Grazing and Burning Japanese Brome (Bromus Japonicus) on Mixed Grass Rangelands

Japanese brome (Bromus japonicus Thunb. ex Murr.) is an introduced, annual cool-season grass adapted to the central and northern Great Plains. Japanese brome has negatively impacted perennial grasses and decreased seasonal animal gains. Prescribed spring burning and defoliation have been effective in reducing brome density or cover, but little information directly compares the two common strategies. The objectives of this study were to 1) compare annual spring burning and grazing to reduce Japanese brome populations; and 2) evaluate trends of vegetative composition and biomass in burned, grazed, and unburned rangelands infested with Japanese brome. Paddocks with Japanese brome were assigned to one of four treatments: 1) annual prescribed spring burning, 2) spring grazing, 3) a combination of annual spring burning and grazing, and 4) an idle control. Treatments were applied annually from 2000 to 2004. Japanese brome density was greatest in the idle control in all years, even when low winter and spring precipitation limited Japanese brome recruitment. Late spring Japanese brome density was similar in all treatments with grazing or burning in four of the five seasons. Spring burning resulted in less than 65% litter cover the last 3 years, whereas the idle control and spring grazing had over 80% litter cover the last 4 years. Western wheatgrass (Pascopyrum smithii [Rydb.] A. Löve) decreased with spring grazing in burned and unburned paddocks. Buffalograss (Bouteloua dactyloides [Nutt] J. T. Columbus) composition decreased in the idle control treatment. Blue grama (Bouteloua gracilis [Willd. ex Kunth] Lag. ex Griffiths) and sideoats grama (Bouteloua curtipendula [Michx.] Torr.) composition varied by year. Even though annual burning and spring grazing were equally effective in limiting Japanese brome density and biomass compared to the idle control, Japanese brome was still present after 5 years, which indicates the difficulty of eradicating Japanese brome from ecosystems where it has become naturalized.     

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.     

Biomass Not Linked to Perennial Grass Mortality Following Severe Wildfire in the Southern High Plains

In March 2006 the East Amarillo Complex (EAC) wildfires burned over 367 000 ha of short and mixed grass prairie of the southern High Plains, USA. We studied EAC wildfire effects on perennial grass mortality and peak standing crop on Deep Hardland and Mixedland Slopes ecological sites. Deep Hardlands were dominated by blue grama (Bouteloua gracilis H.B.K. [Griffiths]) and buffalograss (Buchloe dactyloides [Nutt.] Engelm.); common species on Mixedland Slopes were little bluestem (Schizachyrium scoparium [Michx.] Nash.) and sideoats grama (Bouteloua curtipendula [Michx.] Torr.) with scattered sand sagebrush (Artemisia filifolia Torr.) sometimes present. We hypothesized that perennial grass mortality would increase and standing crop would decrease following severe wildfire, and that these responses would be greater than documented prescribed fire effects. Frequency of perennial grass mortality was higher on both sites in burned areas than nonburned areas through three growing seasons following wildfire; however, standing crop was minimally affected. Results suggest that post-wildfire management to ameliorate wildfire effects is not necessary, and that wildfire effects in this area of the southern High Plains are similar to prescribed fire effects.     

Prescribed Fire,Grazing, and Herbaceous Plant Production in Shortgrass Steppe

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

Evaluation of Native and Introduced Grasses for Reclamation and Production

Crested wheatgrass (Agropyron cristatum [L.] Gaertn.) and Russian wildrye (Elymus junceus Fisch.) are commonly used for reseeding in the more xeric Mixed Prairie of the Canadian prairies because they are perceived to be more productive than native species. However, they have been implicated in soil deterioration. The objectives of our study were to compare the aboveground net primary production and soil organic carbon (C) among monoculture communities of selected native grass species, crested wheatgrass, and Russian wildrye and to compare the native grass monocultures with their mixtures. In 1995, a 5-year study was initiated on Dark Brown Chernozemic (Typic Haploboroll) soil near Lethbridge, Alberta. Ten treatments consisting of monocultures of introduced and selected native species and mixtures of native species were established in a randomized complete block design with 4 replications. Aboveground net primary production and soil organic C were measured. Monocultures of 2 native species, green needlegrass (Stipa viridula Trin.) and blue grama (Bouteloua gracilis [H.B.K.] Lag. ex Steud.), were more productive than crested wheatgrass or Russian wildrye under both normal moisture and drought conditions. Monocultures of these native species also tended to be more productive than their mixtures. The western wheatgrass (A. smithii Rydb.) monoculture and the western wheatgrass–blue grama mixture experienced the greatest yield reduction as a result of drought. Treatment effects on soil organic C were not detected (P > 0.05) 5 years after seeding. Soils of the June grass (Koeleria macrantha [Ledeb.] J.A. Schultes f.) community had less (P < 0.05) macro-organic C than most other treatments.     

Enhancing Native Grass Productivity by Cocultivating With Endophyte-Laden Calli

The influence native endophytes have on grass establishment and productivity was evaluated by cocultivating Bouteloua eriopoda (Torr.) Torr. (black grama) or Sporobolus cryptandrus (Torr.) Gray (sand dropseed) seedlings with endophyte-laden calli from three of four native grass and shrub species: Atriplex canescens (Pursh) Nutt. (fourwing saltbush), S. cryptandrus, Sporobolus airoides (Torr.) Torr. (alkali sacaton), and B. eriopoda in vitro. Following cocultivation, grass seedlings were hardened and transferred to three replicate field plots, each containing 16 grass plants of a single species that had been cocultivated with a single callus species. Plant establishment rates, heights, crown diameters, aboveground biomass, seed yields, and seed quality were compared. In B. eriopoda (black grama), significant increases in plant biomass were not observed. However, early plant heights and crown diameters, establishment rates, and stolon production were higher in some callus treatments. In S. cryptandrus (sand dropseed), all variables were positively influenced by one or more of the endophyte treatments. Biomass increases ranged from 2.5- to threefold over untreated plants, and harvested seed increased 5.9-fold in plants treated with endophytes from A. canescens (fourwing saltbush). Seed quality, determined by purity, germination rates, and tetrazolium assays, did not differ across endophyte treatments for either grass. There is evidence that endophyte transfer is responsible for the altered vigor of treated plants.     

Potential Consequences of Repeated Severe Drought for Shortgrass Steppe Species

Future climate projections indicate temperatures in the shortgrass steppe region are likely to increase up to 3°C by midcentury, with a corresponding reduction in soil moisture even without precipitation deficit. Although periodic drought is a natural disturbance in shortgrass rangeland, negative effects on characteristic shortgrass species are possible as the frequency and severity of drought events increase in comparison with recent historic norms. As part of a study intended to detect vegetation changes at a shortgrass steppe site on Colorado’s eastern plains, frequency and canopy cover percentage were measured in 37 permanently marked plots over a period of 17 yr. The study period included the two lowest total annual precipitation yr (2002 and 2012) in the period of record for regional weather stations, exceeding even the driest years of the extended 1930s drought. Growing season mean temperatures during those drought years were 1°C and 1.6°C above the 1971 ? 2000 average, respectively. Three of the six perennial grass species monitored showed a decline over the period of the study. Blue grama (Bouteloua gracilis), a dominant and important forage species in the shortgrass steppe, declined in both cover and frequency, while alkali sacaton (Sporobolus airoides), not an important forage species, slightly increased. In addition to changes in graminoid dominance, we observed an increase in cholla (Cylindropuntia imbricata) and a decrease in sandsage (Artemisia filifolia) densities between 1999 and 2015. Even if total productivity of the shortgrass steppe is maintained under warming and drying conditions, changes in species composition have implications for rangeland quality with regard to its use for livestock grazing and use by wildlife such as small mammals and songbirds.     

A Nondestructive Method to Estimate Standing Crop of Purple Threeawn and Blue Grama

We used multiple regression analysis to develop models to predict standing crop of purple threeawn (Aristida purpurea Nutt.) and blue grama (Bouteloua gracilis [H.B.K.] Griffiths) nondestructively. Data were collected for 3 yr on the Texas Tech University Native Rangeland, Lubbock, TX, USA. Independent variables included plant length and area measurements (basal area and cross-sectional area at a 7.5-cm plant height and at 50% of total plant height). One hundred randomly selected plants of each species were measured in June 2008; 50 plants of each species were measured in June 2009 and 2010. Coefficients of determination exceeded 0.91 for both species in all 3 yr of measurement. For both species and years, cross-sectional area at 7.5 cm was the most important single predictor variable. For each species, models differed among years. Our regression models were successful at predicting mid- to late-season standing crop of purple threeawn and blue grama grass and provide an effective method for nondestructive monitoring of these species. This approach should be applicable to similar morphotypes of these species.     

Long-Term Livestock Exclusion in an Arid Grassland Alters Vegetation and Soil

Changes in soil and vegetation due to livestock grazing are occurring in arid lands throughout the world. The most extreme cases result in desertification, which is seen as largely irreversible, because of altered soil properties. To understand better how long-term livestock removal affects soil properties and vegetation, we compared water-infiltration rates, soil bulk density, and perennial grass cover inside and outside a long-term livestock exclosure in an arid grassland site in southeastern Arizona, United States. The site had not been desertified at the time of this study. Exclusion of livestock for 40 yr was associated with lower bulk density and higher water infiltration in both the dry and wet seasons. Perennial grass cover was higher and two native grasses, Eragrostis intermedia and Bouteloua hirsuta were significantly more common (P < 0.05) in the ungrazed area. These findings parallel our results from a desertified site and suggest that changes in soil physical properties associated with long-term livestock removal are not an artifact of desertification and can take place in a system that has remained in a grassland state. Our data suggest that, although significant changes in species composition have occurred, this grassland is relatively resilient to substantial changes in soil physical properties.     

Absence of a Grass/Fire Cycle in a Semiarid Grassland: Response to Prescribed Fire and Grazing

Many nonnative invasive grasses alter fire regimes to their own benefit and the detriment of native organisms. In southern Arizona the nonnative Lehmann lovegrass (Eragrostis lehmanniana Nees) dominates many semiarid grasslands where native grasses were abundant. Managers are wary of using prescribed fire in this fire-prone community partly due to the perceived effects of a grass/fire cycle. However, examples of the grass/fire cycle originate in ecosystems where native plants are less fire-tolerant than grasses and the invasive plant does not mimic the physiognomy of the native community. We investigate the effects of prescribed fire and livestock grazing on a semiarid grassland community dominated by a nonnative invasive grass. Lehmann lovegrass does not appear to alter the fire regime of semiarid grasslands to the detriment of native plants. Prescribed fire reduced the abundance of Lehmann lovegrass for 1 to 2 yr while increasing abundance of native grasses, herbaceous dicotyledons and fall richness, and diversity. Effects of livestock grazing were less transformative than the effects of fire in this long-grazed area, but grazing negatively affected native plants as did the combination of prescribed fire and livestock grazing. Although Lehmann lovegrass produces more fuel than native plants, fire frequency in semiarid grasslands appears to be limited by the paucity of above-average precipitation, which constrains high fuel loads. In addition, many native grasses tolerate high temperatures produced by Lehmann lovegrass fires. Consistent with previous research, fire does not promote the spread of Lehmann lovegrass, and more importantly human alteration of the fire regime is greater than the nominal effects of Lehmann lovegrass introduction on the fire regime.     

Long-Term Effects of a Summer Fire on Desert Grassland Plant Demographics in New Mexico

Plant demographic responses to an experimental summer fire were monitored for 12 yr on the Sevilleta National Wildlife Refuge, New Mexico, to determine recovery rates of burned plants and evaluate fire effectiveness in preventing shrub invasion of desert grasslands. Fourteen common species of grasses, shrubs, yucca, and cacti were measured for mortality, resprouting, regrowth, herbivory, and reproduction. After the first postfire growing season, black grama (Bouteloua eriopoda [Torr.] Torr.) declined 80% in size, whereas blue grama (Bouteloua gracilis [Willd. ex Kunth] Lag. ex Griffiths) exhibited no decline. Linear regression indicated that B. eriopoda needed 11 yr to recover. Spike dropseed (Sporobolus contractus A.S. Hitchc.) and purple three-awn (Aristida purpurea Nutt.) showed postfire declines in plant sizes, requiring 4- and > 5-yr recovery times, respectively. Sand muhly (Muhlenbergia arenicola Buckl.) exhibited no fire impact. Snakeweed (Gutierrezia sarothrae [Pursh] Britt. & Rusby) sustained 61% fire mortality and reduction in regrowth canopy size. Creosotebush (Larrea tridentata [Sesse & Moc. ex DC.] Coville) had 12% mortality, but survivors recovered over 12 yr. Fourwing saltbush (Atriplex canescens [Pursh] Nutt.) sustained 62% mortality, but recovered plant size in 5–6 yr. Winterfat (Krascheninnikovia lanata [Pursh] A. D. J. Meeuse & Smit) suffered 7% mortality, but required 9+ yr to recover. Pale desert-thorn (Lycium pallidum Miers) survived fire, recovering prefire canopy size in 3 yr. Torrey joint-fir (Ephedra torreyana Watson) exhibited < 1% mortality, and recovered in 2–3 yr. Soapweed yucca (Yucca glauca Nutt.) had < 2% mortality, recovered plant sizes in 2 yr, and increased numbers of rosettes 17%. Chollas (Opuntia imbricata [Haw.] DC. and Opuntia clavata Engelm.) suffered high mortality rates and required > 12 yr recovery times. Results demonstrated that summer fire may counter some shrub and cacti invasion in central New Mexico, but once shrubs mature, fire is less effective in removing woody plants to restore southwestern grasslands.     

Rangeland Livestock Production in Relation to Climate and Vegetation Trends in New Mexico

A large statewide historical database involving livestock numbers, vegetation cover, precipitation, air temperature, and drought frequency and severity allowed us to explore relationships between climate and rangeland livestock grazing levels and livestock productivity from 1920 to 2017. Trends in vegetation cover and livestock grazing levels from 1984 to 2017 were also explored. Our climate time series was divided into two periods, 1920 ? 1975 and 1976 ? 2017, based on an apparent accelerated increase in mean annual air temperatures that began in the mid-1970s. Both mean annual precipitation (MAP) and mean annual air temperature (MAT) differed (P ≤ 0.05) between the two periods. MAP and MAT were 9.6% and 3.4% higher in period 2 compared with period 1, respectively. From the 1920s to 2010s the livestock grazing level and weaned calf numbers fell 30% and 40%, respectively, despite a significant increase in MAP. Long-term declines in livestock grazing levels and in weaned calf numbers were significantly (P ≤ 0.05) correlated with increasing MAT (r = ? 0.34 and r = ? 0.43, respectively). No long-term trends (1984–2017) in woody or perennial herbaceous cover were detected at the level of the entire state of New Mexico. Woody plant cover dynamics for New Mexico were not related to livestock grazing levels. However, at the county level we detected a 2% increase in woody plant cover coupled with a 9% decrease in cattle animal units between 2000 and 2002 and 2015 and 2017 for 19 select counties well distributed across New Mexico. Increases in woody plant cover varied greatly among counties and were higher for eastern than western New Mexico. Both global and New Mexico data show the climate warming trend is accelerating. Our findings have relevance to several other parts of the world because New Mexico occurs at midlatitude, has varied topography and climatic conditions, and several different range vegetation types.     

Managing Grasslands to Maximize Migratory Shorebird Use and Livestock Production

Grasslands are important to domestic and wild animals. Migratory shorebirds are important components of coastal rangeland ecosystems. Buff-breasted Sandpiper (BBSA, Calidris subruficollis) and American golden-plover (AMGP, Pluvialis dominica) are two insectivorous, migrant shorebirds that rely on livestock-grazed grasslands in the Southern Cone of South America during their nonbreeding season, as well as on migration in North America. We studied habitat selection of these species and contrasted their needs with livestock requirements needed to develop recommendations for grazing management that benefit wildlife and livestock production. Short grass height was positively related to BBSA and AMGP abundance, with ideal grass heights from 2 to 5 cm. However, maximum livestock production is associated with grass height over 6 cm. The amount of forest cover, which is used to provide shade to livestock, was negatively related to the occurrence of both shorebird species, likely due to higher risks of predation. Grassland improvement did not affect BBSA but negatively affected AMGP abundance. Short grass habitat was selected by both shorebird species in spite of the higher arthropod biomass in taller grasslands, suggesting that other factors besides food abundance, such as the ability to detect prey and predators, are driving habitat selection. To enhance shorebird (and other wildlife) conservation and livestock production, we recommend managers adjust grazing intensity so that grass height is > 6 cm from mid-February to September, when the Nearctic migrant shorebirds are absent, and from 2 to 5 cm from October to early February when shorebirds are present. These austral summer adjustments should be restricted to paddocks with low forest cover so that livestock production in paddocks with high forest cover remains maximized. All adjustments should be evaluated by each farmer to ensure adequate economic returns are met.     

Broom snakeweed (Gutierrezia sarothrae) Population Change in Central New Mexico: Implications for Management and Control

This paper examines changes in broom snakeweed populations (Gutierrezia sarothrae [Pursh] Britt. & Rusby) from 1979 to 2014 at three prairie grassland sites in New Mexico. Data gathered each fall were used to study broom snakeweed population dynamics and to estimate the probability that the relatively short-lived subshrub will die off or invade blue grama (Bouteloua gracilis [H.B.K. Lag]) rangelands. Annual broom snakeweed standing crop data were used to categorize populations as None (< 100 kg ha^? 1), Light (< 300), Moderate (< 750), or Heavy (≥ 750). Ordered logit regression was then used to estimate the frequency of transition between these categories over time depending on environmental and site factors. Significant variables found to influence annual variation in broom snakeweed included the broom snakeweed standing crop and density observed the previous period (+ effect for continued broom snakeweed); grass standing crop the previous period (?); rainfall received from April to June (+); and average temperatures during April (+) and June (?). The probability of broom snakeweed invading an area that is currently without the plant ranges from about 1% to > 40% depending on environmental conditions and the amount of grass standing crop present. Transition probability estimates were also used in a Monte Carlo simulation model to evaluate the economics of broom snakeweed control. The economics of chemical broom snakeweed control were most strongly related to the rate of snakeweed reinvasion on treated areas and to the probability of natural die-off if infested areas were not sprayed.     

Plant and Bird Community Dynamics in Mixed-Grass Prairie Grazed by Native and Domestic Herbivores

Native colonial and large ungulate herbivores infrequently coexist on contemporary landscapes but frequently would have in the past, and understanding these interactions is important for conservation in working landscapes—those lands managed for biological and economic objectives. Although many factors contribute to grassland bird declines, consistent and long-term removal of native herbivores from western grasslands promotes homogenous landscapes that are now uniformly grazed by cattle (Bos taurus). This shift in grassland disturbance patterns limits habitat availability for specialized grassland species. We investigated vegetation and bird community dynamics in pastures grazed by domestic cattle and a native colonial herbivore, the black-tailed prairie dog (Cynomys ludovicianus). The study occurred in the northern mixed-grass prairie of the United States on four experimental pastures stratified by the proportion of prairie dog occupancy to create an ecological gradient. Vegetation and bird surveys were conducted from 2012 to 2015 on and off prairie dog colonies. Vegetation and bird communities were not different along the experimental pasture gradient but did differ relative to location on versus off town. Prairie dogs induced changes in the plant community with midstatured grasses like side-oats grama (Bouteloua curtipendula) and green needlegrass (Nassella viridula) being associated with off-colony sites while on-colony sites were associated with disturbance-tolerant species such as fetid marigold (Dyssodia papposa). The bird community responded to changes in vegetation structure resulting from prairie dogs with grasshopper sparrows (Ammodramus savannarum) being more abundant off colonies in areas with greater vegetation structure, while bird species with more complex life histories, such as the upland sandpiper (Bartramia longicauda), were associated with both on ? and off ? prairie dog colonies. Our findings demonstrate the importance of maintaining spatial heterogeneity in working landscapes and show that native colonial herbivores can help achieve this in the presence of herbivory by domestic cattle.     

Plant Interspaces Resulting From Contrasting Grazing Management in Northern Mixed-Grass Prairie: Implications for Ecosystem Function

We assessed plant interspaces in July 2007 using continuous line intercepts in twice-replicated pastures of northern mixed-grass prairie with contrasting grazing treatments: 1) long-term (25 yr) heavily grazed, dominated by the bunchgrass blue grama (Bouteloua gracilis), and 2) ungrazed, dominated by the rhizomatous grass western wheatgrass (Pascopyrum smithii). The number of plant interspaces was 26% higher in pastures heavily grazed, but the amount of soil surface occupied by plant interspaces was 27% greater without grazing. Plant interspaces were larger without grazing (14.8 ±  cm, mean ± 1 SE) than heavily grazed (8.9 ±  cm). Plant interspaces represented 87% and 68% of the total soil surface in the ungrazed and heavily grazed communities, respectively. The percentage of soil surface covered by plant interspaces < 20 cm was higher for the heavily grazed (94%) compared to the ungrazed (79%). Litter cover in the plant interspaces was higher without grazing (80 ± 1%) compared to the heavily grazed (57 ± 3%). Grazing-induced structural changes from a rhizomatous- to a bunchgrass-dominated vegetation community were manifest in the size and distribution of plant interspaces. Ecological consequences for erosion from raindrop impacts in larger plant interspaces in the ungrazed community are likely offset by greater litter cover in these communities; conversely, lower litter cover in heavily grazed pastures may increase erosion potential despite occurrence of smaller plant interspaces and less proportion of the soil surface covered by interspaces. Management practices that increase the cover of litter in plant interspaces should reduce the potential of erosion from water and wind in this semiarid rangeland.     

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.     

Livestock Grazing Impacts on Desert Vegetation,Khirthar National Park,Pakistan

The impact of livestock grazing on desert vegetation in Khirthar National Park, Pakistan, was investigated by comparing dry and wet season plant species composition, richness, cover, and a grazing index for quadrats outside (“open”) and inside (“exclosed”) native mammal breeding enclosures that had excluded livestock for 6 years. A total of 93 plant species were recorded in the dry season, 88 species in exclosed quadrats and 50 in open quadrats. While only 5 species were unique to open quadrats, 43 species were found only in the exclosed quadrats. Species richness was higher in the exclosures because of the presence of more grass and herb species, while grazing was higher in the open. After rain, species richness and cover were significantly higher than in the dry season because of the growth of summer ephemeral herbs and grasses, but richness was no longer different between the exclosure and open treatments. Although some herbaceous species may have been adversely affected by livestock grazing, overall species richness suggests strong ecosystem resilience to grazing, with levels no different after seasonal rains regardless of grazing level. Many grass and herb species absent from open sites during the dry season reappeared after rain, which suggests that livestock grazing may eliminate them as the dry season proceeds, but that a soil seed or bud bank persists.     

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.