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On the Ground • Adaptive management should explicitly involve stakeholders, emphasize multiple iterations of identifying and prioritizing outcomes, and tightly link science-informed monitoring to decision-making benchmarks for effective feedback loops. • Short-term monitoring procedures should be simple, quick, and based on consistent methods that are focused on locations where meaningful change is expected or uncertainty is high. • Long-term monitoring procedures should emphasize consistent methodology across years that provides broader ecosystem context for multiple ecosystem services (e.g., watershed protection and grassland bird habitat). • Incorporating timely feedback from monitoring improves the capacity for rapid decision-making when benchmarks are attained and management should be modified.

Coverage of living (green) vegetation influences rangeland processes and biodiversity but remains a challenge to quantify at small spatial grain. We describe a technique for rapid airborne (unmanned aerial vehicle) measurements of continuous spatial coverage of living vegetation at a resolution (spatial grain) of 8 cm ground sampling distance. We then applied this technique at the pasture (paddock) scale (tens of hectares) in two contrasting grassland ecosystems (semiarid shortgrass steppe in northeastern Colorado, United States and mesic grassland in central Texas, United States) to determine effects of locally relevant grazing treatments on spatial variability and dependence (pattern) in fractional coverage of green vegetation (fractional vegetation cover; FVC). Site-specific regression models developed using reflectance in visible and near-infrared wavebands explained 90% and 89% of variance in FVC for semiarid and mesic grassland, respectively. Mean FVC was similar among shortgrass steppe pastures differing in grazing treatment (light or heavy grazing by cattle, moderate cattle grazing with prairie dogs present). In contrast, FVC was lower with rotational compared with continuous, year-long grazing in the mesic grassland. Heavy grazing in shortgrass steppe and rotational grazing in mesic grassland increased the spatial uniformity in FVC by reducing spatial variability and increasing spatial dependence in FVC, the latter by increasing the similarity in FVC values among spatially separated patches. Unmanned aerial vehicle−enabled remote sensing provides for FVC at sufficiently small spatial grain to characterize spatial variation in FVC at the pasture scale. Results can be used to evaluate the effectiveness of management actions intended to alter spatial variation in FVC to achieve conservation or diversity objectives. Enhanced capacity to monitor FVC at small spatial grain promotes adaptive management of grasslands.

Frequent, severe defoliation reduces grass production and can alter plant species composition in grasslands. Multipaddock rotational grazing has been proposed as a grazing strategy that may reduce the frequency and intensity of defoliation on palatable grass plants without altering stocking rates. Previous studies evaluated this hypothesis using small, homogeneous paddocks and nonadaptive rotation schedules and found small and inconsistent differences between continuous and rotational grazing systems. Using a stakeholder-driven collaborative adaptive management (CAM) framework, we conducted the first ranch-scale experimental investigation into tiller defoliation patterns in the context of adaptive multipaddock rotational grazing. We monitored tiller defoliation frequency and intensity in 10 paired 130-ha pastures assigned to either a collaborative adaptive multipaddock rotational grazing treatment (CARM, one livestock herd) or a season-long continuous grazing treatment (traditional rangeland management [TRM]; 10 separate herds) in shortgrass steppe. Consistent with previous studies, we observed that frequencies of grazing and regrazing on a palatable, cool-season grass (western wheatgrass, Pascopyrum smithii) were much more sensitive to stocking rate than grazing system. Under moderate stocking rates used in both CARM and TRM treatments, roughly two-thirds of western wheatgrass tillers remained ungrazed annually, regardless of grazing system. Thus, season-long rest is present in season-long continuous and rotational grazing systems. Frequencies of tiller regrazing were low (5−15%) and similar between CARM and TRM treatments. Although defoliation patterns were similar between treatments at the whole-ranch scale, CARM enhanced spatial and temporal heterogeneity in defoliation frequencies among individual pastures. Pastures grazed earlier in the season or for longer experienced more defoliation. Managers implementing adaptive, multipaddock rotational grazing could use this heightened and predictable variability to strategically manage impacts of grazing on western wheatgrass at the individual pasture scale. The CAM model enabled our team to identify and directly address key stakeholder hypotheses and resulted in coproduction of management-relevant research.

Collaborative adaptive management (CAM) is hypothesized to benefit management of rangeland ecosystems, but the presumed benefits have seldom been quantified, and never in a multipaddock rotational grazing system. Here, we evaluated average daily weight gain (ADG) of livestock (kg steer−1 d−1) in four grazing management treatments during the summers of 2016−2018 in a semiarid shortgrass steppe. These four treatments had the same stocking rate but differed in stocking densities. The three lowest stocking densities were implemented using nonadaptive grazing management, while the highest stocking density was implemented using CAM by an 11-member Stakeholder Group. Three of the four treatments used multipaddock rotational grazing. Growing season precipitation varied from drought in 2016 to near average in 2017 and dry in 2018. During nondrought years, ADG under nonadaptive grazing declined linearly as stocking density increased from low to high. This relationship was not significant during drought (2016). CAM increased absolute livestock production by 0.13 to 0.19 kg steer−1 d−1 in nondrought years, or a 23−25% relative increase in ADG. This benefit of CAM arose from the Stakeholder Group's ability to rotate cattle in response to spatiotemporal heterogeneity across the landscape—i.e., the ability to graze the “right pastures at the right time.” Multiplying the additional grazing season livestock gains achieved through CAM by the monetary value of gains ($ kg−1) resulted in an estimated additional gross revenue return from CAM of $48.16 to $55.54 per steer annually, as compared with revenues from nonadaptive multipaddock rotational grazing under nondrought conditions. These results indicate that CAM, supported with substantial and timely monitoring data, can minimize decreases in livestock production associated with high stocking densities used in multipaddock rotation systems. However, in this experimental context, the economic benefits of increased livestock production associated with CAM were likely insufficient to offset the substantial cost of this approach.

Livestock distribution in extensive rangelands of North America can present management challenges to land managers. Understanding the role of topography on livestock distribution, within and across diverse rangeland ecosystems, could provide land managers valuable information for adaptive management of livestock to address both conservation and production goals from these ecosystems. Here, we examine the influence of topography on grazing distribution unevenness and intensity of use of beef cattle in seven rangeland ecosystems spanning arid, semiarid, and subtropical environments. We focused on grazing distribution during the late growing season (summer and autumn) periods when topographic variation in rangelands is more coupled to low and nonuniform availability of high-quality forage. Pasture size and water sources strongly influence grazing distribution across ecosystems. High unevenness of grazing occurred in pastures with extensive distances to water, low stock density, and more rugged topography. Conversely, more uniform grazing distribution occurred in smaller, well-watered pastures that support higher stock density (animals per unit area) and gentler terrain. Comparison of two topographic indices, topographic wetness index and topographic position class index, in terms of their ability to predict cattle grazing distribution, revealed that categorical topographic position classes were more effective. For most arid and semiarid rangelands, livestock grazing distributions showed affinities for lowlands and flat plains compared with open slopes and uplands. In contrast to drier rangelands, livestock grazing distributions exhibited preference for upland and sloped areas of subtropical pastures, as low-lying areas with water-inundation likely curtailed selection. Across these diverse rangeland ecosystems of North America, results provide benchmark information on livestock grazing distribution to formulate improvements in adaptive management and decision making and incorporate technological advancements in precision livestock management to integrate abiotic environmental information with spatial movements of livestock and temporal vegetation dynamics.

A comprehensive understanding of multipaddock, rotational grazing management on rangelands has been slow to develop, and the contribution of adaptive management (Briske et al. 2011) and sufficient scale (Teague and Barnes 2017) have been identified as key omissions. We designed an experiment to compare responses of vegetation and cattle in an adaptively managed, multipaddock, rotational system with that of a season-long, continuous system at scales comparable with those of a working ranch. We hypothesized that 1) year-long rest periods in the adaptively managed, rotational pastures would increase the density and productivity of perennial C3 graminoids compared with continuously grazed pastures and 2) adaptive management, supported with detailed monitoring data, would result in similar cattle performance in the rotational as in the continuously grazed pastures. However, we found little supporting evidence for grazing management effects on C3 graminoid abundance or production under either above-average or below-average precipitation conditions during the 5-yr experiment. Furthermore, adaptive rotational grazing resulted in a 12–16% reduction in total cattle weight gain relative to continuous grazing each year. Our work shows that the implementation of adaptive management by a stakeholder group provided with detailed vegetation and animal monitoring data was unable to fully mitigate the adverse consequences of high stock density on animal weight gain. Under adaptive rotational grazing, C3 perennial grass productivity and stocking rate both increased following above-average precipitation. But when adaptive rotational management was directly compared with continuous grazing with the same increase in stocking rate, continuous grazing achieved similar vegetation outcomes with greater cattle weight gains. We suggest that managers in semiarid rangelands strive to maintain cattle at stock densities low enough to allow for maximal cattle growth rates, while still providing spatiotemporal variability in grazing distribution to enhance rangeland heterogeneity and long-term sustainability of forage production.

Grassland birds have experienced some of the steepest population declines of any guild of birds in North America. The shortgrass steppe contains some of North America's most intact grasslands, which makes the region particularly important for these species. It is well known that grassland birds differentially respond to variation in vegetation structure generated by spatiotemporally varying disturbance like grazing management. However, understanding how species respond to characteristics beyond vegetation structure or grazing could better inform management for these species in the shortgrass steppe. We analyzed point count data for 5 grassland bird species breeding on the Central Plains Experimental Range in northeastern Colorado from 2013 to 2017 to examine the predictive capacity of models representing fine-scale (∼5 ha) vegetation attributes (vegetation structure and cover type) and topography, combined with interannual precipitation variability (i.e. vegetation-abiotic models). We then compared these models to models based on grazing management treatments (applied to whole pastures, ∼130 ha) and edaphic conditions (ecological sites), which represented information more generally available to rangeland managers. Precipitation, vegetation structure, and vegetation cover type influenced all species in a manner consistent with, but more nuanced than, vegetation structure alone. These models also explained more variation in abundance for species that responded to grazing management. Thus, while grazing management can be applied adaptively to improve habitat for these species, our more detailed vegetation-abiotic models identified species-specific habitat components that could be targeted for management. For example, not grazing pastures with extensive, homogenous stands of mid-height grasses (e.g., Hesperostipa comata) for an entire growing season during wet years could be one strategy to enhance Grasshopper Sparrow (Ammodramus savannarum) abundance and stockpile residual forage for future utilization by livestock. Our models provide a better understanding of and reveal nuances in the suite of environmental conditions to which grassland birds respond in shortgrass steppe rangelands. LAY SUMMARY We lack clear understanding of which environmental characteristics might support declining bird species breeding in the shortgrass steppe of the United States. These bird species often breed on lands managed for cattle grazing and are known to respond to vegetation structure generated by grazing and/or soil conditions. We sought to evaluate how precipitation and different types of vegetation cover (e.g., shrubs, shortgrasses) could explain additional variation in bird abundance in this system. We found vegetation cover, vegetation structure, and precipitation could explain more variation in abundance than cattle grazing management and/or ecological sites (i.e. unique soil types with associated plant communities) for most bird species. For bird species that did not respond to grazing management, ecological site and year effects explained more variation in abundance than vegetation characteristics and precipitation. Precipitation conditions, types of vegetation cover, and ecological sites often are not considered when developing grazing management plans to support grassland birds; incorporating these factors into management plans may help support populations of these declining species.

Many arid and semi‐arid rangelands exhibit distinct spatial patterning of vegetated and bare soil‐dominated patches. The latter potentially represent a grazing‐induced, degraded ecosystem state, but could also arise via mechanisms related to feedbacks between vegetation cover and soil moisture availability that are unrelated to grazing. The degree to which grazing contributes to the formation or maintenance of degraded patches has been widely discussed and modeled, but empirical studies of the role of grazing in their formation, persistence, and reversibility are limited.We report on a long‐term (17 years) grazing removal experiment in a semi‐arid savanna where vegetated patches composed of perennial grasses were interspersed within large (>10 m2) patches of bare soil.Short‐term (3 years) grazing removal did not allow bare patches to become revegetated, whereas following long‐term (17 years) grazing removal, bare soil patches were revegetated by a combination of stoloniferous grasses and tufted bunchgrasses. In the presence of grazers, stoloniferous grasses partially recolonized bare patches, but this did not lead to full recovery or to the establishment of tufted bunchgrasses.These results show that grazers alter both the balance between bare and vegetated patches, as well as the types of grasses dominating both patch types in this semiarid savanna.Synthesis: Large herbivores fundamentally shaped the composition and spatial pattern of the herbaceous layer by maintaining a two‐phase herbaceous mosaic. However, bare patches within this mosaic can recover given herbivore removal over sufficiently long time scales, and hence do not represent a permanently degraded ecosystem state., The stability and spatial pattern of degraded and vegetated patches in dryland ecosystems has been modeled and discussed for decades, with few empirical studies. We present one of the first long‐term experiments that demonstrate these patterns are maintained by large herbivore grazing and can disappear when herbivores are removed.

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.

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.

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.

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.

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.

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.

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.

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.

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 (

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.

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.

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.

Advances in global positioning system (GPS) technology have dramatically enhanced the ability to track and study distributions of free-ranging livestock. Understanding factors controlling the distribution of free-ranging livestock requires the ability to assess when and where they are foraging. For four years (2008–2011), we periodically collected GPS and activity sensor data together with direct observations of collared cattle grazing semiarid rangeland in eastern Colorado. From these data, we developed classification tree models that allowed us to discriminate between grazing and non-grazing activities. We evaluated: (1) which activity sensor measurements from the GPS collars were most valuable in predicting cattle foraging behavior, (2) the accuracy of binary (grazing, non-grazing) activity models vs. models with multiple activity categories (grazing, resting, traveling, mixed), and (3) the accuracy of models that are robust across years vs. models specific to a given year. A binary classification tree correctly removed 86.5% of the non-grazing locations, while correctly retaining 87.8% of the locations where the animal was grazing, for an overall misclassification rate of 12.9%. A classification tree that separated activity into four different categories yielded a greater misclassification rate of 16.0%. Distance travelled in a 5 minute interval and the proportion of the interval with the sensor indicating a head down position were the two most important variables predicting grazing activity. Fitting annual models of cattle foraging activity did not improve model accuracy compared to a single model based on all four years combined. This suggests that increased sample size was more valuable than accounting for interannual variation in foraging behavior associated with variation in forage production. Our models differ from previous assessments in semiarid rangeland of Israel and mesic pastures in the United States in terms of the value of different activity sensor measurements for identifying grazing activity, suggesting that the use of GPS collars to classify cattle grazing behavior will require calibrations specific to the environment and vegetation being studied.

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

Restoring historical disturbance regimes to enhance habitat for grassland birds can conflict with livestock production goals and has been controversial because of uncertainty in the frequency and pattern of different disturbances prior to European settlement. We studied nesting habitat for the mountain plover (Charadrius montanus) in relation to prescribed fire, grazing by large herbivores (cattle), and grazing by black- tailed prairie dogs (Cynomys ludovicianus) in the shortgrass steppe of northeastern Colorado. Breeding mountain plovers primarily occurred on black-tailed prairie dog colonies or areas burned during the previous dormant season. Vegetation surrounding mountain plover nests and foraging locations was characterized by a fine-scale mosaic of prostrate ( 35% bare soil in a given square meter, with this fine-scale pattern distributed over a broad (>100-m radius) area. Mountain plovers rarely occupied grassland lacking prairie dogs or recent fire, but those that did selected sites with similar vegetation height and bare soil exposure as sites on burns and prairie dog colonies. Vegetation structure at mountain plover-occupied sites was also similar to random sites on burns and prairie dog colonies, but differed substantially from sites managed only with cattle. Intensive cattle grazing at twice the recommended stocking rate during spring (Mar-May) or summer (May-Oct) for 6 years produced significantly less bare soil than burns and prairie dog colonies, particularly following years with average or above-average precipitation. Thus, intensive cattle grazing did not substitute for prairie dog grazing or fire in terms of effects on vegetation structure and mountain plover habitat. Both prescribed burning and increased size and distribution of black- tailed prairie dog colonies appear to be effective and complementary means to manage for mountain plover breeding habitat in shortgrass steppe. Provision of mountain plover habitat has tradeoffs with traditional management for livestock production. Thus, managers need to clearly define desired outcomes for manage- ment to provide multiple ecosystem goods and services. 2012 The Wildlife Society.

We used very large scale aerial (VLSA) photography to quantify spatial patterns in bare soil in the northeastern Colorado shortgrass steppe. Using three pairs of pastures stocked at moderate (0.6 animal unit months lAUM] · ha -1 ) versus very heavy (1.2 AUM · ha -1 ) rates, we detected greater bare soil under very heavy (mean = 22.5%) versus moderate stocking (mean = 13.5%; P = 0.053) and a lower coefficient of variation across pastures under very heavy (0.48) versus moderate stocking (0.75; P = 0.032). Bare soil exhibited significant positive spatial autocorrelation across distances of 60–120 m under moderate stocking (Moran's I = 0.14), while patchiness at this scale was eliminated under very heavy grazing ( I = -0.05). Across distances of 120–480 m, we observed no spatial autocorrelation with either stocking rate. Spatial autocorrelation was greatest at a separation distance of 2 m ( I = 0.48–0.58) but was unaffected by stocking rate at this scale. Thus, very heavy grazing did not increase spatial autocorrelation in bare soil across scales of 2–480 m. Means and variability in the distribution of bare soil were not influenced by ecological site. Bare soil increased primarily at the scale of individual plant clusters through both increases in the density of small (2–20 cm) bare patch intercepts and increases in the frequency of bare patch intercepts of 20–60 cm (rather than s 20 cm). Our approach demonstrates the utility of VLSA for analyzing interactions between grazing and other landscape features and highlights the importance of spatially explicit sampling across broad scales (pastures) while testing for potential shifts in patchiness of bare soil at the scale of plant interspaces.

We examined the independent and combined effects of prescribed fire and livestock grazing on herbaceous plant production in shortgrass steppe of northeastern Colorado in the North American Great Plains. Burning was implemented in March, before the onset of the growing season. During the first postburn growing season, burning had no influence on soil moisture, nor did it affect soil nitrogen (N) availability in spring (April–May), but it significantly enhanced soil N availability in summer (June–July). Burning had no influence on herbaceous plant production in the first postburn growing season but enhanced in vitro dry matter digestibility of blue grama (Bouteloua gracilis [Willd. ex Kunth] Lag. ex Griffiths) forage sampled in late May. For the second postburn growing season, we found no difference in herbaceous plant production between sites that were burned and grazed in the previous year versus sites that were burned and protected from grazing in the previous year. Our results provide further evidence that prescribed burns conducted in late winter in dormant vegetation can have neutral or positive consequences for livestock production because of a neutral effect on forage quantity and a short-term enhancement of forage quality. In addition, our results indicate that with conservative stocking rates, deferment of grazing during the first postburn growing season may not be necessary to sustain plant productivity.

Domestic livestock have the potential to function as ecosystem engineers in semiarid rangelands, but prevailing management practices largely emphasize livestock production and uniform use of vegetation. As a result, variation in vegetation structure might not occur at appropriate spatial and temporal scales to achieve some contemporary conservation objectives. Here, we introduce the utility of livestock as ecosystem engineers and address potential benefits and consequences associated with heterogeneity-based management practices for conservation grazing in the semiarid rangelands of the western North American Great Plains. To illustrate the potential value of this approach, we provide specific examples where engineering effects of livestock could alter vegetation heterogeneity at within-pasture (, 100 ha) and among-pasture (,100 ha to thousands of hectares) scales to improve habitat for declining native grassland birds. Experimental evaluations of the efficacy of livestock to achieve desired modifications to vegetation structure are needed, along with the economic aspects associated with implementing heterogeneity-based management practices. Using livestock as ecosystem engineers to alter vegetation structure for grassland bird habitat is feasible in terms of application by land managers within the context of current livestock operations, and provides land managers important tools to achieve desired contemporary objectives and outcomes in semiarid rangelands of the western North American Great Plains.

Over the past century, fire has been widely suppressed in the western Great Plains, in part because of the potential negative effects on forage production for livestock. More recently, interest in the use of prescribed fire in shortgrass steppe has increased because of the potential applications for wildlife management, control of unpalatable plant species, and restoration of historic disturbance regimes. We studied the effects of prescribed burns conducted during late winter on herbaceous production, forage nitrogen content, and plant species composition of shortgrass steppe on the Pawnee National Grassland in northeastern Colorado. Late-winter burns conducted in moderately grazed sites under a wide range of precipitation conditions during 1997–2001 did not negatively affect herbaceous production in either the first or the second postburn growing season. Burning followed by a severe drought in 2002 reduced production by 19% in the second postburn growing season of 2003. Burns temporarily suppressed the abundance of broom snakeweed (Gutierrezia sarothrae) and prickly pear cactus (Opuntia polyacantha) and enhanced forage nitrogen content during May and June of the first postburn growing season. These findings suggest that, except following severe drought, prescribed burns conducted during late winter in grazed shortgrass steppe for objectives unrelated to livestock production can also have neutral or positive consequences for livestock.

Summary 1. African savannas are complex socio-ecological systems with diverse wild and domestic herbivore assemblages, which adapt spatially to intra- and interannual variation in forage quantity and quality, predation and disease risks. 2. As African savannas become increasingly fragmented by growing human populations and their associated ecological impacts, adaptive foraging options for wild and domestic herbivore populations are correspondingly limited, resulting in declining wildlife populations and impoverished pastoral societies. In addition, competition for grazing by expanding domestic herbivore populations threatens the viability of wild herbivore populations occupying similar grazing niches. 3. Conservation initiatives are further impacted by conflicts between wildlife and local communities of people who often receive little benefit from adjacent protected areas, creating conflict between the livelihood-orientated goals of communities and the conservation-oriented goals of the international community and those with vested interests in wildlife. Conservation strategies facilitating the alignment of these opposing goals of communities and conservationists are needed. 4. Synthesis and applications. Key to understanding facilitative and competitive interactions between wild and domestic herbivores are the concepts of niche differentiation and functional resource heterogeneity. Uncontrolled incursions of burgeoning domestic herbivore populations into protected areas (PAs) threaten the conservation of wild herbivore biodiversity. However, domestic herbivores can be managed to minimize competition with wild herbivores and to enhance habitat by maximizing grassland structural heterogeneity (greater adaptive foraging options), creation of nutrient hotspots in the landscape and facilitation of high-quality grazing. Ecosystem service benefits to communities through controlled access to grazing resources in PAs, associated with appropriate disease management, can provide a conservation payment to promote communities’ support of conservation of key wildlife migratory ranges and corridors outside PAs.

Black-tailed prairie dogs (Cynomys ludovicianus) are a key component of the disturbance regime in semi-arid grasslands of central North America. Many studies have compared community and ecosystem characteristics on prairie dog colonies to grasslands without prairie dogs, but little is known about landscape-scale patterns of disturbance that prairie dog colony complexes may impose on grasslands over long time periods. We examined spatiotemporal dynamics in two prairie dog colony complexes in southeastern Colorado (Comanche) and northcentral Montana (Phillips County) that have been strongly influenced by plague, and compared them to a complex unaffected by plague in northwestern Nebraska (Oglala). Both plague-affected complexes exhibited substantial spatiotemporal variability in the area occupied during a decade, in contrast to the stability of colonies in the Oglala complex. However, the plague-affected complexes differed in spatial patterns of colony movement. Colonies in the Comanche complex in shortgrass steppe shifted locations over a decade. Only 10% of the area occupied in 1995 was still occupied by prairie dogs in 2006. In 2005 and 2006 respectively, 74 and 83% of the total area of the Comanche complex occurred in locations that were not occupied in 1995, and only 1% of the complex was occupied continuously over a decade. In contrast, prairie dogs in the Phillips County complex in mixed-grass prairie and sagebrush steppe primarily recolonized previously occupied areas after plague-induced colony declines. In Phillips County, 62% of the area occupied in 1993 was also occupied by prairie dogs in 2004, and 12% of the complex was occupied continuously over a decade. Our results indicate that plague accelerates spatiotemporal movement of prairie dog colonies, and have significant implications for landscape-scale effects of prairie dog disturbance on grassland composition and productivity. These findings highlight the need to combine landscape-scale measures of habitat suitability with long-term measures of colony locations to understand the role of plague-affected prairie dogs as a grassland disturbance process.

Grazing intensity elicits changes in the composition of plant functional groups in both shortgrass steppe (SGS) and northern mixed-grass prairie (NMP) in North America. How these grazing intensity-induced changes control aboveground net primary production (ANPP) responses to precipitation remains a central open question, especially in light of predicted climate changes. Here, we evaluated effects of four levels (none, light, moderate, and heavy) of long-term (>30 yr) grazing intensity in SGS and NMP on: (1) ANPP; (2) precipitation-use efficiency (PUE, ANPP : precipitation); and (3) precipitation marginal response (PMR; slope of a linear regression model between ANPP and precipitation). We advance prior work by examining: (1) the consequences of a range of grazing intensities (more grazed vs. ungrazed); and (2) how grazing-induced changes in ANPP and PUE are related both to shifts in functional group composition and physiological responses within each functional group. Spring (April-June) precipitation, the primary determinant of ANPP, was only 12% higher in NMP than in SGS, yet ANPP and PUE were 25% higher. Doubling grazing intensity in SGS and nearly doubling it in NMP reduced ANPP and PUE by only 24% and 33%, respectively. Increased grazing intensity reduced C3 graminoid biomass and increased C4 grass biomass in both grasslands. Functional group shifts affected PUE through biomass reductions, as PUE was positively associated with the relative abundance of C3 species and negatively with C4 species across both grasslands. At the community level, PMR was similar between grasslands and unaffected by grazing intensity. However, PMR of C3 graminoids in SGS was eightfold higher in the ungrazed treatment than under any grazed level. In NMP, PMR of C3 graminoids was only reduced under heavy grazing intensity. Knowing the ecological consequences of grazing intensity provides valuable information for mitigation and adaptation strategies in response to predicted climate change. For example, moderate grazing (the recommended rate) in SGS would sequester the same amount of aboveground carbon as light grazing because ANPP was nearly the same. In contrast, reductions in grazing intensity in NMP from moderate to light intensity would increase the amount of aboveground carbon sequestrated by 25% because of increased ANPP.

Large herbivores can both positively and negatively affect primary productivity and rates of nutrient cycling in different ecosystems. Positive effects of grazers in grasslands have been attributed to migratory behavior of the dominant ungulate species and soil fertility. We studied the effects of grazers on aboveground net primary productivity (ANPP) and N cycling on central Kenyan rangeland characterized by intense, chronic grazing by a mixed community of cattle and resident native ungulates. Exclosure studies conducted at high and low levels of soil fertility showed that both soil fertility and annual rainfall patterns mediate the effects of grazers on ANPP and N cycling. In a low-rainfall year with short (1 month) growing seasons, grazers reduced aboveground productivity regardless of soil nutrient availability. However, in a high-rainfall year with a 5-month growing season, grazers increased ANPP on nutrient-rich glades and suppressed ANPP on nutrient-poor bushland sites. Concomitant studies of grazer effects on N cycling revealed complex interactions with the seasonal pattern of N-mineralization and inorganic N availability. Grazers increased the size of the inorganic N pool available to plants at the onset of the growing season, particularly in nutrient-rich glades. However, grazers also decreased N mineralization rates at all sites early in the growing season. Measures of N availability via ion-exchange resin bags suggested that the combined effects of grazers on inorganic N pool fluctuations and N-mineralization rates resulted in a net increase in N availability at glade sites and a net decrease in N availability at bushland sites. The net effect of grazers on soil N availability mirrored grazer effects on ANPP in the high-rainfall year. Overall, our results suggest that grazer effects on N dynamics are closely linked to effects on productivity and resilience to drought. Furthermore, even under optimal conditions of high soil fertility and above-average rainfall, grazer promotion of ANPP in this chronically grazed system dominated by resident ungulates was small compared to systems dominated by migratory ungulates.

The effects of grazing by white-tailed deer ( Odocoileus virginianus ) on populations of Trillium spp. were examined in remnant, old-growth patches of the highly fragmented Big Woods forest ecosystem in south- eastern Minnesota. We conducted three separate studies involving an exclosure experiment, transplant exper- iments, and comparisons of Trillium populations among study sites. The highest grazing intensity was ob- served where deer occurred at high overwinter concentrations ( z 25-35/km 2 ); significantly lower grazing intensities occurred at low overwinter density ( z 5-10/km 2 ). Deer focused their grazing on large, reproduc- tive plants; at sites with high deer density, Trillium population structure was skewed toward small plants, and deer consistently caused over 50% reduction in reproduction during the growing season. Protection of indi- vidual plants from deer for two growing seasons resulted in dramatically increased flowering rates and sig- nificantly greater leaf area compared to control plants. No significant impact of current-year herbivory on re- production in the following year was detected. Nevertheless, flowering rates at one site with high overwinter deer densities for at least the past 5 years suggest that the cumulative effects of grazing over several years can reduce reproduction in subsequent years. Transplant experiments with Trillium grandiflorum also showed that deer had significant effects on growth and reproduction where deer occur at high density. Our results suggest that changes in landscape structure and local deer abundance have altered plant-deer relationships such that grazing can lead to the local extirpation of sensitive forbs such as Trillium spp. As a result, active, long-term management of deer at low densities appears necessary for the conservation and restoration of fragmented forest communities in eastern North America.

Plants are eaten by a tremendous array of herbivores, including almost half of known insect species. Although herbivores consume most plants to some degree, many plants are also relatively well defended, and herbivore populations are often limited by predators. The net result of these processes is that the extent of herbivory, and the strength of its effects on plant populations and ecosystem processes, are highly variable. Herbivores strongly influence plants in aquatic environments, productive environments and environments with nutritious, poorly defended plants or few predators. Effects of herbivores can also be accentuated through positive feedbacks between herbivory and soil resources, in which herbivore-mediated changes in plant community composition accelerate or decelerate nutrient cycling. Although research on herbivory has focused primarily on natural systems, few of these systems are free of human influence. Humans dramatically change plant–herbivore relationships by removing predators, increasing plant resource availability and moving both plants and herbivores around the globe. Key concepts Plants defend themselves effectively, using a combination of chemical defences and physical defences and tolerance. Plant defence theory aims to explain variation among species and ecosystems in the types and amounts of plant defence. In addition to plant defences, the extent of herbivory is limited by predation, which can greatly reduce herbivore abundance. Despite plant defences and predation, herbivores often have strong effects on plants. Positive feedbacks between plant resources, plant traits and herbivores can increase the influence of herbivores on plants and ecosystems. Humans dramatically alter plant–herbivore dynamics by moving plants and herbivores, reducing the abundance of predators, increasing nutrient availability and changing the spatial distribution of plant communities. Keywords: grazing; herbivory; plant defence; plant productivity and diversity; predation

White-tailed deer (Odocoileus virginianus) can cause major changes in the composition and structure of forest communities by browsing shrubs and tree seedlings and grazing understory forbs. Such effects have become an increasingly pervasive management concern in protected natural areas and parks where conservation of native plant communities is a primary objective. The magnitude of these effects can vary widely according to variations in local deer numbers and availability of alternate food sources. We used measurements from 11 maple-basswood forest fragments in southcentral Minnesota to examine the predictability of deer grazing intensity on understory forbs based on local winter deer density, composition of the landscape surrounding each forest fragment, and characteristics of forb populations within the forest. In early summer, grazing intensity on 6 palatable forb species at most sites was inversely correlated with the availability of alfalfa within a 1.5-km radius of the stand (r 2 = 0.66); winter deer density and forb flowering rate within the stand were additional important predictors of grazing intensity. Later in the growing season, most variability in the intensity of grazing among forest fragments could be explained either by the availability of row crops, alfalfa, and fields within a 1.5-km radius of the stand (r 2 = 0.75) or by a combination of winter deer density and forb abundance within the stand (r 2 = 0.75). Results show that parks and preserves with low densities of palatable plant species in the forest understory may be especially susceptible to effects of deer grazing. Changes in landscape composition (e.g., increased row-cropping or conversion of land to residential developments) should be an important consideration in the management of deer densities in areas designed to protect native forest communities.

In the Great Plains of central North America, sustainable livestock production is dependent on matching the timing of forage availability and quality with animal intake demands. Advances in remote sensing technology provide accurate information for forage quantity. However, similar efforts for forage quality are lacking. Crude protein (CP) content is one of the most relevant forage quality determinants of individual animal intake, especially below an 8% threshold for growing animals. In a set of shortgrass steppe paddocks with contrasting botanical composition, we (1) modeled the spatiotemporal variation in field estimates of CP content against seven spectral MODIS bands, and (2) used the model to assess the risk of reaching the 8% CP content threshold during the grazing season for paddocks with light, moderate, or heavy grazing intensities for the last 22 years (2000–2021). Our calibrated model explained up to 69% of the spatiotemporal variation in CP content. Different from previous investigations, our model was partially independent of NDVI, as it included the green and red portions of the spectrum as direct predictors of CP content. From 2000 to 2021, the model predicted that CP content was a limiting factor for growth of yearling cattle in 80% of the years for about 60% of the mid-May to October grazing season. The risk of forage quality being below the CP content threshold increases as the grazing season progresses, suggesting that ranchers across this rangeland region could benefit from remotely sensed CP content to proactively remove yearling cattle earlier than the traditional October date or to strategically provide supplemental protein sources to grazing cattle. EEA Concepción del Uruguay Fil: Irisarri, Jorge Gonzalo Nicolás. Rothamsted Research. Sustainable Agriculture Sciences; Reino Unido Fil: Durante, Martin. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Concepción del Uruguay; Argentina Fil: Durante, Martin. Instituto Nacional de Investigación Agropecuaria (INIA). Estación Experimental INIA Tacuarembó. Programa Pasturas y Forrajes; Uruguay Fil: Derner, Justin D. United States Department of Agriculture-Agricultural Research Service. Rangeland Resources Research Unit; Estados Unidos Fil: Oesterheld, Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentina Fil: Oesterheld, Martin. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentina Fil: Augustine, David J.. United States Department of Agriculture–Agricultural Research Service. Rangeland Resources and Systems Research Unit; Estados Unidos