• Grazing Management in Tropical Savannas: Utilization and Rest Strategies to Manipulate Rangeland Condition

      Ash, Andrew J.; Corfield, Jeff P.; McIvor, John G.; Ksiksi, Taoufik S. (Society for Range Management, 2011-05-01)
      Grazing management is important for sustaining the productivity and health of rangelands. However, the effects of grazing management on herbage growth and species composition in the tropical savannas of northern Australia are not well known. In this eight-year study the influences of utilization rate and resting pastures from grazing on vegetation dynamics were measured at three sites in northeast Queensland, Australia. The sites had high, medium, and low soil fertility, and there were two land condition classes (States I and II) at each site. Severe drought occurred during the first four years, but above-average rainfall was received in the second half of the study. High utilization rates reduced biomass, perennial grass basal area, and ground cover. The reduction in biomass was due to both higher consumption and decreased primary production. State I condition plots at the high and medium soil fertility sites were initially dominated by decreaser perennial grasses, but these declined at all utilization levels, particularly the high rate. They were largely replaced by exotic perennial grasses. At the low fertility site there were no exotic grasses, and the decreaser grasses increased in all treatments, with the increases greatest in plots with low utilization or medium utilization plus resting. In the State II condition plots at the high and medium fertility sites, low or moderate utilization, led to an increase in both decreaser and exotic perennial grasses; with high utilization the decreaser perennial grasses declined and were replaced largely by exotic perennial grasses. This study clearly demonstrated that either conservative stocking with year-round grazing or a grazing system that includes some wet-season resting will help maintain land in a desirable state or help facilitate the transition from a less desirable ecological state to one more desirable for pastoral production and rangeland condition.
    • Effects of Plant Secondary Compounds on Nutritional Carrying Capacity Estimates of a Browsing Ungulate

      Windels, Steve K.; Hewitt, David G. (Society for Range Management, 2011-05-01)
      Carrying capacity estimates based on digestible protein (DP) and energy (DE) are useful in comparing effects of land management practices or the ability of different vegetation communities to support herbivores. Plant secondary compounds that negatively affect forage quality would be expected to change nutritionally based estimates of carrying capacity. We evaluated the effect of plant secondary compounds on nutritionally based carrying capacity estimates of white-tailed deer (Odocoileus virginianus Zimmerman) in Tamaulipan thorn scrub of northern Mexico. Forage biomass, nutrient concentration, and tannin concentration (protein- precipitating capacity) were measured for 23 forage items during spring and summer in three replicate pastures. Nitrogen in phenolic amines was estimated for the two principal woody browse species in deer diets and was assumed to be unavailable for amino acid synthesis. Carrying capacity estimates were calculated based on three dietary concentrations of DP and DE. Nutritional carrying capacity estimates that accounted for antinutritional compounds were reduced 50+/-6%, 28+/-8%, and 0+/-0% (mean +/- SE) for diets of high, medium, and low DE concentration, respectively, compared to estimates from models that ignored the effects of these compounds. Accounting for effects of plant secondary compounds reduced DP-derived carrying capacity estimates 4 +/- 3%, 47 +/- 9%, and 9 +/- 8% for diets with high, medium, and low concentrations of DP, respectively. High variation in percent reduction in carrying capacity estimates occurred because of site and seasonal variation in plant species composition and biomass, making application of a single correction factor to account for plant secondary compound effects on carrying capacity infeasible. Protein-precipitating capacity of tannins accounted for > 98% of the reductions in carrying capacity estimates based on DP. Our results clearly demonstrate the need to consider effects of tannins on ungulate carrying capacity estimates based on DP and DE. Estimates can be further refined by accounting for nonprotein nitrogen and other antinutritional compounds in all forage items.
    • Forage Quality of Plant Species Consumed by Capybaras (Hydrochoerus hydrochaeris) in the Paraná River Delta, Argentina

      Corriale, María J.; Arias, Santiago M.; Quintana, Rubén D. (Society for Range Management, 2011-05-01)
      The capybara (Hydrochoerus hydrochaeris) is a selective herbivore that may show a preference for certain plant species. Such a preference is likely to be explained by the nutritional benefits hypothesis, stating that the nutritional value of species selected by capybaras is higher than that of avoided ones. Therefore, the objectives of this work are to evaluate the nutritional value of the plant species eaten by capybaras in the Lower Delta of the Paraná River, and to test the nutritional benefits hypothesis by analyzing forage quality. Samples of consumed plant species were collected from habitats located in the study area. We also collected plant species that are very abundant in the field but absent in the capybara’s diet, some of which are consumed by other native herbivores such as coypus (Myocastor coypus). Their nutritional quality was analyzed by estimating the following variables: water content, ash percentage, percentage of organic matter, acid detergent fiber, nitrogen percentage, crude protein, and caloric energy. The protein to fiber ratio was calculated and the water content was determined. The species consumed and not consumed by capybaras had a similar nutritional composition for all the variables analyzed (P < 0.05). A similar result was observed when comparing within consumed species, except for the caloric energy content, which was significantly higher in species consumed in greater proportion than availability (P < 0.05). Water content was at its minimum in species consumed in greater proportion than availability, and at its maximum in unconsumed species. No significant differences were found between consumed Poaceae and the rest of the consumed plant species for any of the analyzed variables. Diet selection by capybaras in the studied area may only be partially related to nutritional quality, and there would be other factors involved in foraging, such as physiological mechanisms of the animal or chemical and structural characteristics of food.
    • Automated Animal Control: Can Discontinuous Monitoring and Aversive Stimulation Modify Cattle Grazing Behavior?

      Ruiz-Mirazo, Jabier; Bishop-Hurley, Greg J.; Swain, Dave L. (Society for Range Management, 2011-05-01)
      Grazing livestock freely select landscape resources, unless they are herded or constrained by fences. Automated animal control (AAC) systems offer an alternative to physical fences by using animal-positioning technology and aversive stimuli to deter animals from staying in sensitive environments and so limit their impact. This paper reports on a replicated field experiment completed to test whether occasional stimuli (audio cue followed by a mild electric stimulus), delivered by discontinuously activated AAC collars, could suffice to modify the grazing behavior of groups of cattle. Four groups of eight steers were confined in 8-ha rectangular paddocks that had an ad libitum supplement feeder located in one end to attract cattle. The steers’ positional information was recorded continuously for 3 d using a GPS receiver encased in a collar fitted around their neck. These data were used to characterize their use of the paddocks without intervention. Subsequently a restriction zone was activated on the collars. This zone contained the supplement feeders and represented approximately 10% of the paddock area. Cattle movement was again monitored during a second 3-d period, in which the steers were subjected to discontinuous aversive stimuli (5 min of stimulation followed by a random 0-30 min interval without stimulation) if they were located inside or moved into the restriction zone. Cattle visits to the restriction zone were shorter and the return interval longer when steers were subjected to discontinuous stimulation. Overall, there was a 97% reduction in the use of the restriction zone between the first and second deployments. These results suggest that grazing impact can be drastically reduced by making a zone less desirable through discontinuous aversive stimulation. Such a discontinuous (25% of the time on) AAC system can reduce power consumption in collars and so help overcome energy supply limitations that hinder commercial AAC applications.
    • Optimized Frequency Measures for Monitoring Trends in Tallgrass Prairie

      DeBacker, Micheal D.; Heywood, John S.; Morrison, Lloyd W. (Society for Range Management, 2011-05-01)
      Prairies exhibit a bimodal frequency distribution of patch occupancy with a few dominant species accounting for most of the primary production and plant biomass and numerous other species occurring infrequently over time and space. Consequently, management interest is often focused on the abundance of common species, and on the persistence of less common species. We used spatially nested arrays of various sized plots to simultaneously measure species’ persistence and abundance at Tallgrass Prairie National Preserve, Kansas. Larger plots captured more species, with 127 species identified at the 10-m scale. Smaller plots, however, provided useful frequency data for measuring the abundance of common species. We defined a plot frame size that delivers a frequency in a 20-50% target range as the optimal plot size, and the frequency of a species sampled at its optimal plot size is termed the optimized frequency. Optimized frequency was estimated for 27 common species for the years 2002- 2006. Of the nine perennial grasses in this group, five exhibited significant interannual variation within the 5-yr period. Bouteloua curtipendula exhibited a significant linear change over the 5-yr period, decreasing in frequency over time. From year to year, changes in optimized frequency among the 27 common species varied in both their trajectory (i.e., the average change), and amplitude (i.e., the average magnitude of change). Between 2005 and 2006, the average change in optimized frequency was 29.1%, the only year with an overall declining trajectory. The declining trajectory between 2005 and 2006 was significantly different from the increasing trajectories observed between 2002 and 2003 and between 2004 and 2005. No significant differences were observed in amplitude. We offer these techniques for aggregating information from multiple spatial scales to characterize the amplitude and trajectory of community-wide changes as tools to help scientists convey the results of multiscale research projects to land managers.
    • Linking Plant Spatial Patterns and Ecological Processes in Grazed Great Basin Plant Communities

      Rayburn, Andrew P.; Monaco, Thomas A. (Society for Range Management, 2011-05-01)
      Observational studies of plant spatial patterns are common, but are often criticized for lacking a temporal component and for their inability to disentangle the effect of multiple community-structuring processes on plant spatial patterns. We addressed these criticisms in an observational study of Great Basin shrub-steppe communities that have been converted to a managed grazing system of planted crested wheatgrass (Agropyron cristatum [L.] Gaertn.) stands. We hypothesized that intraspecific interference and livestock grazing were important community-structuring processes that would leave unique spatiotemporal signatures. We used a survey-grade global positioning system to quantify crested wheatgrass spatial patterns along a chronosequence of stands that differed only in time since planting (9-57 yr), as well as in a 57-yr-old grazing exclosure to examine pattern formation in the absence of grazing. Three replicate survey plots were established in each stand, and a total of 6 197 grasses were marked with a spatial error of < 2 cm. The data were analyzed using L-statistics in program R, and hypothesis testing was conducted using Monte Carlo simulation procedures. We detected fine-scale regularity, frequently considered a sign of interference via resource competition, in all stands including the exclosure. Coarser-scale aggregation, which we attributed to the effects of prolonged grazing disturbance, was only detected in the oldest grazed stand. Our results suggest that interference acts over finer spatial and temporal scales than grazing in structuring these stands, reinforcing the importance of interference in semiarid communities. Analysis of exclosure data suggests that, in the absence of grazing, crested wheatgrass stands organize into a statistically regular pattern when primarily influenced by interference. In the presence of prolonged grazing, crested wheatgrass stands become more heterogeneous over time, likely a result of seedling mortality via disturbance by cattle.
    • Comparison of Point Intercept and Image Analysis for Monitoring Rangeland Transects

      Cagney, J.; Cox, S. E.; Booth, D. T. (Society for Range Management, 2011-05-01)
      There is global recognition that sustainable land use requires monitoring that will detect change on a scale that protects the resource. That fundamental necessity is threatened where labor-intensive methods and high labor costs cause sampling deficiencies and increased Type-II error rates (false negatives). Ground-based imaging is a monitoring method that reduces monitoring labor costs. Nadir (vertical) images acquired with common digital cameras can be manually analyzed for cover using free software. We used an innovative field protocol to acquire standardized, freehand, nadir images (samples) of rangeland, then compared point intercept (PI) and image-analysis techniques. Between methods, precision (repeatability) across users was equivalent; cover measurements were often different, and the image-analysis technique took only a third as long to complete. Image analysis has several advantages over PI besides the reduced labor cost: Images are permanent resource records available for reanalysis if data are questioned, if software improves, or if management objectives change; and image analysis is less biased by moving vegetation, moving pointing devices, and bright vegetation color.
    • Above-Ground Net Primary Production for Elymus lanceolatus and Hesperostipa curtiseta After a Single Defoliation Event

      Pantel, A.; Romo, J. T.; Bai, Y. (Society for Range Management, 2011-05-01)
      Above-ground net primary production (ANPP) of northern wheatgrass (Elymus lanceolatus [Scribn. J. G. Sm.] Gould) and western porcupine grass (Hesperostipa curtiseta [Hitchc.] Barkworth) was determined after defoliation to a 7.5 cm stubble height on five landform elements in the Northern Mixed Prairie that had been ungrazed for >25 yr. Landform elements included north aspect-concave slopes, north aspect-convex slopes, south aspect-concave slopes, south aspect-convex slopes, and level uplands. ANPP was determined for 2 yr after defoliating plots once in May, June, July, August, September, October, November, or April. Northern wheatgrass and western porcupine grass ANPP varied among landform elements (P < 0.01), but not with the month of defoliation 3 landform element interaction (P > 0.22). Month of defoliation did not influence ANPP of northern wheatgrass (P>0.69), but that of western porcupine grass was reduced by August and September defoliations (P < 0.01). ANPP of both grasses was insensitive to landform element in terms of defoliation responses. Northern wheatgrass ANPP was not responsive to temporal aspects of a single defoliation. With the exception of August and September defoliations, western porcupine grass also was insensitive to a single defoliation in different months. Land managers should consider rest (1 yr nongrazing) following grazing of western porcupine grass in August or September, whereas responses to defoliation in different months suggest northern wheatgrass can be grazed annually.
    • Impact of Stocking Rate and Rainfall on Sheep Performance in a Desert Steppe

      WangHan, Zhongwu; Jiao, Shuying; Han, Guodong; Zhao, Mengli; Willms, Walter D.; Hao, Xiying; Wang, Jian’an; Din, Haijun; Havstad, Kris M. (Society for Range Management, 2011-05-01)
      Livestock performance is a critical indicator of grassland production systems and is influenced strongly by precipitation and stocking rates. However, these relationships require further investigation in the arid Desert Steppe region of northeastern China. We employed a randomized complete block design with three replications and four grazing treatments (nongrazed exclosure [Control]), lightly grazed [LG], moderately grazed [MG], and heavily grazed [HG]) by sheep in a continuously grazed system (June to November), to test the effect of stocking rate on sheep performance. The planned stocking rates were 0, 0.15, 0.30, and 0.45 sheep ha-1 mo-1, for the control, LG, MG, and HG treatments, respectively. However, actual stocking rates were calculated for each paddock in each year based on a 50-kg sheep equivalent (SE). Annual net primary production (ANPP) was determined at peak standing crop in August 2004 to 2008. Live weight gain was determined for the summer and fall periods, as well as the total grazing period, in each year. ANPP decreased with increasing stocking rate, and daily live weight gain per head decreased linearly with increasing stocking rates over the total grazing period but in a quadratic manner over the summer period with a plateau at the lower rates. Maximum sheep production per unit area over the total grazing season occurred at about 2 SE ha-1 for about a 5-mo grazing period, but individual gains per sheep were predicted to decline after about 1 SE ha-1 presumably because of forage limitations. However, in order to achieve stable annual production, we recommend that the Desert Steppe be grazed at about 0.77 SE ha-1 for a 5-mo period (0.15 SE ha-1 mo-1). This estimate is based on published grazing strategies that consider an average ANPP with a recommended utilization rate of 30%.
    • Foraging Behavior of Alberes Cattle in a Mediterranean Forest Ecosystem

      Bartolomé, Jordi; Plaixats, Josefina; Piedrafita, Jesus; Fina, Marta; Adrobau, Edward; Aixàs, Aida; Bonet, Marina; Grau, Jordi; Polo, Lluis (Society for Range Management, 2011-05-01)
      The dietary composition of the semiferal cattle population in the Alberes Natural Park in northeastern Spain was determined four times per year, from June 2002 to February 2004, by microhistological analysis of a total of 120 fecal samples. Woody species, mainly the Quercus and Erica genera, formed the bulk of the diet, reaching 89% of it in winter. However, in spring and summer, the proportion of woody and herbaceous species varied between samples, depending on the habitat where they were collected. The forest samples contained 67% woody species in summer, whereas grassland samples only contained 44%. The results showed that the Alberes cattle population grazed actively in Mediterranean forests and consumed a high proportion of the most combustible species, such as the Erica genus (39% of the epidermal fragments in winter samples). Even when grassland habitat was utilized, in spring and summer, one-third of the diet was from woody species. Some bovines, such as the Alberes cattle breed, can therefore survive year-round in a forest habitat with little forage supplementation, and the consumption of a predominantly woody diet would be expected to reduce forest fire hazards.
    • A Mark-Recapture Technique for Monitoring Feral Swine Populations

      Reidy, Matthew M.; Campbell, Tyler A.; Hewitt, David G. (Society for Range Management, 2011-05-01)
      Techniques to monitor populations of feral swine (Sus scrofa) relative to damage control activities are needed on rangelands. Our objectives were to describe and assess a mark-recapture technique using tetracycline hydrochloride (TH) for monitoring feral swine populations. We established bait stations at study sites in southern and central Texas. During 1 d, we replaced normal soured corn bait with bait containing TH and counted the number of feral swine that consumed bait with observers. We conducted feral swine removal using box-style traps and helicopters, at which time we collected teeth for TH analysis. In southern Texas, we estimated population reduction to be 43%. In central Texas, we estimated population reduction of 31%. Our mark-recapture population monitoring technique would complement programs to manage feral swine populations and damage through lethal control./Se necesitan técnicas para monitorear poblaciones de cerdos ferales (Sus scrofa) para actividades de control de daños en pastizales naturales. Nuestros objetivos fueron describir y evaluar una técnica de marca-recaptura utilizando hidrocloruro de tetraciclina (HT) para monitorear las poblaciones de cerdos ferales. Establecimos estaciones con cebo en las a ́reas de estudio en el sur y el centro de Tejas. Durante un día, remplazamos el cebo de maíz fermentado con cebo conteniendo HT y con observadores, contamos el número de cerdos ferales que consumieron el cebo. En el sur de Tejas, se estimó una reducción del 43% de la población. En el centro de Tejas, la reducción estimada fue del 31% de la población. Nuestra técnica de monitoreo de marca-recaptura podría complementar programas de manejo de control letal de las poblaciones de cerdos ferales y los daños que los mismos ocasionan.
    • Allelopathic Cover Crop Prior to Seeding Is More Important Than Subsequent Grazing/Mowing in Grassland Establishment

      Milchnas, Daniel G.; Vandever, Mark W.; Ball, Leonard O.; Hyberg, Skip (Society for Range Management, 2011-05-01)
      The effects of grazing, mowing, and type of cover crop were evaluated in a previous winter wheat-fallow cropland seeded to grassland under the Conservation Reserve Program in eastern Colorado. Prior to seeding, the fallow strips were planted to forage sorghum or wheat in alternating strips (cover crops), with no grazing, moderate to heavy grazing, and mowing (grazing treatments) superimposed 4 yr after planting and studied for 3 yr. Plots previously in wheat had more annual and exotic species than sorghum plots. Concomitantly, there were much greater abundances of perennial native grass and all native species in sorghum than wheat cropped areas. The competitive advantage gained by seeded species in sorghum plots resulted in large increases in rhizomatous western wheatgrass. Sorghum is known to be allelopathic and is used in crop agriculture rotations to suppress weeds and increase crop yields, consistent with the responses of weed and desired native species in this study. Grazing treatment had relatively minor effects on basal and canopy cover composition of annual or exotic species versus perennial native grass or native species. Although grazing treatment never was a significant main effect, it occasionally modified cover crop or year effects. Opportunistic grazing reduced exotic cheatgrass by year 3 but also decreased the native palatable western wheatgrass. Mowing was a less effective weed control practice than grazing. Vegetative basal cover and aboveground primary production varied primarily with year. Common management practices for revegetation/restoration currently use herbicides and mowing as weed control practices and restrict grazing in all stages of development. Results suggest that allelopathic cover crop selection and opportunistic grazing can be effective alternative grass establishment and weed control practices. Susceptibility, resistance, and interactions of weed and seeded species to allelopathic cover species/cultivars may be a fruitful area of research.