• Crested wheatgrass-cheatgrass seedling competition in a mixed-density design

      Francis, M. G.; Pyke, D. A. (Society for Range Management, 1996-09-01)
      Plant competition experiments have historically used designs that are difficult to interpret due to confounding problems. Recently, designs based on a "response function" approach have been proposed and tested in various plant mixture settings. For this study, 3 species were used that are important in current revegetation practices in the Intermountain West. 'Nordan' ('Agropyron desertorum [Fish. ex Link] Shult.) and 'Hycrest' (A. cristatum [L.] Gaertn. X desertorum) crested wheatgrass are commonly-used revegetation species on rangelands susceptible to cheatgrass (Bromus tectorum L.) invasion, although little quantitative data exist that compare their competitive abilities. We evaluated the competitive ability of Hycrest and Nordan seedlings in 2-species mixtures with cheatgrass in a greenhouse study. Linear and nonlinear models were developed for a range of densities (130-520 seeds m-2) for each species to predict median above-ground biomass and tiller numbers and to further test the usefulness of this design for evaluating species to rehabilitate rangelands. In both experiments, increasing Hycrest and Nordan densities reduced their own biomass and tiller production while increasing Hycrest densities reduced cheatgrass biomass and tiller production. Nordan did not affect cheatgrass biomass and tiller production. However, increasing cheatgrass densities reduced Hycrest and Nordan biomass and tiller production, and its own biomass and tiller production. The competition index i.e. substitution rate, indicated that Hycrest seedlings were better competitors with cheatgrass than Nordan, although in all mixtures, cheatgrass plants were the superior competitors. Further field research using this design, where environmental inputs are less optimal and diverse, is needed to validate these results and to further evaluate the use of this approach in examining effects of intra- and interspecific competition.
    • Decision support software for estimating the economic efficiency of grazingland production

      Kreuter, U. P.; Rowan, R. C.; Conner, J. R.; Stuth, J. W.; Hamilton, W. T. (Society for Range Management, 1996-09-01)
      Decision support software has evolved in a number of disciplines to facilitate efficient allocation of resources. Such tools are especially useful where the response of complex systems to human activity are difficult to predict. Decision support systems empower managers to rapidly analyze the ecological and economic implications of alternative management strategies. The Grazingland Alternative Analysis Tool (GAAT), has been developed to estimate the economic efficiency of a wide range of grazingland production systems. Systems that can be analyzed, either individually or in combination, include livestock, wildlife, leased grazing, grain and forage crops, wood products and other nonforage crops. The planning horizon, discount rate, available forage, consumption by class of animal, herd management practices, product yields, product and input prices, and improvement investments must be specified by the user. The GAAT program calculates the resulting annual forage balance for all enterprises being analyzed and the net present value and internal rate of return for the specified management interventions during the planning period. Two examples are presented to demonstrate the flexibility of GAAT for analyzing the economic efficiency of grazingland production systems. The first example analyzes the use of prescribed burning to control Ashe juniper (Juniper ashei Buckholz) and the second determines the economic effect of changing a dairy from a concentrate-dependent to a grazing-dependent system.
    • Effects of bison grazing, fire, and topography on floristic diversity in tallgrass prairie

      Hartnett, D. C.; Hickman, K. R.; Walter, L. E. (Society for Range Management, 1996-09-01)
      Grazed and ungrazed sites subjected to different fire frequencies were sampled on the Konza Prairie Research Natural Area in northeast Kansas after 4 years of bison grazing (1987-1991). The objective was to study effects of bison grazing on plant species composition and diversity components (plant species richness, equitability, and spatial heterogeneity) in sites of contrasting fire frequency. Cover and frequency of cool-season graminoids (e.g. Poa pratensis L., Agropyron smithii Rydb., Carex spp.) and some fortes (e.g. Aster ericoides [A. Gray] Howell, and Oxalis stricta L.) were consistently higher in sites grazed by bison than in ungrazed exclosures, whereas the dominant warm-season grasses (Andropogon gerardii Vitman, Sorghastrum nutans [L.] Nash, Panicum virgatum L., Schizachyrium scoparium [Michx.] Nash) and other forbs (e.g. Solidago missouriensis Nutt.) decreased in response to bison. Plant species diversity (H') and spatial heterogeneity in all areas sampled were significantly increased by bison. Increased heterogeneity and mean species richness in grazed prairie (40 species per sample site) compared to ungrazed prairie (29 species per site) were likely a result of greater microsite diversity generated by bison, whereas preferential grazing of the dominant grasses and concomitant increases in subordinate species resulted in an increase in equitability of species abundances. Species/area relationships indicated greater effects of bison on plant species richness with increasing sample area. Increases in plant diversity components associated with bison grazing were generally greater in annually burned than in 4-year burned sites. Effects of ungulate grazers on floristic diversity have important implications given recent evidence that plant species diversity and the compositional and production stability of grassland plant communities are positively related.
    • Effects of severity of defoliation on root functioning in grasses

      Thornton, B.; Millard, P. (Society for Range Management, 1996-09-01)
      Grass shoots after defoliation can be supplied with the nitrogen required for regrowth by either root uptake or remobilization of stores. Whilst it is accepted that after a single defoliation inhibition of root uptake and remobilization from root occurs, it has not been established how the capability of roots to supply nitrogen by uptake and from storage is affected with differing severities of regular defoliation, as experienced by grazed swards. The objective was to examine this question using Agrostis castellana Boiss et Reut., Festuca rubra L., Lolium perenne L. and Poa trivialis L., grasses associated with sites of differing fertility, grown in sand culture and defoliated weekly at a height of either 4 or 8 cm. Nitrogen was supplied as NH4NO3 in a complete nutrient solution. The use of 15N as a tracer allowed the nitrogen supplied to the shoot by root uptake and remobilization to be discriminated over a 35 day period. An increased severity of defoliation resulted in decreased root mass, and increased nitrogen uptake per unit root weight for all species. Increased severity of defoliation did not affect uptake on a per plant basis for A. castellana, 0.54 mg N (plant)-1 (week)-1 and P. rubra, 0.40 mg N (plant)-1 (week)-1, whilst mg N (plant)-1(week)-1 decreased from 0.54 to 0.14, and 0.54 to 0.34 for L perenne and P. trivialis respectively. For plants clipped at 4 or 8 cm, over 88% and 77% respectively of uptake appeared in the shoot. Nitrogen was remobilized from roots to the shoot for A. castellana and F. rubra when clipped at 4 cm, and for A. castellana, L. perenne and P. trivialis when clipped at 8 cm. Uptake by roots was more important than remobilization from roots in supplying nitrogen to the shoot. The ability to maintain the supply of nitrogen by uptake and remobilization to the shoot with increased severity of defoliation was species dependent.
    • Feeding by a native grasshopper reduces broom snakeweed density and biomass

      Thompson, D. C.; McDaniel, K. C.; Torell, L. A. (Society for Range Management, 1996-09-01)
      Broom snakeweed [Gutierrezia sarothrae (Pursh) Britton and Rusby] destruction by 1, 3, or 5 snakeweed grasshoppers [Hesperotettix viridis (Thomas)] per plant was quantified and compared with forage gain the year of and the year after herbivory. Grasshoppers were caged (6.25m2 cages) in 1991 and 1992 over dense stands of broom snakeweed growing in association with shortgrass rangeland near Corona and Folsom, New Mexico. A significant negative relationship between grasshopper feeding pressure in each cage and broom snakeweed biomass was found. The dry weight of broom snakeweed herbage removed per grasshopper per day was 45 mg at Folsom and 85 mg at Corona. Feeding by grasshoppers stocked at 5 per plant killed 91% of the broom snakeweed resulting in a 75% reduction in biomass. Mortality varied between sites and years; however, 3 grasshoppers per plant killed about 69% of the broom snakeweed and reduced biomass by 61%. One grasshopper per plant killed 53% of the broom snakeweed and reduced biomass an average of 39%. In 1991, removal of most broom snakeweed by the high density of grasshoppers increased standing crop of grasses 23% at the end of the treatment year and 44% one year after treatment compared with grasshopper-free cages at the 2 sites. Feeding by low and medium densities of grasshoppers did not increase grass biomass in most situations. The increase in grass biomass only after grasshoppers removed most of the broom snakeweed is similar to the response observed from other methods of broom snakeweed removal such as band thinning, chemical control, and burning. Preferred host plants such as broom or threadleaf snakeweed must be present for "specialist" snakeweed grasshoppers to occur. However, if snakeweed grasshoppers are present, care should be taken to ensure their survival.
    • Germination of warm-season grasses under constant and dynamic temperatures

      Roundy, B. A.; Biedenbender, S. H. (Society for Range Management, 1996-09-01)
      Fifteen collections of 10 native and exotic grasses were germinated at constant 25 degrees C, and at gradual and abruptly alternating temperature regimes characteristic of wet seed bed temperatures in the southwest desert grassland in summer, winter, and spring. All species but bristle grass (Setaria macrostachya H.B.K. and S. leucopila Schum.) had high total germination under summer and spring temperatures (mean- 60% and 67%, respectively) and all but bristlegrass and bush muhly (Muhlenbergia porteri Scribn.) had relatively high total germination under winter temperatures (mean-53%). In general, total germination percentage was similar for gradual and abruptly alternating temperature regimes within a season. Constant 25 degrees C and abruptly alternating temperature germination percentages were similar enough to those at more realistic gradually alternating temperatures for most species to permit use of these tests to calculate estimates of summer bulk seeding rates. Time to 50% germination (D50) was slightly less for gradual than abruptly alternating summer temperatures, but was generally similar for these regimes under winter and spring temperatures. To determine if germination responses to constant temperatures could be used to estimate responses to dynamic temperatures, 12 collections of 8 species were tested for germination at constant temperatures of 5.4,10, 20, 25, 30, 35, 40, and 45 degrees C. Total germination and rate of germination (1/D50) increased and decreased as third-order polynomial functions of temperature. Polynomial regression estimates of 1/D50 were used to calculate estimates of D50 for diurnally alternating temperature that were within an average of 0.6 and 13 days of measured values for summer and spring temperatures respectively. Linear regression estimates of 1/D50 for suboptimal to optimal temperatures were similarly used to estimate D50 for dynamic winter temperature regimes that averaged within 3.6 days of measured values for most of the species. Differences between estimated and measured D50 for bush muhly under winter temperatures, and for Lehmann lovegrass (Eragrostis lehmanniana Nees) collections under winter and spring temperatures, indicate sensitivity of these species to extreme temperature in addition to accumulated heat. Similar measured and estimated D50 for most of the collections for summer, winter, and spring temperatures indicates that these species are primarily responding to cumulative heat effects. Even though most of the species have high germination percentages for winter or spring temperatures, field seedling emergence is much less likely in winter and Possibly less likely in spring than in summer. Slower germination rates during these cooler seasons would require long periods of soil water availability at the surface to allow germination.
    • Habitat use by white-tailed deer on cross timbers rangeland following brush management

      Leslie, D. M.; Soper, R. B.; Lochmiller, R. L.; Engle, D. M. (Society for Range Management, 1996-09-01)
      Seasonal habitat use by white-tailed deer (Odocoileus virginianus Zimmerman) was monitored with radio telemetry in 1988-89 to determine responses to experimental brush treatments, 5-6 years post-treatment, in the cross timbers region of central Oklahoma. The study area was a mosaic of brush treatments: tebuthiuron (N-[5-(1,1-dimethylethyl)-1,3,4-thiazol-2-yl 1]-N,N'-dimethylurea) herbicide, tebuthiuron with an annual spring burn, triclopyr ([(3,5,6-trichlor-2-pyridinyl)oxy]acetic acid) herbicide, triclopyr with an annual spring burn, and no herbicide with annual spring burning. Control areas with no burning or herbicide applications also were evaluated. Herbicides were applied in 1983, and fires were initiated in 1985. Annual home range (95% harmonic mean) averaged 99.9 ha, and no differences in size among seasons or between sexes were observed. Both sexes selected and avoided specific brush treatments throughout the year. Female deer selected or avoided more human-altered habitats in specific contrasts of main treatment groups (e.g., treated vs. control, herbicide vs. no herbicide, fire vs. no fire, etc.) than males. Both sexes selected fire treatments in summer and were most particular in their choice of main treatment groups in summer and fall habitat use between the sexes was most similar in winter and most disparate in fall. The mosaic of habitat types resulting from the variable herbicide and burn application pattern probably influenced deer habitat use in the cross timbers region through combined effects of increased mid-story cover and forage production as they relate to reproductive activities and nutritional needs of female deer in particular.
    • Impact of grazing on soil nutrients in a Pampean grassland

      Lavado, R. S.; Sierra, J. O.; Hashimoto, P. N. (Society for Range Management, 1996-09-01)
      Cattle exclusion induced dramatic changes in the plant community and modifications in nutrient cycling in grazed native grasslands of the Flooding Pampa (Argentina). The study was carried out to analyze the effect of grazing on the status and spatial variability of soil organic matter, nitrogen and phosphorus. Sampling was performed in the late summer and early spring. Geostatistical methods were used to study the spatial dependence of these soil properties. Organic carbon (OC) and total nitrogen (TN) showed spatial structure only in the ungrazed area with a similar range of dependence (39 m and 36 m respectively). The occurrence of litter in this area lead to a large and spatially homogeneous C input to the soil, which would be the key factor of the spatial structure of organic carbon and total nitrogen. Mineral nitrogen content 1(NO3(-1)-N + (NH4+)-N] was higher in the ungrazed area on both sampling dates. The mineral N content showed a large short-range variability (nugget variation) independent of grazing history. A significant decrease in the extractable P (Bray & Kurtz #1) in the grazed area was found. The extractable P exhibited spatial structure only in the ungrazed area. However, its spatial pattern was different from those of organic carbon and total nitrogen: the range of dependence was higher (57 m) and the spatial structure exhibited a great irregularity. The differences between C, N, and P variability were possibly related to their dynamics in the soil. No evidence of effects of animal excrete on nutrient content or spatial variability was found.
    • Mechanisms that result in large herbivore grazing distribution patterns

      Bailey, D. W.; Gross, J. E.; Laca, E. A.; Rittenhouse, L. R.; Coughenour, M. B.; Swift, D. M.; Sims, P. L. (Society for Range Management, 1996-09-01)
      Grazing distribution patterns of large herbivores are affected by abiotic factors such as slope and distance to water and by biotic factors such as forage quantity and quality. Abiotic factors are the primary determinants of large-scale distribution patterns and act as constraints within which mechanisms involving biotic factors operate. Usually there is a proportional relationship between the time large herbivores spend in a plant community and the available quantity and quality of forage. This grazing pattern may result from decisions made by animals at different spatial and temporal scales. Foraging velocity decreases and intake rate increases in areas of abundant palatable forage. These non-cognitive mechanisms that occur at smaller spatial scales (bites, feeding stations, small patches) could result in observed grazing patterns. However, large herbivores also appear to select areas (patches and feeding sites) to graze. Optimal foraging models and other models assume animals use "rules of thumb" to decide where to forage. A cognitive mechanism assumes animals use spatial memory in their foraging decisions. With such abilities, large herbivores could return to nutrient-rich sites more frequently than to nutrient-poor sites. Empirical studies indicate that large herbivores have accurate spatial memories and have the ability to use spatial memory to improve foraging efficiency. Body size and perceptual abilities can constrain the choices animals can make during foraging. A conceptual model was developed to demonstrate how cognitive foraging mechanisms could work within constraints imposed by abiotic factors. Preliminary predictions of the model correspond to observed grazing patterns. Recognizing that large herbivores may use previous experiences to decide where to forage may be useful in developing new techniques to modify grazing patterns. Grazing distribution patterns appear to result from decisions and processes made at a variety of spatial and temporal scales.
    • Performance of rose clover and hairy vetch interseeded into Old World bluestem

      Volesky, J. D.; Mowrey, D. P.; Smith, G. R. (Society for Range Management, 1996-09-01)
      Old World bluestems (Bothriochloa spp.) are extensively used throughout the Southern Plains. Interseeding these stands with persistent nitrogen-fixing legumes could reduce N fertilizer input, extend the grazing season, and enhance diet quality. The objective of this study was to evaluate production and persistence of 'Overton R18' and TXR20 rose clover (Trifolium hirtum All.) and hairy vetch (Vicia villosa Roth) when interseeded into Old World bluestem. Treatments included these interseeded annual legumes and bluestem + 100 kg/ha N fertilizer. Both rose clover and vetch produced a measurable quantity of forage by early spring before bluestem began to grow. Crude protein and in vitro dry matter digestibility were higher in legume treatments when legumes were actively growing. Total season forage production was similar (6,460 kg/ha; P > 0.05) between rose clover and bluestem + N treatments except during 1991 when production under the Overton R18 treatment was less than bluestem + N or TXR20 rose clover. Average rose clover seed production (26 kg/ha) was greater than vetch (2 kg/ha; P < 0.05) resulting in greater rose clover forage compared to vetch during natural reseeding years. Rose clover plant counts 4 years after the original seeding showed an average of 22 plants/m2. Both rose clover entries appear to have excellent potential over previously available germplasm because of improved cold tolerance and the ability to produce substantial quantities of seed for natural reseeding even after close defoliation.
    • Potential of new tetraploid germplasm in Russian wildrye

      Asay, K. H.; Johnson, D. A.; Jensen, K. B.; Sarraj, W. M.; Clark, D. H. (Society for Range Management, 1996-09-01)
      Induced and natural tetraploids have been proposed as promising sources of germplasm in breeding programs to improve Russian wildrye [Psathyrostachys juncea (Fisch.) Nevski]. Studies were conducted under semiarid conditions to evaluate the potential of tetraploid (2n=4x=28) Russian wildrye germplasm recently obtained from Kazakhstan. The teraploids had significantly heavier seeds, greater seedling vigor, and they were significantly taller, and had longer and wider leaves than standard diploid (2n=2x=14) cultivars. Carbon isotope discrimination, which has been negatively correlated with water-use efficiency in cool-season grasses, was significantly lower in the tetraploid accessions than the diploid cultivars. Dry matter and seed yield of these unselected tetraploid accessions were superior to the diploid cultivar Vinall and equivalent to more recently developed diploid cultivars, Bozoisky-Select and Syn-A. In general, relative phenological development and forage quality of the tetraploid populations did not differ significantly from the diploid cultivars; however, water content, which has been associated with greater succulence, was significantly higher in the tetraploid accessions. Significant variation was found among entries within ploidy levels for most characters indicating that genetic variability is available for additional improvement through selection. Results indicate that these tetraploid accessions can be used in the development of promising breeding populations and support earlier conclusions that tetraploid germplasm should receive emphasis in future Russian wildrye breeding programs.
    • Selaginella densa reflectance: Relevance to rangeland remote sensing

      Hall-Beyer, M.; Gwyn, Q. H. J. (Society for Range Management, 1996-09-01)
      Selaginella densa Ryd. is a shallow-rooted spikemoss that grows on sparsely vegetated short and mid-grass prairie. It covers a proportion of bare soil which may rival that covered by grasses. Not a forage plant, it is treated in agronomic research as background to the edible plants. Even when it appears to the eye as dry and without active chlorophyll, its spectral reflectance resembles more closely that of forage plants than that of soil background. It is distinguishable from dense stands of chlorophyll-rich fortes and grasses using the normalized differential vegetation index, but S. densa in all cases resembles sparse grasses. Its presence must be considered when estimating range condition using remote sensing techniques.
    • Soil quality response of reestablished grasslands to mowing and burning

      Schacht, W. H.; Stubbendieck, J.; Bragg, T. B.; Smart, A. J.; Doran, J. W. (Society for Range Management, 1996-09-01)
      Prescribed burning and mowing are management practices commonly used on grasslands even though there is limited knowledge of long-term effects on soil quality. The influences of mowing and burning on soil quality were determined on 2 reestablished tallgrass sites in eastern Nebraska dominated by silty clay loam soils. Burn treatments included seasonal (i.e., October, May, or July) prescribed burning at either 1-year or 4-year intervals. Mow treatments included seasonal mowing at 4-year intervals. Both burn and mow treatments have been imposed at Site 1 since fall 1981. Only the burn treatments have been applied at Site 2 since fall 1979. Soil quality measurement were made at both sites in summer 1994. Season of application of the mow and burn treatments and season X treatment interactions were not significant. Infiltration rates at Site 1 for the mow and annual burn treatments were slower than for the control, whereas infiltration rate was comparable for the year burn treatments and the control. Unlike Site 1, the 1-year and 4-year burn treatments at Site 2 had similar infiltration rates, and the burn treatments had slower infiltration rates than the control. Generally, soil bulk density, pH, electrical conductivity, total nitrogen content, and organic matter content were similar for all treatments. Results demonstrate that repeated burning or mowing treatments can detrimentally impact infiltration rates on silty clay loam sites; however, soil properties other than those measured would need to be studied to explain infiltration response.
    • Technical Note: Spring grazing preference of wheatgrass taxa by Rocky Mountain elk

      Jones, T. A.; Urness, P. J.; Nielson, D. C. (Society for Range Management, 1996-09-01)
      We measured the grazing preference of 3 castrated male Rocky Mountain elk (Cervus elaphus nelsoni) for 2 crested (Agropyron desertorum [Fischer ex Link] Schultes), 5 thickspike (Elymus lanceolatus ssp. lanceolatus [Scribner &J.G. Smith] Gould), 3 Snake River (proposed name E. lanceolatus ssp. wawawaiensis), and 2 bluebunch wheatgrass (Pseudoroegneria spicata [Pursh] A. Love) entries. Number of bites and visits were highly correlated in early May (r2=0.77) and late May (r2=0.83). 'Critana' and 'Elbee' thickspike and 'Hycrest' and 'Nordan' crested wheatgrasses can be recommended for seedings for elk spring grazing where these grasses are adapted.
    • Viewpoint: Concept design in range management science

      Scarnecchia, D. L. (Society for Range Management, 1996-09-01)
      This paper is an analysis of general principles involved in designing concepts for range science. It discusses the diversity of conceptuality in range science, from dimensional units to variables to simple models to more complex decision-aiding models. It examines how considerations of abstraction, confounding, and generalization allow development of multi-objective concepts needed in a range management science of many variable, interactions, and models. Examples related to each principle are provided. The paper discusses the importance of avoiding internal confounding within concepts and the necessity that such confounding be avoided in order to allow clear analyses. Ad hoc indices are characterized as inadequate substitutes for explicit models of more complex concepts such as preference and diet selection. Design efforts emphasizing multiple objectives will produce concepts of general use in range management science.