increased with repeated defoliation at both intensities. Defoliation did not affect Ps. spicata survival in the first year, but a single defoliation in the second year resulted in increased survival. In both A. cristatum and Ps. spicata, higher-intensity defoliation reduced the boost to survival resulting from defoliation frequency. Seedlings with more tillers had greater survival probabilities, but tiller number was unaffected by defoliation. Further research may elucidate mechanisms seedlings use to compensate for or benefit from defoliation. In the meantime, managers should aim to select defoliation-tolerant species if they anticipate herbivory will be problematic for restoration sites.

Background: Annual grass invasion and dominance creates a self-sustaining cycle that promotes wildfires and reduces forage abundance. Restoring native plant species to annual grass-invaded ...

Rangeland seeding practices in the Intermountain western United States are predominantly implemented in the year immediately following wildfire for the purposes of Emergency Stabilization and Rehabilitation (ESR). This necessarily links restoration and rehabilitation outcomes to the probability of a single year providing sufficiently favorable microclimatic conditions for desirable plant establishment. Field research studies in rangeland restoration are also typically of limited duration, and published results may not represent the full spectrum of conditions likely to be experienced at a given site. We propose that location-specific and temporal weather analysis may enhance the interpretation of historical planting data, support expanded inferences from short-term field studies, and facilitate meta-analysis of diverse field studies in rangeland restoration. We describe access and use of new databases and tools that can be used to characterize and rank weather and soil-microclimatic variables and suggest some standard graphs and weather metrics to establish a longer-term perspective for the interpretation of rangeland restoration outcomes. Tools of this type may also be useful in the interpretation of a wide range of agricultural and natural resource applications that are driven by similar weather inputs, particularly in arid and semiarid systems that exhibit high annual and seasonal variability in precipitation and temperature.

Hydrothermal (HT) models can be used to characterize seed germination response to field-variable conditions of temperature (T) and water potential (Ψ). Hydrothermal response data are relatively difficult to generate, which limits their utility for large-scale comparisons of inter- and intraspecies germination response. Previous studies have hypothesized that HT germination response can be estimated using a simple model for thermal-time accumulation above a fixed threshold of environmental Ψ (wet-thermal [WT] model). The purpose of this study was to test this hypothesis by explicitly comparing HT and WT germination rates and estimated cumulative germination response of 13 rangeland grass seedlots under simulated conditions of field-variable T and Ψ. We used a 44-yr weather record to parameterize a seedbed-microclimate model for estimation of hourly T and Ψ at seeding depth for a sandy loam soil type at the Orchard field test site in southwestern Ada County, Idaho. Hydrothermal and WT germination responses for each hour of the simulation were estimated for 13 range grass seedlots. We found that overestimation of germination rate by thermal accumulation at low Ψ contributed relatively little to WT model error rates, and that >95% of the variability in predicted germination response could be explained by WT germination response above a Ψ threshold of −0.3 to −0.5 MPa. Given the pulse-like nature of favorable germination conditions in the field, this modeling approach may have immediate and wide potential application, as there are a relatively large number of thermal-germination datasets currently available for rangeland plant species.

High disturbance frequency, low water availability, and advantageous growth mechanisms of invasive annual compared to native perennial grasses reduce native grass establishment throughout arid rangelands. Modifying seeding dispersal processes, including seeding rate and time, may increase native grass recruitment by influencing safe site occupation. A better understanding of seedling development through life history stages and the ecological processes occurring during these stages may be necessary to comprehend modified dispersal dynamics on plant community assembly. We tested the effects of spring vs. fall annual grass seeding times, adding water, and varying annual and perennial grass propagule pressure on perennial and annual grass recruitment in an eastern Oregon shrub-steppe ecosystem. Across species, survival rates were lowest between germination and emergence stages. However, perennial grass germination rates were highest when perennials were seeded with annual grasses in autumn. Perennial grass recruitment was generally low, especially when annual grass propagule pressure was higher than 150 seeds m−2. Although, by the second growing season, perennial grasses had the highest density when perennials were seeded with annuals in autumn and water was added. Consequently, modifying native perennial grass dispersal, like priority autumn seeding and increasing propagule pressure, should produce higher perennial grass recruitment across arid lands.

Our ability to restore rangelands is limited, and it is unknown if seedling herbivory on its own, or in interaction with other stressors, is a major contributor to restoration failure. To address this, we conducted two experiments: a No Defoliation (ND) experiment (n = 48), in which seedlings from three perennial grasses (crested wheatgrass [Agropyron cristatum {(L.} Gaertn.], bluebunch wheatgrass [Psuedoroegnaria spicata {Pursh} A. Love], Sandberg bluegrass [Poa secunda J Presl]) were subjected to wet and dry water regimes for 4 mo, and a concurrent Defoliation (D) experiment (n = 95), in which seedlings were factorially assigned to two defoliation treatments—frequency (LOW, HIGH) and intensity (30% vegetation removal, 70% vegetation removal). Indicators of seedling performance were aboveground and belowground biomass (AGB and BGB), root:shoot ratio, tillering, and mortality. The effect size statistic, Hedge’s g, allowed for comparisons between performance measures. Water stress induced reductions in most performance measures: BGB (g = ND: –1.3; D: –1.6), root:shoot ratio (g = ND: n.s.; D: –0.2), and tillering (g = ND: –1.7; D: –1.2), though not significantly for all species. For ABG, water stress interacted with defoliation, reducing performance less at an intensity of 70% (g = –2.0) as opposed to 30% (g = –3.0), but not always significantly in the former. Water stress also caused less reduction in AGB when no defoliation occurred (ND: –0.8; g = D: –2.5). Intensity and frequency of defoliation interacted; seedlings were generally resistant to reductions in performance except at high frequency, 70% defoliation. Agropyron cristatum and P. spicata displayed similar sensitivity to treatments, mostly in terms of changes in AGB and BGB, while P. secunda also experienced increased mortality and reduced tillering. If these differences in sensitivity result in differential survival, herbivory could impact species postrestoration population demographics.

Increasing extremes in climate related weather events pose a major threat to plant recruitment in drylands. Research has shown facilitation effects by shrubs to improve recruitment in arid regions, however it remains unclear if these effects vary between soil types, early life stages and in both severe precipitation and drought events. We test if shrubs facilitate abundance of both seedlings and juveniles between two soil types in artificial high precipitation, ambient and severe drought conditions. When the effect of shrubs was considered, seedling and juvenile responses were similar between sites. Shrubs increased seedling abundance by 40.9% in drought. In high precipitation, shrubs increased seedling abundance by 20% at one site and juvenile abundance 15% at both sites. These findings support the notion that shrubs can improve recruitment in both severe precipitation and drought years, but the strength of this effect varies with soil. Our results indicate that resource islands generated by shrubs in high precipitation years, may be an important factor driving population dynamics in arid systems as years oscillate between wet and dry.

Compensatory increases in net photosynthetic assimilation rates (Anet) following herbivory are well documented in adult rangeland grasses but have not been quantified in bunchgrass seedlings, which may be more sensitive to tissue loss than established plants. To address this, we twice removed 30% and 70% leaf area of seedlings of crested wheatgrass (Agropyron cristatum [L.] Gaertn., var. Hycrest II) and the native bluebunch wheatgrass (Psuedoroegnaria spicata [Pursh] A. Love, var Anatone) and compared Anet and aboveground and belowground growth of these to unclipped control plants. Compensatory Anet occurred only after the second clipping, roughly 1 month after the first, and was similar in magnitude and duration between species and treatments, ca. 26% higher than control plant Anet for 2 weeks following clipping. Despite similar compensatory Anet between species, increases in Anet were more proportional with increased stomatal conductance to water vapor (gs) in crested wheatgrass. This resulted ...

Integration of knowledge regarding impacts of historical cultivation on soils for restoration planning is limited even though these legacies can affect land productivity and future land uses for decades. Old fields are often actively transformed through restoration, afforestation, or rehabilitation seeding. Rehabilitation seeding with the introduced perennial grass crested wheatgrass (Agropyron cristatum) was employed on approximately 2 million hectares in the western United States, including old fields in the Great Basin desert region. Seeding continues to be the primary treatment in restoration today, yet a minimal amount is known regarding how the underlying cultivation legacies affect these soils over the long term. We studied sites where rehabilitation seedings overlapped old fields and adjacent noncultivated land to compare soil properties including soil texture, pH, soil organic carbon (SOC), nitrogen (N), and C:N ratios. Because these sites were identical in all aspects except former culti...

Plant reproduction is highly sensitive to stress from severe weather. While facilitation has been shown to buffer negative impacts along stress gradients, less is known about facilitating plant reproduction in drought periods. Because intensity and frequency of drought are predicted to increase, plant reproductive facilitation has important implications for a species ability to adapt to changes in climate. Our primary study objective is to test if nurse shrubs act as reproductive micro-refugia across soil types, by improving reproductive potential of perennial bunchgrass neighbors subjected to severe drought. To investigate this objective, we designed a fully factored study testing direct interaction between shrub and bunchgrasses in eastern Oregon sagebrush steppe, at two sites with different soil types. The study consisted of six simple effect treatments combining three moisture regimes (moist, ambient, and drought) with two shrub conditions (shrub intact or shrub removed). Our results indicate when facilitation of reproductive potential occurs, it occurs strongly and particularly in drought, consistent with the stress gradient hypothesis (SGH), where several species produced at least 54% more inflorescences in the presence of shrub neighbors. In addition, we found facilitation to be consistent with the SGH at the species level likely reflecting differences in plant strategy and perception of strain, but to follow alternative SGH models more closely at the site level where facilitation declined on the drier soil. Ultimately, our findings highlight the importance of facilitation in improving plant reproductive potential in drought, and support the role of nurse shrubs as micro-refugia in a changing climate.

Sagebrush steppe ecosystems in the western United States are characterized by harsh environmental conditions with high annual and seasonal variability in both precipitation and temperature. Environmental variability contributes to widespread failure in establishing stands of desired species on degraded and invaded landscapes. To characterize seasonal microclimatic patterns and planting date effects on restoration outcomes, we evaluated long-term simulations of seed germination response of cheatgrass (Bromus tectorum L.), bottlebrush squirreltail (Elymus elymoides [Raf] Swezey), and Idaho fescue (Festuca idahoensis Elmer) to annual patterns of soil temperature and moisture. Extremely high annual variability in both the conditions favorable for germination and patterns of post-germination drought and thermal stress make it difficult to justify general inferences about seedbed treatment and planting date effects from individual, short-term field studies. We discuss the interpretation of individual-year and seasonal plant establishment factors and offer a mechanistic model for interpreting planting date and year effects on initial seedling establishment. Historical ranking and mechanistic descriptions of individual-year seedbed conditions may allow for expanded inferences through meta-analysis of limited-term field experiments.

Seed dispersal dynamics strongly affect plant community assembly in restored annual grass—infested ecosystems. Modifying perennial grass seeding rates and frequency may increase perennial grass establishment, yet these impacts have not yet been quantified. To assess these effects, we established a field experiment consisting of 288 plots (1 m2) in an eastern Oregon annual grass—dominated shrubsteppe ecosystem. In this study, the amount, timing, and frequency of perennial grass seeding events, soil moisture availability, and annual grass seed bank density were manipulated. We found that more frequent perennial grass seeding events combined with high perennial grass seeding rates produced the highest perennial grass density and biomass 2 years following seeding. However, we also found that if annual grass seed density was 1500 seeds · m-2 or higher, perennial grass density and biomass decreased, regardless of seeding strategy. Because of this finding, it appears that a threshold is crossed between...

Weed prevention is recognized as one of the most cost-effective management strategies for invasive plants. In the field of invasive plant management increasing emphasis is being directed toward proactive management. However, land managers are still somewhat reluctant to aggressively employ prevention programs. Part of this reluctance could be due to lack of understanding of what a comprehensive prevention program entails. The purpose of this paper is to improve strategic decision-making for site-specific prevention programs, such as those on ranches or in watersheds. Our interest is in advancing prevention planning for land managers—the people who are faced with the constant pressure of potential invasive species infestations on a day-to-day basis. To facilitate more widespread use of prevention programs we are proposing definitions for key terminology to standardize and facilitate communication about prevention programs. Additionally, we present a flow model with the steps necessary to successfully implement such programs. The model has three categories from which specific prevention planning occurs: (1) education, (2) early detection and eradication, and (3) interruption of movement. The flow model directs users through a series of interlinked steps. Finally, we provide a case study in which a ranch manager implemented a prevention program using this framework. By using this model, managers are poised to conduct more strategic planning. This model also has applications in outreach and education programs to assist land managers in prevention planning.

Prevention programs are often assumed to be the most cost-effective method for managing invasive plants. However, there is very little information available about economic and biological factors that determine the forage benefits resulting from prevention programs. We developed an easy to use economic model to assess potential savings in livestock forage that might result from implementing prevention programs. The model can be used to determine potential loss in forage production caused by invasive plants and to estimate potential income savings by preventing invasive plant infestations. The model compares a prediction of populations with and without a prevention program using a logistic growth function. Animal unit month (AUM) price and interest rates are the primary economic input variables. The primary biological input variables are amount of invasive plant utilization, size of the initial infestation, and the spread rate with and without prevention. Our model suggests that as the AUM price increases and/or the interest rate decreases, the total savings increases for each AUM that was protected through a prevention program. The model also shows savings per AUM increases as the size of the initial infestation decreases, suggesting that prevention should focus on eliminating seed sources and seed production early in the program. Using our model inputs, the savings per AUM was about $9.20 for each percent reduction in spread rate over 100 yr.

Rangeland management is largely focused on managing vegetation change. Objectives may include managing against change if the desired vegetation is in place, or attempting to create a shift in vegetation if the desired plant community is not present. There is a rich body of research documenting influences of disturbance and management on rangeland vegetation. However, in many cases the information is largely observational and does not identify mechanisms driving change. We propose using the regeneration niche concept to more effectively predict when vegetation change is possible and to suggest successional direction. Simply stated, as plants die and leave gaps in the community, recruitment of new individuals will dictate successional direction. Recruitment requires that propagules are present, that the propagules find safe sites in which to establish, and that the seedlings and young plants are able to compete with existing vegetation and survive. In many rangeland communities, perennial bunchgrasses are a key to stability and invasion resistance. Existing literature shows that most rangeland bunchgrasses have average life spans of 10 yr or less, so periodic recruitment is necessary to maintain communities in which they are a major component. Disturbance can influence plant population dynamics, and we suggest classifying disturbances based on how they influence mortality and recruitment. We also suggest that more emphasis be placed on the concept of critical transitions and less on the degree of disturbance per se. In other words, a small disturbance at the wrong point in community composition (low plant density and high gap size for example) can cause a transition, whereas major disturbance in a high condition community may yield little risk of transition. We suggest that a focus on mortality and recruitment will provide a mechanistic approach for predicting vegetation change and making management decisions. We refer to this approach as recruitment-based management.

Summary Seeding native plants is a key management practice to counter land degradation across the globe, yet the majority of seeding efforts fail, limiting our ability to accelerate ecosystem recovery. Recruitment requires transitions through several seed and seedling stages, some of which may have overriding influences on restoration outcomes. We lack, however, a general framework to understand and predict differences in these critical demographic processes across species. Functional traits influence fitness, and consequently, trait variation could provide the basis for a framework to explain and predict variation in life stage transition probabilities. We used seed and seedling traits, and field probabilities of germination, emergence, seedling establishment, and survival for 47 varieties of drylands grasses under two watering treatments to identify critical life stage transitions and quantify the effect of traits on cumulative survival through the first growing season. Variation in germination and emergence probabilities explained over 90% of the variation in cumulative survival regardless of seedling survival probabilities or watering treatment, with emergence probability being the strongest predictor of cumulative survival. Coleoptile tissue density and seed mass had significant effects on emergence and germination, respectively, explaining 10–23% of the variation in transition probabilities. Synthesis and applications. While the majority of functional trait work has centred on linking leaf and root traits to resource acquisition and utilization, our study demonstrates that traits associated with germination and emergence may have prevailing influences on restoration outcomes. A portion of these traits have been examined, but there is substantial opportunity to identify other key traits driving these demographic processes. These advancements will underpin our ability to develop trait-based frameworks for overcoming recruitment barriers and facilitating recovery of degraded systems across the globe.

Plant invasion and restoration outcomes are largely driven by the timing and magnitude of seed dispersal, and by the performance of dispersed species in an environment. Because seed dispersal controls recruitment of newly arriving species and facilitates safe site occupation, assembly will differ depending on seed dispersal processes and variable environmental conditions. The objective of this study was to identify how annual and perennial grasses assembled when dispersal times, propagule pressure, and water availability were modified. To assess these effects, we conducted a field experiment in an annual grass invaded shrub-steppe ecosystem in eastern Oregon. We tested the effects of seeding annual and perennial grasses in autumn or delaying annual grass seeding until spring, adding water, and varying annual and perennial grass seeding rate by 150, 1,500, 2,500, or 3,500 seeds m−2 on perennial and annual grass seedling emergence through time and final density and biomass. Providing perennial grasses a priority effect by delaying annual grass seeding until spring initially facilitated perennial grass establishment, but this effect did not persist into the second growing season. We found that if annual grass propagule pressure exceeded 150 seeds m−2, perennial grass recruitment was limited. In addition, higher water availability increased perennial grass establishment, but was dependent upon annual grass propagule pressure. These findings suggest that seeding perennial grasses into annual grass dominated systems is more dependent upon the existing propagule pressure of annual grasses than the priority effects of perennial grasses, the propagule pressure of perennial grasses, or water availability.

Invasive annual grasses tend to construct thinner and less dense root and leaf tissue than native perennial grasses. This allows invasive annuals to grow faster and produce more biomass in the arid grasslands of the United States. Based on these differences we tested the hypotheses that: 1) Competitive effects of the native perennial on the invasive annual will increase as plant developmental stage increases and as drought stress increases. 2) Drought stress will reduce the competitive effect of invasive annuals on native perennials proportionately more than drought stress reduces the competitive effect of native perennials on the invasive annual. 3) Facilitation among native perennial grass seedlings will decrease as developmental stage increases. Competitive effects of native squirreltail, on invasive medusahead, increased as the initial developmental stage of squirreltail increased, but not vice versa. Drought stress reduced the competitive effect of medusahead on squirreltail target biomass more than drought stress reduced the competitive effect of squirreltail on medusahead target biomass. While both squirreltail and medusahead displayed intraspecific facilitation, the net effect of their interspecific interaction was negative for both species. Habitat amelioration manifests itself differently depending on species traits, and can create conditions that simultaneously benefit one species while hindering another.

Little is known about how cultivation legacies affect the outcome of rehabilitation seedings in the Great Basin, even though both frequently co-occur on the same lands. Similarly, there is little known about how these legacies affect native species reestablishment into these seedings. We examined these legacy effects by comparing areas historically cultivated and seeded to adjacent areas that were seeded but never cultivated, for density of seeded crested wheatgrass (Agropyron cristatum [L.] Gaertn.) and native perennial grasses, vegetation cover, and ground cover. At half of the sites, historically cultivated areas had lower crested wheatgrass density (P ,0.05), and only one site had a higher density of crested wheatgrass (P ,0.05). Likewise, the native shrub Wyoming big sagebrush (Artemisia tridentata Nutt. subsp. wyomingensis Beetle & Young) had lower cover (P ,0.05) in historically cultivated areas at half the sites. Sandberg bluegrass (Poa secunda J. Presl.) density was consistently lower in historically cultivated areas relative to those seeded-only. At sites where black greasewood (Sarcobatus vermiculatus [Hook.] Torr.) and bottlebrush squirreltail (Elymus elymoides [Raf.] Swezey) were encountered, there was either no difference or a higher density and cover within historically cultivated areas (P ,0.05). Likewise, cover of exotic forbs, especially halogeton (Halogeton glomeratus [M. Bieb.] C. A. Mey.), was either not different or higher in historically cultivated areas (P ,0.05). Bare ground was greater in historically cultivated areas at three sites (P ,0.05). These results suggest that cultivation legacies can affect seeding success and re-establishment of native vegetation, and therefore should not be overlooked when selecting research sites or planning land treatments that include seeding and or management to achieve greater native species diversity.

Multiple species of annual grasses are invading sagebrush-steppe communities throughout the western United States. Most research has focused on dominant species such as Bromus tectorum (cheatgrass), yet other, less studied annual grasses such as Taeniatherum caput-medusae (medusahead) and Ventenata dubia (ventenata) are spreading rapidly. Future precipitation regimes are expected to have less frequent but more intense rain events, which may affect soil moisture availability and favor these ‘newer’ invasives over cheatgrass. We conducted a full factorial, growth chamber study examining the effects of two watering regimes (small/frequent, large/infrequent rain pulses) across nine soil types on the growth of cheatgrass, medusahead and ventenata. We tested a hypothesis that medusahead or ventenata would have greater growth than cheatgrass with larger/infrequent rain events. The two watering regimes had relatively strong effects on soil water content, but generally did not impact plant growth. In contrast, variation in soil properties such as clay content, pH and soil N correlated with a two- to four-fold change in plant growth. The three invasive grass species generally respond similarly to changes in precipitation regimes and to edaphic factors. Nevertheless, medusahead had 30–40% overall greater root growth compared to the other species and a 15% increase in root growth in response to the large/infrequent watering treatment. Our findings reveal that 1) greater biomass allocation to roots and 2) greater responsiveness of root growth to differing precipitation regimes of medusahead may favor its ecological success over other invasive annuals under future climate scenarios.

Because invasive annual grasses can strongly influence soil resource availability and disturbance regimes to favor their own persistence, there is a great need to understand the interrelationships among invasive plant abundance, resource availability, and desirable species prominence. These interrelationships were studied in two salt desert sites where the local abundance of downy brome (Bromus tectorum L.) varied spatially and increased more than 12-fold over a 3-yr period. We measured downy brome percentage cover, resource availability, and soil chemical and physical properties within 112 plots per site and found significant negative associations between downy brome abundance and both soil water content (P ,0.05; r¼� 0.27 to � 0.49) and nitrate accumulation (P ,0.05; r¼� 0.34 to � 0.45), which corroborated with the direction and strength of multivariate factor loadings assessed with principal component analysis. We then applied factorial combinations of prescribed burning and preemergence herbicide at management-relevant scales (i.e., 6 to 46 ha) as well as biomass removal to smaller plots (12.25 m 2 ) at both sites to determine their impact on downy brome, soil resources, and resident plant species. Burning and herbicide applications, especially when combined, significantly reduced downy brome cover (P¼0.069 to 0.015), which in turn increased soil nitrate accumulation and water content in the spring. Furthermore, for one shrubland site that was seeded 6 yr previously, the combination of burning and herbicide treatments significantly increased perennial grass percentage cover in the 2 yr posttreatment (P ,0.05). Results not only demonstrate the strong relationships between downy brome abundance, soil resources, and residence species for impoverished salt desert shrub ecosystems, but also suggest that restoration and management efforts must include tactics that facilitate resource use by the residual plant community or establish a greater abundance of species capable of high resource acquisition in the spring.

Advancing our ability to use invasive plants for producing commodities is central to the agricultural industry. Our objective was to evaluate Russian knapweed (Acroptilon repens [L.] DC.) as a winter feed supplement for ruminant livestock. In Experiment 1, we utilized three ruminally cannulated steers in a completely randomized design to compare the ruminal degradation characteristics of alfalfa and Russian knapweed. In the second experiment, Russian knapweed and alfalfa were compared as protein supplements using 48 midgestation, beef cows (530 65 kg) offered ad libitum hard fescue (Festuca brevipila Tracey) straw in an 84-d study. Treatments included an unsupplemented control and alfalfa or Russian knapweed provided on an isonitrogenous basis. In Experiment 1, the rate and effective degradability of neutral detergent fiber was greater for alfalfa compared with Russian knapweed (P � 0.02). Ruminal lag time for NDF (period before measurable disappearance began) was greater for knapweed (P¼0.03). Soluble nitrogen, rate of N degradation, rumen degradable N, and effective degradability of N were all greater for alfalfa compared with Russian knapweed (P ,0.01). In Experiment 2, supplementation increased (P ,0.01) cow weight gain and BCS compared to the unsupplemented control with no difference between alfalfa and Russian knapweed (P¼0.47). There was no difference (P¼0.60) in the quantity of straw offered between the unsupplemented cows and supplemented groups, but alfalfa fed cows were offered approximately 11% more (P¼0.03) than Russian knapweed-fed cows. Total DM offered to cows was greater (P ,0.01) for supplemented compared with unsupplemented cows with no difference noted between alfalfa and Russian knapweed (P¼0.79). Russian knapweed is comparable to alfalfa as a protein supplement for beef cows consuming low-quality forage. Using Russian knapweed as a nutritional supplement can help solve two major production problems; managing an invasive weed, and providing a feedstuff that reduces an impediment in livestock production systems.

Our objective was to evaluate the cost/benefit of a single herbicide application or targeted grazing of invasive annual grasses during restoration of partially invaded sagebrush steppe ecosystems used for livestock production. The cost/benefit model used is based on estimating the production of vegetation in response to implementing management and modeling cost/benefit economics associated with that prediction. The after-tax present value of added animal unit months (AUMs) obtained was lower than the present value of after-tax treatment costs after 20 yr for a single herbicide treatment, but higher than the present value of after-tax treatment costs for the grazing management scenario. Even at the highest weed utilization level, the value of added AUMs did not offset the cost of the treatment after 20 yr. However, the grazing treatment resulted in a value of added AUMs higher than the costs after 20 yr. Depending on the invasive weed utilization level, break-even points with targeted grazing occurred at anywhere from the first year to 7 yr. This assessment clearly shows that grazing management can be economically viable for managing annual grass-infested rangeland. In the future, models like the one used here can be improved by incorporating the rangeland management and restoration benefits on the wide variety of goods and services gained from rangeland.

Functional differences between native and exotic species potentially constitute one factor responsible for plant invasion. Differences in trait values between native and exotic invasive species, however, should not be considered fixed and may depend on the context of the comparison. Furthermore, the magnitude of difference between native and exotic species necessary to trigger invasion is unknown. We propose a criterion that differences in trait values between a native and exotic invasive species must be greater than differences between co-occurring natives for this difference to be ecologically meaningful and a contributing factor to plant invasion. We used a meta-analysis to quantify the difference between native and exotic invasive species for various traits examined in previous studies and compared this value to differences among native species reported in the same studies. The effect size between native and exotic invasive species was similar to the effect size between co-occurring natives except for studies conducted in the field; in most instances, our criterion was not met although overall differences between native and exotic invasive species were slightly larger than differences between natives. Consequently, trait differences may be important in certain contexts, but other mechanisms of invasion are likely more important in most cases. We suggest that using trait values as predictors of invasion will be challenging.

In a previous article, Beschta et al. (Environ Manag 51(2):474-491, 2013) argue that grazing by large ungulates (both native and domestic) should be eliminated or greatly reduced on western public lands to reduce potential climate change impacts. The authors did not present a balanced synthesis of the scientific literature, and their publication is more of an opinion article. Their conclusions do not reflect the complexities associated with herbivore grazing. Because grazing is a complex ecological process, synthesis of the scientific literature can be a challenge. Legacy effects of uncontrolled grazing during the homestead era further complicate analysis of current grazing impacts. Interactions of climate change and grazing will depend on the specific situation. For example, increasing atmospheric CO₂ and temperatures may increase accumulation of fine fuels (primarily grasses) and thus increase wildfire risk. Prescribed grazing by livestock is one of the few management tools available for reducing fine fuel accumulation. While there are certainly points on the landscape where herbivore impacts can be identified, there are also vast grazed areas where impacts are minimal. Broad scale reduction of domestic and wild herbivores to help native plant communities cope with climate change will be unnecessary because over the past 20-50 years land managers have actively sought to bring populations of native and domestic herbivores in balance with the potential of vegetation and soils. To cope with a changing climate, land managers will need access to all available vegetation management tools, including grazing.

Cultivation legacies affect native vegeta- tion in old fields of the Great Basin, USA for nearly a century after these fields are abandoned. We hypoth- esized that cultivation lowered soil nutrients and that this legacy would differentially impact plant perfor- mance of four representative Great Basin species. To test these hypotheses, we compared soil nutrients (C, N, P, K, Mg and Ca) between two formerly cultivated and adjacent noncultivated sites in two soil series. We then compared the plant growth and foliar nutrient content of an exotic grass (Bromus tectorum L.), two native grasses (Elymus elymoides (Raf.) Swezey and Achnatherum hymenoides (Roem. and Schult.) Barkworth), and a native forb (Sphaeralcea grossu- lariifolia (Hook. and Arn.) Rydb) grown in these soils in the greenhouse and in the field. Only one sampling site had reduced soil nutrients associated with culti- vation legacies, where most of the negative effects on plant performance were found. E. elymoides appeared to be less affected by cultivation legacies than did A. hymenoides, which had a reduced survivorship and 20 % less above-ground biomass in cultivated soils. No species, including B. tectorum, were favored by cultivation. Our findings suggest that cultivation legacies can affect plant performance of different species in different ways and that altered soil nutrients may interact with other abiotic and biotic cultivation legacies in complex ways.

Within the sagebrush steppe ecosystem, sagebrush plants influence a number of ecosystem properties, including nutrient distribution, plant species diversity, soil moisture, and temperature, and provide habitat for a wide variety of wildlife species. Recent increases in frequency and size of wildfires and associated annual grass expansion within the Wyoming big sagebrush alliance have increased the need for effective sagebrush restoration tools and protocols. Our objectives were to quantify the success of Wyoming big sagebrush transplants relative to transplant stock (nursery seedlings vs. wildlings) across different ecological sites and vegetation types and to test the hypothesis that reduction of herbaceous vegetation would increase survival of transplanted sagebrush. We used a randomized block (reps¼5) design at each of three sites—1) cheatgrass dominated, 2) native plant dominated, and 3) crested wheatgrass dominated—near Elko, Nevada. Treatments included plant stock (nursery stock or locally harvested wildlings) and herbicide (glyphosate) to reduce competition from herbaceous vegetation. Transplants were planted in the spring of 2009 and 2010 and monitored for survival. Data were analyzed for site and treatment effects using mixed-model ANOVA. Surviving plant density at and 2 yr postplanting was generally highest (up to 3-fold) on the native site (P , 0.05). Density of surviving transplants was almost 3-fold higher for nursery stock on most sites for the 2009 planting, but differences in survival by planting stock were minimal for the 2010 planting. Glyphosate application increased surviving plant density up to 300% (depending on site) for both years of planting. High labor and plant material investments (relative to traditional drilling or broadcasting) may limit the size of projects for which sagebrush transplants are practical, but these costs may be partially offset by high success relative to traditional methods. Our data indicate that sagebrush transplants can be effective for establishing sagebrush on depleted sites.

Summary 1. Drylands support over 2 billion people and are major providers of critical ecosystem goods and services across the globe. Drylands, however, are one of the most susceptible biomes to degradation. International programmes widely recognize dryland restoration as key to combating global dryland degradation and ensuring future global sustainability. While the need to restore drylands is widely recognized and large amounts of resources are allocated to these activities, rates of restoration success remain overwhelmingly low. 2. Advances in understanding the ecology of dryland systems have not yielded proportional advances in our ability to restore these systems. To accelerate progress in dryland restoration, we argue for moving the field of restoration ecology beyond conceptual frameworks of ecosystem dynamics and towards quantitative, predictive systems models that capture the probabilistic nature of ecosystem response to management. 3. To do this, we first provide an overview of conceptual dryland restoration frameworks. We then describe how quantitative systems framework can advance and improve conceptual restoration frameworks, resulting in a greater ability to forecast restoration outcomes and evaluate economic efficiency and decision-making. Lastly, using a case study from the western United States, we show how a systems approach can be integrated with and used to advance current conceptual frameworks of dryland restoration. 4. Synthesis and applications. Systems models for restoration do not replace conceptual models but complement and extend these modelling approaches by enhancing our ability to solve restoration problems and forecast outcomes under changing conditions. Such forecasting of future outcomes is necessary to monetize restoration benefits and cost and to maximize economic benefit of limited restoration dollars.

One of the most challenging problems for land managers is advancing infestations of invasive weeds. Treating weeds is often really only treat- ing a symptom. A fundamental tenet of Eco- logically Based Invasive Plant Management (EBIPM) is that managers must treat the underlying ecological cause of inva- sion to successfully direct vegetation dynamics toward desired species. DOI: 10.2458/azu_rangelands_v34i6_sheley

Preventing invasion by nonnative or undesirable plant species and controlling ongoing invasion are two key management issues on rangelands world- wide. Invasive species cause considerable ecological and economic cost, including lost biodiversity and reduced productivity. Invasive plants cause approximately $5 billion in direct losses to ranchers and range managers each year.1 Despite the ecological and economic costs of invasive plant species, few widely effective solutions to these problems have been developed. Tools to address the problem such as graz- ing strategies, herbicide applications, prescribed burning, and rangeland seeding have only limited success, failing as often as succeeding because invasive plant management is much more complex than merely reducing weed abundances.2 It is becoming clear that numerous biological and nonbiological factors determine if invasive species management can be suc- cessful. DOI: 10.2458/azu_rangelands_v34i6_leffler

D esigning restoration strategies based on succes- sional management requires an initial assessment of the functional status of ecological attributes across a management unit. Seriously damaged rangelands may not have the capacity for self-repair and often experience continued degradation. 1 Over the past 20 years, there has been a concentrated effort to develop a practical and effective protocol for assessing the status of rangeland health and managing vegetation change in heavily degrad- ed rangelands. In the mid-1990s, a US National Research Council panel and a Society for Range Management task group advocated the use of early warning indicators to assess soil stability, water cycle, energy ow, nutrient cycling, and the resilience and resistance of plant communities to change following disturbances. Currently a widely adopted range- land health assessment tool in the United States is “Inter- preting Indicators of Rangeland Health, version 4,” described by Pyke et al. 2 and Pellant et al. 3 This qualitative rangeland health assessment protocol provides early warnings of altered ecological processes and can help identify potential candidate locations for establishing quantitative monitoring plots for long-term trend studies. DOI: 10.2458/azu_rangelands_v34i6_vasquez

The need for practical revegetation strategies for managing medusahead-infested rangeland is substantial and unmet. Our objective was to test the potential for using the single-entry approach (simultaneous application of herbicide and seed with one entry) developed for other invasive-weed infested systems for revegetating medusahead-infested rangeland. Since areas infested with medusahead are frequently burned and burning may help control medusahead and provide a more suitable seedbed for desired species, we also tested the single-entry approach in conjunction with burning. Our primary hypotheses were that (1) the combination of imazapic and seeding would provide best establishment of desired species and (2) burning would enhance the efficacy of imazapic on medusahead and enhance seedling establishment. Treatments included three seeding rates (none, 13.2, or 25.0 kg ha−1 of an even mixture of all species), two herbicides (0 and 52 g a.i. ha−1 imazapic; with and without), and two burning regimes (burned, not burned) applied mid-October 2006 on two sites. In late July, 2008 through 2010, plant density and biomass were sampled. We found that the simultaneous application of imazapic and seeding resulted in establishment of desired species where they were absent. Imazapic application without seeding increased perennial bunchgrass density where enough residual plants existed before treatment. Burning tended to improve the control of medusahead with imazapic and promoted desired species. Even though follow-up treatments may be necessary, applying imazapic and seeding in a single-entry approach may provide a more practical initial revegetation strategy than multi-entry approaches on rangeland devoid of desired residual species. This procedure should reduce the costs of treatment application and make revegetating annual grass-infested rangeland more affordable.

Producers facing infestations of invasive annual grasses regularly voice the need for practical revegetation strategies that can be applied across broad landscapes. Our objective was to determine the potential for scaling up the single-entry approach for revegetating medusahead-infested rangeland to broader, more heterogeneous landscape-scale revegetation of winter annual grass–infested rangeland. We hypothesized, when applied on a highly variable landscape scale, the combination of imazapic and seeding would provide highest abundance of perennial grasses and lowest amount of annual grasses. Treatments included a control, seeding of crested wheatgrass (‘Hycrest’) and Sandberg's bluegrass, spraying (60 g ai ha−1 imazapic), and a simultaneously applied combination of spraying and seeding. The HyCrest and Sandberg's bluegrass seeding rates were 19 and 3.4 kg ha−1, respectively. The treatments were applied to large plots (1.4 to 8 ha) and replicated five times, with each replication located in different watersheds throughout southeastern Oregon. This study shows that the single-entry approach can be scaled up to larger landscapes, but variation within establishment areas will likely be high. This procedure should reduce the costs over multientry treatment applications and make revegetating annual grass–infested rangeland across landscapes more affordable.

Invasive plants have many serious impacts on range- land throughout the world. They can displace desir- able species, alter the ecological function of the eco- system, destroy wildlife habitat, decrease productivity, and facilitate frequent wild res, with impacts costing bil- lions of dollars annually. Major invasive plant management programs are established in most countries. Although a sub- stantial effort to manage plant invasions is underway in the United States, the conservation bene ts are questionable because these programs are expensive and risky to imple- ment for the long term. Ecologically Based Invasive Plant Management (EBIPM) has the potential to provide an im- proved decision-making process, but managers are often uncertain about how to get started implementing this type of program. DOI: 10.2458/azu_rangelands_v34i6_smith