• Seed size distribution, germination, and emergence of 6 switchgrass cultivars

      Aiken, G. E.; Springer, T. L. (Society for Range Management, 1995-09-01)
      Switchgrass (Panicum virgatum L.) has potential as a forage and biomass crop, but difficult establishment has limited its use. Germination and emergence were studied for 6 cultivars of switchgrass ('Alamo', 'Blackwell', 'Cave-in-Rock', 'Kanlow', 'Pathfinder', and 'Trailblazer'). Germination studies were conducted to determine the effect of light on germination and coleoptile length, and to determine the effect of seed size (40, 50, 60, 70, and 80 degrees air valve settings for a South Dakota seed blower) on germination. A greenhouse study was also conducted to examine the effect of seed size, planting depth, (5, 10, and 20 mm), and soil type (sand and 2 silt loams) on emergence. Germination of unsized seed increased linearly as duration in the germination chamber increased from 7 to 21 days for all cultivars. Although presence of light did not affect germination, coleoptile length under continuous darkness averaged 4.1 cm and was greater than the 1.0 cm measured for those with daily light exposure of 16 hours. Both germination and emergence increased nonlinearly as seed size increased. For both silt-loam soils, emergence was low and not affected by planting depth. A nonlinear decline in emergence with increased planting depth was detected in sand 7 days after planting, but not after 14 and 21 days. Results of the study indicate that seed size and soil texture had a greater effect on emergence than did planting depth down to a depth of 20 mm.
    • Shrub preference and utilization by big game on New Mexico reclaimed mine land

      Wood, M. K.; Buchanan, B. A.; Skeet, W. (Society for Range Management, 1995-09-01)
      Mined lands are reclaimed so the land can be used for other purposes after mining. At the La Plata Mine in New Mexico, post-mining land uses include livestock grazing and providing wildlife habitat. The objective of this research was to evaluate use of seeded and volunteer shrubs by mule deer (Odocoileus hemionus) and elk (Cervus canadensis) during the first opportune season, which occurred 7 years following reclamation. Twelve species of shrubs (10 planted and 2 volunteer) were found on 4 different topdressing treatments. Five branches of shrubs for each species were marked and lengths measured prior to and following the winter wildlife grazing season to determine amount of use. Greatest use by both deer and elk was on curlleaf mountain mahogany (Cercocarpus ledifolius Nutt.), followed in decreasing order by fourwing saltbush (Atriplex canescens [Pursh] Nutt.), rubber rabbitbrush (Chrysothamnus nauseosus [Pall.] Britton), common winterfat (Ceratoides lanata [Pursh] Moq.), shadscale (A triplex confertifolia [Torr. and Frem.] Wats.), antelope bit terbrush (Pursia tridentata [Pursh] DC.), big sagebrush (Artemisia tridentata Nutt.), skunk bush sumac (Rhus trilobata Nutt.), Utah juniper (Juniperus osteosperma [Torr.]Little), fringed sagebrush (Artemisia frigida Willd.), service berry (Amelanchier alnifolia Nutt.), and pinyon pine (Pinus edulis Engelm.). The greatest shrub utilization was on the Jocity topdressing treatment, which is the name of the soil series from which the topdressing was obtained. The Jocity soil series was found on a flood plain site dominated by greasewood (Sarcobatus vermiculatus [Hook.] Torr.). Other shrub utilization, in decreasing order of use, was on topdressing that was a mixture of Jocity and Atrac topdressing, spoil topdressing, and Atrac topdressing, which is a soil series found on an upland site dominated by big sagebrush.
    • Soil carbon and nitrogen of Northern Great Plains grasslands as influenced by long-term grazing

      Frank, A. B.; Tanaka, D. L.; Hofmann, L.; Follett, R. F. (Society for Range Management, 1995-09-01)
      Three mixed prairie sites at Mandan, N.D. were grazed heavily (0.9 ha steer-1), moderately (2.6 ha steer-1), or left ungrazed (exclosure) since 1916. These sites provided treatments to study the effects of long-term grazing on soil organic carbon and nitrogen content and to relate changes in soil carbon and nitrogen to grazing induced changes in species composition. Blue grama [Bouteloua gracilis (H.B.K) Lag. ex Griffiths] accounted for the greatest change in species composition for both grazing treatment. Relative foliar cover of blue grama was 25% in 1916 and 86% in 1994 in the heavily grazed pasture and 15% in 1916 to 16% in 1994 in the moderately grazed pasture. Total soil nitrogen content was higher in the exclosure (1.44 kg N ha-1) than in either grazing treatment (0.92 and 1.07 kg N ha-1 for moderately and heavily grazed, respectively) to 107-cm depth. Soil organic carbon content avg 72, 6.4, and 7A kg m-2 to 30.4 cm soil depth and 14.1,11.7, and 14.0 kg m-2 to 106.7 cm soil depth for the exclosure, moderately grazed, and heavily grazed treatments, respectively. Compared to the exclosure the moderately grazed pasture contained 17% less soil carbon to the 106.7 cm depth. Heavy grazing did not reduce soil carbon when compared to the exclosure. Based on 13C analysis and soil organic carbon data to 15.2 cm depth, blue grama or other C4 species contributed 24% or 12 kg m-2 of the total carbon in the heavily grazed and 20% or 0.8 kg m-2 of the total carbon in the moderately grazed pastures during the 1916 to l99l time period. The increase in blue grama, a species with dense shallow root systems, in the heavily grazed pasture probably accounted for maintenance of soil carbon at levels equal to the exclosure. These results suggest that changes in species composition from a mixed prairie to predominantly blue grama compensated for soil carbon losses that may result from grazing native grasslands.
    • Use of degree-days in multiple-temperature experiments

      Romo, J. T.; Eddleman, L. E. (Society for Range Management, 1995-09-01)
      This research compared results from germination and growth when the experiment duration was chronologically set or based on degree-days. Seeds of smooth brome (Bromus inermis Leyss.), plains rough fescue (Festuca altaica Trin. subsp. hallii (Vasey) Harms), prairie coneflower (Ratibida columnifera (Nutt.) Woot. and Standl.), and silver sagebrush (Artemisia cana Pursh.) were germinated at 5, 10, 15, 20, and 25 degrees C for 28 days or 400 degree-days (Base temperature = 0 degrees C). Root and shoot weights of seedlings of these species were compared at 5, 10, 15, 20, 25 and 30 degrees C after growing them 20 days or 200 degree-days. With the exception of prairie coneflower, optimal temperatures for germination were 2 to 4 degrees C lower when incubated 400 degree-days compared to 28 days. Total germination for prairie coneflower was not significantly different (P = 0.454) at 28 days or 400 degree-days. Interacting effects of the duration of experiments and temperature significantly (P less than or equal to 0.001) influenced root and shoot weight of all species. Except for shoot weight of smooth brome, predicted optimum temperatures for root and shoot growth were 7 to 21 degrees C lower at 200 degree-days than 20 days. These experiments illustrate that results from germination and growth studies can vary substantially depending on whether chronological time or degree-days are used as the end point. Thus, ecological interpretations or management recommendations can be quite different. Degree-days may be more meaningful than chronological units for germination and growth studies because they integrate time and temperature. The use of degree-days as an end point for experiments rather than chronological time deserves further consideration by researchers.
    • Vegetal recovery following wildfire in seeded and unseeded sagebrush steppe

      Ratzlaff, T. D.; Anderson, J. E. (Society for Range Management, 1995-09-01)
      Following an August wildfire, sagebrush (Artemisia L.)/grass benchlands adjacent to Pocatello, Ida., were seeded with a mixture of exotic wheatgrasses and forbs by rangeland drill in November 1987. The effects of seeding on vegetation development in the immediate postfire years were evaluated by comparing plant density, vegetal cover, species composition, species diversity, and standing crop in seeded areas to that in unseeded control plots in 1988 and 1989. We also examined cover of bare ground, litter, and growth form between treatments and between sampling periods. Twenty paired 10-m transects were established in seeded and unseeded areas on each of 3 plots on the burned benches. Plant density, vegetal cover, and species diversity were lower in the seeded areas than in the unseeded areas in 1988 and 1989. Species composition, species richness, and standing crop were similar between treatments. Establishment of seeded species was poor, probably as a result of drought conditions in 1987 and 1988. Most plants observed in seeded and unseeded areas in the spring of 1988 sprouted from established perennials. Even though the first postfire season was a drought year, plant cover in the unseeded areas (18.3%) approached that estimated by a U.S. interagency task force as needed to stabilize soils on that site. In the following year, which had average precipitation, plant cover in both treatments exceeded the task force's estimate of prefire cover. Because the indigenous plant species recovered rapidly, seeding of this burn was unnecessary to establish plant cover and counterproductive in terms of erosion potential. These results serve to emphasize that objective criteria should be established for evaluating the necessity of postfire seeding.
    • Viewpoint: The state and transition model applied to the herbaceous layer of Argentina's calden forest

      Llorens, E. M. (Society for Range Management, 1995-09-01)
      The ecological trends in the vegetation of the caldén (Prosopis caldenia Burk.) forest of central Argentina have generally been explained with a model that assumed a unique equilibrium state or "climax." This model does not adequately explain the ecological changes that occur in the understory of the caldén forest. Recently, models that present different stable states of vegetation have been suggested. These vegetation states do not change unless relatively drastic management or climatic actions occur. Observations of vegetation changes, grazing regimes, and other aspects of management permitted the development of a basic scheme to explain changes in the herbaceous layer in the caldén forest, based on the state and transition model. Five stable states and 9 transitions are proposed to account for current herbaceous associations and their origins. This model seems to more accurately explain transitions between the different vegetation states in the area, some of which could not be readily explained by the "climax" model.