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The fire-exotic annual grass cycle is a severe threat to shrub-steppe rangelands, and a greater understanding of how livestock grazing relates to the problem is needed to guide effective management interventions. Grazing effects vary throughout shrub-steppe rangelands because livestock are selective in their use within pastures. Thus, knowing where cattle are located and concentrate their use in a postfire landscape is important for enhancing plant community resiliency to disturbance and resistance to exotic annual grass invasion. We asked how the distribution and intensity of cattle use varied across 113 000 ha of recently burned, environmentally varied shrub-steppe. Generalized linear mixed effects models were used to determine the relationship of cattle dung (presence/absence and counts), which was recorded during the third to fifth postfire year (after grazing deferment) on 1166 (531-m2) plots, to water sources, burn severity, grass cover, and topographic predictors. Our distribution and intensity of use models revealed similar relationships between cattle use and landscape predictors. Cattle use was greater in areas that were flatter and closer to water and that had moderate burn severity and less heat load and ruggedness. Slope had the strongest effect on cattle use of the predictors. The probability of cattle being present decreased by 10% for every 5° increase in slope until slope exceeded 15°, and then the effect of slope weakened. Despite moderate slopes (X̄ = 14°), cattle use was greater in areas of moderate burn severity, presumably because these areas provided greater perennial grass production. While there was much unexplained variation, these models suggest that cooler climate, water access, topographic factors, and burn severity affect maneuverability to create greater livestock use of certain areas within grazing pastures. Restoration investment planning or assessments and expectations of restoration success could be improved by considering that these livestock hotspots may recover differently from the surrounding landscape.
Restoration of native shrub species is challenging but direly needed in arid and semiarid rangelands globally as native shrubs provide critical habitat for wildlife and livestock forage. Restoration of antelope bitterbrush (Purshia tridentata Pursh DC), a wildlife-important shrub, is often a priority on western US rangelands. One challenge to bitterbrush restoration is competitive exotic annual grasses. Exotic annual grasses can be successfully controlled with pre-emergent herbicides, but the effects of controlling exotic annual grasses with pre-emergent herbicides on bitterbrush survival and growth are unknown. We evaluated the effects of applying a pre-emergent herbicide, imazapic, to control exotic annual grasses on planted bitterbrush seedlings and existing vegetation for 2 yr post treatment at five sites in southeastern Oregon. Imazapic application reduced exotic annual grass cover and density but did not improve bitterbrush establishment. Exotic annual grass control did lead to an increase in native perennial bunchgrass cover. We suspect the lack of treatment effect was caused by high mortality of bitterbrush seedlings from drought in the first year. By the second year, bitterbrush was largely lost across the study sites with only four individuals surviving. The high bitterbrush seedling mortality observed in this study highlights that multiple barriers to restoration success likely exist in arid and semiarid rangelands. For successful restoration, land managers and restoration practitioners need to have a plan and resources for overcoming multiple barriers, which may require several restoration attempts should initial attempts be unsuccessful.
Stuart P. Hardegree, Alex R. Boehm, Nancy F. Glenn, Roger L. Sheley, Patrick A. Reeves, Neal J. Pastick, Ahmad Hojjati, Stephen P. Boyte, Josh Enterkine, Corey A. Moffet, Gerald N. Flerchinger
Invasive annual grasses now dominate millions of hectares of rangeland in the Intermountain Western United States. Local annual grass distribution, however, has been shown to follow landscape patterns of slope, aspect, and elevation that are correlated with ecological resilience to stress and disturbance and resistance to annual grass invasion. Although these patterns have previously been linked to soil-climate classes, several mechanistic factors in native-plant seedling establishment are also associated with both topography and seasonal weather patterns in the year following planting. In this study we used the Simultaneous Heat and Water (SHAW) model to estimate long-term weather effects on soil microclimate and hydrothermal-germination models to predict germination response of one fast- and one slow-germinating native grass as a function of planting date, slope, aspect, and elevation in the Boise Foothills in southwestern Idaho. Higher elevation and northerly aspect sites are more likely to defer germination of seeded species until late enough in the fall that they avoid postgermination/preemergence freezing mortality. These sites are also more favorable for survival of emerged seedlings through mid to late summer. Slope, aspect, and elevation effects on modeled restoration outcomes are consistent with previously modeled general patterns of ecological resilience and resistance as a function of soil hydrothermal class, but inclusion of slope and aspect effects may produce finer-scale metrics for mapping these patterns over space. The probabilistic nature of microclimatic variability as a function of elevation may yield useful insights into successful restoration approaches for reestablishment of native plant communities in lower-elevation ecosystems with inherently lower ecological resilience and resistance. The generally arid climate in this region, however, may limit successful restoration outcomes at lower elevation in most years even under conditions of long-term annual grass control.
Rangelands provide ecosystem services for livestock and habitat for many wildlife species. However, the key features that determine their value for biodiversity conservation need to be assessed regionally. To elucidate the structural attributes that drive bird and rodent assemblages in semiarid rangelands in the southern Mexican Plateau, we studied patches of rangelands dominated by herbaceous plants (open) and xerophytic shrub communities (closed). We hypothesized that different guilds and species of birds and rodents are influenced differently by rangeland condition and different habitat components, and that bird assemblages had a higher turnover rate between patches than rodents. We surveyed the birds and rodents during the three regional climatic seasons and measured ground plant cover of herbs, shrubs, nopales, and trees. Through an information-theoretic approach we tested the effect of range condition and season on all variables of habitat and bird and rodent species richness and abundance. Habitat components (shrubs and nopales) most often included in the best/most parsimonious models explained bird and rodent abundances. Rodent species turnover is lower among rangeland plots of the same type geographically separated than between nearby plots of different type. In contrast, bird species turnover was higher because their higher mobility allows them to explore landscape patches than might offer complementation and/or supplementation. Rangelands in the southern Mexican Plateau should be viewed not only as livestock-producing areas but also as landscape components that can and should be used to effectively support biodiversity conservation, complementing the conservation role of other regional habitats. The high biodiversity conservation potential of the rangelands we studied should be recognized, and both habitat conditions should be incorporated in any regional conservation plans.
A potential mechanism for lower livestock weight gains with rotational grazing is the additional movement and associated energy expenditures incurred with rotation of animals among paddocks. We evaluated these metrics in 2016 and 2017 using pedometers affixed to free-ranging naïve yearling steers grazing semiarid, shortgrass steppe under contrasting grazing management treatments with the same stocking rate: traditional season-long (mid-May to October) grazing management and collaborative adaptive rangeland management (CARM) at a ranch scale (2-600 ha: ten 130-ha paddocks for each treatment). Mean daily number of steps by steers in paddocks during the grazing season, excluding those associated with moves between paddocks, were 3.0% lower (2016) and 7.8% greater (2017) for CARM, but energy expenditures did not differ significantly between treatments in either year. Daily step counts decreased in traditional rangeland management (TRM) as the grazing season progressed. Step counts decreased from day 1 to day 8 in CARM paddocks following rotation of steers. Steers in the TRM treatment took more steps daily than CARM steers in the first third of the grazing season, but this reversed in the last third of the grazing season. These findings suggest that observed 12%–16% reductions in livestock weight gains with CARM were not influenced by differences in total grazing season steps as energy expenditures of steers did not differ. Two additive influences of within-season steer movement dynamics suggest that forage quality was the primary driver for the decrease in weight gains in CARM. First, fewer steps in the early growing season, when forage quality is highest, indicate reduced selectivity for nutrient-rich patches. Second, more steps by yearlings in the late growing season suggest that these heavier animals expending more energy for maintenance were searching to satisfy gut fill as forage quantity and quality on offer per steer was limiting with the 10-fold higher stocking density.
High interannual variability in production occurs in many semiarid rangelands, including the perennial-dominated sagebrush steppe, in response to variable weather conditions. Describing the effects of weather on the dynamics of sagebrush steppe has implications for a broad set of management objectives including forage and wildlife habitat. Here, we investigated the effects of seasonal weather and plant associations, related to abiotic characteristics, on herbaceous production dynamics across 44 intact, representative sagebrush steppe sites across eastern Oregon from 2003 to 2012. We tested for the effects of sampling year, lagged precipitation, and potential evapotranspiration predictors, as well as prior year biomass and plant association on production of major herbaceous functional groups. We also tested for synchrony across functional groups and plant associations. We found that spring precipitation was the most consistent predictor of production. However, several other variables including prior year weather significantly affected production. Production sensitivity to weather was combined with high synchrony across functional groups and associations, suggesting low potential for production stability associated with these factors in sagebrush steppe in the northern Great Basin.
Prairie dogs and livestock have long been viewed as competitors for forage resources, causing widespread exterminations of prairie dogs, resulting in the decline of other threatened and endangered wildlife species. In this study we model the impacts that prairie dogs exhibit on the long-term profitability and cow herd dynamics of a ranch over a 40-yr production period on a representative cow-calf ranch operation in the Thunder Basin Ecoregion of Wyoming. More specifically, we evaluate the effects of prairie dogs on a cow-calf operation through two forage/livestock use assumptions; the first is simply loss of forage due to prairie dog consumption, and the second scenario assumes there is no available forage for livestock on prairie dog colonies. We also include three different potential prairie dog population dynamic scenarios: unmanaged prairie dogs, unmanaged prairie dogs with increased colony expansion during drought, and prairie dogs managed for a target colony size. As expected, our results indicate that prairie dogs decrease forage availability for grazing, thus reducing the average cow herd size on a ranch, the annual returns from livestock sales, and the maximized net present value of annual returns. Further, the magnitude of these impacts and the financial feasibility of managing prairie dogs largely depends on the effects prairie dogs exhibit on forage resources and how cattle use these forage resources.
Sergio A. Arispe, Dustin D. Johnson, Katherine L. Wollstein, April Hulet, K. Scott Jensen, Brad W. Schultz, James E. Sprinkle, Michele F. McDaniel, Thomas Ryan, Mark Mackenzie, Sean Cunningham
Rangeland wildfire is a wicked problem that cuts across a mosaic of public and private rangelands in the western United States and countless countries worldwide. Fine fuel accumulation in these ecosystems contributes to large-scale wildfires and undermines plant communities' resistance to invasive annual grasses and resilience to disturbances such as fire. Yet it can be difficult to implement fuels management practices, such as grazing, in socially and politically complex contexts such as federally managed rangelands in the United States. In this Research-Partnership Highlight, we argue that private-public partners in such settings must be strategic in their selection of tasks to generate “small wins” in order to build the trust, competency, and legitimacy needed to advance an approach for landscape-scale fine fuels management. We highlight a fine fuels reduction partnership consisting of public and private entities in southeastern Oregon that established a research and education project and applied dormant season grazing on three pastures within the Vale District Bureau of Land Management. We describe the impetus for the partnership, antecedents, strategic tactics, and ongoing learning and reflection used to revise processes. In this example, implementing dormant season grazing as a research and education project allowed the partners to assess the efficaciousness of the treatment, as well as the operational logistics and administrative competencies necessary to apply the treatment to manage fine fuels at broader scales. Because dormant season grazing may, in some instances, conflict with established practices and norms, small-scale projects such as this allow partners to refine understandings of the social and administrative conditions that make implementation possible. Generating small wins through projects such as this is a critical precursor for partnerships seeking to take on larger, more complex endeavors that involve increasing ecological, economic, and social uncertainty.
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