• 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.
    • 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.
    • 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.
    • 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.
    • 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.
    • 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.