Welcome to the Rangeland Ecology & Management archives. The journal Rangeland Ecology & Management (RE&M; v58, 2005-present) is the successor to the Journal of Range Management (JRM; v. 1-57, 1948-2004.) The archives provide public access, in a "rolling window" agreement with the Society for Range Management, to both titles (JRM and RE&M), from v.1 up to five years from the present year.

The most recent years of RE&M are available through membership in the Society for Range Management (SRM). Membership in SRM is a means to access current information and dialogue on rangeland management.

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Print ISSN: 0022-409x

Online ISSN: 1550-7424


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  • Very-High-Resolution Panoramic Photography to Improve Conventional Rangeland Monitoring

    Nichols, Mary H.; Ruyle, George B.; Nourbakhsh, Illah R. (Society for Range Management, 2009-11-01)
    Rangeland monitoring often includes repeat photographs as a basis for documentation. Whereas photographic equipment and electronics have been evolving rapidly, photographic monitoring methods for rangelands have changed little over time because each picture is a compromise between resolution and area covered. Advances in image sensors, storage media, and image-processing software allow enormous amounts of information to be collected efficiently and inexpensively, so multiple pictures taken at full zoom can be combined into a single high-resolution panoramic image. This project was initiated to integrate very-high-resolution panoramic images with conventional rangeland monitoring methods addressing three resource management categories: riparian areas, wildlife, and invasive species. 
  • Smoke Solutions and Temperature Influence the Germination and Seedling Growth of South African Mesic Grassland Species

    Ghebrehiwot, Habteab M.; Kulkarni, Manoj G.; Kirkman, Kevin P.; Van Staden, Johannes (Society for Range Management, 2009-11-01)
    Fire, natural or of anthropologic origin, is a recurrent phenomenon in South African mesic grassland. The species composition of these grasslands is sensitive to fire, particularly fire frequency. However, the mechanisms involved in influencing species composition are not fully understood. Currently there is a general suggestion that plant-derived smoke and smoke-isolated biologically active butenolide compound provide an important germination cue for a range of Poaceae species. Studies also show that these smoke solutions play a role in vegetative growth of many plants. We examined if this fire-response syndrome is related to the effect of plant-derived smoke-water (1:500 v/v) and smoke-derived butenolide compound (1028 M) on seed germination and seedling growth of six major constituent species of the grassland. In addition, the interaction of the smoke solutions with temperature was examined by incubating seeds at a range of temperatures. Treating seeds with smoke-water and butenolide, the germination rate and final germination percentage were greater in three of the six species. Themeda triandra Forssk. and Tristachya leucothrix Trin. ex Nees showed the greatest response, with final germination increased from 43% to 67% and 35% to 63%, respectively. With increasing temperature (> 30 degreesC), Aristida junciformis Trin. Rupr., Hyparrhenia hirta (L.) Staph, and Panicum maximum Jacq. responded positively to the test solutions. In nearly all the species tested, smoke- water-treated seeds produced significantly longer shoots or roots. However, the degree of response varied from species to species and across different temperatures. Findings from this study suggest that plant-derived smoke and its interaction with temperature may significantly influence the germination and seedling growth of the South African mesic grassland species, which can further alter the grassland composition. 
  • Can Regeneration of Green Ash (Fraxinus pennsylvanica) be Restored in Declining Woodlands in Eastern Montana?

    Lesica, Peter (Society for Range Management, 2009-11-01)
    Green ash (Fraxinus pennsylvanica Marsh.) dominates many deciduous woodlands at the western margin of its range in eastern Montana. Evidence suggests that the majority of green ash woodlands are in degraded condition with declining tree canopies and ground layers dominated by exotic grasses. The dense sod formed by these perennial grasses was hypothesized to interfere with green ash regeneration from seed. The purpose of this study was to test potential methods of restoring green ash regeneration in these declining woodlands. The effects of preseeding grazing and herbicide treatment and postgermination fertilizer on the recruitment, survival, and growth of green ash seedlings at each of four study sites typical of declining green ash woodlands in southeastern Montana were assessed. Six green ash trees at each of three sites were cut to examine the relationship of age, size, and health to sprouting ability and growth. Herbicide application had a positive effect on green ash recruitment and survival of green ash seedlings in woodlands with a dense sod of exotic grasses; seedling survival after 3-4 yr was ca. 10 times greater in herbicide-treated plots compared to controls or grazed plots. Seedlings grew slowly although fertilizer had a small positive effect on growth at one site. All coppiced trees produced basal sprouts, but sprout growth was severely curtailed at two of the three sites by deer browsing, suggesting that coppicing could increase tree canopy cover by replacing weakened trees with new and more vigorous boles and branches, but only where browsing by cattle and deer is reduced. Maintaining eastern Montana green ash woodlands in good condition should be given priority because restoration will be difficult. 
  • Effect of Simulated Browsing on Aspen Regeneration: Implications for Restoration

    Jones, Bobette E.; Lile, David F.; Tate, Kenneth W. (Society for Range Management, 2009-11-01)
    Aspen (Populus tremuloides Michx.) is a disturbance-dependent, fire-resilient, shade-intolerant, clonal species that is in decline throughout western North America. The objective of this study was to examine the effects of intensity and season of browsing on annual height growth of aspen suckers. The goal was to aid development of livestock grazing strategies to restore stands in decline due to excessive livestock browsing. We implemented 33 combinations of intensity and season of browse on aspen suckers in three aspen stands on Eagle Lake Range District, Lassen National Forest, California, USA, during 2003 and 2004. Greatest growth was on suckers with no terminal leader browse and < 25% of biomass removed from branches. Lowest growth occurred when 90% of terminal leader length and 50% of branch biomass was removed. Growth was most negatively affected by browse on terminal leader. Growth was lowest for suckers browsed midseason only and suckers browsed both early and midseason. Occurrence of conifer in the stand overstory significantly reduced sucker growth. Managers should minimize browse on terminal leaders, midseason browse over consecutive years, and repeated browse during a growing season. 
  • Defoliation Timing Effects on Spotted Knapweed Seed Production and Viability

    Benzel, Katie R.; Mosley, Tracy K.; Mosley, Jeffrey C. (Society for Range Management, 2009-11-01)
    Spotted knapweed (Centaurea stoebe L.), a perennial invasive forb that reproduces largely by seed, often forms new flowers after prescribed sheep grazing or mowing is applied during the bolting or flowering stage. It is unknown if these new flowers produce viable seeds by the end of the growing season. The purpose of this 2-yr study was to determine the appropriate timing (or timings) or combination (or combinations) of timings of defoliation on spotted knapweed to reduce its viable seed production. Spotted knapweed plants on foothill rangeland in west-central Montana were hand-clipped at seven different timings and frequencies of defoliation: June (bolting stage); July (late-bud-early flowering stage); August (full-flowering stage); June + July; June + August; July + August; or June + July + August. Unclipped plants were controls. Plants clipped in the bolting stage were defoliated at 35-40% relative utilization. Plants clipped at all other timings had 100% of their buds and flowers removed, plus 3 cm of each bud or flower stem. Plant response was evaluated from mid-August through September, whenever the seed heads of each treatment’s plants reached maturity but while their seed-head bracts remained tightly closed. Clipping at any timing or combination of timings reduced the number of buds and flower heads per plant (P < 0.01), number of seeds per plant (P < 0.01), percentage of viability of seeds (P < 0.01), and number of viable seeds per plant (P < 0.01) compared with no clipping. Clipping during the bolting stage reduced the number of viable seeds by nearly 90% compared with no clipping. Clipping during the late-bud-early-flower or full-flower stage reduced the number of viable seeds by nearly 100% compared with no clipping. Spotted knapweed defoliation via prescribed sheep grazing or mowing in summer should suppress viable seed production of spotted knapweed. 
  • Livestock Browsing, Not Water Limitations, Contributes to Recruitment Failure of Dobera glabra in Semiarid Ethiopia

    Tsegaye, Diress; Moe, Stein R.; Haile, Mitiku (Society for Range Management, 2009-11-01)
    The study used nursery and field experiments to investigate why recruitment of Dobera glabra (Forssk) Poir., a native food source for both humans and livestock, often fails in the semiarid rangelands of Afar, Ethiopia. We hypothesized that soil water limitations and browsing by livestock would be the primary mechanisms accounting for the failure of natural regeneration. We used three sets of experiments—1) seedling performance in response to shade and watering in a nursery, 2) field regeneration with and without browsing, and 3) regeneration beneath trees with and without browsing—to examine regeneration success. Seedlings were established in plots from seeds sown directly into the soil for nursery and field experiments, but natural germination occurred beneath trees. Survival and relative growth rates (RGR) were used to monitor seedling performance. Seedlings that received neither shade nor watering treatments had lower seedling survival (53 +/- 15%) as compared with other treatment combinations. Highest seedling survival was recorded under shade and 1 d watering wk-1 treatment combinations (92 +/- 1%). However, shade treatments had a minimal increase on seedling RGR. Water limitation is not a crucial limiting factor for D. glabra recruitment, as 53% of the seedlings survived without both shade and supplemental water for 1 yr. Field experiments, however, demonstrated that browsing greatly reduced seedling survival (below 15%) and suppressed growth of surviving seedlings, suggesting that browsing is the major factor preventing natural recruitment. Natural recruitment of D. glabra is unlikely with the existing continuous and intensive grazing/browsing in Afar rangelands, where the mobility of pastoralists is restricted. We suggest that planting nursery-raised seedlings in home gardens of settled pastoralists and establishment of grazing reserves in some key range sites that contain D. glabra could help offset the recruitment failure of native food species D. glabra in Afar rangelands. 
  • Influence of Livestock Grazing and Climate on Pinyon Pine (Pinus edulis) Dynamics

    Barger, Nichole N.; Adams, Henry D.; Woodhouse, Connie; Neff, Jason C.; Asner, Gregory P. (Society for Range Management, 2009-11-01)
    Over the last century there has been marked expansion and infilling of pinyon (Pinus spp.)-juniper (Juniperus spp.) woodlands into grassland and shrubland ecosystems across the western United States. Although range expansions in pinyon-juniper populations have been documented with changing climate throughout the Holocene, over the last century, local scale impacts such as livestock grazing, changes in fire regimes, and increasing atmospheric CO2 concentrations are thought to be more recent drivers of pinyon-juniper woodland distribution. Our objective was to examine the role of historical livestock grazing relative to past climate in regulating pinyon (Pinus edulis Engelm.) recruitment and growth over the last century in a persistent pinyon-juniper woodland. We compared pinyon dynamics on a remote mesa site, minimally grazed by domestic livestock, to a nearby historically grazed site in southeastern Utah. The presence of a significant number of old trees (> 200 yr) at both sites suggests that these populations were well established prior to the 20th century. No differences in pinyon density or basal area were observed between grazed and ungrazed sites. Stand age structure data showed that pinyon recruitment across these sites was highly synchronous, with a large recruitment event occurring during the early 1900s; 17% of the pinyons on both sites dated to the 1920s. Climatic conditions during this decade were consistently cool and wet—conditions known to support enhanced recruitment and growth in pinyon pines. Pinyon growth was also strongly synchronous across sites (r = 0.96). Pinyon growth was significantly correlated with winter/spring precipitation and negatively correlated with June temperature. Taken together, our results suggest that past climate may be more important in structuring pinyon populations than historical land use in these persistent pinyon-juniper woodlands. Given future climate projections of increasing temperature and more extended drought periods, regeneration of pinyon populations following the recent regional-scale dieback may be slow. Moreover, prolonged drought combined with potentially slow regeneration times for pinyon under future climate scenarios could result in substantial declines in pinyon populations across the region, a result that land managers should consider when planning for future restoration treatments in persistent pinyon-juniper woodlands. 
  • Geospatial Assessment of Grazing Regime Shifts and Sociopolitical Changes in a Mongolian Rangeland

    Sankey, Temuulen Tsagaan; Sankey, Joel B.; Weber, Keith T; Montagne, Cliff (Society for Range Management, 2009-11-01)
    Drastic changes have occurred in Mongolia’s grazing land management over the last two decades, but their effects on rangelands are ambiguous. Temporal trends in Mongolia’s rangeland condition have not been well documented relative to the effects of long-term management changes. This study examined changes in grazing land use and rangeland biomass associated with the transition from the socialist collective to the current management systems in the Tsahiriin tal area of northern Mongolia. Grazing lands in Tsahiriin tal that were formerly managed by the socialist collective are now used by numerous nomadic households with their privately owned herds, although the lands remain publicly owned. Grazing pressure has more than tripled and herd distribution has changed from a few spatially clustered large herds of sheep to numerous smaller herds of multiple species. Landsat image- derived normalized-difference vegetation index estimates suggest that rangeland biomass significantly decreased (P < 0.001) from the collective to the postcollective periods. The observed decrease was significantly correlated with changes in the grazing management system and increased stocking density (P < 0.001), even when potential climate-induced changes were considered. Furthermore, field- and Satellite Pour l’Observation de la Terre imagery-based rangeland assessments in 2007 and 2008 indicate that current rangeland biomass is low. Spatial pattern analyses show that the low biomass is uniform throughout the study site. The observed decrease in rangeland biomass might be further accelerated if current grazing land use continues with no formal rangeland management institution or organized, well-structured efforts by the local herding households. 
  • Understanding Change: Integrating Rancher Knowledge Into State-and-Transition Models

    Knapp, Corrine Noel; Fernandez-Gimenez, Maria E. (Society for Range Management, 2009-11-01)
    Arid and semiarid rangelands often behave unpredictably in response to management actions and environmental stressors, making it difficult for ranchers to manage for long-term sustainability. State-and-transition models (STMs) depict current understanding of vegetation responses to management and environmental change in box-and-arrow diagrams. They are based on existing knowledge of the system and can be improved with long-term ecological monitoring data, histories, and experimentation. Rancher knowledge has been integrated in STMs; however, there has been little systematic analysis of how ranchers describe vegetation change, how their knowledge informs model components, and what opportunities and challenges exist for integrating local knowledge into STMs. Semistructured and field interviews demonstrated that rancher knowledge is valuable for providing detailed management histories and identifying management-defined states for STMs. Interviews with ranchers also provided an assessment of how ranchers perceive vegetation change, information about the causes of transitions, and indicators of change. Interviews placed vegetation change within a broader context of social and economic history, including regional changes in land use and management. Despite its potential utility, rancher knowledge is often heterogeneous and partial and can be difficult to elicit. Ranchers’ feedback pointed to limitations in existing ecological site-based approaches to STM development, especially issues of spatial scale, resolution, and interactions among adjacent vegetation types. Incorporating local knowledge into STM development may also increase communication between researchers and ranchers, potentially yielding more management-relevant research and more structured ways to document and learn from the evolving experiential knowledge of ranchers. 
  • Knowledge in Practice: Documenting Rancher Local Knowledge in Northwest Colorado

    Knapp, Corrine Noel; Fernandez-Gimenez, Maria E. (Society for Range Management, 2009-11-01)
    For more than 150 years, ranchers in the West have gained insight about natural systems through daily interaction and management of landscapes, but this knowledge has never been systematically documented and analyzed. We interviewed 26 ranchers from a single watershed to understand how ranchers acquire their knowledge, document what they know about rangeland ecosystems, and explore how this knowledge varies within the ranching community. This exploratory study offers insight into the types of knowledge ranchers possess without attempting to survey all rancher knowledge or ascribe this set of knowledge to all ranchers. We identified three major knowledge categories in interviews: active knowledge applied to management decisions, embedded knowledge from living in place, and integrative knowledge that links ecological, economic, and social aspects of rangeland systems. We found rancher knowledge complemented scientific knowledge in its ability to provide site-specific information on management practices and ecological responses, and insight regarding potential indicators of rangeland health. Knowledge varies widely within the ranching community, and knowledgeable ranchers are readily identified through community referrals. Ranchers gained their knowledge primarily through experience and social interactions, and this knowledge is an untapped source of context-specific information. We did find that economic constraints, social norms, and proximity to the system might limit application of knowledge to practice. There is also a danger that this accumulated and dynamic knowledge base will be lost over the next generation, as many family ranches are sold to new ranchers or for nonranching uses. Based on our findings, we propose that more dialogue within ranching communities and between ranchers and scientists may lead to more sustainable land management practices and effective outreach efforts, and could expand and strengthen the informal social networks through which much rancher knowledge is shared and on which the social sustainability of ranching communities depends. 
  • Managing Complex Problems in Rangeland Ecosystems

    Boyd, Chad S.; Svejcar, Tony J. (Society for Range Management, 2009-11-01)
    Management of rangelands, and natural resources in general, has become increasingly complex. There is an atmosphere of increasing expectations for conservation efforts associated with a variety of issues from water quality to endangered species. We argue that many current issues are complex by their nature, which influences how we approach them. We define a complex problem as one that varies in time and space. In other words, one answer may not be correct for all sites or during all years. For simple problems a generalized answer may be sufficient, and even for complex problems, general rules provide a good starting point. However, we suggest that it is important to distinguish between simple and complex problems. Several key obstacles emerge when considering complex natural resource problems, namely, 1) no single entity can handle all aspects of the problem and 2) significant knowledge gaps exist and will continue to exist into the future. We suggest that overcoming these obstacles will benefit from 1) a framework for effective partnerships and 2) a mechanism for continuous learning. Managing complex problems will require some combination of the following: 1) a process-based understanding of the problem (i.e., what causes variation in time and space), 2) adaptive management, and 3) effective coordination of research and management. There are many examples of organizations applying portions of these approaches to complex problems; however, it seems that in many cases the process has simply evolved in that direction rather than being a planned strategy. We suggest that as a profession we need to have a discussion about the nature of the problems we are addressing and how researchers and managers can jointly address these problems. 
  • Influence of Abrams M1A1 Main Battle Tank Disturbance on Tallgrass Prairie Plant Community Structure

    Althoff, Peggy S.; Kirkham, Mary Beth; Todd, Timothy; Thien, Stephen J.; Gipson, Philip S. (Society for Range Management, 2009-09-01)
    The Department of Defense’s Range and Training Land Assessment program provides information and recommendations to range managers regarding the condition of training lands. This information is used to assist in scheduling training areas and in monitoring the effectiveness of rehabilitation projects. Fort Riley Military Installation is a major training reservation located in the Flint Hills of northeastern Kansas, within the tallgrass prairie ecosystem. A randomized complete block design composed of three treatments (M1A1 Abrams tank traffic during wet and dry soil conditions, and a nontrafficked control) with three replications was established in each of two soil types, a silty clay loam and a silt loam soil, on Fort Riley in 2003. Disturbance was created by driving the tank for five circuits in a figure-eight pattern during either during wet or dry soil conditions. Two additional experimental treatments were added during the study: five additional tank passes on one-half of each figure eight in 2004 and burning in 2006. Two areas, a curve and straightaway, within each traffic intensity (and later, burn treatment) subplot were designated for sampling. Aboveground biomass, species composition, and ground cover were measured during each growing season. Recovery of grass and total aboveground biomass in silty clay loam soil was delayed for curve areas and following disturbance in wet soil conditions, respectively. Species composition and ground cover continued to exhibit significant disturbance effects in 2007, with greatest damage observed for repeated traffic under wet soil conditions. Fire effects on vegetation were variable and generally greater for undisturbed control plots than for disturbed areas. The tallgrass prairie typically is considered to be among the most resilient of military training lands, but our research suggests that resiliency is dependent upon soil type and training conditions, and may require longer periods of recovery than previously thought. 
  • Root Responses to Short-Lived Pulses of Soil Nutrients and Shoot Defoliation in Seedlings of Three Rangeland Grasses

    Arredondo, José Tulio; Johnson, Douglas A. (Society for Range Management, 2009-09-01)
    Root proliferation is important in determining root foraging capability of rangeland grasses to unpredictable soil-nutrient pulses. However, root proliferation responses are often confounded by the inherent relative growth rate (RGR) of the particular species being compared. Additionally, inherent biomass allocation to roots (R:S ratio) can be associated with root RGR, hence likely influencing root foraging responses. The influence of relative growth rate and biomass allocation patterns on the speed and efficiency of root foraging responses at the critical seeding stage was examined in two important perennial rangeland grasses that occur widely in the Great Basin Region of the United States (Whitmar bluebunch wheatgrass [Pseudoroegneria spicata {Pursh} Löve] and Hycrest crested wheatgrass [Agropyron desertorum {Fisch. ex Link} Schult. 3 A. cristatum L. Gaert.]) as well as in the widespread exotic invasive annual grass, cheatgrass (Bromus tectorum L.). Greenhouse-grown seedlings were exposed to four nutrient regimes: uniform-low, uniform-high, soil-nutrient pulse, soil-nutrient depletion, and to either no clipping or clipping (80% removal of standing shoot biomass). Hycrest was the only species that exhibited root proliferation responses to the short- lived nutrient pulse, and this response occurred through root elongation rather than initiation of lateral root branches. Overall, defoliation inhibited proliferation-based root responses to a larger extent than topological-based root responses. Defoliated plants of Hycrest interrupted root development (topological index did not change) following shoot defoliation compared to undefoliated plants. In contrast, root topological developmental patterns were the same for defoliated and undefoliated plants of Whitmar, whereas cheatgrass exhibited an intermediate response between Whitmar and Hycrest. Our results suggest that inherent biomass allocation to roots contributes to enhanced capabilities of proliferation-based root responses. 
  • Wild Ungulate Herbivory of Willow on Two National Forest Allotments in Wyoming

    Meiman, Paul J.; Thorne, Mark S.; Skinner, Quentin D.; Smith, Michael A.; Dodd, Jerrold L. (Society for Range Management, 2009-09-01)
    Willows (Salix) are important riparian plants and often used to indicate riparian condition. Many herbivores feed on willows, but there is limited information about willow browsing by wildlife except in national parks. This study was conducted to estimate wild ungulate herbivory of willow on two US Forest Service allotments in northern Wyoming and to compare these values to published estimates for national parks. We also compared total annual and seasonal willow utilization by wildlife between sites dominated by willows of different heights. The effects of height category, site, and season on willow utilization were determined with a repeated measures analysis. Four permanent willow utilization transects were established at each of six study sites per allotment on two allotments, in communities supporting planeleaf (Salix planifolia Pursh), Wolf’s (Salix wolfii Bebb), Drummond’s (Salix drummondiana Barratt ex Hook.), or Eastwood’s (Salix eastwoodiae Cock. ex A. Heller) willow. Twenty-five twigs were marked per transect (distributed across 6-12 plants/transect). Lengths of marked twigs were recorded on four dates to estimate willow utilization for winter/spring, summer, and late summer/fall periods. Total annual willow utilization on one allotment (53%) was similar to published estimates for national parks (P 5 0.0864), whereas utilization for the other allotment (58%) was greater (P = 0.0421) than national parks. Seasonal patterns of willow utilization differed among sites within height categories (P < 0.001). Total annual willow utilization by wildlife also varied by site within height category (P = 0.0165) but was not greater for short (43-56%) versus tall (59-63%) willow communities. Wildlife browsing of willow in this study equaled, or exceeded, estimates for national parks, where concern has been expressed about willow community conditions. Generalizations about willow utilization for tall and short willow communities are problematic. Management decisions should be based on site-specific information as opposed to generalizations. 
  • Modeling Bare Ground With Classification Trees in Northern Spain

    Weber, Keith T.; Alados, Concepción L.; Bueno, C. Guillermo; Gokhale, Bhushan; Komac, Benjamin; Pueyo, Yolanda (Society for Range Management, 2009-09-01)
    Bare ground abundance is an important rangeland health indicator and its detection is a fundamental part of range management. Remote sensing of bare ground might offer solutions for land managers but also presents challenges as modeling in semiarid environments usually involves a high frequency of spectral mixing within pixels. Classification tree analysis (CTA) and maximum likelihood classifiers were used to model bare ground in the semiarid steppes of the middle Ebro valley, Aragon, Spain using Satellite Pour l’Observation de la Terre 4 (SPOT 4) imagery and topographic data such as elevation, slope, aspect, and a morphometric characterization model. A total of 374 sample points of bare-ground fraction from sixteen 500-m transects were used in the classification and validation process. Overall accuracies were 85% (Kappa statistic = 0.70) and 57% (Kappa statistic = 0.13) from the CTA and maximum likelihood classifiers, respectively. Although spectral attributes were essential in bare-ground classification, the topographic and morphometric properties of the landscape were equally critical in this modeling effort. Although the specific layers best suited for each specific model will vary from region to region, this study provided an important insight on both bare-ground modeling and the potential advantages of CTA. 
  • Remote Sensing of Spatial and Temporal Vegetation Patterns in Two Grazing Systems

    Blanco, Lisandro J.; Ferrando, Carlos A.; Biurrun, Fernando N. (Society for Range Management, 2009-09-01)
    One constraint that range scientists must face in grazing studies is the lack of accurate and repeatable techniques for discriminating grazing effects from both temporal variability and spatial heterogeneity of vegetation. Both forms of variability contribute to inconsistent grazing system effects on vegetation response and forage production in semiarid ecosystems. Remote sensing may be an efficient tool for detecting differences in spatial and temporal patterns of grazing impact on vegetation. The purpose of this study was to evaluate the spectral data derived from satellite images as a tool for comparing grazing system impacts on spatial and temporal vegetation patterns. We evaluated the effect of two grazing systems, ‘‘Continuous’’ (C) and ‘‘Two-Paddocks Rest-Rotation’’ (TPRR), on vegetation cover from 1996 to 2006 in a semiarid ecosystem of Argentina. We compared grazing effects on vegetation cover using two indices derived from the Normalized Difference of Vegetation Index (NDVI) data from Landsat Thematic Mapper images. We observed a slight advantage in NDVI improvement for the TPRR over the C. Even though, in both grazing systems, an upward vegetation trend occurred only in areas located far from the watering points, TPRR showed higher relative vegetation cover near the watering point than C. We consider this methodology an important step for monitoring vegetation changes and making management decisions in livestock systems of semiarid regions because grazing system impacts may be compared for both spatial and temporal vegetation patterns. However, we think that the key next step is to develop procedures that discriminate between forage and nonforage components. 
  • A Case Study Evaluating Economic Implications of Two Grazing Strategies for Cattle Ranches in Northwest Argentina

    Quiroga, R. Emiliano; Blanco, Lisandro J.; Ferrando, Carlos A. (Society for Range Management, 2009-09-01)
    In the Argentinean Chaco Arido region, cattle production based on cow-calf operations is the principal source of agricultural income, and rangeland is the main forage source for cattle. Traditional grazing strategy (TGS, high stocking rate and continuous grazing) is considered the main cause of current rangeland degradation. Research shows that rangeland and cattle production improvements are possible when using a conservative grazing strategy (CGS, moderate stocking rate and rest rotation grazing). The aim of this research was to compare the effects of TGS and CGS applications on economic results for a cattle ranch in the region. To achieve this objective we used an approach that included estimations of forage and cattle production, and economic results. The study period was 1972/73–1983/84. Results showed that during the study period forage production and herd size were almost doubled with CGS, but maintained with TGS. The difference in net income between CGS and TGS (in Argentinean pesos, ), increased linearly from negative (–2.88 ha-1) to positive (4.48 ha-1) in the first 4 yr, and then was maintained at positive values (averaging 4.48 ha-1). Data suggest that CGS leads to higher productivity and better economic results than TGS in the medium and long terms. 
  • Opuntia Forage Production Systems: Status and Prospects for Rangeland Application

    Guevara, J. C.; Suassuna, P.; Felker, P. (Society for Range Management, 2009-09-01)
    This paper reports recent findings in Opuntia genetics, nutrient fertilization, and cultivation with promise to overcome limitations for Opuntia-based forage production systems. The essentially spineless, fast-growing Opuntia ficus-indica (L.) Mill. has been planted on millions of hectares for forage in tropical areas of Brazil and North Africa. The spiny, cold-hardy Opuntia species have been used for forage in Mexico and the southwestern United States, after the cladodes have been chopped or singed to remove the spines. Due to the recent increases in fuel prices, burning of the spines is more costly. Where only spiny varieties exist, some range animals forage on them without manipulation. As a result, spines frequently penetrate and form lesions on mouth and esophageal tissues, leading to serious health issues. Slow growth and low protein (ca. 5%) of the native Opuntia spiny species on nonfertilized rangeland is an impediment to greater use of Opuntia for forage. The only spineless species adaptable to US Department of Agriculture cold hardiness zones, 8 (i.e., Opuntia ellisiana Griffiths) is relatively slow growing. Full sibling crosses indicate spine heritability is probably single-gene controlled. Interspecific hybrids between the frost-sensitive, fast-growing, and spineless O. ficus-indica with cold-hardy, spiny, slower-growing O. lindheimerii Engelm. have produced spineless progeny, with greater cold hardiness than O. ficus-indica, and greater productivity than cold-hardy, spineless O. ellisiana. Nitrogen limitations on water-use efficiency of Opuntia have been overcome for the 120 million ha of semiarid northeastern Brazil with added nitrogen and phosphorus fertilization. With control of competing vegetation and fertilization, this system has 40 t dry matter ha-1 of 9.2% crude protein forage with 600 mm rainfall in 16 mo. Opuntia ficus-indica plantations were profitable even though a duplication of fertilizer current prices was considered. 
  • Do Ruminants Alter Their Preference for Pasture Species in Response to the Synchronization of Delivery and Release of Nutrients?

    Hill, J.; Chapman, D. F.; Cosgrove, G. P.; Parsons, A. J. (Society for Range Management, 2009-09-01)
    When offered a free choice between different forage species presented in a pasture association, ruminants will choose a mixed diet, even when one dietary component could meet all of their nutritional needs. Thus, preference and selection cannot be explained simply by the common measures of species nutritive or feeding value. The question then arises, what is the nutritional basis of the dietary choices that animals make? The objective of this paper is to review the role of synchronization of forage composition factors and nutrient release patterns on the processes controlling preference in grazing ruminants. The satiety theory is used as a model system to explore outcomes of changing the physico-chemical attributes of forages on grazing behavior of sheep and cattle. The review will examine further the biological basis for the alteration in meal pattern, duration and extent in ruminants offered clover only (relatively high rumen degradable protein content) compared to animals eating only grass (with relatively low rumen degradable protein content), or a mixture of grass and clover. One theory that has been proposed to explain the induction of satiety in grazing ruminants is the rate of release of ammonia from the soluble protein fraction of the forage, and subsequent uptake in the blood. By mixing grass with the clover, the animal is able to increase the duration of the meal potentially reflecting a ‘‘better’’ dietary balance of energy to soluble protein that controls the rate of accumulation of ammonia in rumen fluid. This concept is evaluated in light of recent data from in vitro studies examining digestive efficiency. From this analysis, it is clear that direct, real-time information on the relationships between forage physico-chemical factors, rumen condition, meal initiation and cessation, and dietary switching is needed to further develop propositions about the control of dietary choices of grazing ruminants. 
  • New Approaches and Tools for Grazing Management

    Laca, Emilio A. (Society for Range Management, 2009-09-01)
    Novel concepts and tools to promote progress in grazing science and management need to incorporate heterogeneity and nonlinear scaling of spatially and temporally distributed ecological interactions such as diet selection, defoliation, and plant growth. Traditional grazing management factors are number of animals, species and category of animals, spatial distribution of forage demand, and temporal distribution of forage demand. These traditional methods have been based on a paradigm that is static, assumes equilibrium conditions, and does not consider scaling issues, neither in time nor in space. Three related issues that can contribute to the progress in the understanding and management of grazing systems are spatial heterogeneity, event- driven dynamics, and scaling effects. Spatial heterogeneity of species and defoliation determine pasture stability by modulating competition and response to heterogeneous defoliation. When pasture species are well mixed, livestock are less able to select their preferred diet. When species are separated into larger and more easily identifiable patches, the selected diet approaches the preferred one. Simultaneously, patchiness in pasture components and redistribution of nutrients by grazing can lend global compositional stability to grass-clover pastures. Grazing at high animal density can be studied using the paradigm of event- driven dynamics. Several mechanisms suggest that grazing systems should have allometric spatial and temporal scaling in addition to the well-recognized allometric scaling of food requirements with body mass. Grazing system performance should scale allometrically with pasture size because both resource distribution and animal movements frequently have fractal properties. As pasture size increases, fewer hierarchical levels of grazing behavior are constrained, and the new spatial patterns introduce nonlinearity in the response to pasture size. Operant conditioning of foraging behavior, conditioned aversions, plant spatial pattern, pasture size and shape, timing and duration of grazing periods, and number of animals are discussed as precision tools to manage grazing systems. 

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