Grazing Distribution Research Articles

Detecting the Influence of Best Management Practices on Vegetation Near Ephemeral Streams With Landsat Data

Various best management practices (BMPs) have been implemented on rangelands with the goals of controlling nonpoint source pollution, reducing the impact of livestock in ecologically important riparian areas, and improving grazing distribution. Providing off-stream water sources to livestock in pastures, cross-fencing, and rotational grazing are common rangeland BMPs that have demonstrated success in drawing livestock grazing pressure away from streams. We evaluated the effects of rangeland BMP implementation with six commercial-scale pastures in the northern mixed-grass prairie. Four pastures received a BMP suite consisting of off-stream water, cross-fencing, and deferred-rotation grazing, and two pastures did not receive BMPs. We hypothesized that the BMPs increased the quantity of riparian vegetation cover relative to the conditions in these pastures during the pre-BMP period and to the two pastures that did not receive BMPs. We used a series of 30-m Landsat normalized difference vegetation index (NDVI) images to track the spatial and temporal changes (1984–2010, n = 24) in vegetation cover, to which NDVI has been well correlated. Validation indicated that the remotely sensed signal from in-channel vegetation was representative of ground conditions. The BMP suite was associated with a 15% increase in the in-channel NDVI (0–30 m from stream centerline) and 18% increase in the riparian NDVI (30–180 m from stream center line). Conversely, the in-channel and riparian NDVI of non-BMP pastures declined 30% and 18% over the study period. The majority of change occurred within 2 yr of BMP implementation. The patterns of in-channel NDVI among pastures suggested that BMP implementation likely altered grazing distribution by decreasing the preferential use of riparian and in-channel areas. We demonstrated that satellite imagery time series are useful in retrospectively evaluating the efficacy of conservation practices, providing critical information to guide adaptive management and decision makers.

Controls over the strength and timing of fire–grazer interactions in a semi‐arid rangeland

Summary The degree to which large herbivores select and forage within recently burned areas is a key driver of vegetation heterogeneity in rangeland ecosystems. However, few studies have quantified the strength and timing of herbivore selection for burned areas or examined how selection strength varies among ecosystems differing in precipitation and primary productivity. We conducted a 4‐year patch‐burning experiment in semi‐arid rangeland of Colorado, USA, where 25% of the area available to cattle was burned each year and burned patches were shifted annually. We used GPS collars with activity sensors to quantify the distribution of free‐ranging cattle at a high temporal resolution (5‐min intervals) during the growing season each year. We used a classification tree model to discriminate between cattle grazing vs. non‐grazing locations, which significantly increased precision in quantifying burn selection strength. We fit generalized linear models predicting the frequency of cattle use of a given location within each study area and month, enabling comparisons between the relative influence of burns and topography on grazing distribution. Across multiple growing seasons, cattle selectively spent 31% of grazing time on recently burnt areas, which comprised 25% of the landscape; this selection strength was half as strong as that documented in mesic rangeland. At a monthly temporal scale, strong cattle selection for burned areas occurred during periods of rapid vegetation growth regardless of when during the growing season this greening occurred. Outside these intervals, burn selection strength was inconsistent and cattle grazing distribution was primarily influenced by topography. Thus, the relative importance of fire and topography in controlling grazer distribution was temporally contingent upon the timing and size of precipitation pulses. Synthesis and applications. Spatiotemporal interactions between fire and herbivores are a consistent feature of both semi‐arid and mesic rangelands, with interaction strength varying across gradients of precipitation and primary productivity. Management of semi‐arid ecosystems to sustain ecological processes should include strategies that allow ungulate herbivores to shift their grazing distribution seasonally in response to fire, topoedaphic variation and precipitation patterns. Combined management of fire and grazing for conservation objectives can be consistent with, and even complementary to, livestock production goals.

Multiple-Paddock Grazing Distributes Utilization Across Heterogeneous Mountain Landscapes: A case study of strategic grazing management

• Grazing capacity increased substantially and rangeland vegetation measurements improved after the Howell Ranch applied strategically planned and managed grazing. Increased capacity was realized from more spatially uniform grazing distribution and harvest efficiency rather than improving conditions over time. • Dividing a ranch into paddocks and grazing them sequentially, especially at high stocking density, can even out distribution of grazing and thus increase grazing capacity. • More even utilization across more, smaller paddocks contributes to explaining and resolving the apparent discrepancy between successful ranch-scale applications of multiple-paddock grazing and small-scale studies that found no benefit to rotational grazing.

Evaluation of Cattle Grazing Distribution in Response to Weed and Legume Removal in Mixed Tall Fescue (Schedonorus phoenix) and Legume Pastures

Grazing experiments were conducted during 2009 and 2010 to investigate the effect of herbicide application and subsequent weed removal on cattle grazing distribution in mixed tall fescue and legume pastures. At each location, herbicide applications were made to one-half of the grazed hectares to remove existing weeds and brush. Weeds and legumes were left nontreated across the remaining half of the grazed hectares at each location. Global positioning system tracking collars were fitted to three beef cows at each site and coordinates from each collar were recorded at 1-h intervals for 3 to 4 mo after herbicide application. At each location, broadleaf weeds were reduced from 1 to 51 kg ha−1, and legumes were completely eliminated in herbicide-treated compared to nontreated portions of the pastures. By the end of the season, the forage grass and legume component of pastures was greater and weed component lower in treated compared to nontreated portions of the pastures. By 3 mo after treatment, the cattle distribution was 1.3 to 5 times greater in herbicide-treated compared to nontreated portions of pastures. Overall, results from these experiments indicate herbicide treatment can increase desirable forage mass and thus modify cattle grazing distribution in pastures.

Grazing Distribution and Diet Quality of Angus, Brangus, and Brahman Cows in the Chihuahuan Desert

Abstract Grazing distribution can be improved by using adapted cattle breeds that travel to distant areas of extensive pastures. A 2-yr study was conducted to evaluate grazing distribution and diet quality of Angus, Brangus, and Brahman cows (seven cows per breed group) in the Chihuahuan Desert during three seasons (winter, early summer, and late summer) using three pastures. Two GPS collars were randomly assigned to each breed group and cow positions were logged every 10 min for 10- to 14-d periods in each pasture (3 periods · season -1 ). In 2008, breed groups were evaluated in separate pastures and data were analyzed as a 3 × 3 Latin square design. In 2009, all breed groups were evaluated at the same time in the same pastures. Fecal samples were collected in 2008 and analyzed using near infrared spectroscopy (NIRS) to estimate diet quality. If positions recorded when cows were resting were excluded, Brahman cows traveled greater distances per day than Angus cows throughout the study and greater ( P ≤ 0.10) than Brangus cows in all but one season during 2009. No differences in average distance to water were detected ( P s 0.10) among breed groups. During early summer in 2008 and early and late summer in 2009, Angus cows maintained a more linear grazing path ( P ≤ 0.10) than Brangus or Brahman cows. Brahman cows displayed more sinuous grazing paths ( P ≤ 0.10) than other breeds during early and late summer seasons in 2009. In 2008, no differences in crude protein content of diets were detected ( P s 0.10) among breed groups during all seasons. Spatial movement patterns of Brahman cows appeared to differ from Angus and Brangus cows; however, there was no evidence to suggest that there was any advantage in use of areas far from water by any breed group.

Cross-fence comparisons: Theory for spatially comprehensive, controlled variable assessment of treatment effects in managed landscapes

Historically monitoring of grazing impacts in rangelands has been seriously compromised by the small area, infrequency and variability of field-based sampling plots. Remote sensing of vegetation cover, which can be a surrogate for overall ecosystem condition, permits adequate spatial and temporal monitoring of land condition but can still be compromised by considerable inter and intra-paddock (field) variability. Cross-fence sample pairs control for local clines and patchiness in spatial and temporal variables such as vegetation, landform, soil type, surface-flows, and rainfall. We describe the theory behind a novel monitoring methodology that utilizes cross-fence sample pairs to rank paddocks, whether adjacent or not, using a system of linear equations and field based or preferably remotely-sensed data. This methodology outputs a condition ranking for each paddock in the system, with the aforementioned spatial and temporal variables controlled. Within paddock variability, such as differential grazing distribution, can be readily incorporated as weighting factors when suitable models are developed. This methodology may also be applicable to other grazing, agricultural and natural systems and applications where land management units have distinguishable boundaries.

Individualistic herds: Individual variation in herbivore foraging behavior and application to rangeland management

Rangeland systems cover vast areas of the earth's surface containing great diversity of life, and contribute to the livelihoods and welfare of millions of people. The management of rangeland systems for ecological and commercial outcomes is driven by a need to understand how grazing animals achieve most efficient and sustainable use of resources within the landscape. This process is multi-faceted; however, advances in understanding how foraging animals form decisions in complex landscapes offers strong potential for enabling rangeland managers to predict, and manage, the grazing distribution of large herbivores. Recently, there have been increasing calls to incorporate variation in individual behavior to enhance management of grazing distributions across resources or landscapes. However, widespread adoption of this approach has not occurred. Here, we review the roles of morphology, physiology, experience, and environmental and social conditions in driving differences in individual foraging behavior in large herbivores, and how these individual differences can be maintained within wild populations. We then synthesise this knowledge to examine if viable opportunities for exploiting individual differences in the behavior of livestock exist. We conclude by identifying remaining important challenges and areas for future research to facilitate using individual variation in foraging behavior to manage grazing patterns in rangeland systems.

Influence of Cow Age on Grazing Distribution in a Mixed-Conifer Forest

Abstract Optimal distribution of cattle on forested rangelands has long been a subject of concern specifically related to uniform and sustainable use of forage resources. Our objective was to determine if cow age influenced distribution and resource use on forested rangelands. This study was conducted from 1991 to 2001 at the US Department of Agriculture Starkey Experimental Forest and Range, northeastern Oregon, a mixed-conifer forested rangeland. We used 43 039 locations of cattle taken from 1 h prior to sunrise until 4 h after sunrise and 4 h prior to sundown until 1 h after sundown from 15 July to 30 August to evaluate cattle distribution patterns during peak foraging time. Cattle were grouped into four age classes: 2- and 3-yr-old cattle, 4- and 5-yr-old cattle, 6- and 7-yr-old cattle, and cattle ≥ 8 yr old. All age classes preferred areas with gentler slopes ( P s 0.05), westerly aspects ( P s 0.05), farther from water ( P s 0.05), and with greater forage production ( P s 0.05) than pasture averages. Cattle older than 3 yr of age selected areas with less canopy closure ( P s 0.05) than the mean value for the pasture. Young cows (s 4 yr old) selected lower elevations and steeper slopes than the oldest cows ( P s 0.05). In summary, cow age and correspondingly its experience directly influences distribution patterns and forage resource use of cattle at the Starkey Experimental Forest and Range.

Fencing artificial waterpoints failed to influence density and distribution of red kangaroos (Macropus rufus)

Provision of artificial waterpoints in Australian rangelands has resulted in an increase in the range and density of kangaroos. At high densities, kangaroos can inhibit vegetation regeneration, particularly in some protected areas where harvesting is prohibited. Fencing off waterpoints has been proposed to limit these impacts. Our aim was to determine whether fencing off waterpoints during a drought (when kangaroos would be especially water-limited) would influence the density and distribution of red kangaroos (Macropus rufus). Two waterpoints were fenced within the first 6 months of the 27-month study and a further two waterpoints were kept unfenced as controls in Idalia National Park, western Queensland. We estimated kangaroo densities around waterpoints from walked line-transect counts, and their grazing distribution from dung-pellet counts. Fencing off waterpoints failed to influence either the density or distribution up to 4 km from the waterpoints. Our results indicate that food availability, rather than the location of waterpoints, determines kangaroo distribution. Few areas in the rangelands are beyond kangaroos’ convenient reach from permanent waterpoints. Therefore, fencing off waterpoints without explicitly considering the spatial context in relation to other available water sources will fail to achieve vegetation regeneration.

Landscape nutritional patterns and cattle distribution in rangeland pastures

On rangelands, uneven or unmanaged livestock distribution can adversely affect plant community composition, riparian function, or displace wildlife. These issues have historic precedents and are still a challenge for those managing rangelands. A thorough understanding of the mechanisms governing livestock distribution can help land and livestock managers avoid or ameliorate many deleterious effects. To that end, this research tested hypotheses that grazing cattle seek nutritionally superior portions of rangeland pastures. Global positioning system (GPS) collars were used to track cattle movement and activity in three, 800+ ha pastures where the spatial distribution of standing crop, crude protein (CP), neutral detergent fiber (NDF), acid detergent fiber (ADF), and forage digestibility ( in situ dry matter disappearance (ISDMD)) were mapped in late spring. Four of five analyses implied grazing cattle spatially responded to forage quantity/quality attributes. Analyses indicated cattle favored higher than average CP ( P = 0.006) and ISDMD ( P = 0.078), and lower than average NDF ( P = 0.003) and standing crop ( P = 0.069) locales. No significant effect ( P = 0.954) occurred with ADF analyses. Correlations among those variables imply cattle may simultaneously respond to more than one nutritional attribute as they select foraging locales. Stepwise regression, however, relating grazing distribution to geophysical and forage quantity/quality characteristics were extremely poor predictors of where cattle grazed. Listed in order of entry, the model implied elevation above or below stock water, horizontal distance to stock water, forage CP content, and degree of slope were the site specific attributes most associated with cattle distribution. We speculate that cattle interactions with landscape level nutritional dynamics may at least partially explain seasonal changes in distribution and forage use by cattle across the landscape. These findings should help land and livestock managers understand, explain, and manipulate livestock distribution on their holdings.

Cattle Grazing Distribution and Efficacy of Strategic Mineral Mix Placement in Tropical Brazilian Pastures

Abstract A study was conducted in Brazil to identify factors affecting grazing distribution of yearling Nelore cross heifers and to evaluate the efficacy of placement of a salt–mineral mix away from water to improve uniformity of grazing. Two pastures (25 ha and 42 ha) were evaluated for four 15-d sessions. Mineral mix was placed 590 m to 780 m from water during two sessions and at water for two sessions. Stubble heights were measured at the beginning and end of each session in 1-ha subunits of each pasture. Cattle locations were recorded on day 13 and 14 of each session by horseback observers. Heifers avoided areas with a preponderance of forbs and taller grass (P 0.10). Stubble height reduction was more uniform (P < 0.05) when the mineral mix was at water compared to away from water. In contrast, heifers spent less time farther from water w...

Factors affecting the management of cattle grazing distribution in northern Australia: preliminary observations on the effect of paddock size and water points

Achieving more uniform grazing at landscape and paddock scales is seen as an important management objective by pastoralists in northern Australia, but it is difficult to attain in practice. This paper presents a brief review of some key factors to be considered in attempts to modify grazing distribution in extensive rangelands by drawing on the preliminary results of a project that is investigating several options for achieving more uniform grazing. Subdividing the landscape into smaller paddocks and, to a lesser extent, installing additional water points in large paddocks are effective in distributing grazing more widely across the landscape. However, these approaches are less effective in achieving uniform grazing within paddocks, and areas of concentrated use still occur even in small paddocks. To achieve spatial grazing objectives, it is necessary to use management tools that operate at the appropriate scale. Attaining more even use within paddocks should therefore be viewed as a separate management objective, requiring different techniques, to obtaining more effective use of the landscape as a whole. Integrating the use of several spatial management tools that act at different scales is likely to be most effective in improving grazing distribution. Our findings also highlight the importance of understanding paddocks in terms of the spatial arrangement of forage resources and their acceptability and quality in relation to water points and other landscape features. Differences between individual cattle in the way they use the landscape are important in producing more uniform use in larger paddocks and may also offer other opportunities for improving the use of landscape resources overall. Finally, the implications of more uniform use for livestock production and other land use values should be considered, with the protection of biodiversity values potentially requiring special management arrangements where more even use is achieved.

Individual Animal Selection Has the Potential to Improve Uniformity of Grazing on Foothill Rangeland

Uneven grazing distribution is a concern in rugged topography, because resources may be adversely impacted if livestock concentrate in gentle terrain near water. A study was conducted to determine if removing cattle with undesirable distribution patterns has the potential to increase uniformity of grazing. Before the study, 2 herds of cattle were observed by horseback observers during early mornings to establish terrain use patterns of individual animals. Cows were ranked on slope use and observed vertical and horizontal distance to water. Based on these rankings, cows were assigned to 1 of 2 treatments, hill climbers (observed on steeper slopes and farther from water) or bottom dwellers (used gentler slopes near water). Hill climber and bottom dweller cows grazed similar, but separate, pastures at 2 ranches during the 3-year study for a total of 8 comparisons. Based on a normalized and integrated index of terrain use from visual observations, hill climber cows used steeper and more distant areas from water ( P = 0.06) than bottom dwellers. Hill climber cows tracked by global positioning system collars used steeper and more distant areas from water than bottom dwellers ( P ≤ 0.09) during the first 4 weeks of the 6 weeks that pastures were grazed based on a normalized index of terrain use. Forage utilization was more uniform ( P < 0.05) across slopes and varying horizontal distances to water in pastures grazed by hill climbers than by bottom dwellers. Stubble heights in riparian and coulee bottom areas were higher ( P = 0.01) when grazed by hill climber cows (13.3 cm) than by bottom dwellers (8.1 cm). This study demonstrates that cattle with divergent grazing patterns when observed in the same pasture continue to use different terrain when separated, and it suggests that individual animal selection has the potential to increase uniformity of grazing. La distribución no uniforme del apacentamiento es un problema en terrenos de topografía rugosa porque los recursos pueden ser afectados adversamente si el ganado se concentra en los terrenos planos cercanos del agua. Se condujo un estudio para determinar si la remoción del ganado con patrones de distribución indeseable tiene potencial para incrementar la uniformidad del apacentamiento. Previo al estudio, dos hatos de ganado se observaron temprano en la mañana con observadores a caballo para establecer los patrones de uso del terreno de animales individuales. Las vacas se clasificaron de acuerdo con el uso de la pendiente del terreno y la distancias observadas vertical y horizontal con respecto a la distancia del agua. Basados en esta clasificación, las vacas fueron asignadas a uno de dos tratamientos: 1) trepadoras de montaña (las observadas en pendientes pronunciadas y lejos del agua) y 2) moradoras del las partes bajas (vacas usuarias de pendientes suaves cercanas del agua). Las trepadoras y las moradoras de las partes bajas apacentaron en forma similar, pero separadas, en potreros en dos ranchos durante los tres años del estudio, para un total de 8 comparaciones. Basados en un índice normalizado e integrado del uso del terreno obtenido de observaciones visuales, determinamos que las vacas trepadoras usaron áreas con mayor pendiente y mas lejanas del agua ( P = 0.06) que las moradoras de las partes bajas. Durante las primeras 4 semanas de las 6 que los potreros fueron apacentados, las vacas trepadoras, rastreadas con collares con Sistema de Posicionamiento Global (GPS), usaron áreas con más pendiente y más distantes del agua que las vacas moradoras de las partes bajas ( P ≤.09), esto se determinó en base a un índice normalizado de uso del terreno. La utilización del forraje fue más uniforme ( P < 0.05) a través de las pendientes y variando horizontalmente las distancias al agua en potreros apacentados por las vacas trepadoras de montaña que en las moradoras de las partes bajas. Las alturas del rastrojo de las áreas ribereñas y valles fueron mayores ( P = 0.01) cuando se pastorearon por la vacas trepadoras de montaña (13.3 cm) que por las moradoras de las partes bajas (8.1 cm). Este estudio demuestra que el ganado con patrones divergentes de apacentamiento, cuando es observado en el mismo potrero, mantiene un uso diferente del terreno que cuando son separados y sugiere que la selección individual del animal tiene potencial para incrementar la uniformidad del apacentamiento.

Individual Animal Selection Has the Potential to Improve Uniformity of Grazing on Foothill Rangeland

Uneven grazing distribution is a concern in rugged topography, because resources may be adversely impacted if livestock concentrate in gentle terrain near water. A study was conducted to determine if removing cattle with undesirable distribution patterns has the potential to increase uniformity of grazing. Before the study, 2 herds of cattle were observed by horseback observers during early mornings to establish terrain use patterns of individual animals. Cows were ranked on slope use and observed vertical and horizontal distance to water. Based on these rankings, cows were assigned to 1 of 2 treatments, hill climbers (observed on steeper slopes and farther from water) or bottom dwellers (used gentler slopes near water). Hill climber and bottom dweller cows grazed similar, but separate, pastures at 2 ranches during the 3-year study for a total of 8 comparisons. Based on a normalized and integrated index of terrain use from visual observations, hill climber cows used steeper and more distant areas from water (P = 0.06) than bottom dwellers. Hill climber cows tracked by global positioning system collars used steeper and more distant areas from water than bottom dwellers (P 0.09) during the first 4 weeks of the 6 weeks that pastures were grazed based on a normalized index of terrain use. Forage utilization was more uniform (P &lt; 0.05) across slopes and varying horizontal distances to water in pastures grazed by hill climbers than by bottom dwellers. Stubble heights in riparian and coulee bottom areas were higher (P = 0.01) when grazed by hill climber cows (13.3 cm) than by bottom dwellers (8.1 cm). This study demonstrates that cattle with divergent grazing patterns when observed in the same pasture continue to use different terrain when separated, and it suggests that individual animal selection has the potential to increase uniformity of grazing.

Impacts of grazing on montane heath vegetation in Wales and implications for the restoration of montane areas

The impact of long-term heavy grazing pressure on montane vegetation and soils was investigated on the Carneddau plateau in North Wales. At this site, historical information suggests that formerly extensive Racomitrium- and Vaccinium-dominated heaths have become degraded and reduced in extent over the last 40–50 years. This coincides with a period when both sheep numbers and atmospheric deposition of nitrogen have greatly increased. Vegetation composition, plant tissue chemistry, soil chemistry and sheep presence were compared between areas of ‘good’ condition Racomitrium and Vaccinium heath and degraded areas. Comparison of species composition data with sheep presence and environmental data showed no significant link between current grazing distribution and species composition in the areas investigated, with all habitats having sheep presence above the recommended maximum for this habitat. Soil chemistry showed several differences between degraded and ‘good’ condition habitats, suggesting that degraded areas had experienced loss of soil organic matter and upper organic horizons. Comparison of soil and vegetation nitrogen content with data from other UK sites suggests a build up of nitrogen has occurred in Carneddau vegetation and soils, possibly related to high levels of nitrogen deposition. It is concluded that restoration of severely degraded areas of montane vegetation may be retarded by deleterious changes in soil properties which could slow recolonisation by montane species. Reductions in stocking density aiming to restore montane communities might have more immediate impact on less degraded areas.

Comparative Morphology of Caucasian Old World Bluestem and Native Grasses

Caucasian old world bluestem (OWB) [Bothrichloa bladhii (Retz) S.T. Blake] has been widely introduced in the southern and central Great Plains as a perennial warm‐season grass for forage and soil conservation. As a result of its widespread introduction, it has escaped into some native rangelands. Once established in native pastures, observations suggest that Caucasian OWB may mature earlier than native vegetation and may be avoided by grazing animals in mixed rangelands, thus altering grazing distribution and over utilizing native species. More advanced morphological development in grasses is also associated with lower forage quality and lower palatability. This study was conducted to examine if morphological development of Caucasian OWB and native perennial warm‐season grass species differs. Monoculture stands of Caucasian OWB, big bluestem (Angropogon gerardii Vitman), little bluestem [Schizachyrium scoparium (Michx.) Nash], and side‐oats grama [Bouteloua curtipendula (Michx.) Torr.] were established in the spring of 2000. After the initiation of first growth in 2002 and 2003, vegetation was hand clipped each week for 8 wk and quantified for morphological stage of development according to the Nebraska staging method. In 2002, a drought season, Caucasian OWB had a greater mean stage weight (MSW) than the native species during Weeks 3 through 7 (P &lt; 0.001). In 2003, Caucasian OWB began the season at a similar morphological stage as the native species, but had a rate of development that was 5 to 11 times greater than the native species. The last 3 wk of the sampling period, MSW of Caucasian OWB was greater than all three native species (P &lt; 0.001). With more advanced morphological development in Caucasian OWB than the native grasses, declining forage quality could affect grazing preference and distribution patterns in mixed swards of Caucasian OWB and native species. The introduction of Caucasian OWB into native rangelands may have impacts that have yet to be understood.

Spatial–temporal arrangements of supplementation to modify selection of feeding sites by sheep

Undesirable grazing distribution results in land degradation and inefficient forage utilization. Rewards like food supplements have been commonly provided at predictable times and locations in the less preferred areas in order to improve grazing distribution. The problem with this approach is the generation of search patterns that are concentrated at certain times and locations, causing either overgrazing of new areas or the rapid return of the animals to the most preferred areas. Our model of spatial–temporal schedule of reinforcement proposes that rewards that are unpredictable in space and time should promote search patterns that are extended in space and time. In order to test predictions from the model, we studied how the spatial–temporal arrangement of supplementation influenced selection of feeding sites by sheep on a grass-legume pasture. Each experimental plot had a fertilized and an unfertilized side (8 m × 16 m each) either adjacent (Trial 1) or separated by an alley (1 m × 32 m) (Trial 2). In both trials groups of three ewes were randomly assigned to each of four treatments resulting from the combination of two spatial and two temporal arrangements of supplementation in the unfertilized side of the pasture. All treatments received the same amount and type of supplement (500 g alfalfa/corn pellets per ewe per day). There were two repetitions per treatment. Animal positions were recorded every 2 min during 2 h daily grazing sessions for 12 (Trial 1) or eight (Trial 2) consecutive days. The response variable was the proportion of time spent on the unfertilized side of the pasture. In Trial 1 neither treatment effects nor the interaction treatment by day was significant ( P > 0.05). In Trial 2, the random spatial and/or temporal arrangements of supplementation tended to increase the occupation of the unfertilized side of the pasture by sheep. The differences among treatments were larger at the beginning of the trial, when the availability of forage was relatively higher than towards the end of the trial, when the availability of forage was relatively lower. In both trials the proportion of time spent on the unfertilized side of the pasture decreased ( P < 0.01) as the daily grazing session progressed from the first half hour to the second half hour to the last hour. Our results raise some interesting possibilities that warrant future tests of the model of spatial–temporal schedule of reinforcement to modify selection of feeding sites by free grazing animals.

Patch burning effects on grazing distribution

Post-fire forage growth is known to be a strong attractant for large herbivores. However, fire has generally been avoided as a grazing distribution tool for fear of localized over utilization of forage resources. Our objectives were to examine whether forage utilization was affected by season of burn, determine cattle grazing preference for burned sites relative to non-burned sites, determine forb response to patch burning, and describe the relationship between end-of-season standing crop and distance from burned sites. Sixteen, 4-ha plots were burned in mid-November or mid-April and left exposed to cattle grazing for the duration of the growing season. Burn treatments were blocked within pastures to allow individual herds access to fall-burned, spring-burned, and non-burned sites. Standing crop estimates for grasses, forbs, and total herbage were made in September by clipping on burned sites and at 50, 100, 200, 400, and 800 m distant from the plot's edge. Standing crop was also sampled in exclosures on burned and non-burned sites. Cattle showed no preference for one burn season over the other. Cattle were strongly attracted to burned sites, reducing grass standing crop 78% within burns compared to 19% outside the influence of burns. Grass standing crop decreased in a predictable manner with proximity to burned plots. Forbs increased 60% to 1,095 kg ha−1 on grazed burned plots, but were unaffected by distance from burns. Patch burning can be employed as an effective, inexpensive grazing distribution tool.

Management strategies for optimal grazing distribution and use of arid rangelands.

Application of existing and novel management techniques can alter traditional livestock grazing patterns and significantly improve the sustainability of arid rangelands. Livestock often congregate and heavily graze riparian areas and other sensitive rangeland, while abundant forage remains in other areas. Increasing the uniformity of grazing can help protect fisheries, wildlife habitat, and other vegetative and watershed resources. For years, managers have improved grazing distribution in extensive arid pastures by developing new water sources. In addition, strategic supplement placement can be used to lure cattle to graze areas that typically receive little use. Placement of low-moisture molasses blocks in steeper areas that were far from water increased forage use by 14% at distances up to 600 m from supplement in foothill rangeland. Recent research has examined the potential of breed and individual animal selection to improve grazing distribution patterns. Cattle breeds developed in mountainous terrain utilize rugged rangeland more uniformly than breeds developed in more gentle terrain. In pastures that were grazed by cattle identified as "hill climbers" (previously observed on rugged terrain), more residual vegetation was left on gentle slopes and areas closer to water than in pastures grazed by cattle identified as "bottom dwellers" (previously observed on gentle terrain near water). Cattle may use rugged rangeland more uniformly after weaning and during periods when temperatures are more moderate and the forage is more homogeneous (spring, early summer, and autumn). Herding shows great promise for protecting sensitive rangeland. Preliminary data show that residual riparian forage in pastures where livestock were herded was up to two times higher than in a control pasture. The integration of herding and strategic supplement placement seems to be more effective than herding alone. Many concerns associated with the sustainability of grazing on arid rangelands can be resolved by manipulating livestock grazing behavior through management.

Patch burning effects on grazing distribution

Post-fire forage growth is known to be a strong attractant for large herbivores. However, fire has generally been avoided as a grazing distribution tool for fear of localized over utilization of forage resources. Our objectives were to examine whether forage utilization was affected by season of burn, determine cattle grazing preference for burned sites relative to non-burned sites, determine forb response to patch burning, and describe the relationship between end-of-season standing crop and distance from burned sites. Sixteen, 4-ha plots were burned in mid-November or mid-April and left exposed to cattle grazing for the duration of the growing season. Burn treatments were blocked within pastures to allow individual herds access to fall-burned, spring-burned, and non-burned sites. Standing crop estimates for grasses, forbs, and total herbage were made in September by clipping on burned sites and at 50, 100, 200, 400, and 800 m distant from the plot's edge. Standing crop was also sampled in exclosures on burned and non-burned sites. Cattle showed no preference for one burn season over the other. Cattle were strongly attracted to burned sites, reducing grass standing crop 78% within burns compared to 19% outside the influence of burns. Grass standing crop decreased in a predictable manner with proximity to burned plots. Forbs increased 60% to 1,095 kg ha-1 on grazed burned plots, but were unaffected by distance from burns. Patch burning can be employed as an effective, inexpensive grazing distribution tool.