Postfire Succession in Big Sagebrush Steppe With Livestock Grazing

Prescribed fire in rangeland ecosystems is applied for a variety of management objectives, including enhancing productivity of forage species for domestic livestock. In the big sagebrush (Artemisia tridentata Nutt.) steppe of the western United States, fire has been a natural and prescribed disturbance, temporarily shifting vegetation from shrub–grass codominance to grass dominance. There is limited information on the impacts of grazing to community dynamics following fire in big sagebrush steppe. This study evaluated cattle grazing impacts over four growing seasons after prescribed fire on Wyoming big sagebrush (Artemisia tridentata subsp. Wyomingensis [Beetle & Young] Welsh) steppe in eastern Oregon. Treatments included no grazing on burned and unburned sagebrush steppe, two summer-grazing applications after fire, and two spring-grazing applications after fire. Treatment plots were burned in fall 2002. Grazing trials were applied from 2003 to 2005. Vegetation dynamics in the treatments were evaluated by quantifying herbaceous canopy cover, density, annual yield, and perennial grass seed yield. Seed production was greater in the ungrazed burn treatments than in all burn–grazed treatments; however, these differences did not affect community recovery after fire. Other herbaceous response variables (cover, density, composition, and annual yield), bare ground, and soil surface litter did not differ among grazed and ungrazed burn treatments. All burn treatments (grazed and ungrazed) had greater herbaceous cover, herbaceous standing crop, herbaceous annual yield, and grass seed production than the unburned treatment by the second or third year after fire. The results demonstrated that properly applied livestock grazing after low-severity, prescribed fire will not hinder the recovery of herbaceous plant communities in Wyoming big sagebrush steppe.     

Eighty Years of Grazing by Cattle Modifies Sagebrush and Bunchgrass Structure

Grazing by cattle is ubiquitous across the sagebrush steppe; however, little is known about its effects on sagebrush and native bunchgrass structure. Understanding the effects of long-term grazing on sagebrush and bunchgrass structure is important because sagebrush is a keystone species and bunchgrasses are the dominant herbaceous functional group in these communities. To investigate the effects of long-term grazing on sagebrush and bunchgrass structure, we compared nine grazing exclosures with nine adjacent rangelands that were grazed by cattle in southeast Oregon. Grazing was moderate utilization (30 ? 45%) with altering season of use and infrequent rest. Long-term grazing by cattle altered some structural aspects of bunchgrasses and sagebrush. Ungrazed bunchgrasses had larger dead centers in their crowns, as well as greater dead fuel depths below and above the crown level compared with grazed bunchgrasses. This accumulation of dry fuel near the meristematic tissue may increase the probability of fire-induced mortality during a wildfire. Bunchgrasses in the ungrazed treatment had more reproductive stems than those in the long-term grazed treatment. This suggests that seed production of bunchgrasses may be greater in ungrazed areas. Sagebrush height and longest canopy diameter were 15% and 20% greater in the ungrazed compared with the grazed treatment, respectively. However, the bottom of the sagebrush canopy was closer to the ground in the grazed compared with the ungrazed treatment, which may provide better hiding cover for ground-nesting avian species. Sagebrush basal stem diameter, number of stems, amount of dead material in the canopy, canopy gap size, and number of canopy gaps did not differ between ungrazed and grazed treatments. Moderate grazing does not appear to alter the competitive relationship between a generally unpalatable shrub and palatable bunchgrasses. Long-term, moderate grazing appears to have minimal effects to the structure of bunchgrasses and sagebrush, other than reducing the risk of bunchgrass mortality during a fire event.     

Cattle Grazing and Vegetation Succession on Burned Sagebrush Steppe

There is limited information about the effects of cattle grazing to longer-term plant community composition and herbage production following fire in sagebrush steppe. This study evaluated vegetation response to cattle grazing over 7 yr (2007–2013) on burned Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis [Beetle & Young] Welsh) steppe in eastern Oregon. Treatments, replicated four times and applied in a randomized complete block design, included no grazing on burned (nonuse) and unburned (control) sagebrush steppe; and cattle grazing at low (low), moderate (moderate), and high (high) stocking on burned sagebrush steppe. Vegetation dynamics were evaluated by quantifying herbaceous (canopy and basal cover, density, production, reproductive shoot weight) and shrub (canopy cover, density) response variables. Aside from basal cover, herbaceous canopy cover, production, and reproduction were not different among low, moderate, and nonuse treatments. Perennial bunchgrass basal cover was about 25% lower in the low and moderate treatments than the nonuse. Production, reproductive stem weight, and perennial grass basal cover were greater in the low, moderate, and nonuse treatments than the control. The high treatment had lower perennial bunchgrass cover (canopy and basal) and production than other grazed and nonuse treatments. Bunchgrass density remained unchanged in the high treatment, not differing from other treatments, and reproductive effort was comparable to the other treatments, indicating these areas are potentially recoverable by reducing stocking. Cover and production of Bromus tectorum L. (cheatgrass) did not differ among the grazed and nonuse treatments, though all were greater than the control. Cover and density of A.t. spp. wyomingensis did not differ among the burned grazed and nonuse treatments and were less than the control. We concluded that light to moderate stocking rates are compatible to sustainable grazing of burned sagebrush steppe rangelands.     

Long-Term Vegetation Trends on Grazed and Ungrazed Chihuahuan Desert Rangelands

Long-term information on the effects of managed grazing versus excluded grazing effects on vegetation composition of desert rangelands is limited. Our study objectives were to evaluate changes in frequency of vegetation components and ecological condition scores under managed livestock grazing and excluded livestock grazing over a 38-yr period at various locations in the Chihuahuan Desert of southwestern New Mexico. Sampling occurred in 1962, 1981, 1992, 1998, 1999, and 2000. Range sites of loamy (1), gravelly (2), sandy (2), and shallow sandy (2) soils were used as replications. Black grama (Bouteloua eriopoda Torr.) was the primary vegetation component at the seven locations. Dyksterhuis quantitative climax procedures were used to determine trends in plant frequency based on a 1.91-cm loop and rangeland ecological condition scores. Frequency measures of total perennial grass, black grama, tobosa (Hilaria mutica Buckley), total shrubs, honey mesquite (Prosopis glandulosa Torr.), and other vegetation components were similar on both grazed and ungrazed treatments (P > 0.1) at the beginning and end of the study. The amount of change in rangeland ecological condition scores was the same positive increase (14%) for both grazed and ungrazed treatments. Major changes (P < 0.1) occurred within this 38-yr study period in ecological condition scores and frequency of total perennial grasses and black grama in response to annual fluctuations in precipitation. Based on this research, managed livestock grazing and excluded livestock grazing had the same long-term effects on change in plant frequency and rangeland ecological condition; thus, it appears that managed livestock grazing is sustainable on Chihuahuan desert rangelands receiving over 25 cm annual precipitation.     

Response of Planted Sagebrush Seedlings to Cattle Grazing Applied to Decrease Fire Probability

Restoration of non-sprouting shrubs after wildfire is increasingly becoming a management priority. In the western U.S., Wyoming big sagebrush (Artemisia tridentata Nutt. ssp. wyomingensis Beetle & Young) restoration is a high priority, but sagebrush establishment from seed is sporadic. In contrast, planting seedlings often successfully restores sagebrush, but is expensive and time consuming. After planting, hence, there is a need to protect the investment from disturbances such as fire that will erase gains in sagebrush recovery. Grazing is likely the only tool that can be applied feasibly across the landscape to decrease wildfire probability, but there are concerns that grazing and associated activities (e.g. trampling) may negatively impact sagebrush seedlings. We investigated effects of grazing by cattle, applied as a fine fuel management strategy, on planted sagebrush seedlings at five blocks for five years. Grazing substantial reduced exotic annual grasses, large perennial bunchgrasses, and total herbaceous cover, thus achieving fuel management goals. Sagebrush cover and reproductive efforts were almost 2-fold greater in grazed compared to non-grazed areas in the final year of the study. This suggests that grazing favored sagebrush, a generally unpalatable shrub, recovery, likely by reducing competition from highly palatable herbaceous vegetation. Density of sagebrush, however, was similar between grazed and non-grazed areas. This research demonstrates that grazing can be strategically applied to reduce the probability of wildfire in areas with planted sagebrush seedlings; thereby, protecting the investment in sagebrush recovery. With more refinement, it also appears that grazing can be utilized to accelerate the recovery of sagebrush and potentially other woody vegetation habitat by modifying the competitive relationship between herbaceous and woody vegetation.     

Influence of 90 Years of Protection From Grazing on Plant and Soil Processes in the Subalpine of the Wasatch Plateau,USA

Human communities in the Intermountain West depend heavily on subalpine rangelands because of their importance in providing water for irrigation and forage for wildlife and livestock. In addition, many constituencies are looking to managed ecosystems to sequester carbon in plant biomass and soil C to reduce the impact of anthropogenic CO₂ on climate. This work builds on a 90-year-old grazing experiment in mountain meadows on the Wasatch Plateau in central Utah. The purpose of this study was to evaluate the influence of 90 years of protection from grazing on processes controlling the input, output, and storage of C in subalpine rangelands. Long-term grazing significantly reduced maximum biomass in all years compared with plots within grazing exclosures. For grazed plots, interannual variability in aboveground biomass was correlated with July precipitation and temperature (R² = 0.51), while there was a weak correlation between July precipitation and biomass in ungrazed plots (R² = 0.24). Livestock grazing had no statistically significant impacts on total soil C or particulate organic matter (POM), although grazing did increase active soil C and decrease soil moisture. Grazing significantly increased the proportion of total soil C pools that were potentially mineralizable in the laboratory, with soils from grazed plots evolving 4.6% of total soil C in 1 year while ungrazed plots lost 3.3% of total soil C. Volumetric soil moisture was consistently higher in ungrazed plots than grazed plots. The changes in soil C chemistry may have implications for how these ecosystems will respond to forecast climate change. Because grazing has resulted in an accumulation of easily decomposable organic material, if temperatures warm and summer precipitation increases as is anticipated, these soils may become net sources of CO₂ to the atmosphere creating a positive feedback between climate change and atmospheric CO₂.     

Sage Grouse Groceries: Forb Response to Piñon-Juniper Treatments

Juniper and piñon coniferous woodlands have increased 2- to 10-fold in nine ecoregions spanning the Intermountain Region of the western United States. Control of piñon-juniper woodlands by mechanical treatments and prescribed fire are commonly applied to recover sagebrush steppe rangelands. Recently, the Sage Grouse Initiative has made conifer removal a major part of its program to reestablish sagebrush habitat for sage grouse (Centrocercus urophasianus) and other species. We analyzed data sets from previous and ongoing studies across the Great Basin characterizing cover response of perennial and annual forbs that are consumed by sage grouse to mechanical, prescribed fire, and low-disturbance fuel reduction treatments. There were 11 sites in western juniper (Juniperus occidentalis Hook.) woodlands, 3 sites in singleleaf piñon (Pinus monophylla Torr. & Frém.) and Utah juniper (Juniperus osteosperma [Torr.] Little), 2 sites in Utah juniper, and 2 sites in Utah juniper and Colorado piñon (Pinus edulis Engelm). Western juniper sites were located in mountain big sagebrush (A. tridentata ssp. vaseyana) steppe associations, and the other woodlands were located in Wyoming big sagebrush (A. tridentata ssp. wyomingensis) associations. Site potential appears to be a major determinant for increasing perennial forbs consumed by sage grouse following conifer control. The cover response of perennial forbs, whether increasing (1.5- to 6-fold) or exhibiting no change, was similar regardless of conifer treatment. Annual forbs favored by sage grouse benefitted most from prescribed fire treatments with smaller increases following mechanical and fuel reduction treatments. Though forb abundance may not consistently be enhanced, mechanical and fuel reduction conifer treatments remain good preventative measures, especially in phase 1 and 2 woodlands, which, at minimum, maintain forbs on the landscape. In addition, these two conifer control measures, in the short term, are superior to prescribed fire for maintaining the essential habitat characteristics of sagebrush steppe for sage grouse.     

Simulating Current Successional Trajectories in Sagebrush Ecosystems With Multiple Disturbances Using a State-and-Transition Modeling Framework

Disturbances and their interactions play major roles in sagebrush (Artemisia spp. L.) community dynamics. Although impacts of some disturbances, most notably fire, have been quantified at the landscape level, some have been ignored and rarely are interactions between disturbances evaluated. We developed conceptual state-and-transition models for each of two broad sagebrush groups—a warm-dry group characterized by Wyoming big sagebrush (Artemisia tridentata Nutt. subsp. wyomingensis Beetle & Young) communities and a cool-moist group characterized by mountain big sagebrush (Artemisia tridentata Nutt. subsp. vaseyana [Rydb.] Beetle) communities. We used the Vegetation Dynamics Development Tool to explore how the abundance of community phases and states in each conceptual model might be affected by fire, insect outbreak, drought, snow mold, voles, sudden drops in winter temperatures (freeze-kill), livestock grazing, juniper (Juniperus occidentalis var. occidentalis Hook.) expansion, nonnative annual grasses such as cheatgrass (Bromus tectorum L.), and vegetation treatments. Changes in fuel continuity and loading resulted in average fire rotations of 12 yr in the warm-dry sagebrush group and 81 yr in the cool-moist sagebrush group. Model results in the warm-dry sagebrush group indicated postfire seeding success alone was not sufficient to limit the area of cheatgrass domination. The frequency of episodes of very high utilization by domestic livestock during severe drought was a key influence on community phase abundance in our models. In the cool-moist sagebrush group, model results indicated at least 10% of the juniper expansion area should be treated annually to keep juniper in check. Regardless, juniper seedlings and saplings would remain abundant.     

Bluebunch Wheatgrass Response to Spring Defoliation on Foothill Rangeland

Spring elk grazing may reduce forage availability for wildlife or livestock in summer and may harm forage resources on foothill rangeland. We quantified bluebunch wheatgrass (Pseudoroegneria spicata [Pursh] A. Love) response to spring defoliation on foothill rangeland in southwestern Montana. Two experiments were conducted simultaneously on a foothill grassland site and a foothill sagebrush steppe site. Bluebunch wheatgrass plants (n = 800) were selected and excluded from wild and domestic ungulates. Clipping treatments were applied in either early spring (mid- to late April) or late spring (mid- to late May), and plants were clipped to 1 of 3 residual heights (3, 6, or 9 cm) for 1, 2, or 3 successive years. Unclipped plants served as controls. Plant response was measured in late June and late July on both sites. April clipping for 3 successive years did not adversely affect bluebunch wheatgrass in June or July (P > 0.05) at either site. On foothill grassland, May defoliation to 3 cm for 2 consecutive years reduced leaf height (P = 0.04) in July. May defoliation for 3 successive years to 3 or 6 cm reduced plant yield (P < 0.05) and leaf height (P < 0.05) in June, and May defoliation for 3 successive years to 3 cm reduced leaf height (P = 0.02) in July. On foothill sagebrush steppe, 3 successive years of May defoliation to ≤ 9-cm stubble heights decreased leaf height in June (P < 0.05). We conclude that foothill rangelands where bluebunch wheatgrass receives moderate or light defoliation (6–9-cm residual stubble heights) in mid- to late May should be limited to no more than 2 successive years of mid- to late May grazing, whereas sites that receive heavy to severe defoliation (≤ 3-cm residual stubble heights) in mid- to late May should not be grazed for 2 successive years during mid- to late May.     

Altered Herbivore Distribution Associated With Focal Disturbance

Natural disturbances historically created structurally diverse patterns across the landscape, and large herbivores concentrated herbivory in areas where disturbance decreased standing senesced biomass that acted as a grazing deterrent through decreased palatability and overall forage quality. However, following European settlement, many natural large-scale disturbance regimes that influence vegetation and herbivore grazing selection were altered or removed and replaced with fine-scale anthropogenic disturbances. It is unclear how fine-scale focal disturbance and alteration of vegetation structure influences livestock distribution and grazing. Therefore we used a tracked vehicle as a disturbance agent in a mesic mixed-grass prairie to assess the influence of focal anthropogenic disturbance on livestock distribution and grazing. Track vehicle disturbance decreased the height of vegetation (P < 0.05) but did not alter plant species composition (P > 0.05). Cattle fecal pat density was greater (P ≤ 0.05) in locations with track vehicle disturbance. Little bluestem tiller height was shorter (P ≤ 0.05) in tracked locations than nontracked locations in grazed treatments, but was not different in nongrazed locations the first growing season following disturbance. Fecal pat density and tiller height were not different (P > 0.05) between tracked and nontracked locations following the second growing season. Therefore, we concluded that fine-scale focal anthropogenic disturbance alters herbivore distribution and defoliation and can maintain structural heterogeneity, but the effect is ephemeral and does not create long-lasting grazing lawns.     

Bison and Cattle Grazing Impacts on Grassland Stream Morphology in the Flint Hills of Kansas

Despite a shift from yr-round bison grazing throughout the Great Plains before European settlement to extensive seasonal cattle grazing, little is known about ungulate grazing impacts on grassland streams. In this study we 1) determine whether grazing management is a significant driver of grassland stream morphology within the Flint Hills Ecoregion (Kansas, United States); 2) determine if yr-round bison grazing (the precolonial condition) and seasonal cattle grazing (the currently dominant grazing practice in the region) result in distinct stream morphology; and 3) determine if the introduction of cattle into ungrazed watersheds produces significant changes to channel morphology. We use a replicated watershed-scale study design and survey 17 streams across four grazing treatments (ungrazed, long-term bison grazed [yr-round], long-term cattle grazed [seasonal], and newly cattle grazed [seasonal]). Baseline geomorphic surveys were completed in 2010 following consistent grazing management since 1992, and resurveys were completed in 2011 and 2013 to determine short-term grazing impacts. Under the conditions of the experiment, we did not detect significant differences (P > 0.10) in channel morphology or stream bed substrate size among grazing treatments following nearly 2 decades of consistent grazing management. Cattle introduction into ungrazed watersheds resulted in modest (P < 0.05) stream widening (0.19 m, 3.9%) following two grazing seasons. Bison grazed watersheds also experienced modest (P < 0.05) stream widening (0.20 m, 5.1%) during the resurvey period. Stream widening from 2010 to 2013 within newly cattle-grazed and long-term bison-grazed treatments indicates that cattle and bison are capable of producing moderate alterations to grassland stream morphology over short time periods. However, longer time periods containing more diverse hydrologic conditions may be necessary to generate larger geomorphic changes between surveys. Although we detected modest changes to stream morphology in response to grazing over short time periods, overall, stream morphology does not vary among grazing treatments in the study area.     

Region-Wide Ecological Responses of Arid Wyoming Big Sagebrush Communities to Fuel Treatments

If arid sagebrush ecosystems lack resilience to disturbances or resistance to annual invasives, then alternative successional states dominated by annual invasives, especially cheatgrass (Bromus tectorum L.), are likely after fuel treatments. We identified six Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis Beetle & Young) locations (152–381 mm precipitation) that we believed had sufficient resilience and resistance for recovery. We examined impacts of woody fuel reduction (fire, mowing, the herbicide tebuthiuron, and untreated controls, all with and without the herbicide imazapic) on short-term dominance of plant groups and on important land health parameters with the use of analysis of variance (ANOVA). Fire and mowing reduced woody biomass at least 85% for 3 yr, but herbaceous fuels were reduced only by fire (72%) and only in the first year. Herbaceous fuels produced at least 36% more biomass with mowing than untreated areas during posttreatment years. Imazapic only reduced herbaceous biomass after fires (34%). Tebuthiuron never affected herbaceous biomass. Perennial tall grass cover was reduced by 59% relative to untreated controls in the first year after fire, but it recovered by the second year. Cover of all remaining herbaceous groups was not changed by woody fuel treatments. Only imazapic reduced significantly herbaceous cover. Cheatgrass cover was reduced at least 63% with imazapic for 3 yr. Imazapic reduced annual forb cover by at least 45%, and unexpectedly, perennial grass cover by 49% (combination of tall grasses and Sandberg bluegrass &lsqb;Poa secunda J. Presl.]). Fire reduced density of Sandberg bluegrass between 40% and 58%, decreased lichen and moss cover between 69% and 80%, and consequently increased bare ground between 21% and 34% and proportion of gaps among perennial plants &spigt; 2 m (at least 28% during the 3 yr). Fire, mowing, and imazapic may be effective in reducing fuels for 3 yr, but each has potentially undesirable consequences on plant communities.     

Herbicide Protection Pods (HPPs) Facilitate Sagebrush and Bunchgrass Establishment under Imazapic Control of Exotic Annual Grasses

Revegetation of exotic annual grass−invaded rangelands is a primary objective of land managers following wildfires. Controlling invasive annual grasses is essential to increasing revegetation success; however, preemergent herbicides used to control annual grasses prohibit immediate seeding due to nontarget herbicide damage. Thus, seeding is often delayed 1 yr following herbicide application. This delay frequently allows for reinvasion of annual grasses, decreasing the success of revegetation efforts. Incorporating seeds into herbicide protection pods (HPPs) containing activated carbon (AC) permits concurrent high preemergent herbicide application and seeding because AC adsorbs and renders herbicides inactive. While HPPs have, largely in greenhouse studies, facilitated perennial bunchgrass emergence and early growth, their effectiveness in improving establishment of multiple species and functional groups in the field has not been assessed. Five bunchgrass species and two shrub species were seeded at two field sites with high imazapic application rates as bare seed and seed incorporated into HPPs. HPPs significantly improved establishment of sagebrush (Artemesia tridentata Nutt. Spp. wyomingensis Beetle & Young) and crested wheatgrass (Agropyron cristatum [L.] Gaertn.) over the 2-yr study. Three native perennial grass species were protected from herbicide damage by HPPs but had low establishment in both treatments. The two remaining shrub and grass species did not establish sufficiently to determine treatment effects. While establishment of native perennial bunchgrasses was low, this study demonstrates that HPPs can be used to protect seeded bunchgrasses and sagebrush from imazapic, prolonging establishment time in the absence of competition with annual grasses.     

Semiarid Rangeland Is Resilient to Summer Fire and Postfire Grazing Utilization

Most wildfires occur during summer in the northern hemisphere, the area burned annually is increasing, and fire effects during this season are least understood. Understanding plant response to grazing following summer fire is required to reduce ecological and financial risks associated with wildfire. Forty 0.75-ha plots were assigned to summer fire then 0, 17, 34 or 50% biomass removal by grazing the following growing season, or no fire and no grazing. Root, litter, and aboveground biomass were measured before fire, immediately after grazing, and 1 yr after grazing with the experiment repeated during 2 yr to evaluate weather effects. Fire years were followed by the second driest and fifth wettest springs in 70 yr. Biomass was more responsive to weather than fire and grazing, with a 452% increase from a dry to wet year and 31% reduction from a wet to average spring. Fire reduced litter 53% and had no first-year effect on productivity for any biomass component. Grazing after fire reduced postgrazing grass biomass along the prescribed utilization gradient. Fire and grazing had no effect on total aboveground productivity the year after grazing compared to nonburned, nongrazed sites (1 327 vs. 1 249 ± 65 kg · ha^-1). Fire and grazing increased grass productivity 16%, particularly for Pascopyrum smithii. The combined disturbances reduced forbs (51%), annual grasses (49%), and litter (46%). Results indicate grazing with up to 50% biomass removal the first growing season after summer fire was not detrimental to productivity of semiarid rangeland plant communities. Livestock exclusion the year after summer fire did not increase productivity or shift species composition compared to grazed sites. Reduction of previous years' standing dead material was the only indication that fire may temporarily reduce forage availability. The consistent responses among dry, wet, and near-average years suggest plant response is species-specific rather than climatically controlled.     

Grazing History Affects Willow Communities in a Montane Riparian Ecosystem

This study was conducted to compare data from 12 grazed and ungrazed areas and to examine the impacts of grazing treatments on a montane willow community during an 11-year period. Data were collected on willow canopy cover, species diversity, height, and stem density in a montane riparian ecosystem between 1988 and 1999 from 4 grazing treatments: long-term grazing (since the early 1900s), long-term grazing exclusion (exclosures built in the 1950s), recent grazing (sections of exclosures opened in 1988), and recent grazing exclusion (exclosures built in 1988). Willow canopy cover increased significantly for all treatments through time, with the recent grazing exclusion treatment becoming similar to that of the long-term exclusion treatment within 5 years. Species diversity was greatest in the long-term grazed treatment. Willow height averaged over treatments increased from 1988 to 1997 (P = 0.0001), but did not increase significantly after that. Height in the long-term exclosure averaged over time from 1988 to 1997 was 1.5 times greater than in the long-term grazing treatment. Stem density of willows was significantly greater in the recent exclosure than in the long-term exclosure (P = 0.008, 180%) and recent grazing treatments (P = 0.02, 120%). Recent grazing exclusion resulted in the greatest increase in canopy cover, height growth, and stem density during the 11 years of study, indicating that these variables respond positively to removal of livestock grazing. Results suggest that continued long-term grazing exclusion may lead to a closed canopy, lower willow species diversity, reduction in new stem height growth, and reduced stem recruitment. Information on the dynamics of willow growth under different grazing treatments should help resource managers determine appropriate livestock utilization levels in similar riparian areas, and develop management plans for these important ecosystems.     

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%.     

Economic Risks of Cheatgrass Invasion on a Simulated Eastern Oregon Ranch

The potential of invasive plants to alter fuel properties over time has implications for the ranchers of semiarid rangelands throughout the world. A prime example of this phenomenon is the cheatgrass (Bromus tectorum L.) invasion of the native shrub-steppe lands in Great Basin of the western United States. The purpose of this study is to develop a bioeconomic model that optimizes simulated ranch behavior given the beginning stages of cheatgrass invasion on a public forage allotment. The bioeconomic model is applied to a typical eastern Oregon 300 cow-calf ranch. Livestock production decisions are simulated over a 40-yr planning horizon using a multiperiod linear programming model. Results showed changes in profit-maximizing ranch management strategies in the form of decreased optimal stocking rates and forage substitution. The net present value of the simulated ranch’s income stream declined, and the probability that the ranch cannot meet its full costs of livestock production and would exit the industry increased as a result. These economic impacts were more pronounced with decreased sale price. Sensitivity analysis showed that overall results in terms of ranch behavior were specific neither to the assumed discount rate nor to the assumed percentage of cheatgrass cover (as long as this percentage is within the reference state) on the public grazing allotment. This study introduces a method for managers to quantify impacts on ranches from fuel-altering invasive plants on public lands, emphasizing the importance of including information about native and invasive forage production characteristics and wildfire frequency as a function of the state of invasion.     

Long-term impacts of livestock grazing and browsing in the Succulent Karoo: a 20-year study of vegetation change under different grazing regimes in Namaqualand§

This study used a fence-line contrast approach to investigate the long-term impact of high grazing pressure on the vegetation at a site in Namaqualand, South Africa. Forty pairs of permanently marked plots were surveyed in 1996, 2006 and 2016. The main objective was to investigate changes in the vegetation structure and species composition between the near-continuously grazed communal rangelands and the relatively lightly grazed commercial rangelands over the 20-year period. The results showed a decline in total vegetation cover in both commercial and communal rangelands in 2016 relative to the two earlier sampling periods. This can be attributed to the low rainfall in 2016 and was due largely to a reduction in annual plant cover, especially on the communal rangeland. Perennial shrub species provide a fodder bank that can be utilised by livestock in times of drought and can buffer short-term deficits in forage supply. However, the annuals that dominate the vegetation of the communal rangeland do not form such fodder banks and consequently do not have the same multi-year buffering capacity as perennial shrubs. This provides the mechanism whereby long-term continuous grazing decreases resilience to rainfall fluctuations and increases livestock variability, thereby promoting non-equilibrium-type dynamics in the system.     

Disturbance Type and Sagebrush Community Type Affect Plant Community Structure After Shrub Reduction

Treatments to reduce shrub cover are commonly implemented with the objective of shifting community structure away from shrub dominance and toward shrub and perennial grass codominance. In sagebrush (Artemisia L.) ecosystems, shrub reduction treatments have had variable effects on target shrubs, herbaceous perennials, and non-native annual plants. The factors mediating this variability are not well understood. We used long-term data from Utah’s Watershed Restoration Initiative project to assess short-term (1 − 4 yr post-treatment) and long-term (5 − 12 yr post-treatment) responses of sagebrush plant communities to five shrub reduction treatments at 94 sites that span a range of abiotic conditions and sagebrush community types. Treatments were pipe harrow with one or two passes, aerator, and fire with and without postfire seeding. We analyzed effect sizes (log of response ratio) to assess responses of sagebrush, perennial and annual grasses and forbs, and ground cover to treatments. Most treatments successfully reduced sagebrush cover over the short and long term. All treatments increased long-term perennial grass cover in Wyoming big sagebrush (A. tridentata Nutt. ssp. wyomingensis Beetle & Young) communities, but in mountain big sagebrush (ssp. vaseyana [Rydb.] Beetle) communities, perennial grasses increased only when seeded after fire. In both sagebrush communities, treatments generally resulted in short-term, but not long-term, increases in perennial forb cover. Annual grasses (largely invasive cheatgrass, Bromus tectorum L.) increased in all treatments on sites dominated by mountain big sagebrush but stayed constant or decreased on sites dominated by Wyoming big sagebrush. This result was unexpected because sites dominated by Wyoming big sagebrush are typically thought to be less resilient to disturbance and less resistant to invasion than sites dominated by mountain big sagebrush. Together, these results indicate some of the benefits, risks, and contingent outcomes of sagebrush reduction treatments that should be considered carefully in any future decisions about applying such treatments.