• Technical Note: Comparison of Techniques for Evaluating the Relative Preference by Sheep Among Saltbush Clones

      Giambalvo, Dario; Stringi, Luigi; Amato, Gaetano (Society for Range Management, 2004-11-01)
      This research compared 4 field methods of evaluating the relative preference by sheep of 28 clones of saltbush (Atriplex halimus L.). The methods were as follows. 1) Leaf dots (LD): 8 leaves per shrub were marked on the lower surface with a small dot using a water-resistant, nontoxic ink. 2) Twig marks (TM): 2 current-year twigs per shrub were marked with 3 lines using the same ink approximately in the middle of the basal, median, and apical thirds. 3) Branch length (BL): 2 branches per shrub were marked with ink at the base of the current year's growth. The twigs were measured from the marked point to the top, before and after sheep browsing. 4) Ocular estimation (OE): the percentage of the total number of current-year twigs browsed was visually estimated for each shrub. The percentage of use was calculated by counting the residual dots (LD) or marks (TM) after browsing and by calculating the difference between the 2 measures in the BL method. The trial was conducted in August and repeated in November and in both grazing periods 4 observations were made. Highly significant differences among clones were observed. The different methods generally gave similar results for the ranking of the clones, but each method showed a different discriminatory capacity. On the basis of the F ratio, the OE method seemed more efficient, although results were subjective and mainly dependent on the experience and skill of the observer. Among the methods based on the counting or measurement of markers, the discriminatory capacity decreased from LD to BL and TM, but the opposite order was observed for the ease of setting and counting the markers.
    • Technical Note: Lightweight Camera Stand for Close-to-Earth Remote Sensing

      Booth, D. Terrance; Cox, Samuel E.; Louhaichi, Mounier; Johnson, Douglas E. (Society for Range Management, 2004-11-01)
      Digital photography and subsequent image analysis for ground-cover measurements can increase sampling rate and measurement speed and probably can increase measurement accuracy. Reduced monitoring time (labor cost) can increase monitoring precision by allowing for increased sample numbers. Multiple platforms have been developed for close-to-earth remote sensing. Here we outline a new, 5.8-kg aluminum camera stand for acquiring stereo imagery from 2 m above ground level. The stand is easily transported to, from, and within study sites owing to its low weight, excellent balance, and break-down multipiece construction.
    • Viewpoint: The Need for Qualitative Research to Understand Ranch Management

      Sayre, Nathan F. (Society for Range Management, 2004-11-01)
      The use and management of rangelands involves both ecological and social processes, and it is in the interaction of these that conservation is or is not achieved. Overall, the ecological dimensions of rangelands and rangeland management have been studied in greater detail and are better understood than the social dimensions. This paper argues that qualitative methods are necessary to understand the management of rangelands by ranchers. Existing studies using quantitative methods have found little correlation between ranchers' management practices and a variety of social factors. One consistent finding of these studies, however, is that profit is a secondary or insignificant motivation among ranchers, casting doubt on the premise that economic self-interest motivates ranchers to embrace improved management practices. The theoretical and methodological implications of this finding have not been adequately recognized in rangeland science. With its greater flexibility and attention to context, qualitative research can reveal social, historical, political, and economic factors that affect ranch management but have eluded quantitative studies. In addition, qualitative methods are better suited to capturing both the processes that generate ranchers' “mental models” and the historical information needed in light of recent theoretical advances in rangeland ecology. Suggestions for future research on ranch management include conducting case studies of smaller areas over longer temporal periods, focusing on interactions among ranchers, giving ranchers a greater role in identifying research needs, studying urbanization and other “new” rangeland issues, and drawing on research about pastoralist societies elsewhere.
    • Douglas Fir and Ponderosa Pine Seed Dormancy as Regulated by Grassland Seedbed Conditions

      Bai, Yuguang; Thompson, Don; Broersma, Klaas (Society for Range Management, 2004-11-01)
      Tree encroachment in the ecotone between grassland and forest of interior British Columbia has resulted in decreasing grazing potential of rangelands. The 2 dominant tree species in this region, Douglas fir (Pseudotsuga menziesii var. glauca) and ponderosa pine (Pinus ponderosa), require stratification for seed dormancy release. The objective of this study was to determine whether seeds of these species can be stratified and dormancy released under grassland conditions. Field stratification experiments were conducted over 4 years using 2 Douglas fir and 3 ponderosa pine seed collections. A laboratory experiment was conducted to determine the effect of seedcoat removal, light, and stratification duration on dormancy release. Dormancy in Douglas fir and ponderosa pine was released after 1 to 2 months of stratification under grassland seedbed conditions when seeds were placed in the field in late fall and early winter. Continuous stratification until the following May was correlated with higher germination rate. One week of stratification in the laboratory was sufficient to break dormancy in the 2 species and a similar effect can be achieved by exposure to light. Seed coat removal for ponderosa pine also released dormancy, indicating that this structure imposes dormancy. Therefore, the grassland seedbeds near the forest edge can provide suitable conditions to break dormancy of Douglas fir and ponderosa pine seeds, contributing to tree encroachment into adjacent grasslands. Managements aiming to control tree encroachment should take the interaction between tree seed and grassland seedbed conditions into consideration, and the control should be focused on the elimination of seeds and seedlings but not on the germination stage.
    • Can Solid Matrix Priming With GA3 Break Seed Dormancy in Eastern Gamagrass?

      Rogis, C.; Gibson, L. R.; Knapp, A. D.; Horton, R. (Society for Range Management, 2004-11-01)
      Development of methods for breaking seed dormancy in eastern gamagrass (Tripsacum dactyloides, L.) could increase its use. Solid matrix priming, the controlled hydration of seed in a system of solid carrier and water, has been used with some success to enhance germination in warm-season grasses. gibberellic acid (ga3), a known promoter of eastern gamagrass germination, can be added to solid matrix priming systems. In this study, systems were evaluated for conditioning eastern gamagrass seeds using the solid carriers Agro-Lig, MicroCel E, and Vermiculite #5. GA3 was added in 0.01 M concentration solutions to systems with water potentials of -0.4 and -0.6 MPa in Agro-Lig and -0.2 and -0.4 in MicroCel E and Vermiculite #5 and compared with systems with deionized water. Priming seed with GA3 increased germination to 18% compared with 13% without GA3. MicroCel E and Vermiculite #5 were suitable materials for controlled hydration of eastern gamagrass seed. Germination was only 11% in Agro-Lig compared with 16%-19% for MicroCel E and Vermiculite #5. Priming with GA3 does not appear to be as successful at breaking seed dormancy as cold, wet stratification.
    • Grass Seedling Recruitment in Cattle Dungpats

      Gokbulak, F.; Call, C. A. (Society for Range Management, 2004-11-01)
      Livestock seed dispersal (fecal seeding) is gaining recognition as a method to reintroduce desirable species to degraded rangelands. A field study was conducted to determine the influence of cattle dungpat thickness on the recruitment of Sandberg bluegrass (Poa secunda Presl.), bluebunch wheatgrass (Psuedoroegneria spicata [Pursh] A. Love), and ‘Hycrest’ crested wheatgrass (Agropyron desertorum [Fisch. ex Link] Schult. × A. cristatum [L.] Gaert.) in naturally and artificially deposited dungpats. Four Holstein heifers each were fed 60 000 seeds of each species. Twenty-four hours after feeding seeds, dung was collected from 2 animals receiving each plant species and formed into uniform, artificial dungpats (2 kg in mass) with thicknesses of 1, 2, and 4 cm, and respective diameters of 40, 28, and 20 cm, and deposited on bare soil. The other 2 animals receiving each plant species were used to deposit natural dungpats, varying in mass, thickness, and diameter, on bare soil. Seedling recruitment in all dungpat types was greatest for crested wheatgrass, followed by Sandberg bluegrass and bluebunch wheatgrass. Recruitment for all species was generally greatest in 1-cm-thick artificial dungpats, followed in order by 2-cm-thick artificial dungpats, natural dungpats, and 4-cm-thick artificial dungpats. Most seedlings, regardless of species, emerged and survived in the interior region of 1- and 2-cm-thick artificial dungpats and at the periphery of 4-cm-thick artificial dungpats. Most seedlings of crested wheatgrass and Sandberg bluegrass emerged and survived in cracks and depressions in the interior region of natural dungpats, whereas more bluebunch wheatgrass seedlings emerged and survived at the periphery of natural dungpats. Results indicate that the efficacy of cattle seed dispersal is influenced by the seedling vigor of species (seeds) consumed and the thickness of dungpats in which the ingested seeds are deposited. Grass species with weak seedling vigor (Sandberg bluegrass and bluebunch wheatgrass) have lower recruitment than species with strong seedling vigor (crested wheatgrass), particularly in dung > 2 cm thick.
    • Black-Tailed Prairie Dog Effects on Montana's Mixed-Grass Prairie

      Johnson-Nistler, Carolyn M.; Sowell, Bok F.; Sherwood, Harrie W.; Wambolt, Carl L. (Society for Range Management, 2004-11-01)
      Forty paired sites were examined on the mixed-grass prairie of northeastern Montana to compare the effects of black-tailed prairie dog (Cynomys ludovicianus) colonies on native range vegetation. Thirty 0.25-m2 quadrats were placed on colonized and uncolonized locations and matched by environmental conditions. Cover and standing crop biomass of each plant species was estimated using a double sampling procedure where every third plot was clipped and estimated. A total of 2 400 quadrats were estimated, whereas 720 quadrats were clipped during the months of May-August of 2000 and 2001. Crude protein, digestibility, neutral detergent fiber, and acid detergent fiber were determined on the basis of vegetative classes (cool-season grasses, warm-season grasses, standing dead grass, forbs, and dwarf shrubs). Pairwise comparisons were made using paired t tests and differences were declared significant at the 0.05 level. Plant biomass of colonized sites was dominated by fringed sagewort (Artemisia frigida Willd.) (42%), blue grama (Bouteloua gracilis [HBK] Lag. ex Steud) (16%), and western wheatgrass (Agropyron smithii Rydb.) (16%). Uncolonized sites were dominated by Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis Beetle and Young) (36%), western wheatgrass (13%), and blue grama (12%). Standing crop biomass, plant species richness, litter, standing crop crude protein, sagebrush canopy cover, and density were greater (P < 0.05) on uncolonized areas compared to colonized areas. Bare ground and crude protein concentration were greater (P < 0.05) on areas colonized by prairie dogs compared to uncolonized areas. Digestibility and fiber content of both areas were not different (P > 0.05). Activities associated with prairie dog colonies reduced plant productivity and plant species richness of the mixed-grass prairie by reducing cool-season perennial grasses and litter, increasing bare ground, and eliminating big sagebrush.
    • Determination of Forage Chemical Composition Using Remote Sensing

      Starks, Patrick J.; Coleman, Samuel W.; Phillips, William A. (Society for Range Management, 2004-11-01)
      Traditional forage nutrient analysis from benchtop near infrared spectroscopy (NIRS) or common laboratory chemical procedures provides accurate, point -based information, but often does not provide it in a timely way to allow changes in forage or animal management. The objective of this study is to determine the feasibility of estimating concentrations of nitrogen, neutral  detergent fiber (NDF), and acid detergent fiber (ADF) of live, standing forages using a handheld hyperspectral spectroradiometer (radiometer), and to compare these estimates to values determined via NIRS and laboratory chemical methods. Calibration equations were developed from canopy reflectance measurements from monocultures of Bermuda grass and then applied to a test data set to predict N, NDF, and ADE Statistical analyses showed that forage composition estimates from the radiometer were equivalent to those from the NIRS. Such a remote-sensing approach would enable real-time assessment of forage quality, would allow mapping of the nutritional landscape, could be used as a tool to better manage pastures and supplements, and would assist in making harvesting decisions.
    • Diets of Nubian and Granadina Goats Grazing on Arid Rangeland

      Mellado, Miguel; Rodríguez, Alvaro; Olvera, Abundio; Villarreal, Jose A.; Lopez, Ramiro (Society for Range Management, 2004-11-01)
      A study was conducted to test the hypothesis that Granadina goats are better suited than Nubian goats to utilize the forage resources of the Chihuahuan desert range. Diet composition (microhistological analysis of fecal samples) and selection relative to availability were investigated among nonpregnant, nonlactating adult Nubian (n = 6) and Granadina (n = 6) goats grazing rangeland during the rainy period. Granadina goats consumed more (P 0.05) shrubs (70.6 %) than Nubians (52.5 %). Atriplex canescens (Pursh.) Nut., Acacia farnesiana (L.) Willd., and Larrea tridentata (DC.) Coy. were more important (P > 0.05) forage species for Granadina than for Nubian goats. Forbs consumption was higher (39.1 %; P < 0.05) for Nubians compared with Granadinas (27.7 %). Grass consumption was 8.4% and 1.7% for Nubian and Granadina goats, respectively (P < 0.01). In general, both breeds showed the greatest preference for shrubs and forbs. The diet overlap between breeds was moderate (similarity index = 68). The evidence of this study suggests that in the Chihuahuan desert range, Granadina goats were folivorous (browsers) and rarely grazed in the rainy season, whereas Nubians diversify their diet utilizing a variety of forage classes.
    • Phenological Effects on Forage Quality of Five Grass Species

      Arzani, H.; Zohdi, M.; Fish, E.; Amiri, G. H. Zahedi; Nikkhah, A.; Wester, D. (Society for Range Management, 2004-11-01)
      Information on nutritive values of each plant part in each phenological stage could help range managers choose suitable grazing times to achieve higher animal performance without detriment to vegetation. Thus, nutritive value of different plant parts of 5 grass species in 3 phenological stages (vegetative, flowering, and seed production) from 2 sites were investigated. Species included: Agropyron tauri Boiss and Bal., Agropyron trichophorum Richt, Bromus tomentellus Boiss, Festuca ovina Hack, and Hordeum bulbosum L. Samples of leaf, stem, and flower from 5 locations at each site for each species were analyzed for dry matter ratio of plant parts, crude protein, acid detergent fiber, neutral detergent fiber, dry matter digestibility, and metabolizable energy. A completely randomized design with a factorial arrangement of species and phenological stage was analyzed with 5 replicates for each location. Plant part was included as a subplot factor in a split plot arrangement. Nutritive values differed significantly (P < 0.05) both within and among plant parts and phenological stages for each species. Phenological stages indicated a significant difference on nutritive value of plant parts, with leaves having the highest nutritive value. Thus, forage with a higher leaf-to-stem ratio should improve animal performance because at the beginning of the 2nd phenological stage, the plant had desirable quantity and quality of forage with higher leaf-to-stem ratio.
    • Browsing and Plant Age Relationships to Winter Protein and Fiber of Big Sagebrush Subspecies

      Wambolt, Carl L. (Society for Range Management, 2004-11-01)
      Plants of 3 big sagebrush subspecies, mountain big sagebrush (Artemisia tridentata ssp. vaseyana [Rydb.] Beetle), Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis Beetle and Young), and basin big sagebrush (Artemisia tridentata Nutt. ssp. tridentata) were sampled for crude protein and acid detergent fiber (ADF) content. The ADF was determined as an indication of energy content and digestibility. Crude protein and ADF levels were compared among the 3 taxa and between lightly and heavily browsed plants and young and mature plants within each subspecies. Current year growth collected in mid-January was sampled to coincide with the season of greatest ungulate browsing on big sagebrush. Crude protein for mountain big sagebrush (8.34%) was less (P ≤ 0.05) than for Wyoming big sagebrush (11.25%) and basin big sagebrush (11.29%). All are well above the maintenance requirements of deer at 7.5% crude protein. The ADF levels between age and browse-use classes were not different (P ≤ 0.05) within any subspecies, although mountain big sagebrush generally had a lower ADF level than the other 2 subspecies. Wyoming big sagebrush was the only taxon with a crude protein difference (1.2%) (P ≤ 0.05) between age classes, although the difference is not biologically significant. Crude protein was not different between browse-use classes within any of the 3 taxa. Crude protein and digestibility do not indicate ungulate preference for these big sagebrush subspecies.
    • Changes in Plant Functional Groups, Litter Quality, and Soil Carbon and Nitrogen Mineralization With Sheep Grazing in an Inner Mongolian Grassland

      Barger, Nicole N.; Ojima, Dennis S.; Belnap, Jane; Shiping, Wang; Yanfen, Wang; Chen, Zuozhong (Society for Range Management, 2004-11-01)
      This study reports on changes in plant functional group composition, litter quality, and soil C and N mineralization dynamics from a 9-year sheep grazing study in Inner Mongolia. Addressed are these questions: 1) How does increasing grazing intensity affect plant community composition? 2) How does increasing grazing intensity alter soil C and N mineralization dynamics? 3) Do changes in soil C and N mineralization dynamics relate to changes in plant community composition via inputs of the quality or quantity of litter? Grazing plots were set up near the Inner Mongolia Grassland Ecosystem Research Station (IMGERS) with 5 grazing intensities: 1.3, 2.7, 4.0, 5.3, and 6.7 sheep ha-1 yr-1. Plant cover was lower with increasing grazing intensity, which was primarily due to a dramatic decline in grasses, Carex duriuscula, and Artemisia frigida. Changes in litter mass and percentage organic C resulted in lower total C in the litter layer at 4.0 and 5.3 sheep ha-1 yr-1 compared with 2.7 sheep ha-1 yr-1. Total litter N was lower at 5.3 sheep ha-1 yr-1 compared with 2.7 sheep ha-1 yr-1. Litter C:N ratios, an index of litter quality, were significantly lower at 4.0 sheep ha-1 yr-1 relative to 1.3 and 5.3 sheep ha-1 yr-1. Cumulative C mineralized after 16 days decreased with increasing grazing intensity. In contrast, net N mineralization (NH+4 + NO-3) after a 12-day incubation increased with increasing grazing intensity. Changes in C and N mineralization resulted in a narrowing of CO2-C:net Nmin ratios with increasing grazing intensity. Grazing explained 31% of the variability in the ratio of CO2-C:net Nmin. The ratio of CO2-C:net Nmin was positively correlated with litter mass. Furthermore, there was a positive correlation between litter mass and A. frigida cover. Results suggest that as grazing intensity increases, microbes become more C limited resulting in decreased microbial growth and demand for N.
    • Grazing Intensity, Aspect, and Slope Effects on Limestone Grassland Structure

      Amezaga, Ibone; Mendarte, Sorkunde; Albizu, Isabel; Besga, Gerardo; Garbisu, Carlos; Onaindia, Miren (Society for Range Management, 2004-11-01)
      Three treatments were used to evaluate the effect of grazing intensity (ca 30% and 50% herbage removal), aspect (north and south), and slope ( 10% and 10%-30%) on plant community structure of mountain grasslands in the Basque Country (Spain). Plant species richness was not significantly affected by grazing intensity, aspect, or slope. Although plant species composition was similar (Sorensen's similarity index = 0.87) between both grazing intensities, species frequency and cover were affected by grazing intensity. Festuca rubra L. and Agrostis capillaris L. were the most common species under both grazing pressures. Moderate grazing intensity (50% herbage removal) plots contained a greater number of plant species with a frequency of more than 50%. The lowest cover for F. rubra corresponded to low grazing intensity, north aspects, and steeper slopes. The lowest cover for A. capillaris was found under low grazing intensity (30% herbage removal) and steeper slopes. Danthonia decumbens (L.) P. C., Potentilla erecta (L.) Räuschal, and Trifolium repens L. were significantly affected by aspect and grazing intensity. Low grazing intensity on sites with northern aspects and steep slopes favored Agrostis curtisii Kerguélen, a species with a low nutritional value. A. capillaris, A. curtisii, P. erecta, and T. repens were sensitive to soil properties and aspect. Nitrogen and K soil concentrations were significantly higher in areas with low grazing intensity, most likely due to greater dead herbage accumulation. Significant (P 0.05) correlations between plant species and soil pH or P concentration were found in areas with low grazing intensity. Reduction in grazing intensity together with the effect of slope and northern aspect has resulted in changes in plant community structure, leading to increases in forages with lower nutritional value.
    • Mycorrhizal Colonization Patterns Under Contrasting Grazing and Topographic Conditions in the Flooding Pampa (Argentina)

      Grigera, Gonzalo; Oesterheld, Martín (Society for Range Management, 2004-11-01)
      Arbuscular mycorrhizae (AM) can ameliorate the impact of disturbance on agroecosystem sustainability. The objective of this study was to describe mycorrhizal colonization patterns in contrasting grazing situations (exclosure and continuous grazing) and topographical positions (upland and lowland) in the flooding pampa (Argentina). We determined the mycorrhizal colonization of the community as a whole and of Dallis grass (Paspalum dilatatum Poir.), a highly palatable, dominant species. We characterized colonization by the proportion of root length occupied by fungi and their different structures. At the community level, there was higher total colonization in the grazed area than in the exclosure. In contrast, Dallis grass showed higher total colonization and higher proportion of vesicles and arbuscules in the exclosure than in the grazed area. For both levels, colonization was higher in the lowland than in the upland position. Differences were observed only in winter and spring, not in summer. Our results show that 1) continuous grazing is associated with an increase of mycorrhizal colonization at the community level and 2) community-level patterns of mycorrhizal colonization cannot be inferred from dominant species. To our knowledge, this is the first characterization of AM abundance at the plant community level under contrasting long-term grazing conditions in a subhumid grassland.
    • Controls on Willow Cutting Survival in a Montane Riparian Area

      Gage, Edward A.; Cooper, David J. (Society for Range Management, 2004-11-01)
      To provide information to guide restoration of montane riparian willow communities, we investigated factors influencing the survival of prerooted and unrooted mountain willow (Salix monticola Bebb) cuttings in 2 degraded montane riparian areas in Rocky Mountain National Park, Colorado. We planted cuttings across a gradient of water table depths and soil textures and evaluated their survival using logistic regression analysis. Our results indicate that depth to groundwater was a critical factor influencing survival of both rooted and unrooted cuttings. We found that few cuttings (7.8% rooted, 3.9% unrooted) survived where summer water table depths exceeded approximately 90 cm. Soil texture was not a significant factor in our logistic models, potentially because of low silt and clay fractions in our plots. Rooted cuttings survived at a higher rate than unrooted cuttings after 1 (55.8% vs. 36.5%, P < 0.001) and 2 (44.5% vs. 26.1%, P < 0.001) years of growth. We conclude that, when combined with appropriate hydrologic data, the use of rooted cuttings represents an effective technique to restore and revegetate degraded montane riparian ecosystems.
    • Stiff Sunflower Population Dynamics on Summer-grazed Sandhills Rangeland

      Reece, Patrick E.; Schacht, Walter H.; Koehler, Ann E. (Society for Range Management, 2004-11-01)
      Thousands of forb species are distributed among the diverse rangelands of North America. However, little is known about livestock grazing effects on the demographics and potential demise of palatable forbs in grassland ecosystems. A study was designed to quantify the cumulative effects of summer grazing on the demographics of stiff sunflower (Helianthus rigidus [Cass.] Desf. spp. subrhomboides [Rydb.] Heiser), a highly palatable, late-seral, perennial forb. Pastures were grazed for 5-7 days in mid-June or mid-July during 1995-1997 at 16, 32, or 48 animal unit days (AUD) per hectare. All grazing treatments reduced the plant height of stiff sunflower. However, population densities were maintained throughout the study at light stocking rates (16 AUD ha-1). In contrast, a single year of heavy stocking (48 AUD ha-1) in June reduced spring stiff sunflower densities 55%. Densities declined about 30% after 1 year at moderate stocking rates (32 AUD ha-1) in either month or heavy stocking in July. After 3 years of short-duration grazing in June, moderate and heavy stocking rates eliminated some colonies and reduced mean pasture densities by about 90% compared with 40% and 70% reductions in moderately and heavily stocked July-grazed pastures, respectively. Reductions in spring densities corresponded to increases in premature senescence the previous year when more than 30% of the plants turned brown before mid-August. Critical levels of premature senescence were likely to occur when more than 60% of stiff sunflower plants within colonies were grazed. Light stocking rates are rare on privately owned Nebraska Sandhills rangeland (4.7 million ha); therefore, vigorous populations of stiff sunflower are most likely to occur in pastures used predominantly during the dormant season.
    • Interactions Among Western Ragweed and Other Sandhills Species After Drought

      Reece, Patrick E.; Brummer, Joe E.; Northup, Brian K.; Koehler, Ann E.; Moser, Lowell E. (Society for Range Management, 2004-11-01)
      Interannual differences in yield and species composition of herbaceous vegetation on semiarid rangelands are common and often related to variations in precipitation regime. Interspecific interactions that occur after drought-induced population fluxes of western ragweed (Ambrosia psilostachya D.C.) were evaluated by removing western ragweed or associated species from 1-m2 quadrats at weekly intervals beginning in early May, June, or July 1991 or 1992 on high-seral sandhills prairie in Nebraska. The composite of peak standing crops for ragweed and each group of associated species was 77% greater during May-October 1991 (2 252 kg ha-1) compared with 1992 (1 275 kg ha-1) when April and May precipitation was 98 mm below average and a late frost occurred. Mean levels of western ragweed herbage up to 436 kg ha-1 had no effect on associated species in 1991 when above average precipitation occurred throughout the growing season. In contrast, when an unusually dry spring occurred in 1992, relatively small mean levels of ragweed (189 kg ha-1) reduced end-of-season standing herbage of rhizomatous C4 grasses on control plots by about 21% (137 kg ha-1) with little effect on other associated species, regardless of when treatments were initiated. Within a given year, western ragweed density was seasonally constant, similar among treatments, and independent of preceding-year species composition. Severe defoliation of western ragweed had little effect on subsequent-year populations, indicating an ability to maintain primordia for several years with limited plant growth. Because western ragweed is not a strong competitor in the presence of vigorous graminoids, deferring use of June- or July-grazed pasture until after July in the subsequent year can minimize increases in western ragweed.
    • Vegetation Change After 65 Years of Grazing and Grazing Exclusion

      Courtois, Danielle R.; Perryman, Barry L.; Hussein, Hussein S. (Society for Range Management, 2004-11-01)
      The Nevada Plots exclosure system was constructed in 1937 following passage of the Taylor Grazing Act to assess long-term effects of livestock grazing on Nevada rangelands. A comparison of vegetation characteristics inside and outside exclosures was conducted during 2001 and 2002 at 16 sites. Data analysis was performed with a paired t test. Out of 238 cover and density comparisons between inside and outside exclosures at each site, 34 (14% of total) were different (P 0.05). Generally, where differences occurred, basal and canopy cover were greater inside exclosures and density was greater outside. Shrubs were taller inside exclosures at 3 sites grazed by sheep (Ovis aries). Perennial grasses showed no vertical height difference. Aboveground plant biomass production was different at only 1 site. Plant community diversity inside and outside exclosures were equal at 11 of 16 sites. Species richness was similar at all sites and never varied 4 species at any site. Few changes in species composition, cover, density, and production inside and outside exclosures have occurred in 65 years, indicating that recovery rates since pre-Taylor Grazing Act conditions were similar under moderate grazing and grazing exclusion on these exclosure sites.