Grazing Density Effects on Cover,Species Composition,and Nitrogen Fixation of Biological Soil Crust in an Inner Mongolia Steppe

Biological soil crusts (BSCs) are important in many arid and semiarid ecosystems for their abilities to fix atmospheric nitrogen (N) and stabilize surface soil. Grazing disturbance has a profound influence on abundance, species composition, and ecological functioning of BSCs. To elucidate the effects of grazing on BSCs in Inner Mongolia grasslands, an investigation was conducted in a typical steppe that had previously been subjected to long-term grazing with six grazing densities (control: 0 sheep · ha^?1, very light: 4 sheep ·ha^?1, light: 8 sheep · ha^?1, medium: 12 sheep · ha^?1, heavy: 16 sheep · ha^?1, and very heavy: 20 sheep · ha^?1). Cover, species composition, potential N-fixing activity, and potential N input of BSC indicate that long-term grazing significantly reduced the importance of BSC in N input and soil stabilization. Such reductions were highly related to grazing density. Very light grazing had no significant effect on the role of BSC in soil stabilization, but resulted in a 13.3% reduction in BSC N input potential. Heavy and very heavy grazing led to a decrease of potential N input by one order of magnitude, and a decline of BSC function via a shift from high coverage of an attached group–dominated BSC community to a low coverage of a vagrant group–dominated community. Constraining grazing level to a very light density—and to a lesser extent, a light grazing density—is likely a preferred practice for conserving BSC and the ecological services it provides in N fixation and soil stabilization.     

Comparison of Season-Long Grazing Applied Annually and a 2-Year Rotation of Intensive Early Stocking Plus Late-Season Grazing and Season-Long Grazing

This research measured steer gains, aboveground biomass remaining at the end of the growing season, and economic returns of tallgrass prairie grazed under season-long stocking (SLS-C) and a grazing system that included a 2-yr rotation of SLS-rotated (SLS-R) and intensive early stocking (IES; 2× normal stocking rate) + late-season grazing at the normal stocking rate (IES + LSG-R). We hypothesized that even though the stocking rate on the IES + LSG-R pasture was above the recommended rate, the greater regrowth availability in the late season would result in steers gaining as well as or better than those stocked SLS at the normal rate. By rotating the IES + LSG treatment with SLS over 2 yr, we anticipated that the aboveground biomass productive capacity of the IES + LSG pasture would be restored in one growing season. Further, we hypothesized that the increased stocking rate with IES + LSG would increase net profit. Comparing traditional season-long stocking to the system, which was a combination of SLS and IES + LSG rotated sequentially over a 2-yr period, the system increased steer gains by 7 kg · hd^?1 and by 30 kg · ha^?1, had a consistent reduction of 429 kg · ha^?1 biomass productivity, and increased net profit by $55.19 per steer and $34.28 per hectare.     

A Case Study Evaluating Economic Implications of Two Grazing Strategies for Cattle Ranches in Northwest Argentina

In the Argentinean Chaco Arido region, cattle production based on cow–calf operations is the principal source of agricultural income, and rangeland is the main forage source for cattle. Traditional grazing strategy (TGS, high stocking rate and continuous grazing) is considered the main cause of current rangeland degradation. Research shows that rangeland and cattle production improvements are possible when using a conservative grazing strategy (CGS, moderate stocking rate and rest rotation grazing). The aim of this research was to compare the effects of TGS and CGS applications on economic results for a cattle ranch in the region. To achieve this objective we used an approach that included estimations of forage and cattle production, and economic results. The study period was 1972/73–1983/84. Results showed that during the study period forage production and herd size were almost doubled with CGS, but maintained with TGS. The difference in net income between CGS and TGS (in Argentinean pesos, $), increased linearly from negative (-$2.88 · ha^-1) to positive ($4.48 · ha^-1) in the first 4 yr, and then was maintained at positive values (averaging $4.48 · ha^-1). Data suggest that CGS leads to higher productivity and better economic results than TGS in the medium and long terms.En la región del Chaco Árido Argentino, la ganadería de cría es la actividad agropecuaria más difundida. Esta actividad se basa principalmente en el forraje que proporciona el pastizal nativo. La estrategia de pastoreo tradicional (EPT, consistente de alta carga animal y pastoreo continuo), se considera la causa principal del estado de degradación actual del pastizal nativo. Varios estudios han mostrado que el mejoramiento de la productividad del pastizal y del ganado es posible cuando se utiliza una estrategia de pastoreo conservativa (EPC, consistente en carga animal moderada y un pastoreo que permita descanso del pastizal en época de crecimiento). El objetivo de esta investigación fue comparar el efecto de la EPT y la EPC sobre el aspecto económico de un rancho ganadero de la región del Chaco Árido. Para lograr dicho objetivo se hizo un análisis en distintas etapas, estimación de la producción forrajera, estimación de la producción ganadera, y estimación del resultado económico. El periodo de estudio fue desde 1972/73 hasta 1983/84. Los resultados mostraron que durante el periodo de estudio la producción de forraje y el tamaño del rodeo se duplicaron para la EPC, mientras que para EPT se mantuvieron. La diferencia en el resultado económico neto entre la EPC y la EPT (en pesos Argentinos, $), se incrementó linealmente desde valores negativos (-$2.88 · ha^-1) a valores positivos ($4.48 · ha^-1) en los cuatro primeros años, para luego mantenerse en un valor promedio de $4.48 · ha^-1. Los resultados sugieren que la EPC permite obtener una productividad más alta y mejores resultados económicos que la EPT a mediano y largo plazo.     

Animal and Vegetation Response to Modified Intensive–Early Stocking on Shortgrass Rangeland

A comparison of animal gains and vegetation trends was made from 2002–2008 between a continuous season-long stocking (SLS) system and a modified intensive–early stocking system (IES) with late-season grazing (IES 1.6× + 1; 1.6 times the number of animals of the SLS system from May 1 to July 15, and 1 times the number of animals of SLS from July 15 to October 1) on shortgrass native rangeland of western Kansas. The continuous season-long stocked system placed animals at a density of 1.37 ha · steer^?1 from May through October, or 2.63 animal unit months (AUM) · ha^?1, whereas the intensive–early stocked system with late-season grazing (3.33 AUM · ha^?1) stocked pastures at 0.85 ha · steer^?1 from May through the middle of July, and then stocked pastures at 1.37 ha · steer^?1 for the remainder of the grazing season by removing the heaviest animals mid-July each yr. Average daily gains (0.78 vs. 0.70 kg · d^?1, P = 0.039) and total animal gain (58 vs. 52 kg, P = 0.042) were different between the continuous season-long stocked and the intensive–early stocked animals during the first half of the grazing season. No difference was found between average daily gain (0.61 vs. 0.62 kg · d^?1, P = 0.726) and total animal gain (48 vs. 49 kg, P = 0.711) for the continuous season-long stocked and intensive–early stocked with late-season grazing animals during the last half of the season. Total individual animal gain (106 vs. 101 kg, P = 0.154) and average daily gain (0.70 vs. 0.66 kg · d^?1, P = 0.152) was not different between the continuous season-long stocked and the intensive–early stocked system animals that were on pasture the entire grazing season. Total beef gain on a land-area basis (96 vs. 77 kg · ha^?1, P = 0.008) was greater for the modified intensive–early stocked system with late-season grazing with greater animal densities. Changes in residual biomass and most key vegetation components at the end of the grazing season were not different between the two systems.     

Effects of Grazing Intensity,Precipitation, and Temperature on Forage Production

Questions have been raised about whether herbaceous productivity declines linearly with grazing or whether low levels of grazing can increase productivity. This paper reports the response of forage production to cattle grazing on prairie dominated by Kentucky bluegrass (Poa pratensis L.) in south-central North Dakota through the growing season at 5 grazing intensities: no grazing, light grazing (1.3 ±  animal unit months [AUM] · ha^-1), moderate grazing (2.7 ±  AUM · ha^-1), heavy grazing (4.4 ±  AUM · ha^-1), and extreme grazing (6.9 ±  AUM · ha^-1; mean ± SD). Annual herbage production data were collected on silty and overflow range sites from 1989 to 2005. Precipitation and sod temperature were used as covariates in the analysis. On silty range sites, the light treatment produced the most herbage (3 410 kg · ha^-1), and production was reduced as the grazing intensity increased. Average total production for the season was 545 kg · ha^-1 less on the ungrazed treatment and 909 kg · ha^-1 less on the extreme treatment than on the light treatment. On overflow range sites, there were no significant differences between the light (4 131 kg · ha^-1), moderate (4 360 kg · ha^-1), and heavy treatments (4 362 kg · ha^-1; P &spigt; 0.05). Total production on overflow range sites interacted with precipitation, and production on the grazed treatments was greater than on the ungrazed treatment when precipitation (from the end of the growing season in the previous year to the end of the grazing season in the current year) was greater than 267.0, 248.4, 262.4, or 531.5 mm on the light, moderate, heavy, and extreme treatments, respectively. However, production on the extreme treatment was less than on the ungrazed treatment if precipitation was less than 315.2 mm. We conclude that low to moderate levels of grazing can increase production over no grazing, but that the level of grazing that maximizes production depends upon the growing conditions of the current year.     

Spatial Redistribution of Nitrogen by Cattle in Semiarid Rangeland

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, cattle-mediated 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 months (AUM) · ha^?1 consumed 3.34 kg N · ha^?1 · yr^?1. Using an independent animal-based method, we estimate that cattle consumed 3.58 kg N · ha^?1 · yr^?1 for the same stocking rate and years. A global positioning system tracking study revealed that cattle spent an average of 27% of their time in pasture corners or adjacent to water tanks, even though these areas represented only 2.5% of pasture area. Based on these measurements, we estimate that cattle stocked at 0.65 AUM · ha^?1 during the summer can remove 0.60 kg N · ha^?1 in cattle biomass gain and spatially redistribute 0.73 kg N · ha^?1 to areas near corners and water tanks. An additional 0.17 kg N · ha^?1 can be lost as NH₃ volatilization from urine patches. Cumulatively, these cattle-mediated pathways (1.50 kg N · ha^?1) may explain the imbalance between current estimates of atmospheric inputs and trace gas losses. While NO_x emission remains the largest pathway of N loss, spatial N redistribution by cattle and N removed in cattle biomass are the second and third largest losses, respectively. Management of cattle-mediated N fluxes should be recognized as one means to influence long-term sustainability of semiarid rangelands.     

Energy and Carbon Costs of Selected Cow-Calf Systems

Fossil fuel-derived inputs can increase cow-calf production per unit of land or labor but can raise financial and environmental concerns. Eleven US cow-calf systems from nine ecological regions in Iowa, South Dakota, Tennessee, and Texas were analyzed to determine quantities of energy used and carbon (C) emitted due to fossil fuel use (excluding emissions from soils and biota) and to determine how management and environment influenced those quantities. Total energy and C cost, calculated cow^?1 or ha^?1, were highly correlated (0.99). Energy use cow^?1 and ha^?1 varied greatly across systems, ranging from 3 000 to 12 600 megajoules (MJ) · cow^?1 · yr^?1 and from 260 to 20 800 MJ · ha^?1 · yr^?1. As stocking rate increased, MJ · cow^?1 increased at an increasing rate. Differences in quantity of fertilizer accounted for most variation in energy use. Fertilizer allowed higher stocking rates but reduced energy efficiency of liveweight marketed. Compared to intensive, higher stocking rate systems, rangeland systems based on native or naturalized forages used little or no fertilizer, but used more energy cow^?1 for crude protein (CP) supplementation, fencing, and pickup trucks. Across all systems, energy used to produce winter feed ranged from 0% to 46% of total energy. Northern systems used higher percentages of total energy for winter feed and fed for more days year^?1, but southern systems that included large amounts of bermudagrass (Cynodon dactylon L.) hay used the most MJ · cow^?1 for winter feed. Systems with high MJ · cow^?1 were vulnerable to shocks in energy prices. Reducing energy use and C emissions from cow-calf operations is possible, especially by reducing fertilizer and hay use, but would likely reduce productivity ha^?1. Forages with high nitrogen use efficiency, locally adapted plants and animals, and replacement of hay with unfertilized dormant forage and CP supplementation could reduce energy use.     

The economic implications of bush encroachment on livestock farming in rangelands of Uganda

The objective of this study was to assess the economic implications of shrub encroachment on pastoral rangeland productivity in Mbarara district, in south western Uganda. Sixty pastoral households were surveyed, thirty of which were grazing on cleared farms (with less than 25% of grazing covered by bush) and thirty were grazing on bushy farms (with more than 75% of grazing land covered by bush). The study was a survey and did not involve rigorous experimental work. Results indicated that cleared farms had higher herbage dry matter yield ranging from 1 850 kg ha^?1 to 2 230 kg ha^?1, compared to a range of 622 kg ha^?1 to 1 190 kg ha^?1 on bushy farms. Heifers on cleared farms reached puberty earlier and calved relatively earlier (12-30 months) as opposed to 24-36 months on bushy farms. The mean calving rate on cleared farms was higher (33.6%) than 22.6% on bushy farms. Mean milk yield on cleared farms was 3.8 L cow^?1 d^?1 compared to 2.4 L cow^?1 d^?1 on bushy farms. Results of body condition score indicated that cattle on cleared range had a higher mean score of 5.8 compared to 4.2 on bushy farms. Mean annual gross income was US$49.393 per cow per annum on cleared farms compared to US$23.351 on bushy farms. Financial efficiency measured by TR/TVC ratio was 1.2 on cleared farms compared to 1.1 on bushy farms. From the findings of the study, it was concluded that shrub encroachment led to reduced herbage DM yield and low levels of crude protein of the pasture, while clearing more than doubled herbage DM production. As a result, animal productivity in terms of milk yield, body condition and reproductive performance were also reduced. Cleared farms were more profitable than bushy ones in terms of gross margins due to higher animal performance and hence higher incomes. The financial efficiency of cleared farms was low due to high costs of shrub control. Shrub encroachment is a serious problem facing pastoral production in Mbarara district and requires adequate attention.     

Impact of Stocking Rate and Rainfall on Sheep Performance in a Desert Steppe

Livestock performance is a critical indicator of grassland production systems and is influenced strongly by precipitation and stocking rates. However, these relationships require further investigation in the arid Desert Steppe region of northeastern China. We employed a randomized complete block design with three replications and four grazing treatments (nongrazed exclosure [Control]), lightly grazed [LG], moderately grazed [MG], and heavily grazed [HG]) by sheep in a continuously grazed system (June to November), to test the effect of stocking rate on sheep performance. The planned stocking rates were 0, 0.15, 0.30, and 0.45 sheep · ha^?1 · mo^?1, for the control, LG, MG, and HG treatments, respectively. However, actual stocking rates were calculated for each paddock in each year based on a 50-kg sheep equivalent (SE). Annual net primary production (ANPP) was determined at peak standing crop in August 2004 to 2008. Live weight gain was determined for the summer and fall periods, as well as the total grazing period, in each year. ANPP decreased with increasing stocking rate, and daily live weight gain per head decreased linearly with increasing stocking rates over the total grazing period but in a quadratic manner over the summer period with a plateau at the lower rates. Maximum sheep production per unit area over the total grazing season occurred at about 2 SE ha^?1 for about a 5-mo grazing period, but individual gains per sheep were predicted to decline after about 1 SE ha^?1 presumably because of forage limitations. However, in order to achieve stable annual production, we recommend that the Desert Steppe be grazed at about 0.77 SE ha^?1 for a 5-mo period (0.15 SE ha^?1 · mo^?1). This estimate is based on published grazing strategies that consider an average ANPP with a recommended utilization rate of 30%.     

Livestock Grazing Impacts on Herbage and Shrub Dynamics in a Mediterranean Natural Park

Shrub encroachment can be explained by the abandonment of extensive livestock farming and changes to land use, and it is a common problem in the Mediterranean mountain pastures of Europe, with direct effects on biodiversity and landscape quality. In this paper, the effects of livestock exclusion vs. grazing on the dynamics of shrub and herbaceous vegetation were analyzed in a Spanish natural park located in a dry Mediterranean mountain area over a 5-yr period. Twelve 10 × 10 m exclosures were set up in six representative pasture areas of the park (with two replicates per location). Each year, the shrub number, volume, and biomass were measured in April, and the herbage height, biomass, and quality were measured in April and December (which represent the start and end of the vegetative growth season). A sustained increase of the shrub population and individual biomass was observed throughout the study, which was reflected in total shrub biomass per ha. Growth was greater in nongrazed exclosures (2 563 kg dry matter [DM] · ha^?1 · yr^?1), but it also happened in the grazed control areas (1 173 kg DM · ha^?1 · yr^?1), with different patterns depending on the location and shrub species. Herbage biomass did not change when grazing was maintained, but it did increase in places where grazing was excluded (291 kg DM · ha^?1 · yr^?1), mostly as a consequence of the accumulation of dead material, with a concomitant reduction in herbage quality. It was concluded that at the current stocking rates and management regimes, grazing alone is not enough to prevent the intense dynamics of shrub encroachment, and further reductions in grazing pressure should be avoided.     

Using Weather Data to Explain Herbage Yield on Three Great Plains Plant Communities

Understanding the drivers that account for plant production allows for a better understanding of plant communities and the transitions within ecological sites and can assist managers in making informed decisions about stocking rates and timing of grazing. We compared climatic drivers of herbage production for 3 plant communities of the Clayey ecological site in southwestern South Dakota: the midgrass community dominated by western wheatgrass (Pascopyrum smithii [Rybd.] A. Love); the mixed-grass community codominated by western wheatgrass, blue grama (Bouteloua gracilis [H.B.K.] Lag. Ex Griffiths), and buffalograss (Buchloe dactyloides [Nutt.] Engelm.); and the shortgrass community dominated by blue grama and buffalograss. We used herbage yield and weather data for the period 1945–1960 collected at the South Dakota State University Range and Livestock Research Station near Cottonwood, South Dakota, to develop stepwise regression models for each plant community. Midgrass herbage production was best predicted by current-year spring (April–June) precipitation, number of calendar days until the last spring day with minimum temperature ≤ -1°C, and previous-year spring precipitation (R² = 0.81). Mixed-grass herbage production was best predicted by current-year spring precipitation and days until the last spring freeze (R² = 0.69). Shortgrass herbage production was best predicted by current-year spring precipitation (R² = 0.52). Midgrass plant communities were, overall, 650 kg·ha^-1 (SE = 92 kg·ha^-1) more productive (P < 0.01) than mixed- or shortgrass plant communities given the same climatic inputs. Our study enables managers to make timely informed decisions regarding stocking rates and timing of grazing on this ecological site in western South Dakota.     

Grazing-Induced Modifications to Peak Standing Crop in Northern Mixed-grass Prairie

Selective grazing can modify the productive capacity of rangelands by reducing competitiveness of productive, palatable species and increasing the composition of more grazing-resistant species. A grazing system (season-long and short-duration rotational grazing) × stocking rate (light: 16 steers · 80 ha^-1, moderate: 4 steers · 12 ha^-1, and heavy: 4 steers · 9 ha^-1) study was initiated in 1982 on northern mixed-grass prairie. Here, we report on the final 16 years of this study (1991–2006). Spring (April + May + June) precipitation explained at least 54% of the variation in peak standing crop. The percentage of variation explained by spring precipitation was similar between stocking rates with short-duration grazing but decreased with increasing stocking rate for season-long grazing. April precipitation explained the greatest percentage of the variation in peak standing crop for the light stocking rate (45%), May precipitation for the moderate stocking rate (49%), and June precipitation for the heavy stocking rate (34%). Peak standing crop was 23%–29% greater with light (1 495 ± 66 kg · ha^-1, mean ± 1 SE) compared to moderate (1 218 ± 64 kg · ha^-1) and heavy (1 156 ± 56 kg · ha^-1) stocking rates, which did not differ. Differences in peak standing crop among stocking rates occurred during average and wet but not dry springs. Neither the interaction of grazing system and stocking rate nor grazing system alone affected standing crop across all years or dry, average, or wet springs. Grazing-induced modification of productive capacity in this northern mixed-grass prairie is attributed to changes in species composition with increasing stocking rate as the less productive, warm-season shortgrass blue grama (Bouteloua gracilis [H.B.K.] Lag. ex Griffiths) increases at the expense of more productive, cool-season midheight grasses. Land managers may need to substantially modify management to offset these losses in productive capacity.     

Grazing Method Effect on Topographical Vegetation Characteristics and Livestock Performance in the Nebraska Sandhills

A study was conducted on upland range in the Nebraska Sandhills to determine differences in plant species frequency of occurrence and standing crop at various topographic positions on pastures grazed with short-duration grazing (SDG) and deferred-rotation grazing (DRG). Pastures within each grazing treatment were grazed at comparable stocking rates (SDG = 1.84 animal unit months (AUM) · ha^?1; DRG = 1.94 AUM · ha^?1) by cow–calf pairs from 1999 to 2005 and cow–calf pairs and spayed heifers from 2006 to 2008. Plant frequency of occurrence data were collected from permanently marked transects prior to, midway through, and at the conclusion of the study (1998, 2003, and 2008, respectively) and standing crop data were collected annually from 2001 to 2008 at four topographic positions (dune top, interdune, north slope, and south slope). Livestock performance data were collected during the last 3 yr of the study (2006 to 2008). Positive change in frequency of occurrence of prairie sandreed (Calamovilfa longifolia [Hook.] Scribn.) was 42% greater on DRG pastures than SDG after 10 yr. Total live standing crop did not differ between DRG and SDG except in 2001 when standing crop was 23% greater on DRG pastures. Standing crop of forbs and sedge was variable between grazing methods on interdune topographic positions depending on year. Average daily gain of spayed heifers (0.84 ±  kg · d^?1 SE) did not differ between SDG and DRG. Overall, SDG was not superior to a less intensively managed grazing method (i.e., DRG) in terms of vegetation characteristics and livestock performance.     

Integrated Grazing and Prescribed Fire Restoration Strategies in a Mesquite Savanna: III. Ranch-Scale Cow–Calf Production Responses

Beef cattle production from rangelands in the Southern Great Plains has decreased in concert with herbaceous forage production declines in response to woody plant encroachment by honey mesquite (Prosopis glandulosa Torr.) over the past 120 yr. Combinations of livestock overstocking and fire suppression are considered to be primary drivers of these changes. This experiment evaluated cow–calf production responses over a 7-yr (1995–2001) period to ranch-scale (1 294–2 130 ha) integrated restoration strategies involving prescribed fire and grazing management. Restoration strategies tested in this year-round grazing ecosystem were 4-pasture, 1-herd rotation with fire (25% of pasture acreage burned each year; 4:1F); an 8-pasture, 1-herd rotation, with fire (8:1F); and a 4-pasture, 1-herd, with fire and aerial application of 0.28 kg · ha^?1 clopyralid + 0.28 kg · ha^?1 triclopyr herbicide (4:1F / H). Restoration strategies were compared to a continuous grazing strategy with no mesquite treatment. All cattle stocking rates were moderate (7.5–15 ha · animal unit^?1 · year^?1) and all fires were applied during late winter. Beef cattle (cow–calf) production variables measured included conception rate, weaned calf percentage, weaning weight, weight of calf per exposed cow, weight of calf per hectare, and supplement fed per cow. We observed significant differences in beef production among strategies primarily during the first 2 yr where the continuous grazing strategy exhibited better overall livestock production than the integrated restoration strategies. Differences in livestock production among strategies were minimal over the last 5 yr of the study. These livestock production results suggest livestock and management adapted to restoration strategies after the first 2 yr. Results point to the need to cautiously transition into integrated grazing and fire restoration strategies when cattle and management are changed and intensified from prior historical protocols.     

Soil Morphologic Properties and Cattle Stocking Rate Affect Dynamic Soil Properties

Soil properties that influence the capacity for infiltration and moisture retention are important determinants of rangeland productivity. Monitoring effects of grazing on dynamic soil properties can assist managers with stocking rate decisions, particularly if monitoring takes into account environmental variability associated with inherent soil morphological properties. On a Pacific Northwest Bunchgrass Prairie in northeast Oregon, we applied three cattle stocking rates (0.52, 1.04, and 1.56 animal unit months · ha^?1) and an ungrazed control in a randomized complete block design for two 42-d grazing seasons and measured the change in four dynamic soil properties: soil penetration resistance, soil aggregate stability, bare ground, and herbaceous litter cover. To address apparent environmental heterogeneity within experimental units, we also utilized a categorical soil factor (termed Edaphic Habitat Types or EHT), determined by characterizing soil depth, texture, and rock fragment content at sample sites. Stocking rate did not affect extent of bare ground or soil aggregate stability. Stocking rate had a significant effect on penetration resistance, which was greatest at the high stocking rate (1.6 J · cm^?1 ± 0.1 SE) and lowest in the control (1.1 J · cm^?1 ± 0.1 SE). For litter cover, the effects of stocking rate and EHT interacted. In two rocky EHTs, litter cover was highest in the controls (60% ± 6 SE; 50% ± 3 SE) and ranged from 27% ± 3 SE to 33% ± 6 SE in the stocking rate treatments. Measures of penetration resistance, aggregate stability, and bare ground were different across EHTs regardless of stocking rate, but did not interact with stocking rate. Our study demonstrates that response of dynamic soil properties to stocking rates should be considered as a useful and accessible approach for monitoring effects of livestock management decisions on rangeland conditions.     

Preemergent Control of Medusahead on California Annual Rangelands With Aminopyralid

Medusahead (Taeniatherum caput-medusae &lsqb;L.] Nevski), the most problematic invasive grass on many California rangelands, is difficult to control selectively in grasslands. Prescribed burning, grazing, and herbicides have been tested with some success but are not practical in all situations. The selective herbicide aminopyralid, normally used for control of certain broadleaf species such as thistles, suppresses some annual grasses when applied pre- or early postemergence. In 2009–2010, we tested the efficacy of aminopyralid for medusahead control in preemergence applications at three foothill rangeland sites in northern California. We compared a rate series of aminopyralid (53, 88, 123, and 245 g · ha^-1 acid equivalent &lsqb;ae]) with rimsulfuron (18 and 35 g · ha^-1 active ingredient) and imazapic (140 g · ha^-1 ae). Plots were 3 × 9 m with four replications at each site. Treatments were applied in early fall 2009. In May 2010, we took visual cover estimates and biomass/seedhead samples in three quadrats per plot. In regression analysis, medusahead cover was found to decrease consistently with increasing rates of aminopyralid. Medusahead control at the highest rates of aminopyralid was consistent across the three sites, averaging 89% ± 3 standard deviation (SD) with 245 g · ha^-1 ae and 59% ± 10 SD with 123 g · ha^-1 ae. Aminopyralid at lower rates, rimsulfuron, and imazapic were less consistent. Cover of other annual grasses increased in plots treated with aminopyralid at all sites. Aminopyralid has potential utility for suppressing medusahead, particularly in sites also infested with invasive members of the Asteraceae. However, the most effective rate (245 g · ha^-1 ae) is registered for use only as a spot application. In situations where this rate can be justifiably used, it would be expected to give season-long control of medusahead, as well as longer-term control of thistles and other susceptible species.     

Vegetation Production Responses to October Grazing in the Nebraska Sandhills

Understanding the long-term effect of summer grazing date and fall stocking rate on herbage production is critical to extending the grazing season in the Nebraska Sandhills. A study was conducted from 1997 to 2002 at the Gudmundsen Sandhills Laboratory located near Whitman, Nebraska, to determine the herbage production response to summer grazing date and October stocking rate on two different sites. Site 1 was dominated by warm-season grasses and site 2 was dominated by cool-season graminoids. At each site, three 0.37-ha pastures were constructed in each of four blocks before application of summer grazing treatments. Pastures in each block were grazed at 0.5 animal-unit months (AUM) · ha^?1 in June or July, or were deferred from summer grazing. Following summer grazing treatments, October stocking rate treatments (no grazing or 1.0, 2.0, or 3.0 AUM · ha^?1) were applied to subunits of each summer grazing date pasture during mid-October. Vegetation was sampled in each pasture in mid-June and mid-August and sorted by functional group to determine the effect of 5 yr of grazing treatments on herbage production and residual herbage. Herbage production was not affected by summer or October grazing treatments on the warm-season grass–dominated site. Increasing October stocking rate, however, reduced cool-season graminoid production and subsequent herbage production 25% by year 5 of the study. Residual herbage at both sites at the end of the October grazing periods explained as much as 16% to 34% of subsequent year’s herbage production. Grazing managers in the Nebraska Sandhills can extend the grazing season by lightly stocking pastures in the summer to facilitate additional fall grazing. Heavy stocking in October over several years on cool-season–, but not warm-season–, dominated sites will reduce production of cool-season graminoids on these sites.     

Vegetation Responses to Pinyon–Juniper Treatments in Eastern Nevada

Comparisons of tree-removal treatments to reduce the cover of single-leaf pinyon (Pinus monophylla Torr. and Frém.) and Utah juniper (Juniperus osteosperma [Torr.] Little), and subsequently increase native herbaceous cover in black sagebrush (Artemisia nova A. Nelson), are needed to identify most cost-effective methods. Two adjacent vegetation management experiments were initiated in 2006 and monitored until 2010 in eastern Nevada to compare the costs and efficacy of various tree reduction methods. One Department of Energy (DOE) experiment compared a control to five treatments: bulldozing imitating chaining ($205 · ha^-1), lop-pile-burn ($2 309 · ha^-1), lop-and-scatter ($1 297 · ha^-1), feller-buncher and chipper ($4 940 · ha^-1), and mastication ($1 136 · ha^-1), whereas a second Bureau of Land Management (BLM) experiment compared one-way chaining ($205 · ha^-1) to a control treatment. Chaining and bulldozing resulted in the least reduction of tree cover among the treatments. In the DOE experiment, forb cover only decreased in the mastication treatment. Litter increased in all methods. Slash cover was lowest in the control and lop-pile-burn treatments, intermediate in the feller-buncher and mastication treatments, and highest in the bulldozing and lop-and-scatter treatments. By 2010, forb cover and the combined cover of dead shrubs and trees were increased and decreased, respectively, by chaining in the BLM experiment. Nonnative annual grass and biotic crust were absent or uncommon before and after treatment implementation. In both experiments, tree removal resulted in a nonsignificant increase in perennial grass cover even 4 yr post-treatment. An ecological return-on-investment (EROI) metric was developed to compare perennial grass cover and tree cover per unit area cost of each active treatment. By 2010, chaining or bulldozing, followed by mastication, showed the highest EROI for improving perennial grass and decreasing tree cover. Mastication is recommended for restoration of smaller tree-encroached areas, whereas land managers should reconsider smooth chaining, despite its negative perceptions, for rapid and cost-efficient restoration of large landscapes obligates.     

Grazing History Effects on Rangeland Biomass,Cover and Diversity Responses to Fire and Grazing Utilization

Exclusion of large grazers from rangelands that evolved with significant grazing pressure can alter natural processes and may have legacy effects by changing magnitude or direction of community responses to subsequent disturbance. Three moderately grazed pastures were paired with 12-ha areas with 15 yr of livestock exclusion. Six treatments were assigned to each in a 2 x 3 factorial arrangement of fire (fall fire or no fire) and grazing utilization (0%, 50%, or 75% biomass removal) to determine grazing history effects on rangeland response to subsequent disturbance. Livestock exclusion increased C₃ perennial grass (1 232 vs. 980 ± 50 kg ? ha^-1) and forbs (173 vs. 62 ± 19 kg ? ha^-1) and reduced C₄ perennial grass (36 vs. 180 ± 25 kg ? ha^-1) with no effect on total current-year biomass. Diversity was greater in pastures than exclosures (H’ = 1.5400 vs. 1.3823 ± 0.0431). Every biomass, cover, and diversity measure, except subshrub biomass, was affected by fire, grazing utilization, or both. Contrary to expectations, grazing history only interacted with fire effects for old standing dead material and interactions with grazing utilization were limited to old dead, bare ground, richness and dominance. Fire by grazing utilization interaction was limited to bare ground. Fire reduced annual grass (64 vs. 137 ± 29 kg ? ha^-1), forbs (84 vs. 133 ± 29 kg ? ha^-1), and diversity (H’ = 1.3260 vs. 1.5005 ± 0.0537) with no difference in total current-year biomass (1 557 vs. 1 594 ± 66 kg ? ha^-1). Grazing to 75% utilization reduced total current-year biomass (1 467 vs. 1 656 ± 66 kg ? ha^-1) and dominance (0.4824 vs. 0.5584 ± 0.0279). Grazing history affected starting points for most variables, but changes caused by grazing utilization or fire were similar between pastures and exclosures, indicating management decisions can be made based on independent knowledge of grazing or fire effects.     

Grazing Deferment Effects on Forage Diet Quality and Ewe Performance Following Summer Rangeland Fire

Complete rest or grazing deferment is a general recommendation to encourage vegetative recovery following fire in the western United States. However, effects of grazing deferments on animal performance have not been determined. Prescribed fires were individually applied to nine separate, 1.5-ha pastures each year (2006 and 2007) for a total of 18 pastures. Grazing was deferred until spring (16 May), early summer (19 June), or late summer (1 August) the growing season after fire. At the end of each deferment, a 70-d (2007) or 41-d (2008) grazing period was initiated. Stocking rates were consistent between treatments within year, but were adjusted between years to achieve the targeted residual biomass of approximately 300 kg · ha^?1. Diet quality was assessed approximately every 15 d throughout each grazing period (three pastures · period^?1) via collection of rumen extrusa throughout the 2-yr study. Ewe body weight was measured on and off-test for each grazing period. Diet extrusa samples for in vitro organic matter disappearance was less (P = 0.03) for late summer than early summer grazing periods and equal to the spring period (62.9, 64.6, and 61.0 ± 0.90%, respectively for spring, early summer, and late summer grazing periods). In vitro neutral detergent fiber disappearance decreased (P = 0.01) by 10.6 percentage units from early grazing to late grazing period in 2007, whereas no differences were observed in 2008. Ewe average daily gain did not differ between spring and early summer grazing periods and were greater (P = 0.03) than the negligible body weight gains of the late summer grazing period. Total gain was 10.9 kg · ha^?1 greater in 2008, and a quadratic response was measured for grazing period in 2007. Results indicate that deferment until early summer may be preferable so that stocking rates can be more accurately determined and animal performance is not diminished.