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Considerable uncertainty remains regarding grazing-induced influences on soil organic carbon (SOC) sequestration in semiarid grassland ecosystems due to three important complications associated with studying such effects: (1) Ecologically meaningful shifts in SOC pools attributable to grazing are difficult to detect relative to inherently large grassland SOC pools, (2) a lack of baseline (pre-treatment) data, and (3) frequent lack of or limited replication of long-term grazing manipulations. SOC sequestration rates were determined in 74-year-old grazing exclosures and paired moderately grazed sites, established across a soil texture gradient, in the western North American shortgrass steppe in northeastern Colorado. We sampled soils (0–20 cm) from 12 exclosures and paired grazed sites to measure SOC concentration and soil radiocarbon ∆14C (‰); the latter allowed us to determine turnover of the SOC pool over a 7-decade period in the presence versus the absence of grazing. Removal of grazing for more than 7 decades substantially altered plant community composition but did not affect total soil C, SOC, soil ∆14C, SOC turnover rate, or total soil N. Grazing effect also did not interact with soil texture to influence any of those soil properties. Soil texture (silt + clay content) did influence total soil C and SOC, and total soil N, but not ∆14C or SOC turnover. Results provide evidence that long-term removal of grazing from semiarid grassland ecosystems in the western North American Great Plains does not enhance long-term SOC sequestration, despite changes in the relative dominance of C3 versus C4 grasses.

Rangelands of the western Great Plains of North America are complex social-ecological systems where management objectives for livestock production, grassland bird conservation, and vegetation structure and composition converge. The Collaborative Adaptive Rangeland Management (CARM) experiment is a 10-year collaborative adaptive management (CAM) project initiated in 2012 that is aimed at fostering science-management partnerships and data-driven rangeland management through a participatory, multistakeholder approach. This study evaluates the decision-making process that emerged from the first 4 yr of CARM. Our objectives were to 1) document how diverse stakeholder experiences, epistemologies, and resulting knowledge contributed to the CARM project, 2) evaluate how coproduced knowledge informed management decision making through three grazing seasons, and 3) explore the implications of participation in the CARM project for rangeland stakeholders. We evaluated management decision making as representatives from government agencies and conservation nongovernmental organizations, ranchers, and interdisciplinary researchers worked within the CARM experiment to 1) prioritize desired ecosystem services; 2) determine objectives; 3) set stocking rates, criteria for livestock movement among pastures, and vegetation treatments; and 4) select monitoring techniques that would inform decision making. For this paper, we analyzed meeting transcripts, interviews, and focus group data related to stakeholder group decision making. We find two key lessons from the CARM project. First, the CAM process makes visible, but does not reconcile differences between, stakeholder experiences and ways of knowing about complex rangeland systems. Second, social learning in CAM is contingent on the development of trust among stakeholder and researcher groups. We suggest future CAM efforts should 1) make direct efforts to share and acknowledge managers’ different rangeland management experiences, epistemologies, and knowledge and 2) involve long-term research commitment in time and funding to social, as well as experimental, processes that promote trust building among stakeholders and researchers over time.

Experiments investigating grazing systems have often excluded ranch-scale decision making, which has limited our understanding of the processes and consequences of adaptive management. We conducted interviews and vegetation monitoring on 17 ranches in eastern Colorado and eastern Wyoming to investigate rancher decision-making processes and the associated ecological consequences. Management variables investigated were grazing strategy, grazing intensity, planning style, and operation type. Ecological attributes included the relative abundance of plant functional groups and categories of ground cover. We examined the environmental and management correlates of plant species and functional group composition using nonmetric multidimensional scaling and linear mixed models. After accounting for environmental variation across the study region, species composition did not differ between grazing management strategy and planning style. Operation type was significantly correlated with plant community composition. Integrated cow-calf plus yearling operations had greater annual and less key perennial cool-season grass species cover relative to cow-calf − only operations. Integrated cow-calf plus yearling ranches were able to more rapidly restock following drought compared with cow-calf operations. Differences in types of livestock operations contributed to variability in plant species composition across the landscape that may support diverse native faunal species in these rangeland ecosystems. Three broad themes emerged from the interviews: 1) long-term goals, 2) flexibility, and 3) adaptive learning. Stocking-rate decisions appear to be slow, path-dependent choices that are shaped by broader social, economic, and political dynamics. Ranchers described having greater flexibility in altering grazing strategies than ranch-level, long-term, annual stocking rates. These results reflect the complexity of the social-ecological systems ranchers navigate in their adaptive decision-making processes. Ranch decision-making process diversity within these environments precludes development of a single “best” strategy to manage livestock grazing.

Semiarid rangelands experience substantial interannual variability in precipitation, which can determine the relative abundance of species in any given year and influence the way that fire affects plant community composition and productivity. Long-term studies are needed to examine potential interactions between fluctuating community composition and the role of fire in these ecosystems. Here, we report on an 11-year (2006 to 2016) study of annual and triennial dormant-season prescribed fires in the semiarid shortgrass steppe of Colorado, USA. Productivity of the dominant C4 shortgrasses was not reduced by dormant-season burns in any year. The C3 annual grass, six-weeks fescue (Vulpia octoflora [Walter] Rydb.) was rare during the first 7 years (2006 to 2012) but, following drought in 2012, increased dramatically in unburned plots (2013 to 2016). Both spring and autumn annual burns reduced fescue biomass during 2014 to 2016 by an average of 87%. Autumn triennial burns prior to the 2013 and 2016 growing seasons similarly reduced fescue (86%), while spring triennial burns implemented prior to the 2012 and 2015 growing seasons did not. Results indicate that burning during fescue establishment can prevent proliferation, but burning two years later when fescue had reached peak abundance was ineffective. All three burn treatments that suppressed fescue subsequently enhanced C4 grass production. We suggest that rangeland managers be aware of the potential for sixweeks fescue germination and establishment during warm, wet winters that follow drought years, and consider the use of dormant-season prescribed fire to adaptively reduce negative impacts on forage production.

Advances in on-animal sensor technologies to monitor location and activity have enhanced the ability to study foraging decisions of free-ranging herbivores. Sensors monitoring jaw movements that quantify ingestive behaviours, such as the RumiWatch (RW) noseband sensor system, have primarily been used in indoor animal housing systems or structurally homogeneous, small pasture (paddock) environments. Continuously monitoring these ingestive behaviours in extensive and heterogeneous rangelands has not been previously conducted. We evaluated the accuracy of the RW noseband sensor system for two grazing seasons in 130-ha pastures (paddocks) composed of native, mixed-species plant communities in a semiarid environment. The noseband sensor was used to compare ingestive behavior at different sites and seasons characterized by varying sward complexity, stocking rate, and levels of forage limitation. We evaluated the noseband sensor against direct visual observations of yearling steers grazing with two different validation studies. First, the time duration of grazing recorded by the sensor was compared to direct visual observation data (Validation Study 1). A high correlation (rs = 0.95) for hourly grazing time resulted between the RW system and visual observations. Second, we examined the ability of the RW system to measure prehension bite rates in distinct plant communities varying in height and leaf angle (Validation Study 2). The accordance between direct observation and measurement by the RW system for bite rate improved from 2019 (Concordance Correlation Coefficient (CCC) = 0.71) to 2020 (CCC = 0.80) after modifications to improve the fit of the halter supporting the noseband sensor. Correlations between the sensor and visual observations increased by ∼17 % with this modification for grazing bouts in mixed-species and midgrass-dominated swards; correlations remained ∼10 % lower in shortgrass-dominated swards. Our results show that the RW system is an effective tool for monitoring free-ranging cattle grazing activity and quantifying bite rates in a heterogeneous rangeland ecosystem. Bite rate measurements are more accurate in swards with vertically oriented stems and leaves compared to lawn-like prostrate swards. Grazing bout length and rumination chew rate may represent behavioral indicators employed in managing animal performance in semiarid rangelands. Our validation study and experimental investigation indicate that the RW noseband sensor is a useful animal-borne sensor technology for research demanding sustained ingestion measurements across mixed-species forage communities.

As grassland birds of central North America experience steep population declines with changes in land use, management of remaining tracts becomes increasingly important for population viability. The integrated use of fire and grazing may enhance vegetation heterogeneity and diversity in breeding birds, but the subsequent effects on reproduction are unknown. We examined the influence of patch-burn grazing management in shortgrass steppe in eastern Colorado on habitat use and reproductive success of 3 grassland bird species, horned lark (Eremophila alpestris), lark bunting (Calamospiza melanocorys), and McCown's longspur (Rhynchophanes mccownii), at several spatial scales during 2011 and 2012. Although no simple direct relationship to patch-burn grazing treatment existed, habitat selection depended on precipitation- and management-induced vegetation conditions and spatial scale. All species selected taller-than-expected vegetation at the nest site, whereas at the territory scale, horned larks and McCown's longspurs selected areas with low vegetation height and sparse cover of tall plants (taller than the dominant shortgrasses). Buntings nested primarily in unburned grassland under average rainfall. Larks and longspurs shifted activity from patch burns during average precipitation (2011) to unburned pastures during drought (2012). Daily survival rate (DSR) of nests varied with time in season, species, weather, and vegetation structure. Daily survival rate of McCown's longspur nests did not vary with foliar cover of relatively tall vegetation at the nest under average precipitation but declined with increasing cover during drought. At the 200-m scale, increasing cover of shortgrasses, rather than taller plant species, improved DSR of larks and longspurs. These birds experience tradeoffs in the selection of habitat at different spatial scales: tall structure at nests may reduce visual detection by predators and provide protection from sun, wind, and rain, yet taller structure surrounding territories may host nest predators. Patch-burn grazing management in combination with other strategies that retain taller-structured vegetation may help sustain a diversity of breeding habitats for shortgrass birds under varying weather conditions.Published 2017. This article is a U.S. Government work and is in the public domain in the USA.

The Northern Great Plains (NGP) region of the USA—which comprises Montana, Wyoming, Colorado, North Dakota, South Dakota, and Nebraska—is a largely rural area that provides numerous ecosystem services, including livestock products, cultural services, and conservation of biological diversity. The region contains 25% of the Nation’s beef cattle and approximately one-third of the confined beef cattle, as well as the largest remaining native prairie in the US—the Northern Mixedgrass Prairie. With rising atmospheric CO2, the NGP is projected to experience warmer and longer growing seasons, greater climatic variability, and more extreme events (e.g., increased occurrence of large precipitation events). These climatic changes may affect livestock production both directly via physiological impacts on animals and indirectly via modifications to forage, invasion of undesirable plants, and increased exposure to parasites. This raises concerns about the vulnerability of grazing livestock operations and confined livestock operations to projected changes in mid- (2050) and late- (2085) twenty-first century climate. Our objectives are to (1) describe the NGP’s exposure to temperature and precipitation trends, inter-annual variability, and extreme events; (2) evaluate the sensitivity of beef cattle production to direct and indirect effects imposed by these projected climatic changes; and (3) provide a typology of adaptation strategies to minimize adverse consequences of projected changes and maximize beneficial consequences. Agricultural managers have developed considerable adaptive capacity to contend with environmental and economic variability. However, projected climatic changes, especially the increased frequency and magnitude of weather extremes, will require even greater adaptive capacity to maintain viable production systems. Consequently, regional vulnerability to projected climatic changes will be determined not only by ecological responses but also by the adaptive capacity of individual managers. Adaptive capacity in the NGP will differ from other regions, in part because projections suggest some opportunities for increased livestock production. Adaptations in both grazing and confined beef cattle systems will require enhanced decision-making skills capable of integrating biophysical, social, and economic considerations. Social learning networks that support integration of experimental and experiential knowledge—such as lessons learned from early adopters and involvement with science-based organizations—can help enhance decision-making and climate adaptation planning. Many adaptations have already been implemented by a subset of producers in this region, providing opportunities for assessment, further development, and greater adoption. Context-specific decision-making can also be enhanced through science-management partnerships, which aim to build adaptive capacity that recognizes multiple production and conservation/environmental goals.

Plant community responses to livestock grazing lack conformity across studies, even those conducted within similar ecosystems. Variability in outcomes can often be traced back to short-term or mid-term weather patterns, differences in grazing timing or intensity, or interactive effects of management and weather. Long-term experimental data are needed to determine how grazing intensity affects plant community composition in semiarid ecosystems where precipitation is low and highly variable. However, long-term grazing intensity experiments, particularly experiments with more than two grazing intensity treatment levels, are quite rare. We capitalized on one of the longest-term grazing studies, with 75 yr of sustained stocking rate treatments (none, light, moderate, and heavy), to identify long-term effects of livestock grazing on plant community composition in shortgrass steppe. Plant community composition was similar between moderately and heavily grazed pastures after 75 yr of continuous, season-long (May to October) grazing treatments, and heavy grazing did not extirpate cool-season perennial graminoids. These findings support the long-term sustainability of livestock grazing in the shortgrass steppe, which has high resistance to season-long heavy grazing. Conversely, ungrazed and lightly grazed pastures experienced relatively large shifts in plant community composition, especially in the past 25 yr. Light or no grazing was associated with increased abundance of cool-season perennial graminoids, as well as several weedy and invasive species. Moreover, across most grazing treatments, several aspects of plant community composition have been shifting directionally during the past 25 yr, which recent experiments in this grassland suggest may be a response to increasing atmospheric (CO2). The shortgrass steppe is not only tolerant of fairly high grazing intensities but also likely requires some level of grazing to resist invasion by weedy annuals and to maintain cover of blue grama, a highly drought-tolerant species.

Small-bodied terrestrial animals such as songbirds (Order Passeriformes) are especially vulnerable to hail-induced mortality; yet, hail events are challenging to predict, and they often occur in locations where populations are not being studied. Focusing on nesting grassland songbirds, we demonstrate a novel approach to estimate hail-induced mortality. We quantify the relationship between the probability of nests destroyed by hail and measured Level-III Next Generation Radar (NEXRAD) data, including atmospheric base reflectivity, maximum estimated size of hail and maximum estimated azimuthal wind shear. On 22 June 2014, a hailstorm in northern Colorado destroyed 102 out of 203 known nests within our research site. Lark bunting (Calamospiza melanocorys) nests comprised most of the sample (n = 186). Destroyed nests were more likely to be found in areas of higher storm intensity, and distributions of NEXRAD variables differed between failed and surviving nests. For 133 ground nests where nest-site vegetation was measured, we examined the ameliorative influence of woody vegetation, nest cover and vegetation density by comparing results for 13 different logistic regression models incorporating the independent and additive effects of weather and vegetation variables. The most parsimonious model used only the interactive effect of hail size and wind shear to predict the probability of nest survival, and the data provided no support for any of the models without this predictor. We conclude that vegetation structure may not mitigate mortality from severe hailstorms and that weather radar products can be used remotely to estimate potential for hail mortality of nesting grassland birds. These insights will improve the efficacy of grassland bird population models under predicted climate change scenarios.

Questions How does long-term exclusion of cattle grazing influence plant community composition in a semiarid grassland? Can spatial variation in the effects of cattle grazing exclusion be explained by variation in soil texture? Location The shortgrass steppe of northeastern Colorado, USA, located in the North American Great Plains. Method We used 16 long-term (72 yr) cattle exclosures to examine the effects of grazers on plant communities, and evaluate whether grazer effects interact with soil texture. Results Although shortgrass steppe communities are relatively unaffected by grazing in the short-term (1-2 decades), exclusion of cattle grazing for seven decades caused a compositional shift from dominance by a C4 shortgrass (Bouteloua gracilis) to co-dominance by a C3 midgrass (Pascopyrum smithii) and B. gracilis. The strength of this shift was highly variable across sites. Soil texture was correlated with the abundance of certain plant species, but did not explain variation in the magnitude of grazer effects. Grazed communities contained perennial and annual growth forms with a diversity of strategies to coexist with grazers and B. gracilis. Ungrazed communities included increased abundance of annual, ruderal forbs and three woody plant species. Grazing effects occurred against a backdrop of changing plant communities: during the past seven decades, C3 perennial graminoids and subshrubs have increased in relative abundance in both grazed and ungrazed communities. Conclusions Our long-term experiment shows that community responses to grazing in this semiarid grassland occur very slowly, but are predictable, with C4 shortgrasses eventually giving way to taller C3 grasses and ruderal forbs. Spatial variation in grazing effects across sites (and lack of a relationship with soil texture) may reflect the importance of fine-scale heterogeneity in C3 grass abundance, and the slow rate at which taller C3 grasses can coalesce into monodominant patches that outcompete C4 shortgrasses. Increased abundance of C3 species over the past seven decades, both in the presence and absence of grazing, may be related to recovery from the severe drought and dust storms of the 1930s as well as enhanced growth of C3 plants under increasing atmospheric [CO2]. This article is protected by copyright. All rights reserved.

Although studies have shown that mammalian herbivores often limit aboveground carbon storage in savannas, their effects on belowground soil carbon storage remain unclear. Using three sets of long‐term, large herbivore exclosures with paired controls, we asked how almost two decades of herbivore removal from a semiarid savanna in Laikipia, Kenya affected aboveground (woody and grass) and belowground soil carbon sequestration, and determined the major source (C3 vs. C4) of belowground carbon sequestered in soils with and without herbivores present. Large herbivore exclusion, which included a diverse community of grazers, browsers, and mixed‐feeding ungulates, resulted in significant increases in grass cover (~22%), woody basal area (~8 m2/ha), and woody canopy cover (31%), translating to a ~8.5 t/ha increase in aboveground carbon over two decades. Herbivore exclusion also led to a 54% increase (20.5 t/ha) in total soil carbon to 30‐cm depth, with ~71% of this derived from C4 grasses (vs. ~76% with herbivores present) despite substantial increases in woody cover. We attribute this continued high contribution of C4 grasses to soil C sequestration to the reduced offtake of grass biomass with herbivore exclusion together with the facilitative influence of open sparse woody canopies (e.g., Acacia spp.) on grass cover and productivity in this semiarid system.

Rangelands are temporally and spatially complex socioecological systems on which the predominant land use is livestock production. In North America, rangelands also contain approximately 80% of remaining habitat for grassland birds, a guild of species that has experienced precipitous declines since the 1970s. While livestock grazing management may benefit certain grassland bird species by generating the vegetation structure and density they prefer, these outcomes are poorly understood for avian species breeding in the shortgrass steppe. We evaluated how two grazing management systems, continuous, season-long grazing and adaptive, rest-rotational grazing, affected grassland bird abundance from 2013 to 2017 in Colorado's shortgrass steppe. We examined grazing impacts in conjunction with ecological sites, which constitute unique soil and plant communities. When grazing management was evaluated in conjunction with spatial variation in ecological sites, we found three of our five focal bird species responded to grazing management. McCown's Longspur abundance decreased in pastures rested from grazing the previous year. The effect of grazing on Horned Lark and Grasshopper Sparrow depended on ecological site: Horned Lark density was highest in pastures that were intensively grazed and Grasshopper Sparrow density was highest in pastures that were rested the previous year in the least productive ecological site. In addition, densities of all species varied across ecological sites. Our results suggest consideration of soil and vegetation characteristics can inform how adaptive management is applied on a landscape to benefit the full suite of breeding grassland birds, including species that have seemingly contrasting habitat needs. For example, a manager could target adaptive drought mitigation practices, such as resting pastures for 1 yr to generate grassbanks, in less productive soils to benefit grassland birds that prefer taller/denser vegetation structure, or could apply intensive, short-duration grazing on less productive soils to benefit species preferring shorter/sparser vegetation. A single year of intensive, short-duration grazing (i.e., one component of our rotational treatment) across the landscape, however, might not create sufficient habitat for species that prefer short/sparse vegetation in our system (e.g., McCown's Longspur). Ultimately, our study indicates how cattle production on rangelands can congruently support grassland bird populations in the shortgrass steppe.

Yeast and fast-growing human tumor cells share metabolic similarities in that both cells use fermentation of glucose for energy and both are highly sensitive to the glucose analog 2-deoxyglucose. Spontaneous mutations in S. cerevisiae that conferred resistance to 2-deoxyglucose were identified by whole genome sequencing. Missense alleles of the HXK2, REG1, GLC7 and SNF1 genes were shown to confer significant resistance to 2-deoxyglucose and all had the potential to alter the activity and or target selection of the Snf1 kinase signaling pathway. All three missense alleles in HXK2 resulted in significantly reduced catalytic activity. Addition of 2DG promotes endocytosis of the glucose transporter Hxt3. All but one of the 2DG-resistant strains reduced the 2DG-mediated hexose transporter endocytosis by increasing plasma membrane occupancy of the Hxt3 protein. Increased expression of the DOG (deoxyglucose) phosphatases has been associated with resistance to 2-deoxyglucose. Expression of both the DOG1 and DOG2 mRNA was elevated after treatment with 2-deoxyglucose but induction of these genes is not associated with 2DG-resistance. RNAseq analysis of the transcriptional response to 2DG showed large scale, genome-wide changes in mRNA abundance that were greatly reduced in the 2DG resistant strains. These findings suggest the common adaptive response to 2DG is to limit the magnitude of the response. Genetic studies of 2DG resistance using the dominant SNF1-G53R allele in cells that are genetically compromised in both the endocytosis and DOG pathways suggest that at least one more mechanism for conferring resistance to this glucose analog remains to be discovered., Author summary Yeast and fast-growing human tumor cells share metabolic similarities in that both cells use fermentation of glucose for energy and both are highly sensitive to the glucose analog 2-deoxyglucose. Another similarity between yeast cells and human tumor cells is that both cells can acquire resistance to 2-deoxyglucose, an outcome that can limit the usefulness of some cancer therapeutics. In this study, we used bakers’ yeast as a model organism to better understand the mechanism of toxicity and acquisition of resistance to 2-deoxyglucose. Spontaneous mutations in S. cerevisiae that conferred resistance to 2-deoxyglucose were isolated and identified by whole genome sequencing, a technology that was not available until recently. Our studies indicate that 2-deoxyglucose becomes toxic after it is phosphorylated by an enzyme called hexokinase. One important route to resistance is to reduce hexokinase activity. Other parallel pathways to resistance include increased expression of a hydrolase that degrades the toxic metabolite, altered localization of glucose transporters and altered glucose signal transduction pathways.

Rangeland ecosystems worldwide are characterized by a high degree of uncertainty in precipitation, both within and across years. Such uncertainty creates challenges for livestock managers seeking to match herbivore numbers with forage availability to prevent vegetation degradation and optimize livestock production. Here, we assess variation in annual large herbivore production (LHP, kg/ha) across multiple herbivore densities over a 78-yr period (1940-2018) in a semiarid rangeland ecosystem (shortgrass steppe of eastern Colorado, USA) that has experienced several phase changes in global-level sea surface temperature (SST) anomalies, as measured by the Pacific Decadal Oscillation (PDO) and the El Nino-Southern Oscillation (ENSO). We examined the influence of prevailing PDO phase, magnitude of late winter (February-April) ENSO, prior growing-season precipitation (prior April to prior September) and precipitation during the six months (prior October to current April) preceding the growing season on LHP. All of these are known prior to the start of the growing season in the shortgrass steppe and could potentially be used by livestock managers to adjust herbivore densities. Annual LHP was greater during warm PDO irrespective of herbivore density, while variance in LHP increased by 69% (moderate density) and 91% (high density) under cold-phase compared to warm-phase PDO. No differences in LHP attributed to PDO phase were observed with low herbivore density. ENSO effects on LHP, specifically La Nina, were more pronounced during cold-phase PDO years. High herbivore density increased LHP at a greater rate than at moderate and low densities with increasing fall and winter precipitation. Differential gain, a weighted measure of LHP under higher relative to lower herbivore densities, was sensitive to prevailing PDO phase, ENSO magnitude, and precipitation amounts from the prior growing season and current fall-winter season. Temporal hierarchical approaches using PDO, ENSO, and local-scale precipitation can enhance decision-making for flexible herbivore densities. Herbivore densities could be increased above recommended levels with lowered risk of negative returns for managers during warm-phase PDO to result in greater LHP and less variability. Conversely, during cold-phase PDO, managers should be cognizant of the additional influences of ENSO and prior fall-winter precipitation, which can help predict when to reduce herbivore densities and minimize risk of forage shortages.

Context Understanding how grazing management decisions influence the productivity and composition of rangeland plant communities is essential for the development of effective strategies to sustainably produce multiple ecosystem goods and services. Informed with experimental measurements, simulation models can advance our understanding and stewardship of rangeland ecosystems. Objective Our main objective was to evaluate the APEX (Agricultural Policy/Environmental eXtender) plant growth modules and grazing animal selectivity in simulating forage production using experimental data collected from both traditional season-long grazing and adaptive rotational grazing management on western rangelands. Specifically, we evaluated APEX's capability to simulate forage productivity and its response to soil types and climate conditions under grazing management options. Methods Capitalizing on a comparative field study with 20 large pastures (> 123 ha each), APEX modifications were evaluated by comparing simulated forage production with experimental data. The field study evaluated traditional grazing (season long grazing on a single pasture) and an alternative grazing system that utilized collaborative adaptive rangeland management with stakeholders engaged in decision making (such as when and where to rotate a single herd). APEX was modified to include rotational grazing based on a user-defined sequence and automatic rotational grazing based on user-defined forage grazing limits and minimum/maximum grazing durations. Results and conclusions The APEX model was able to simulate the relative differences in forage production between grazing treatments, across years, and among soil types; however, APEX underestimated forage production in 2015 and 2017 due to overestimating drought stress for the warm season perennial grass functional group. Simulation of grazing management scenarios showed that the collaborative adaptive management decision criteria resulted in grazing durations that produced more forage than consistent 7- or 14-day rotation intervals. Significance These modifications were needed to capture the complexity of semiarid environments and thus enhance APEX to better assess grazing management decisions on forage production in regions such as the Western US Great Plains.

On the Ground•Adaptive management can be used to manage complexity, such as how to match forage production variability across years and within portions of a grazing season with animal demand through management flexibility.•Adaptive management strategies should incorporate flexibility and feedback mechanisms informed by appropriate seasonal weather variables and monitoring metrics to both increase resiliency of rangeland ecosystems and reduce risk for the ranching enterprise associated with drought.•For management flexibility, we provide four general strategies that ranchers can use to deal with drought: 1) predict it using weather and climate forecasting tools, 2) track it, 3) employ conservative stocking rates, and 4) utilize inherent spatial variability.•Adaptive grazing management plans that seek to integrate drought prediction tools, conservative but flexible stocking, and existing and predicted spatial heterogeneity in forage quantity and quality can be incorporated into conservation practices where spatial heterogeneity in forage resources within and among allotments/pastures is often not explicitly monitored or considered when planning livestock movements.

In the North American Great Plains, multigenerational ranches and grassland biodiversity are threatened by dynamic and uncertain climatic, economic, and land use processes. Working apart, agricultural and conservation communities face doubtful prospects of reaching their individual goals of sustainability. Rangeland research could serve a convening platform, but experimental studies seldom involve local manager communities. The Collaborative Adaptive Rangeland Management (CARM) project, however, has undertaken a ten-year, ranch-level, participatory research effort to explore how community-engaged research can increase our understanding of conservation and ranching goals. Using ethnographic data and the nature-culture concept&mdash, which recognizes the inseparability of ecological relationships that are shaped by both biological and social processes&mdash, we examine the CARM team&rsquo, s process of revising their management objectives (2016&ndash, 2018). In CARM&rsquo, s early days, the team established locally-relevant multifunctional goals and objectives. As team members&rsquo, understanding of the ecosystem improved, they revised objectives using more spatially, temporally and ecologically specific information. During the revision process, they challenged conventional ecological theories and grappled with barriers to success outside of their control. The emerging CARM nature-culture, based on a sense of place and grounded in hope, provides insights into effective community-engaged research to enhance rangeland livelihood and conservation outcomes.

Learning is recognized as central to collaborative adaptive management (CAM), yet few longitudinal studies examine how learning occurs in CAM or apply the science of learning to interpret this process. We present an analysis of decision-making processes within the collaborative adaptive rangeland management (CARM) experiment, in which 11 stakeholders use a structured CAM process to make decisions about livestock grazing and vegetation management for beef, vegetation, and wildlife objectives. We analyzed four years of meeting transcripts, stakeholder communications, and biophysical monitoring data to ask what facilitated and challenged stakeholder decision making, how challenges affected stakeholder learning, and whether CARM met theorized criteria for effective CAM. Despite thorough monitoring and natural resource agency commitment to implementing collaborative decisions, CARM participants encountered multiple decision-making challenges born of ecological and social complexity. CARM was effective in achieving several of its management objectives, including reduced ecological uncertainty, knowledge coproduction, and multiple-loop social learning. CARM revealed limitations of the idealized CAM cycle and challenged conceptions of adaptive management that separate reduction of scientific uncertainty from participatory and management dimensions. We present a revised, empirically grounded CAM framework that depicts CAM as a spiral rather than a circle, where feedback loops between monitoring data and management decisions are never fully closed. Instead, complexities including time-lags, trade-offs, path-dependency, and tensions among stakeholders' differing types of knowledge and social worlds both constrain decision making and foster learning by creating disorienting dilemmas that challenge participants' pre-existing mental models and relationships. Based on these findings, we share recommendations for accelerating learning in CAM processes.

Grazing land models can assess the provisioning and trade-offs among ecosystem services attributable to grazing management strategies. We reviewed 12 grazing land models used for evaluating forage and animal (meat and milk) production, soil C sequestration, greenhouse gas emission, and nitrogen leaching, under both current and projected climate conditions. Given the spatial and temporal variability that characterizes most rangelands and pastures in which animal, plant, and soil interact, none of the models currently have the capability to simulate a full suite of ecosystem services provided by grazing lands at different spatial scales and across multiple locations. A large number of model applications have focused on topics such as environmental impacts of grazing land management and sustainability of ecosystems. Additional model components are needed to address the spatial and temporal dynamics of animal foraging behavior and interactions with biophysical and ecological processes on grazing lands and their impacts on animal performance. In addition to identified knowledge gaps in simulating biophysical processes in grazing land ecosystems, our review suggests further improvements that could increase adoption of these models as decision support tools. Grazing land models need to increase user-friendliness by utilizing available big data to minimize model parameterization so that multiple models can be used to reduce simulation uncertainty. Efforts need to reduce inconsistencies among grazing land models in simulated ecosystem services and grazing management effects by carefully examining the underlying biophysical and ecological processes and their interactions in each model. Learning experiences among modelers, experimentalists, and stakeholders need to be strengthened by co-developing modeling objectives, approaches, and interpretation of simulation results.

As anthropogenic influences on the world’s rangelands accelerate, there is an urgency for humanity to develop a greater understanding of key drivers, and processes, underlying ecological dynamics and function, to inform improved management strategies. Browsing and grazing ungulates are important components of human-dominated and natural ecosystems, contributing to agricultural output and associated livelihoods, as well as to biodiversity and ecosystem services. A review of key concepts pertinent to the dynamics and management of browsing and grazing ungulates highlights the emergence of functional heterogeneity as a general, or unifying, theme guiding their management, whatever the scale or system. It is also clear that management of ungulate density, and the intensity of herbivory, especially in smaller-scale sedentary systems (e.g. ranches or small protected areas), is a critical determinant of functional heterogeneity. We demonstrate how the functional heterogeneity concept can be applied to the management of grazing and browsing ungulates over a range of scales and ecosystems.

Knowledge of climatic and management influences on large herbivore production (LHP, kg ha−1) is needed for low productivity, semiarid grasslands to address potential consequences of both increasing climate variability and the need to increase animal protein for human consumption. Here, we evaluate the influence of climatic variability and herbivore density on LHP in semiarid grassland using a unique long-term (80 years: 1939–2018) grazing study with three grazing intensities based on forage utilization (light, moderate and heavy). Seasonal variation in precipitation, but not temperature, was the primary influence on LHP. Winter (October-March) and spring (April-June), but not summer (July-September), precipitation during the current year positively influenced LHP across the 3 grazing intensities, whereas prior growing season (prior April-September) precipitation was consistently a negative influence. Although spring precipitation was the most influential seasonal weather variable for LHP, the effect of winter precipitation closely followed under all three grazing intensities, suggesting that non-growing season precipitation is essential for soil water storage to initiate production of sufficient high-quality forage in the subsequent grazing season, resulting in a positive feedback on LHP. A key finding from our analysis was that the effect of summer precipitation is smaller than the combined effects of winter and spring precipitation. As such, much of the variation in LHP can be predicted by seasonal weather parameters that are known early in the growing season. The magnitude of seasonal precipitation effects on LHP was greatest for heavy grazing; consequently LHP with heavy grazing is more reliant on primary production produced in the current year to increase LHP as forage quantity is more limiting than forage quality. Moreover, stability of LHP across years (range: 7.5 to 34.6 kg ha−1) was less with heavy grazing, which results in “boom-bust” economics that threaten sustainability of operations. Management adaptations to mitigate climatic variability, therefore, will be most necessary and advantageous when land managers employ heavy grazing intensities. Despite the substantial interannual variability in precipitation that characterizes semiarid grasslands, our results show that proactive flexibility by land managers in adjusting grazing management decisions to seasonal precipitation amounts forecasted for the winter and spring seasons would reduce enterprise risk and improve confidence in decision-making, profitability, production efficiency and environmental sustainability from semiarid grasslands.

Predicting impacts on phenology of the magnitude and seasonal timing of rainfall pulses in water-limited grassland ecosystems concerns ecologists, climate scientists, hydrologists, and a variety of stakeholders. This report describes a simple, effective procedure to emulate the seasonal response of grassland biomass, represented by the satellite-based normalized difference vegetation index NDVI, to daily rainfall. The application is a straightforward adaptation of a staged linear reservoir that simulates the pulse-like entry of rainwater into the soil and its redistribution as soil moisture, the uptake of water by plant roots, short-term biomass development, followed by the subsequent transpiration of water through foliage. The algorithm precludes the need for detailed, site specific information on soil moisture dynamics, plant species, and the local hydroclimate, while providing a direct link between discrete rainfall events and consequential biomass responses throughout the growing season. We applied the algorithm using rainfall data from the Central Plains Experimental Range to predict vegetation growth dynamics in the semi-arid shortgrass steppe of North America. The mean annual rainfall is 342 mm, which is strongly bifurcated into a dominantly ‘wet’ season, where during the three wettest months May, June and July the mean monthly rainfall is approximately 55 mm month−1; and a ‘dry’ season, where during the three driest months December, January and February, the mean monthly rainfall is approximately 7 mm month−1. NDVI data from the Moderate Resolution Imaging Spectroradiometer MODIS MOD13Q1 16 day, 250 m × 250 m product were used as a proxy for grassland phenology for the period-of-record 2000–2013. Allowing for temporal changes in basic parameters of the response function over the growing season, the predicted response of the model tracks the observed NDVI metric with correlation coefficients exceeding 0.92. A two-stage series reservoir is preferred, whereby the characteristic time for transfer of a rainfall event to the peak response of NDVI decreases from 24 days early growing season to 12 days late growing season, while the efficiency of a given volume of rainfall to produce a correspondingly similar amount of aboveground biomass decreases by a factor of 40% from April to October. Behaviours of the characteristic time of greenup and loss of rainfall efficiency with progression of the growing season are consistent with physiological traits of cool-season C3 grasses versus warm-season C4 grasses, and with prior research suggesting that early season production by C3 grasses is more responsive to a given amount of precipitation than mid-summer growth of C4 shortgrasses. Our model explains >90% of seasonal biomass dynamics. We ascribe a systematic underprediction of observed early season greenup following drought years to a lagged or ‘legacy’ effect, as soil inorganic nitrogen, accumulated during drought, becomes available for future plant uptake.

Increasingly, the restoration of large carnivores is proposed as a means through which to restore community structure and ecosystem function via trophic cascades. After a decades-long absence, African wild dogs (Lycaon pictus) recolonized the Laikipia Plateau in central Kenya, which we hypothesized would trigger a trophic cascade via suppression of their primary prey (dik-dik, Madoqua guentheri ) and the subsequent relaxation of browsing pressure on trees. We tested the trophic-cascade hypothesis using (1) a 14-year time series of wild dog abundance; (2) surveys of dik-dik population densities conducted before and after wild dog recovery; and (3) two separate, replicated, herbivore-exclusion experiments initiated before and after wild dog recovery. The dik-dik population declined by 33% following wild dog recovery, which is best explained by wild dog predation. Dik-dik browsing suppressed tree abundance, but the strength of suppression did not differ between before and after wild dog recovery. Despite strong, top-down limitation between adjacent trophic levels (carnivore- herbivore and herbivore-plant), a trophic cascade did not occur, possibly because of a time lag in indirect effects, variation in rainfall, and foraging by herbivores other than dik-dik. Our ability to reject the trophic-cascade hypothesis required two important approaches: (1) temporally replicated herbivore exclusions, separately established before and after wild dog recovery; and (2) evaluating multiple drivers of variation in the abundance of dik-dik and trees. While the restoration of large carnivores is often a conservation priority, our results suggest that indirect effects are mediated by ecological context, and that trophic cascades are not a foregone conclusion of such recoveries.

Anthropogenic changes to disturbance regimes in grasslands, and associated homogenization of vegetation structure, have been implicated as factors contributing to declines in populations of grassland birds in North America. We examined the influence of patch-burn grazing management, which employs spatiotemporal interactions between fire and livestock grazing guided by historical disturbance patterns, on vegetation structure and bird abundance in shortgrass steppe in northeastern Colorado, USA. All study pastures were grazed by cattle at moderate stocking rates from May to October each year. In the patch-burn treatment, we burned 25% of each pasture in autumn (Oct or Nov) each year during 2007–2010; control pastures were not burned. Patch-burn grazing management increased vegetation heterogeneity by generating short (

Monitoring of aboveground net primary production (ANPP) is critical for effective management of rangeland ecosystems but is problematic due to the vast extent of rangelands globally, and the high costs of ground-based measurements. Remote sensing of absorbed photosynthetically active radiation (APAR) can be used to predict ANPP, potentially offering an alternative means of quantifying ANPP at both high temporal and spatial resolution across broad spatial extents. The relationship between ANPP and APAR has often been quantified based on either spatial variation across a broad region or temporal variation at a location over time, but rarely both. Here we assess: (i) if the relationship between ANPP and APAR is consistent when evaluated across time and space; (ii) potential factors driving differences between temporal versus spatial models, and (iii) the magnitude of potential errors relating to space for time transformations in quantifying productivity. Using two complimentary ANPP datasets and remotely sensed data derived from MODIS and a Landsat/MODIS fusion data product, we find that slopes of spatial models are generally greater than slopes of temporal models. The abundance of plant species with different structural attributes, specifically the abundance of C4 shortgrasses with prostrate canopies versus taller, more productive C3 species with more vertically complex canopies, tended to vary more dramatically in space than over time. This difference in spatial versus temporal variation in these key plant functional groups appears to be the primary driver of differences in slopes among regression models. While the individual models revealed strong relationships between ANPP to APAR, the use of temporal models to predict variation in space (or vice versa) can increase error in remotely sensed predictions of ANPP. Fil: Gaffney, Rowan. United States Department of Agriculture. Agricultural Research Service; Argentina Fil: Porensky, Lauren. United States Department of Agriculture. Agricultural Research Service; Argentina Fil: Gao, Feng. United States Department of Agriculture. Agricultural Research Service; Argentina Fil: Irisarri, Jorge Gonzalo Nicolás. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentina Fil: Durante, Martín. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentina. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Entre Ríos. Estación Experimental Agropecuaria Concepción del Uruguay; Argentina Fil: Derner, Justin. United States Department of Agriculture. Agricultural Research Service; Argentina Fil: Augustine, David. United States Department of Agriculture. Agricultural Research Service; Argentina

Management strategies that allow for spatiotemporal interactions between fire and herbivores can potentially achieve multiple management goals related to livestock production and wildlife conservation, but little is known about such interactions in semiarid grasslands where fire has traditionally been viewed as having few management applications. We studied patch burn grazing management in the shortgrass steppe of northeastern Colorado, comparing unburned pastures to pastures where 25% of the area was burned in October or November each year over 4 years. Our objective was to examine the interactive effects of patch burns and the subsequent response by pronghorn (Antilocapra americana) on plains pricklypear (Opuntia polyacantha) and wind erosion rates. We monitored abundance of plains pricklypear and wind erosion rates throughout the experiment and quantified seasonal pronghorn densities and postburn damage to plains pricklypear cladodes during the latter 2 years of the study. Pronghorn density was 26 times greater in winter and 7 times greater in spring on patch burns compared with unburned pastures. By late winter, densities of bitten or uprooted plains pricklypear cladodes were five times greater on patch burns compared with unburned pastures. Patch burns, as well as the subsequent response of pronghorn, reduced plains pricklypear density by 54–71% during the first year after the burns, and density remained suppressed for up to 6 years after burns. Wind erosion rates on patch burns were greater compared with unburned pastures but were two orders of magnitude lower than rates measured on fallow croplands in the region. Autumn patch burns can be a valuable means to suppress plains pricklypear and thereby increase grass available for livestock consumption in the shortgrass steppe. These outcomes can be achieved without increasing wind erosion in a manner that threatens long-term soil sustainability and without negative consequences for livestock weight gains.

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State-and-transition models for semiarid grasslands in the North American Great Plains suggest that the presence of herbivorous black-tailed prairie dogs (Cynomys ludovicianus) on a site 1) creates a vegetation state characterized by increased dominance of annual forbs and unpalatable bunchgrasses and increased bare soil exposure and 2) requires long-term (> 40 yr) prairie dog removal to transition back to a vegetation state dominated by palatable perennial grasses. Here, we examine 1) how the recent history of prairie dog occupancy on a site (1–10 yr) influences the magnitude of prairie dog effects on vegetation composition and 2) how occupancy history affects vegetation dynamics following extirpation of prairie dogs. We used a natural experiment in the shortgrass steppe of northeastern Colorado, USA, where prairie dogs were extirpated from multiple sites during an outbreak of epizootic plague. On sites occupied by prairie dogs for 1–4 yr prior to extirpation, plant cover and composition recovered to conditions similar to unoccupied sites within a single growing season. Larger reductions in perennial C4 grasses occurred on sites occupied for the prior 7–10 yr compared to sites with shorter occupancy histories (

We studied land-cover associations at nest sites and reproductive success of two Buteo species of conservation concern on the southern Great Plains, USA. The study area was in Cimarron County, Oklahoma, where land use is dominated by row-crop agriculture, livestock grazing, and grasslands enrolled in the Conservation Reserve Program (CRP). Ferruginous hawks (B. regalis) were uncommon and nested primarily in and around the Rita Blanca National Grassland. Swainson's hawks (B. swainsoni) were common and nested throughout the study area. Territories of ferruginous hawks contained more sandsage (Artemisia filifolia) habitat and less cropland and CRP lands than random sites, whereas territories of Swainson's hawks mirrored proportions of available landcover. Our results suggest that proportion of nearby sandsage habitat is an important factor in determining Swainson's hawk reproductive success. In addition, ferruginous hawk nest sites were located in areas that contained significantly more sandsage habitat than randomly selected sites in the study area. Nest-site availability may have constrained the distribution of buteos in our study area and is probably a major factor limiting nesting density of ferruginous hawks. Ferruginous hawks typically nest on man-made platforms (e.g., nest platforms and windmills) that in the study area were most common in and around the Rita Blanca National Grassland. Our results suggest that conversion of native grasslands to cropland may have negative consequences for ferruginous and Swainson's hawks. This relationship has been previously demonstrated in several studies of ferruginous hawks, but not for Swainson's hawks. In particular, loss of sandsage habitat on the southern Great Plains may have contributed to range declines in ferruginous hawks and decreased breeding success for Swainson's hawks.

In semi-arid grasslands of the North American Great Plains, fire has traditionally been viewed as having few management applications, and quantitative measurements of fire behavior in the low fuel loads characteristic of this region are lacking. More recently, land managers have recognized potential applications of prescribed fire to control undesirable plant species and to manage habitat for wildlife in this region. Working in the shortgrass steppe of northeastern Colorado over a 7-year period, we quantified peak temperatures, heating duration, and heat dosage produced near ground level during prescribed burns conducted under a wide range of fuel loads and weather conditions. We use an information theoretic approach to develop models that predict peak temperature and heat dosage as a function of weather parameters and fuel loads. Under the weather conditions that we examined, successful burns (>80 % of target area burnt) occurred with fuel loads varying from 350 kg ha−1 to 1175 kg ha−1, while burns with fuel loads

In arid and semiarid ecosystems, fire can potentially affect ecosystem dynamics through changes in soil moisture, temperature, and nitrogen cycling, as well as through direct effects on plant meristem mortality. We examined effects of annual and triennial prescribed fires conducted in early spring on soil moisture, temperature, and N, plant growth, and plant N content in semiarid shortgrass steppe. Annual burning increased soil inorganic N availability throughout the growing season, which was associated with increased soil temperature and a reduction in aboveground N in C3 plants. Furthermore, the increase in soil inorganic N pools with annual burning was modest and did not facilitate success of ruderal species. Negative fire effects on C3 plant production could be due to increased soil temperature, reduced soil moisture, or direct negative effects on C3 plant meristems, although fuel loads and fire temperatures were low relative to other grasslands. Triennial burning had intermediate effects on N availability and C3 plant production compared to annual burning and unburned controls. Results show that prescribed burns can be used in the management of this semiarid grassland without facilitating annual plant invasion, but excessively frequent burning can reduce production of C3 plants.

Disturbed xeric grasslands with short, sparse vegetation provide breeding habitat for mountain plovers (Charadrius montanus) across the western Great Plains. Maintaining local disturbance regimes through prairie dog conservation and prescribed fire may contribute to the sustainability of recently declining mountain plover populations, but these management approaches can be controversial. We estimated habitat- specific mountain plover densities and nest survival rates on black-tailed prairie dog (Cynomys ludovicianus) colonies and burns in the shortgrass steppe of northeastern Colorado. Mountain plover densities were similar on prairie dog colonies (5.9birds/km 2 ; 95% CI ¼4.7-7.4) and sites burned during the preceding dormant season (6.7birds/km 2 ; 95% CI ¼4.6-9.6), whereas the 29-day nest survival rate was greater on prairie dog colonies (0.81 in 2011 and 0.39 in 2012) compared to the burned sites (0.64 in 2011 and 0.17 in 2012). Reduced nest survival in 2012 compared to 2011 was associated with higher maximum daily temperatures in 2012, consistent with a previous weather-based model of mountain plover nest survival in the southern Great Plains. Measurements of mountain plover density relative to time since disturbance showed that removal of prairie dog disturbance by sylvatic plague reduced mountain plover density by 70% relative to active prairie dog colonies after 1 year. Plover densities declined at a similar rate (by 78%) at burned sites between the first and second post-burn growing season. Results indicate that black-tailed prairie dog colonies are a particularly important nesting habitat for mountain plovers in the southern Great Plains. In addition, findings suggest that prescribed burning can be a valuable means to create nesting habitat in landscapes where other types ofdisturbances (such as prairie dog colonies) are limited in distribution and size. Published 2014. This article is a U.S. Government work and is in the public domain in the USA.

Diet composition of free-roaming animals has been persistently difficult to quantify. Fecal DNA (fDNA) metabarcoding is an emerging novel technology to reconstruct botanical composition of diets. Validation studies comparing fDNA metabarcodion to fed diets are lacking. A blind 6-week feeding study using 5 heifers (416–527 kg) fed different diets weekly with fecal samples collected from individuals 7 days after the introduction of each new diet was conducted. Diets were: (1) C3 grass hay (creeping meadow foxtail (Alopecurus arundinaceus)), (2) C4 grass hay (foxtail millet (Setaria italica), (3) C3 grass hay + C4 grass hay + alfalfa hay (Medicago sativa) (equal 1/3 proportions dry matter, 17.0%, 30.5%, and 52.5% by crude protein contribution, respectively), (4) C3 grass hay + C4 grass hay + alfalfa hay (equal proportions) + minor component of Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis) leaves (fed at 25 grams per heifer per day equal to 0.29% by dry matter contribution; crude protein content unknown), (5) alfalfa hay + minor components of crested wheatgrass (Agropyron cristatum), western wheatgrass (Pascopyrum smithii), and blue grama (Bouteloua gracilis) that included steams, leaves, and seed heads (varying proportions by dry matter ranging from 0.02 to 0.15% but 0.05%, 0.04%, and 0.01% by crude protein contribution), and (6) alfalfa hay. Single species diets were fed ad libitum. Diets with multiple forage species were fed at metabolic weight-based amounts with minor diet components introduced 2-3 days after major diet components. At the species level, fed diets and fDNA metabarcoding diets were dissimilar due to misidentification of major C3 and C4 diet components. For C3, A. arundinaceus was under the same Operational Taxonomic Unit (OTU) as Phleum pratense (not present in the C3 sourced hay), so blind identification was initially wrong. For C4, S. italica was identified as Setaria palmifolia, which does not grow in the region. Microscopic evaluation of seeds for both misidentifications verified the correct species identification and the fDNA error. Minor dietary components were detected in only 1 of 5 heifers for all species. Increasing the utility of fDNA metabarcoding for accurately determining the diet composition of free-roaming animals will necessitate: 1) improving the reference library of voucher species specimens, 2) understanding by technical and scientific staff that multiple species may be attributed to the same OTU, and 3) greater verification of fDNA metabarcoding results using field-derived plant composition data, especially in rangeland settings where plant diversity can be intrinsically high.

Summary 1. The degree to which large herbivores select and forage within recently burned areas is a key driver of vegetation heterogeneity in rangeland ecosystems. However, few studies have quantified the strength and timing of herbivore selection for burned areas or examined how selection strength varies among ecosystems differing in precipitation and primary productivity. 2. We conducted a 4-year patch-burning experiment in semi-arid rangeland of Colorado, USA, where 25% of the area available to cattle was burned each year and burned patches were shifted annually. We used GPS collars with activity sensors to quantify the distribution of free-ranging cattle at a high temporal resolution (5-min intervals) during the growing season each year. We used a classification tree model to discriminate between cattle grazing vs. non-grazing locations, which significantly increased precision in quantifying burn selection strength. We fit generalized linear models predicting the frequency of cattle use of a given location within each study area and month, enabling comparisons between the relative influence of burns and topography on grazing distribution. 3. Across multiple growing seasons, cattle selectively spent 31% of grazing time on recently burnt areas, which comprised 25% of the landscape; this selection strength was half as strong as that documented in mesic rangeland. 4. At a monthly temporal scale, strong cattle selection for burned areas occurred during periods of rapid vegetation growth regardless of when during the growing season this greening occurred. Outside these intervals, burn selection strength was inconsistent and cattle grazing distribution was primarily influenced by topography. Thus, the relative importance of fire and topography in controlling grazer distribution was temporally contingent upon the timing and size of precipitation pulses. 5. Synthesis and applications. Spatiotemporal interactions between fire and herbivores are a consistent feature of both semi-arid and mesic rangelands, with interaction strength varying across gradients of precipitation and primary productivity. Management of semi-arid ecosystems to sustain ecological processes should include strategies that allow ungulate herbivores to shift their grazing distribution seasonally in response to fire, topoedaphic variation and precipitation patterns. Combined management of fire and grazing for conservation objectives can be consistent with, and even complementary to, livestock production goals.

Summary 1. Large mammalian herbivores are well recognized to play important roles in regulating woody cover and biomass in savannas, but the extent to which browsing ungulates are capable of regulating woody populations in the absence of other disturbances such as fire is unclear. Moreover, the degree to which browser effects on savannas operate through effects on woody plant recruitment vs. mortality has rarely been examined. 2. We conducted a 10-year, replicated herbivore exclusion experiment in a semi-arid savanna in East Africa (mean annual rainfall = 514 mm), where fires have been actively suppressed for decades. Browsers dramatically influenced recruitment, growth and mortality of all size classes of woody vegetation. A decade of herbivore exclusion resulted in a sevenfold increase in recruitment, a 2.5-fold decrease in mortality and a threefold increase in woody biomass inside exclosures, while biomass outside exclosures remained relatively unchanged. 3. At the plant community level, extensive browsing of seedlings by small-bodied ungulates suppressed woody recruitment in this semi-arid system, generating a ‘browsing trap’ comparable to the ‘fire trap’ reported for mesic systems. Browsing by large- and medium-bodied ungulates reduced both growth and survival of individuals in larger size classes. 4. At the plant species level, browser impacts were variable. Although browsers negatively influenced recruitment of all species, they had little to no impact on the mortality of some dominant species, resulting in a longterm, browser-driven shift in woody species composition that was largely mediated via their differential effects on plant mortality rates rather than recruitment. 5. Synthesis. Our results demonstrate unequivocally that, even in the absence of fire, native browsing ungulates can exert dramatic ‘top-down’ controls in semi-arid savannas, influencing all aspects of woody plant demography. Besides suppressing woody plant recruitment, browsers can also have substantial cumulative long-term impacts on growth and mortality rates of woody plants, including adults, which can differ between species in ways that fundamentally alter the structure and function of woody vegetation. In semi-arid rangelands, intact communities of native browsing ungulates thus provide a critical ecosystem service by regulating woody cover, and their removal (or extinction) from these systems can lead to rapid woody encroachment.

Potential competition between native and domestic herbivores is a major consideration influencing the management and conservation of native herbivores in rangeland ecosystems. In grasslands of the North American Great Plains, black-tailed prairie dogs (Cynomys ludovicianus) are widely viewed as competitors with cattle but are also important for biodiversity conservation due to their role in creating habitat for other native species. We examined spatiotemporal variation in prairie dog effects on growing-season forage quality and quantity using measurements from three colony complexes in Colorado and South Dakota and from a previous study of a fourth complex in Montana. At two complexes experiencing below-average precipitation, forage availability both on and off colonies was so low (12-54 g/ m 2 ) that daily forage intake rates of cattle were likely constrained by instantaneous intake rates and daily foraging time. Under these dry conditions, prairie dogs (1) substantially reduced forage availability, thus further limiting cattle daily intake rates, and (2) had either no or a small positive effect on forage digestibility. Under such conditions, prairie dogs are likely to compete with cattle in direct proportion to their abundance. For two complexes experiencing above-average precipitation, forage quantity on and off colonies (77-208 g/m 2 ) was sufficient for daily forage intake of cattle to be limited by digestion rather than instantaneous forage intake. At one complex where prairie dogs enhanced forage digestibility and (N) while having no effect on forage quantity, prairie dogs are predicted to facilitate cattle mass gains regardless of prairie dog abundance. At the second complex where prairie dogs enhanced digestibility and (N) but reduced forage quantity, effects on cattle can vary from competition to facilitation depending on prairie dog abundance. Our findings show that the high spatiotemporal variation in vegetation dynamics characteristic of semiarid grasslands is paralleled by variability in the magnitude of competition between native and domestic grazers. Competitive interactions evident during dry periods may be partially or wholly offset by facilitation during periods when forage digestibility is enhanced and forage quantity does not limit the daily intake rate of cattle.

Th e response of semiarid grasslands to small, non-colonial herbivores has received little attention, focusing primarily on the eff ects of granivore assemblages on annual plant communities. We studied the long-term eff ects of both small and large herbivores on vegetation structure and species diversity of shortgrass steppe, a perennial semiarid grassland considered marginal habitat for small mammalian herbivores. We hypothesized that 1) large generalist herbivores would aff ect more abundant species and proportions of litter-bare ground-vegetation cover through non-selective herbivory, 2) small herbivores would aff ect less common species through selective but limited consumption, and 3) herbivore eff ects on plant richness would increase with increasing aboveground net primary production (ANPP). Plant community composition was assessed over a 14-year period in pastures grazed at moderate intensities by cattle and in exclosures for large (cattle) and large-plus-small herbivores (additional exclusion of rabbits and rodents). Exclusion of large herbivores aff ected litter and bare ground and basal cover of abundant, common and uncommon species. Additional exclusion of small herbivores did not aff ect uncommon components of the plant community, but had indirect eff ects on abundant species, decreased the cover of the dominant grass Bouteloua gracilis and total vegetation, and increased litter and species diversity. Th ere was no relationship between ANPP and the intensity of eff ects of either herbivore body size on richness. Exclusion of herbivores of both body sizes had complementary and additive eff ects which promoted changes in vegetation composition and physiognomy that were linked to increased abundance of tall and decreased abundance of short species. Our fi ndings show that small mammalian herbivores had disproportionately large eff ects on plant communities relative to their small consumption of biomass. Even in smallseeded perennial grasslands with a long history of intensive grazing by large herbivores, non-colonial small mammalian herbivores should be recognized as an important driver of grassland structure and diversity.

Colonial burrowing herbivores can modify vegetation structure, create belowground refugia, and generate landscape heterogeneity, thereby affecting the distribution and abundance of associated species. Black-tailed prairie dogs (Cynomys ludovicianus) are such a species, and they may strongly affect the abundance and composition of grassland bird communities. We examined how prairie dog colonies in the North American Great Plains affect bird species and community composition. Areas occupied by prairie dogs, characterized by low percent cover of grass, high percent cover of bare soil, and low vegetation height and density, supported a breeding bird community that differed substantially from surrounding areas that lacked prairie dogs. Bird communities on colony sites had significantly greater densities of large-bodied carnivores (Burrowing Owls [Athene cunicularia], Mountain Plovers, [Charadrius montanus], and Killdeer [Charadrius vociferus]) and omnivores consisting of Horned Larks (Eremophila alpestris) and McCown's Longspurs (Rhynchophanes mccownii) than bird communities off colony sites. Bird communities off colony sites were dominated by small-bodied insectivorous sparrows (Ammodramus spp.) and omnivorous Lark Buntings (Calamospiza melanocorys), Vesper Sparrows (Pooecetes gramineus), and Lark Sparrows (Chondestes grammacus). Densities of 3 species of conservation concern and 1 game species were significantly higher on colony sites than off colony sites, and the strength of prairie dog effects was consistent across the northern Great Plains. Vegetation modification by prairie dogs sustains a diverse suite of bird species in these grasslands. Collectively, our findings and those from previous studies show that areas in the North American Great Plains with prairie dog colonies support higher densities of at least 9 vertebrate species than sites without colonies. Prairie dogs affect habitat for these species through multiple pathways, including creation of belowground refugia, supply of prey for specialized predators, modification of vegetation structure within colonies, and increased landscape heterogeneity. Asociaciones de Comunidades de Aves de Pastizales con Perros de la Pradera en la Gran Llanura de Norte America Resumen Los herbivoros excavadores coloniales pueden modificar la estructura de la vegetacion, crear refugios subterraneos y generar heterogeneidad en el paisaje, por lo tanto afectan la distribucion y abundancia de especies asociadas. Los perros de la pradera (Cynomys ludovicianus) son una de esas especies, y pueden afectar significativamente la abundancia y composicion de comunidades de aves de pastizales. Examinamos como afectan las colonias de perros de la pradera a las especies de aves y la composicion de la comunidad en la Gran Llanura de Norte America. Las areas ocupadas por perros de la pradera, caracterizadas por un bajo porcentaje de cobertura de pasto, alto porcentaje de cobertura de suelo desnudo y baja altura y densidad de la vegetacion, soportaban una comunidad de aves que difirio sustancialmente en areas que no tenian perros de la pradera. Las comunidades de aves en sitios con colonias tuvieron significativamente mayores densidades de carnivoros de talla grande (Athene cunicularia,Charadrius montanusyCharadrius vociferus) y omnivoros (Eremophila alpestrisyRhynchophanes mccownii) que las comunidades de aves en sitios sin colonias. Las comunidades de aves en sitios sin colonias fueron dominadas por gorriones insectivoros de talla pequena (Ammodramus spp.) y omnivoros (Calamospiza melanocorys,Pooecetes gramineusyChondestes grammacus). Las densidades de 3 especies de preocupacion para la conservacion y una especie cinegetica fueron significativamente mayores en los sitios con colonias, y la fuerza de los efectos de los perros de la pradera fue consistente en el norte de Gran Llanura. La modificacion de la vegetacion por los perros de la pradera sostiene a un conjunto diverso de especies de aves estos pastizales. Colectivamente, nuestros resultados y los de estudios previos muestran que las areas con colonias de perros de la pradera en la Gran Llanura de Norte America soportan densidades mas altas de por lo menos 9 especies de vertebrados que en los sitios sin colonias. Los perros de la pradera afectan el habitat de esas especies por diferentes vias, incluyendo la creacion de refugios subterraneos, proveyendo presas para depredadores especializados, modificando la estructura de vegetacion en las colonias e incrementando la heterogeneidad del paisaje.

Nitrogen (N) availability can strongly influence forage quality and the capacity for semiarid rangelands to respond to increasing atmospheric CO2. Although many pathways of nitrogen input and loss from rangelands have been carefully quantified, cattlemediated N losses are often poorly understood. We used measurements of cattle N consumption rate, weight gains, and spatial distribution in shortgrass rangeland of northeastern Colorado to evaluate the influence of cattle on rangeland N balance. Specifically, we estimated annual rates of N loss via cattle weight gains and spatial redistribution of N into pasture corners and areas near water tanks, and used previous studies to calculate ammonia volatilization from urine patches. Using measurements of plant biomass and N content inside and outside grazing cages over 13 yr, we estimate that cattle stocked at 0.65 animal unit

A large number of empirical and mechanistic simulation models and decision support tools have been produced for rangelands. Collectively, these models have considerably increased our fundamental knowledge and understanding of the dynamics of ecosystem functions, processes, and structure. We explore three areas where models for rangeland management are often challenging for land managers and enterprise-level decision making: 1) coping with spatiotemporal and climatic variability in implementing scenario forecasting, risk assessments, and adaptive management; 2) addressing outputs of multiple ecosystem goods and services and determining whether they are synergistic or competitive; and 3) integrating experimental and experiential knowledge and observations into decision making. Increasing the utility of models for rangeland management remains a key frontier and a major research need for the modeling community and will be achieved less by further technical advances and model complexity and more by the use of existing topoedaphic databases, the capacity to readily incorporate new experimental and experiential knowledge, and the use of frameworks that facilitate outcome-based, adaptive decision making at the enterprise level with associated economic considerations. Opportunities exist for increasing the utility of models for decision making and adaptive rangeland management through better matching of model complexity with enterprise-level, decision-making goals. This could be accomplished by incorporating a fundamental understanding of herbivory, fire, and spatiotemporal interactions with weather patterns that affect multiple ecosystem functions. Most important, effective models would allow land managers in a changing and variable climate to 1) evaluate trade offs in producing multiple goods and services, 2) optimize the application of conservation practices spatially (comparing costs and benefits accrued across different timescales), and 3) incorporate manager capacity, including experience, skills, and labor input.

Aerial surveys using line-intercept methods are one approach to estimate the extent of prairie dog colonies in a large geographic area. Although black-tailed prairie dogs (Cynomys ludovicianus) construct conspicuous mounds at burrow openings, aerial observers have difficulty discriminating between areas with burrows occupied by prairie dogs (colonies) versus areas of uninhabited burrows (uninhabited colony sites). Consequently, aerial line-intercept surveys may overestimate prairie dog colony extent unless adjusted by an on-the-ground inspection of a sample of intercepts. We compared aerial line-intercept surveys conducted over 2 National Grasslands in Colorado, USA, with independent ground-mapping of known black-tailed prairie dog colonies. Aerial line-intercepts adjusted by ground surveys using a single activity category adjustment overestimated colonies by ≥94% on the Comanche National Grassland and ≥58% on the Pawnee National Grassland. We present a ground-survey technique that involves 1) visiting on the ground a subset of aerial intercepts classified as occupied colonies plus a subset of intercepts classified as uninhabited colony sites, and 2) based on these ground observations, recording the proportion of each aerial intercept that intersects a colony and the proportion that intersects an uninhabited colony site. Where line-intercept techniques are applied to aerial surveys or remotely sensed imagery, this method can provide more accurate estimates of black-tailed prairie dog abundance and trends. Published 2012. This article is a U.S. Government work and is in the public domain in the USA.

Precipitation pulses in arid ecosystems can lead to temporal asynchrony in microbial and plant processing of nitrogen (N) during drying/wetting cycles causing increased N loss. In contrast, more consistent availability of soil moisture in mesic ecosystems can synchronize microbial and plant processes during the growing season, thus minimizing N loss. We tested whether microbial N cycling is asynchronous with plant N uptake in a semiarid grassland. Using (15)N tracers, we compared rates of N cycling by microbes and N uptake by plants after water pulses of 1 and 2 cm to rates in control plots without a water pulse. Microbial N immobilization, gross N mineralization, and nitrification dramatically increased 1-3 days after the water pulses, with greatest responses after the 2-cm pulse. In contrast, plant N uptake increased more after the 1-cm than after the 2-cm pulse. Both microbial and plant responses reverted to control levels within 10 days, indicating that both microbial and plant responses were short lived. Thus, microbial and plant processes were temporally synchronous following a water pulse in this semiarid grassland, but the magnitude of the pulse substantially influenced whether plants or microbes were more effective in acquiring N. Furthermore, N loss increased after both small and large water pulses (as shown by a decrease in total (15)N recovery), indicating that changes in precipitation event sizes with future climate change could exacerbate N losses from semiarid ecosystems.