• Editorial: A Scientifically Rigorous and User-Friendly Rangeland ecology & Management

      Sheley, R.; Boyd, C.; Dobrowolski, J.; Hardegree, S.; James, J.; Mangold, J. (Society for Range Management, 2016)
    • Daily Forage Intake by Cattle on Natural Grassland: Response to Forage Allowance and Sward Structure

      Trindade, J.K.D.; Neves, F.P.; Pinto, C.E.; Bremm, C.; Mezzalira, J.C.; Nadin, L.B.; Genro, T.C.M.; Gonda, H.L.; Carvalho, P.C.F. (Society for Range Management, 2016)
      We investigated the hypothesis that not only forage allowance but also sward structure affects daily forage intake by beef heifers on natural grasslands of the Pampa Biome (southern Brazil). We used data from a long-term experiment, which has been managed by forage allowance levels since 1986. The objective was to investigate sward management targets that maximize daily forage intake. During January and December 2009, we evaluated the effect of forage allowance on forage mass, sward height and tussock frequency, and its consequences on dry matter intake (DMI). The experiment was arranged in a randomized complete block design with two replicates. Treatment was level of daily forage allowance (4, 8, 12, and 16 kg dry matter [DM] per 100 kg of animal body weight [BW]). Data were analyzed using regression, principal component analysis, and descriptive analyses from three-dimensional contour graphs with the data of sward structure, DMI, and DMI rate. Results demonstrated that DMI was positively correlated to forage allowance. However, higher levels of forage allowance can cause lower intake rates of forage and nutrients. We concluded that sward targets which promoted higher DMI and DMI rate were: daily forage allowance of ∼ 12 kg of dry matter per 100 kg of the animal's body weight, forage mass between 1 800 and 2 300 kg DM·ha-1, sward height between 11.5 and 13.4 cm, and tussock frequency lower than 30% of occurrence in the pastures. Within these targets, a high intake of nutrients was obtained, indicating the potential use of sward structure as a tool for managing natural grasslands in order to promote high intake of forage and nutrients by cattle. © 2016 Society for Range Management. Published by Elsevier Inc. All rights reserved.
    • Cattle as Dispersal Vectors of Invasive and Introduced Plants in a California Annual Grassland

      Chuong, J.; Huxley, J.; Spotswood, E.N.; Nichols, L.; Mariotte, P.; Suding, K.N. (Society for Range Management, 2016)
      Plant invasions are a threat to rangelands in California. Understanding how seeds of invasive plants are dispersed is critical to developing sound management plans. Domestic livestock can transport seeds long distances by ingesting and passing seeds in dung (endozoochory) or by the attachment of seeds to skin and fur (epizoochory). Our objective was to characterize the role of cattle as seed dispersers of both invasive and noninvasive species via endozoochory and epizoochory in a Sierra foothills rangeland. To quantify endozoochory, we sampled dung from two dry-season grazing periods and evaluated seed content by growing dung for 3 months in a greenhouse. To quantify epizoochory, we collected seeds directly from the fur of 40 cattle. We categorized the invasion status and functional groups of all species found and quantified landscape-scale vegetation composition in order to determine whether dispersal mode was associated with functional group, invasion status, or vegetation composition. Finally, we evaluated the potential for the noxious weed medusahead (Taeniatherum caput-medusae [L.] Nevski) to travel long distances on cattle fur using a detachment experiment with a model cow. We found that forbs were more likely to be dispersed by endozoochory, and invasive species were more likely to be dispersed by epizoochory. Medusahead was dispersed exclusively by epizoochory and was able to travel up to 160 m on a model cow. Our results suggest that cattle may be an important dispersal vector for both invasive and noninvasive plants. © 2016 Society for Range Management. Published by Elsevier Inc. All rights reserved.
    • A Critical Examination of Timing of Burning in the Kansas Flint Hills

      Gene Towne, E.; Craine, J.M. (Society for Range Management, 2016)
      Frequent burning is a crucial ecological and economic component of the Kansas Flint Hills. Although burning is important for the preservation of tallgrass prairie and improving livestock production, it has become a controversial societal issue because of its potential impact on air quality standards. Over the past 80 years, recommendations on burning in Kansas have ranged from total fire exclusion to burning only in late April; and for the past 40 years, the concept that burning should only occur in late spring has become ingrained in the cultural practices of rangeland management. Yet the scientific basis for these recommendations has received little rigorous scrutiny. Herein, we critically review the research on dormant-season burning in the Flint Hills that formed the foundation for modern burn practices in Kansas. Close examination of the historical data does not support the tenet that burning must be limited to a narrow window in late spring. Many conclusions of the research that led to recommending burning only in late spring were ambiguous, not subjected to statistical analysis, or were influenced by an antiburn bias. Current research suggests that timing of a burn is not as critical as ranchers have been led to believe and burning does not have to be restricted to a narrow window in late April. There is an absence of scientific evidence that burning earlier in the spring adversely affects forage production, plant species composition, soil moisture, or cattle weight gain. Although there is a need for research on the consequences of burning grazed pastures at different times of the year, expanding the window for burning earlier in the dormant season should help alleviate air quality issues downwind of the burned areas and potentially be beneficial to ranchers. © 2016 Society for Range Management. Published by Elsevier Inc. All rights reserved.
    • Voices of Change: Narratives from Ranching Women of the Southwestern United States

      Wilmer, H.; Fernández-Giménez, M.E. (Society for Range Management, 2016)
      The gendered contexts of rangeland decision-making in the southwestern United States are poorly understood. We conducted life-history interviews with 19 ranching women and analyzed the resulting transcripts using narrative analysis. Interviews revealed eight common themes in these women ranchers' experiences: 1) learning from older generations, 2) finding a personal career path, 3) operating livestock businesses, 4) breaking gender barriers, 5) leading communities, 6) aging and going on alone, 7) living close to the land, and 8) passing the ranching tradition to the next generation. Women's roles as ranch decision-makers, community-keepers, and business operators evolve throughout their lifetimes, as do their needs for decision-making support from outreach. We suggest that women's life stages and gendered contexts be considered in further rangeland management research, policy, and extension. © 2016 The Society for Range Management. Published by Elsevier Inc. All rights reserved.
    • Topographic Context of the Burn Edge Influences Postfire Recruitment of Arid Land Shrubs

      Condon, L.A.; Weisberg, P.J. (Society for Range Management, 2016)
      Although fire is becoming frequent in arid lands throughout the world, little is known about the recruitment pattern of many arid land shrub species after fire. We explored topographic and edaphic correlates of postfire recruitment for four shrub species 6 years following wildfire in central Nevada, United States. We hypothesized that the spatial pattern of shrub recruitment varies with fire-related species traits according to the topographic position of the burn edge, which correlated with postfire seed sources. Where the burn edge fell on a ridge, the frequency of the colonizing shrub, Artemisia tridentata ssp. vaseyana, decreased with distance from the burn edge, whereas the frequency of facultative resprouting specieswas independent or increased with distance. Where the burn edge fell behind a ridge, there were fewer shrubs overall and a greater proportion of resprouting species. Most individuals of resprouting species were adults, suggesting immediate, fire-stimulated recruitment. Interactions among topographic position and distance from the burn edge influence the recruitment patterns of shrub species and have implications for the postfire species assemblage that are predictable on the basis of firerelated plant traits. We demonstrate how the topographic position of the burn edge influences postfire recovery trajectories of the shrub community. © 2016 The Society for Range Management. Published by Elsevier Inc. All rights reserved.
    • Temporal Variability in Microclimatic Conditions for Grass Germination and Emergence in the Sagebrush Steppe

      Hardegree, S.P.; Sheley, R.L.; Duke, S.E.; James, J.J.; Boehm, A.R.; Flerchinger, G.N. (Society for Range Management, 2016)
      Sagebrush steppe ecosystems in the western United States are characterized by harsh environmental conditions with high annual and seasonal variability in both precipitation and temperature. Environmental variability contributes to widespread failure in establishing stands of desired species on degraded and invaded landscapes. To characterize seasonal microclimatic patterns and planting date effects on restoration outcomes, we evaluated long-term simulations of seed germination response of cheatgrass (Bromus tectorum L.), bottlebrush squirreltail (Elymus elymoides [Raf] Swezey), and Idaho fescue (Festuca idahoensis Elmer) to annual patterns of soil temperature and moisture. Extremely high annual variability in both the conditions favorable for germination and patterns of post-germination drought and thermal stress make it difficult to justify general inferences about seedbed treatment and planting date effects from individual, short-term field studies. We discuss the interpretation of individual-year and seasonal plant establishment factors and offer a mechanistic model for interpreting planting date and year effects on initial seedling establishment. Historical ranking and mechanistic descriptions of individual-year seedbed conditions may allow for expanded inferences through meta-analysis of limited-term field experiments. © 2015 Published by Elsevier Inc. on behalf of The Society for Range Management.
    • Spatially Explicit Rangeland Erosion Monitoring Using High-Resolution Digital Aerial Imagery

      Gillan, J.K.; Karl, J.W.; Barger, N.N.; Elaksher, A.; Duniway, M.C. (Society for Range Management, 2016)
      Nearly all of the ecosystem services supported by rangelands, including production of livestock forage, carbon sequestration, and provisioning of clean water, are negatively impacted by soil erosion. Accordingly, monitoring the severity, spatial extent, and rate of soil erosion is essential for long-term sustainable management. Traditional field-based methods of monitoring erosion (sediment traps, erosion pins, and bridges) can be labor intensive and therefore are generally limited in spatial intensity and/or extent. There is a growing effort to monitor natural resources at broad scales, which is driving the need for new soil erosion monitoring tools. One remote-sensing technique that can be used to monitor soil movement is a time series of digital elevation models (DEMs) created using aerial photogrammetry methods. By geographically coregistering the DEMs and subtracting one surface from the other, an estimate of soil elevation change can be created. Such analysis enables spatially explicit quantification and visualization of net soil movement including erosion, deposition, and redistribution. We constructed DEMs (12-cm ground sampling distance) on the basis of aerial photography immediately before and 1 year after a vegetation removal treatment on a 31-ha Piñon-Juniper woodland in southeastern Utah to evaluate the use of aerial photography in detecting soil surface change. On average, we were able to detect surface elevation change of ±8-9cm and greater, which was sufficient for the large amount of soil movement exhibited on the study area. Detecting more subtle soil erosion could be achieved using the same technique with higherresolution imagery from lower-flying aircraft such as unmanned aerial vehicles. DEM differencing and processfocused field methods provided complementary information and a more complete assessment of soil loss and movement than any single technique alone. Photogrammetric DEM differencing could be used as a technique to quantitatively monitor surface change over time relative to management activities. © 2016 The Society for Range Management. Published by Elsevier Inc. All rights reserved.
    • Seed Dormancy Mechanisms in Basalt Milkvetch and Western Prairie Clover

      Jones, T.A.; Johnson, D.A.; Bushman, B.S.; Connors, K.J.; Smith, R.C. (Society for Range Management, 2016)
      A greater diversity of native legumes and forbs is desirable for rangeland restoration practice in the Intermountain Region of the western United States. But for such diversity to materialize in the seed marketplace and to be effective in restoration practice, seeds that germinate reliably in seed fields and on restoration sites are needed. We measured germination response of two native legumes, basalt milkvetch (Astragalus filipes Torr. ex A. Gray) and western prairie clover (Dalea ornata [Douglas] Eaton & Wright), after eight germination treatments. Treatments were a factorial combination of 1) seed scarification with sandpaper (or unscarified), 2) a substrate of moist sand (or blotter paper), and 3) a 3-wk prechill at 5° (or nonprechilled). Cumulative germination increased linearly throughout the 10-wk course of the experiment for all treatment combinations in both species. Scarification increased germination of western prairie clover, but prechilling and substrate had no effect. In contrast, prechilling, scarification, and a sand substrate all increased germination of basalt milkvetch. Hence, for this species the prechilled/scarified/sand treatment combination displayed the numerically highest germination for all 10 wk (30-43%), and the nonprechilled/unscarified/blotter paper treatment combination always germinated lowest (1-3%). Results were consistent with physical dormancy (hard-seededness) limiting germination of western prairie clover and combinational dormancy (i.e., co-occurrence of physical and physiological dormancy) limiting germination of basalt milkvetch. Of the two species, we have found basalt milkvetch to be the more difficult to establish from seed. By prechilling acid-scarified seed in moist sand, basalt milkvetch was successfully established in two field trials seeded in mid-April. Nonprechilled mechanically (sandpaper) scarified seed germinated as high as prechilled acid-scarified seed. By scarifying and prechilling basalt milkvetch seed to address physical and physiological dormancy mechanisms, respectively, this seed-treatment protocol may be "scaled up" to produce large quantities of germinable seed. © 2015 Published by Elsevier Inc. on behalf of The Society for Range Management.
    • Grasshopper Responses to Fire and Postfire Grazing in the Northern Great Plains Vary Among Species

      Branson, D.H.; Vermeire, L.T. (Society for Range Management, 2016)
      Rangeland management practices such as burning and grazing may affect the development, survival, and reproduction of grasshopper populations. Experiments in the northern Great Plains that examine effects of fire and grazing utilization on grasshoppers are lacking. As part of a larger study examining vegetation responses to late summer fire and postfire grazing utilization in semiarid mixed prairie in eastern Montana to aid in postfire management decisions, we examined grasshopper responses to late summer fire and postfire grazing intensity. The experiment was repeated using adjacent blocks, with blocks receiving fire treatment in either 2003 or 2004 and grazing in the following year. Treatments were no fire and no grazing, and summer fire followed by grazing at 0%, 17%, or 50% forage utilization on a biomass basis. Grasshopper sampling was conducted before fire and for 2 years post fire. Fire reduced grasshopper density 36-53% across experiments, sampling periods, and postfire grazing treatments, but the effects of grazing and fire were species dependent. The two most abundant grasshopper species, Ageneotettix deorum (Scudder) and Opeia obscura (Thomas), were reduced 80% and 84% the first year after the 2003 fire, but only O. obscura was affected following the 2004 fire. Late summer fire appears to be a useful management tool to reduce populations of some grasshopper species in the northern Great Plains, while other species appear more responsive to food limitation from increased postfire grazing utilization. Fire effects were largely driven by two species, indicating that late-season fire impacts could be species dependent. © 2015 Published by Elsevier Inc. on behalf of The Society for Range Management.
    • Forage and Weather Influence Day versus Nighttime Cow Behavior and Calf Weaning Weights on Rangeland

      Sawalhah, M.N.; Cibils, A.F.; Maladi, A.; Cao, H.; Vanleeuwen, D.M.; Holechek, J.L.; Rubio, C.M.B.; Wesley, R.L.; Endecott, R.L.; Mulliniks, T.J.; et al. (Society for Range Management, 2016)
      We determined the effects of two forage allowance levels (LOW vs. HIGH) and weather conditions on daytime and nighttime movement patterns of young rangeland-raised cows. We also investigated whether calf weaning weights (n = 42) were significantly related to postcalving movement patterns of the dam. Global positioning system data were collected over 4 years by recording 5-min interval locations of 52 crossbred cows grazing a 146-ha woodland/grassland pasture for approximately 20 days. The pasture was stocked moderately in 2004 (73 AUMs) and 2005 (78 AUMs) and lightly in 2006 (34 AUMs) and 2007 (32 AUMs). Estimated forage allowance was lowin 2004 and 2005 (347 and 438 kg herbage · cow-1, respectively) and high in 2006 and 2007 (1104 and 1884 kg herbage · cow-1, respectively). We calculated distance traveled, path sinuosity, woodland preference, and area explored for each cow during 24 h (D + N), daytime (DAY), and nighttime (PRE dawn and POST sunset) periods. Cows in LOW traveled farther than counterparts in HIGH during D + N and DAY (P < 0.01) periods but traveled shorter or similar distances during POST (P = 0.05) and PRE (P = 0.29) nighttime periods, respectively. Cows in LOW exhibited more sinuous movement paths than cows in HIGH during DAY, PRE, and POST periods (P < 0.01). Cows in LOW explored larger areas and spent more time in woodlands than counterparts in HIGH (P < 0.01). Weather factors associated with thermal comfort affected daily variation in both daytime and nighttime movement patterns of cows. A dam's movement patterns in the weeks immediately following calving were correlated (P < 0.01) with steer but not heifer calf WW. Moderate stocking rates (LOW treatment) induced behaviors that resulted in higher woodland preference and heavier steer calf WW. © 2016 The Society for Range Management. Published by Elsevier Inc. All rights reserved.
    • Factors Influencing Winter Mortality Risk for Pronghorn Exposed to Wind Energy Development

      Taylor, K.L.; Beck, J.L.; Huzurbazar, S.V. (Society for Range Management, 2016)
      Evaluating the influence of energy development on pronghorn (Antilocapra americana) winter mortality risk is particularly critical given that northern populations already experience decreased survival due to harsh environmental conditions and increased energetic demands during this season. The purpose of our study was to evaluate pronghorn mortality risk over 3 winters (2010, 2010-2011, 2011-2012) on a landscape developed in 2010 for wind energy production (Dunlap Ranch) in south-central Wyoming, United States. We obtained locational data and survival status of 47 adult female pronghorn captured and equipped with Global Positioning System (GPS) transmitters. Overall, 17 pronghorn died during winter seasons, with 76.4% (13) of deaths occurring during the winter with highest snow accumulation (2010-2011). Survival (Š) was lowest in winter 2010-2011 (Š = 0.53, 90% confidence interval [CI]: 0.37-0.70) and highest in winters 2010 (Š = 0.97, 90% CI: 0.92-1.00) and 2011-2012 (Š = 0.91, 90% CI: 0.82-1.00). We modeled mortality risk for pronghorn using Cox's proportional hazards model inclusive of time-dependent and time-independent covariates within anthropogenic, environmental, and wind energy variable classes. Across winters, pronghorn winter mortality risk decreased by 20% with every 1.0-km increase in average distance from major roads (hazard ratio = 0.80, 90% CI: 0.66-0.98), decreased by 4.0% with every 1% increase in average time spent in sagebrush (Artemisia spp. L; hazard ratio = 0.96, 90% CI: 0.95-0.98), and decreased by 92% with every 1 unit (VRM × 1000) increase in terrain ruggedness (hazard ratio = 0.08,90% CI: 0.01-0.68). Pronghorn winter survival was not influenced by exposure to wind energy infrastructure; however, pronghorn survival may be impacted by larger-scale wind energy developments than those examined in our study. We recommend wildlife managers focus on conserving sagebrush stands in designated pronghorn winter range. © 2016 The Society for Range Management. Published by Elsevier Inc. All rights reserved.
    • Corrigendum to Temperature and Precipitation Affect Steer Weight Gains Differentially by Stocking Rate in Northern Mixed-Grass Prairie (Rangeland Ecology & Management (2013) 66 (438-444))

      Reeves, J.L.; Derner, J.D.; Sanderson, M.A.; Petersen, M.K.; Vermeire, L.T.; Hendrickson, J.R.; Kronberg, S.L. (Society for Range Management, 2016)
    • Vegetation Response to Piñon and Juniper Tree Shredding∗

      Bybee, J.; Roundy, B.A.; Young, K.R.; Hulet, A.; Roundy, D.B.; Crook, L.; Aanderud, Z.; Eggett, D.L.; Cline, N.L. (Society for Range Management, 2016)
      Piñon (Pinus spp.) and juniper (Juniperus spp.) expansion and infilling in sagebrush (Artemisia L.) steppe communities can lead to high-severity fire and annual weed dominance. To determine vegetation response to fuel reduction by tree mastication (shredding) or seeding and then shredding, we measured cover for shrub and herbaceous functional groups on shredded and adjacent untreated areas on 44 sites in Utah. We used mixed model analysis of covariance to determine significant differences among ecological site type (expansion and tree climax) and treatments across a range of pretreatment tree cover as the covariate. Although expansion and tree climax sites differed in cover values for some functional groups, decreasing understory cover with increasing tree cover and increased understory cover with tree reduction was similar for both ecological site types. Shrub cover decreased by 50% when tree cover exceeded 20%. Shredding trees at ≤ 20% cover maintained a mixed shrub (18.6% cover)-perennial herbaceous (17.6% cover) community. Perennial herbaceous cover decreased by 50% when tree cover exceeded 40% but exceeded untreated cover by 11% (20.1% cover) when trees were shredded at 15-90% tree cover. Cheatgrass (Bromus tectorum L.) cover also increased after tree shredding or seeding and then shredding but was much less dominant (< 10% cover) where perennial herbaceous cover exceeded 42%. Sites with high cheatgrass cover on untreated plots had high cheatgrass cover on shredded and seeded-shredded plots. Seeding and then shredding decreased cheatgrass cover compared with shredding alone when implemented at tree cover ≥ 50%. Vegetation responses to shredding on expansion sites were generally similar to those for tree cutting treatments in the SageSTEP study. Shredding or seeding and then shredding should facilitate wildfire suppression, increase resistance to weed dominance, and lead toward greater resilience to disturbance by increasing perennial herbaceous cover. © 2016 The Society for Range Management. Published by Elsevier Inc. All rights reserved.
    • Seed Production and Seedling Fitness are Uncoupled from Maternal Plant Productivity in Three Aridland Bunchgrasses

      Drenovsky, R.E.; Thornhill, M.L.; Knestrick, M.A.; Dlugos, D.M.; Svejcar, T.J.; James, J.J. (Society for Range Management, 2016)
      Maintaining self-sustaining populations of desired plants is fundamental to rangeland management, and understanding the relationships among plant growth, seed production, and seedling recruitment is critical to these efforts. Our objective was to evaluate how changes in maternal plant soil resource environment influences maternal plant biomass and seed production and seedling fitness in three widespread perennial bunchgrass species (Elymus elymoides [Raf.] Sezey, bottlebrush squirreltail; Festuca idahoensis Elmer, Idaho fescue; and Pseudoroegneria spicata [Pursh] A. Löve, bluebunch wheatgrass). We supplied water and nutrients to adult plants growing in the field and measured their productivity and fecundity. Then, in the laboratory, growth chamber, and field we assessed effects of the maternal water and nutrient additions on offspring performance. Across the three study species, vegetative traits were more plastic than reproductive traits, with resource addition measurably increasing plant growth but not seed production. Germination was high in both the laboratory and field across treatments, although seeds from irrigated maternal plants tended to have higher field germination. Seedling relative growth rate, leaf mass ratio, and relative root elongation rate (RRER) were highly variable, although RRER tended to be higher in seedlings derived from irrigated maternal plants. In the field, seedling survivorship was low across all species, but survivorship doubled in seedlings produced by P. spicata plants that received additional water through the growing season. Overall, our results suggest that biomass production and fecundity responses to nutrients are decoupled in the species and environment tested but maternal effects can have significant, although variable, impacts in some grassland species. As a result, biomass responses to natural and anthropogenic changes in resource availability may not be strong predictors of how altered resource supply may ultimately influence plant community dynamics in aridland systems. © 2016 The Society for Range Management. Published by Elsevier Inc. All rights reserved.
    • Livestock Use has Mixed Effects on Slender Orcutt Grass in Northeastern California Vernal Pools

      Merriam, K.E.; Gosejohan, M.C.; Weisberg, P.J.; Bovee, K.M. (Society for Range Management, 2016)
      Land managers often face the dilemma of balancing livestock use with conservation of sensitive species and ecosystems. For example, most of the remaining vernal pools in California are grazed by livestock. Vernal pools are seasonal wetlands that support many rare and endemic species, such as slender Orcutt grass (Orcuttia tenuis Hitchc.). Although studies in other areas of California have demonstrated that livestock use may benefit some vernal pool specialist species, grazing has been considered a threat to slender Orcutt grass in northeastern California. We evaluated the effects of livestock use on slender Orcutt grass using a replicated, paired design across a range of environmental conditions and grazing management regimes. Frequency, density, cover, reproductive potential, and height of slender Orcutt grass was compared in plots where livestock had been excluded with plots where grazing occurred. We found that livestock do not directly graze slender Orcutt grass, so the effects of livestock use on this species are indirect. These indirect effects are complex, including both positive, neutral, and negative effects. Year had the largest effect on slender Orcutt grass, probably as a result of variation in annual precipitation patterns. Livestock use had no effect in some years; in other years slender Orcutt grass was twice as abundant in unfenced than in fenced plots. Litter cover was also lower in unfenced plots in these years, suggesting that livestock use may benefit slender Orcutt grass in some years by reducing litter accumulation. Conversely, livestock use negatively affected slender Orcutt grass in pastures where livestock hoofprint cover was high, including pastures that were grazed early in the season. By considering patterns of annual variation in environmental factors such as precipitation, site conditions, and season of grazing, land managers can balance the needs of sensitive vernal pool species with maintaining livestock utilization on public lands. © 2016 The Society for Range Management. Published by Elsevier Inc. All rights reserved.
    • Impacts of Imazapyr and Triclopyr Soil Residues on the Growth of Several Restoration Species

      Douglass, C.H.; Nissen, S.J.; Meiman, P.J.; Kniss, A.R. (Society for Range Management, 2016)
      Herbicides are frequently used in natural systems to control invasive plants, but nontarget impacts from persistent soil residues can result in unintended ecosystem effects. Imazapyr and triclopyr are herbicides that are widely used in noncrop areas such as rangelands to manage perennial weeds, especially woody species such as tamarisk (saltcedar). Due to widespread environmental and anthropogenic changes in the American southwest, tamarisk, which is commonly thought to co-occur only with riparian plants, is increasingly being found in communities of upland rangeland species. Using an in vitro study combined with high-performance liquid chromatography (HPLC) analyses, imazapyr and triclopyr degradation rates were determined in six Colorado soils. In addition, the relative sensitivity of desirable species to the two herbicides was determined in a field dose response study. Exponential decay models estimated that triclopyr degradation (half-lives of 5-16 days) was 20 times more rapid than imazapyr degradation (half-lives of 82-268 days). All species tested were sensitive to imazapyr residues, but the degree of sensitivity was strongly dependent on soil properties. Sensitive species (alkali sacaton and western wheatgrass) were tolerant of imazapyr residues in some soils 20-23 months after applications. Relatively insensitive species (slender wheatgrass) were tolerant of imazapyr residues in the same soils 10 months after applications. American licorice was sensitive to triclopyr residues up to 89 days after applications, and several grasses (including sideoats grama) showed minor sensitivity. Our study indicates that there is an interaction between the spatial variability in herbicide degradation driven by edaphic properties and the sensitivity of plants to a herbicide, which could be exploited by management practitioners to aid in site rehabilitation. Specifically, managers could stagger planting of species temporally on the basis of their sensitivity to herbicide residues or could target areas of treated sites for planting that are known to have soil types facilitating relatively rapid herbicide degradation. © 2016 The Society for Range Management. Published by Elsevier Inc. All rights reserved.
    • Evidence-Targeted Grazing Benefits to Invaded Rangelands Can Increase over Extended Time Frames

      Rinella, M.J.; Bellows, S.E. (Society for Range Management, 2016)
      Targeted grazing uses livestock to address woody plant encroachment, flammable biomass accumulations, exotic weed invasions, and other management issues. In principle, a feature distinguishing targeted grazing from production-orientated grazing is stocking regimes (i.e., rates, timings, and durations) are chosen to encourage heavy defoliation of unwanted plants at sensitive growth stages. In practice, there are limited data available to guide stocking regime choices. Those data that do exist derive mostly from short-term studies, so the long-term effects of targeted grazing most concerning to managers remain highly uncertain. In a previous study, we imposed clipping treatments to identify defoliation levels and timings effective against the invader leafy spurge (Euphorbia esula L.). Most treatments simulated defoliation by sheep, the animal most commonly used for leafy spurge grazing, though a baseline treatment simulated defoliation by cattle, an animal tending to avoid leafy spurge. The two most effective treatments, which gave similar responses through the end of the previous study, defoliated leafy spurge and other species either before or during leafy spurge flowering. One goal of the current study was to determine if these responses remained similar or diverged over 5 additional treatment years. The other goal was to determine if differences between simulated sheep and cattle grazing treatments increased over time. In the current study, it became increasingly clear that defoliation before flowering was most damaging to leafy spurge, even though defoliation during flowering removed greater leafy spurge biomass. Compared with simulated cattle grazing, simulated sheep grazing before flowering reduced leafy spurge biomass production 74% (52%, 86%) [mean (95% confidence interval)] and increased resident species (mostly grasses) biomass production 40% (14%, 74%) by study's end. Leafy spurge biomass differences between treatments increased gradually over the study period, suggesting long-term research is needed to accurately compare targeted grazing treatments. © 2016 The Society for Range Management. Published by Elsevier Inc. All rights reserved.