• Clipping effects on root architecture and morphology of 3 range grasses

      Arredondo, J. T.; Johnson, D. A. (Society for Range Management, 1998-03-01)
      Although defoliation is known to affect root growth in range plants, little information is available concerning the effect of defoliation on root architecture and its relationship to root morphological characteristics. This study evaluated the influence of clipping on root architecture and morphology of 3 range grasses from the Intermountain West: 'Whitmar', a cultivar of blue-bunch wheatgrass [Pseudoroegneria spicata (Pursh) A. Lovel]; 'Hycrest', a cultivar of hybrid crested wheatgrass [Agropyron desertorum (Fisch. ex Link) Schult. X A. cristatum (L.) Gaert.]; and cheatgrass (Bromus tectorum L.). Greenhouse-grown seedlings were clipped once or twice at 3 intensities of defoliation (0, 50, and 70%). The topology (pathlength-slope index), geometry (link length and root diameter), and morphology (total root length and specific root length) of roots of the 3 grasses were evaluated 28, 35, and 42 days after planting. Root topology (Peslope index) did not vary among defoliation treatments but did vary among species across harvests. Root branching of the grazing-tolerant Hycrest decreased through time, while root branching of the grazing-sensitive Whitmar increased through time. Cheatgrass maintained a highly branched root system throughout the experiment. Specific root length in Hycrest and Whitmar decreased through time, indicating that roots became coarser with age. Similar to its topological response, cheatgrass did not exhibit changes in specific root length through time. There were apparent tradeoffs between link lengths of the main axis and lateral roots of the seminal root, which may lead to important changes in root branching density, root production costs, and probably root function.
    • Comparison of rangeland vegetation sampling techniques in the Central Grasslands

      Stohlgren, T. J.; Bull, K. A.; Otsuki, Y. (Society for Range Management, 1998-03-01)
      Maintaining native plant diversity, detecting exotic species, and monitoring rare species are becoming important objectives in rangeland conservation. Four rangeland vegetation sampling techniques were compared to see how well they captured local plant diversity. The methods tested included the commonly used Parker transects, Daubenmire transects as modified by the USDA Forest Service, a new transect and "large quadrat" design proposed by the USDA Agricultural Research Service, and the Modified-Whittaker multi-scale vegetation plot. The 4 methods were superimposed in shortgrass steppe, mixed grass prairie, northern mixed prairie, and tallgrass prairie in the Central Grasslands of the United States with 4 replicates in each prairie type. Analysis of variance tests showed significant method effects and prairie type effects, but no significant method X type interactions for total species richness, the number of native species, the number of species with less than 1% cover, and the time required for sampling. The methods behaved similarly in each prairie type under a wide variety of grazing regimes. The Parker, large quadrat, and Daubenmire transects significantly underestimated the total species richness and the number of native species in each prairie type, and the number of species with less than 1% cover in all but the tallgrass prairie type. The transect techniques also consistently missed half the exotic species, including noxious weeds, in each prairie type. The Modified-Whittaker method, which included an exhaustive search for plant species in a 20 x 50 m plot, served as the baseline for species richness comparisons. For all prairie types, the Modified-Whittaker plot captured an average of 42.9 (+/- 2.4; 1 S.E.) plant species per site compared to 15.9 (+/- 1.3), 18.9 (+/- 1.2), and 22.8 (+/- 1.6) plant species per site using the Parker, large quadrat, and Daubenmire transect methods, respectively. The 4 methods captured most of the dominant species at each site and thus produced similar results for total foliar cover and soil cover. The detection and measurement of exotic plant species were greatly enhanced by using ten 1 m2 subplots in a multi-scale sampling design and searching a larger area (1,000 m2) at each site. Even with 4 replicate sites, the transect methods usually captured, and thus would monitor, 36 to 66% of the plant species at each site. To evaluate the status and trends of common, rare, and exotic plant species at local, regional, and national scales, innovative, multi-scale methods must replace the commonly used transect methods of the past.
    • Cultural methods for establishing Wyoming big sagebrush on mined lands

      Schuman, G. E.; Booth, D. T.; Cockrell, J. R. (Society for Range Management, 1998-03-01)
      Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis Beetle &Young) is one of the most widely distributed shrub species in Wyoming and the Rocky Mountain and Northern Plains region. Its reestablishment on mined lands has generally proven difficult however, because of low seedling vigor, an inability to compete with herbaceous species, poor seed quality, and altered edaphic conditions. Field research evaluating the effect of topsoil management, mulching practice, and plant competition have shown that all of these factors significantly influence initial sagebrush establishment. Greater sagebrush establishment occurred on fresh topsoil compared to 5-year-old stockpiled topsoil. Stubble, surface-applied mulch, and elimination of herbaceous competition also significantly increased establishment in the first growing season. A cool, wet second-year growing season (April-September) resulted in large increases in sagebrush seedling density across all treatments; however, soil management and competition treatment effects were still apparent in the second year. Mulch type had limited effects on sagebrush seedling density by the third year of the study. This research indicates that big sagebrush seed viability in the soil is longer than previously thought and that seed dormancy, safe site development, and climactic conditions play important roles in germination, establishment, and seedling survival of this species.
    • Differences in soil water use by annual broomweed and grasses

      Yoder, C. K.; Boutton, T. W.; Thurow, T. L.; Midwood, A. J. (Society for Range Management, 1998-03-01)
      The use of water in the upper 1 m of the soil profile by 3 common herbaceous species of the southern Great Plains was examined by labeling soil water with 2H2O and H2(18)O. Uptake of labeled water from the 15 cm depth was approximately equal for all species. However, water uptake from the 75 cm depth was significantly greater by annual broomweed [Amphiachyris dracunculoides (DC.) Nutt] than either sideoats grama [Bouteloua curtipendula (Michx.) Torr] or curlymesquite [Hilaria belangeri (Steud.) Nash]. Although both grasses had greater root length density than annual broomweed at the 75 cm depth, annual broomweed's rate of water extraction from the 75 cm depth was nearly twice that of sideoats grama or curlymesquite. Greater access to and more rapid utilization of deeper soil water by annual broomweed relative to the grass species may partially explain annual broomweed's success at invading grasslands and reducing grass production in semi-arid rangelands.
    • Effect of sheep grazing on a leafy spurge-infested Idaho fescue community

      Olson, B. E.; Wallander, R. T. (Society for Range Management, 1998-03-01)
      Leafy spurge (Euphorbia esula L), an aggressive Eurasian forb, is invading native upland ranges dominated by bluebunch wheatgrass (Pseudoroegneria spicata [Pursh] A. Love) and Idaho fescue (Festuca idahoensis Elmer) in the Northern Rocky Mountain Province. Our objective was to determine cumulative effects of 3 summers (1992-1994) of repeated sheep grazing on a leafy spurge infested-Idaho fescue community. Targhee ewes were systematically rotated through paddocks in small pastures. Leafy spurge stem and Idaho fescue and bluebunch wheatgrass plant densities, and frequencies of other species were determined before grazing in 1992, 1993 and 1994, and in 1995, 9 months after grazing ended. Number of viable leafy spurge seeds in seedbanks was determined in 1992 and 1995. Plant heights were measured each year. Density of leafy spurge seedlings was low in grazed and ungrazed areas in 1992 and 1994, whereas density was higher in ungrazed than grazed areas in 1993 and 1995. Grazing did not increase or decrease density of mature leafy spurge stems from 1992 to 1995. Grazing increased density of Idaho fescue but reduced density of bluebunch wheatgrass. Kentucky bluegrass, (Poa pratensis L.), Sandberg bluegrass (Poa sandbergii Vasey), annual bromegrasses (Bromus spp.), and sedge (Carex spp.) frequencies increased in grazed areas. Number of viable leafy spurge seeds in the seedbank was lower in 1995 than in 1992; this reduction was greater in grazed than ungrazed areas. Three years of repeated sheep grazing reduced numbers of leafy spurge seed in the seedbank and seedling densities, but had no effect on density of mature leafy spurge stems. There was minimal effect on the cool season native grasses, possibly because the site was grazed primarily in midsummer when these grasses are dormant. Thus, a long-term commitment to repeated sheep grazing may help to control leafy spurge, although grazed sites should be monitored regularly to ensure that other undesirable species do not increase at the expense of the native plant community.
    • Efficacy and costs of controlling eastern redcedar

      Ortmann, J.; Stubbendieck, J.; Masters, R. A.; Pfeiffer, G. H.; Bragg, T. B. (Society for Range Management, 1998-03-01)
      Eastern redcedar (Juniperus virginiana L.) is reducing grassland productivity across much of the Great Plains. Control methods include broadcast prescribed fire, herbicides, cutting, and individual tree ignition. All methods have disadvantages when used alone. Fire can be ineffective against larger trees. Intensive methods can be too expensive for low-productivity grasslands. The objectives of this research were to determine the effects of broadcast prescribed fire alone as measured at 3 weeks after fire; to compare the effects of picloram herbicide application with or without fire, sawing with or without fire, and individual tree ignition with fire; and to compare all treatment costs. Treatments were applied at a central Nebraska rangeland site in 1993 and 1994. Fire mortality was 77% in 1993 and 67% in 1994. Either picloram or cutting after fire provided nearly 100% control of trees < 3 m tall, but cutting was more effective for trees > 3 m tall. Total mortality due to treatment combinations generally was higher in 1993, when burning conditions were more favorable. Burning, at an estimated cost of 4.96 ha-1, before picloram application or cutting reduced total costs by nearly half. Picloram application costs were reduced from 90.10 ha-1 to 47.95 ha-1, and cutting costs from 62.92 ha-1 to 39.26 ha-1. Burning first also reduced cutting time from 362 min ha-1 to 184 min ha-1, but did not significantly decrease picloram application time. Prescribed fire should precede intensive treatment applications if possible, both to reduce costs and improve total effectiveness. Because the costs and effectiveness of burning followed by either picloram or cutting are similar, managers should choose the method most suitable to individual circumstances.
    • Methods alter interpretation of treatment impacts on winter-fat shrublands

      Hild, A. L.; Wester, D. B. (Society for Range Management, 1998-03-01)
      Monitoring shrubland vegetation change is important to rangeland assessment. Methods used to document shrubs vary with the intended use of information and the unit of observation. This study documents different interpretations of winterfat (Ceratoides lanata (Pursh.) J.T. Howell) response to defoliation, grazing history, and community position treatments from 1992 through 1994 when the interpretations were based upon 2 different methods of observation. In some cases, results from observations of individual winterfat plants differed from results that were based on unit-area observations. Individual plants did not reflect the same impacts of grazing history that were found from observing the collective response of plants in 11-m2 plots. Although plant results reflect impacts on individuals, plot results can indicate impacts of shrub canopy on surrounding vegetation as well. Comparisons of studies using different means of observation may lead to conflicting interpretations unless these effects are recognized.
    • Ponderosa pine aboveground growth after cattle removal of terminal tissue

      Karl, M. G.; Doescher, P. S. (Society for Range Management, 1998-03-01)
      Mismanagement of livestock can result in herbivory on Pinus seedlings with potential for growth loss. From 1986 to 1990 on a conifer plantation in the Mixed-Conifer Zone of southwestern Oregon we measured the aboveground growth of ponderosa pine (Pinus ponderosa Douglas ex Lawson &C. Lawson var. ponderosa) seedlings that had sustained (1) removal of terminal stem or bud tissue by cattle, and (2) no removal (control). In 1990 (year 5 of the plantation), cumulative, absolute height and stem volume on seedlings that sustained terminal tissue removal were similar to control seedlings. In 1988, relative height growth was comparable between control seedlings and seedlings sustaining tissue removal in May 1987. In contrast, 1988 relative height growth was -22% (P < 0.05) for seedlings sustaining tissue removal in August 1987, compared with control seedlings. Relative stem volume growth in 1988 ranged from -21 to -26% (P < 0.05) for seedlings sustaining tissue removal in (1) August 1987, (2) April or May 1988, and (3) 1987 and 1988, compared with control seedlings. Reduced relative growth was short-term. Relative growth rates for seedlings sustaining tissue removal were comparable to control by the first or second year after removal. Seedlings sustaining tissue removal before winter bud set (April and May) were more likely to recover by the first year than seedlings sustaining tissue removal after winter bud set (August). We propose that if silviculturists prescribe cattle grazing early in the growing season and terminal tissue is removed at that time, they can still achieve understory vegetation control and enhanced soil water availability without jeopardizing long-term aboveground growth of ponderosa pine. The lack of spatial replication of treatments (terminal tissue removal dates) limits spatial extrapolation of our findings. The credibility of our findings should be tested with additional research on the growth response of ponderosa pine seedlings subsequent to actual live-stock herbivory, conducted with spatially replicated treatments.
    • Radiometry for predicting tallgrass prairie biomass using regression and neural models

      Olson, K. C.; Cochran, R. C. (Society for Range Management, 1998-03-01)
      Standing forage biomass (SFB) and the percent of standing biomass composed of forbs (PCTF) were modeled across the growing season. Samples representing stages of plant maturity from early vegetative to dormant were collected from grazed and ungrazed native tallgrass paddocks using a 0.5 X 0.5 m quadrat. Total biomass was measured during all years of the study (1992-1995). Grass and forb biomass were measured separately during 1995. Height of canopy closure also was measured during 1995. Before clipping, plots were scanned with a multispectral radiometer. Models were prepared using simple regression, multiple regression (MR), or a commercial neural network (NN) computer program. Potential inputs to MR and NN models of SFB and PCTF included Julian day of harvest (JD), range site, canopy closure height (CH), incident radiation, spectral reflectance values (RFV) at 8 discreet bandwidths, and the normalized difference vegetation index (NDVI). The NDVI alone accounted for little variability (R2 = 0.13) in SFB during all years of the study. The optimal MR model for the same data set (SFB = 3.5[JD] - 43.7[460 nm RFV] + 1099[NDVI] - 992; R2 = 0.62) accounted for a greater amount of the variability in SFB. The capacity to describe variation in SFB for the 1995 data with MR was improved when CH was included as a variable (R2 = 0.58 versus 0.78). A NN model accounted for the most variation in SFB across the entire study (R2 = 0.76). During 1995, the capability of a NN to account for variation in SFB within the training data was similar whether or not CH was included as an input (R2 = 0.86); however, prediction of SFB from validation data using the same NN was improved by using CH as an input variable. Little variation in PCTF was accounted for by a MR model (R2 = 0.23); however, a considerably larger proportion of the variation in PCTF was accounted for when an NN was used (R2 = 0.59). Seasonal changes in SFB and PCTF were described with an acceptable degree of accuracy by forage reflectance characteristics that were adjusted for time of season and canopy complexity. Moreover, when provided with the same potential inputs, NN predicted SFB and PCTF from validation data more accurately than MR models.
    • Rehabilitation of Mediterranean dwarf-shrub range-land with herbicides, fertilizers, and fire

      Henkin, Z.; Noy-Meir, I.; Kafkafi, U.; Gutman, M. (Society for Range Management, 1998-03-01)
      An experiment was conducted on a Mediterranean hill range dominated by communities of spiny dwarf-shrubs (mainly prickly burnet Sarcopoterium spinosum (L.) Spach) in order to determine the effects of P fertilizer application, shrub control and fire on the herbaceous and shrub components of the community. Herbicide (2,4-D) application eliminated almost all the shrubs in the first year and their regeneration was relatively slow: 6 years after the application, shrub cover was less than one-third of what it was at the beginning of the experiment. After fire, regeneration was rapid and original shrub cover was restored within 6 years. A single application of phosphorus fertilizer (4.5-9.0 g P m-2) significantly retarded regeneration of shrub cover and produced a three to five fold increase in herbaceous biomass production. The residual effect of the fertilizer application was still significant at the end of the 7-year monitoring period. The herbaceous vegetation in the P-fertilizer treatments was dominated by annual legume species throughout the experiment. The prolonged response of the herbaceous sward patches to a single P application appeared to be caused by the gradual release of phosphate from the applied fertilizer and also by the summer grazing system that facilitated recycling of soil nutrients on the site. Above-ground biomass on herbaceous sward patches increased not only as a consequence of nutrient amelioration, but also because of reduced competition from the lower shrub cover following fire or herbicide application. Shrub recovery that was dependent on the residual cover in the first year following fire and/or herbicide treatment, was further retarded by competition from the vigorous herbaceous vegetation that benefited from nutrient amelioration. The implications of these results for range improvement depend to a large degree on the economic conditions relevant to the grazing system.
    • Sheep grazing and plant cover dynamics of a shadscale community

      Alzerreca-Angelo, H.; Schupp, E. W.; Kitchen, S. G. (Society for Range Management, 1998-03-01)
      Despite extensive coverage and long-term use, the extent to which shadscale [Atriplex confertifolia (Torr. &Frem.) Wats.] community dynamics are driven by grazing rather than by climate and inherent plant characteristics is unresolved. We analyze a 59-year data set from the Desert Experimental Range, southwestern Utah, with the objective of discriminating between grazing and non-grazing effects on cover dynamics. Canopy cover of (5 x 20 ft) 9.3 m2 plots were estimated in 1935, 1958, 1969, 1975, and 1994. Treatments were time (5 dates), grazing (ungrazed versus grazed), and season (spring versus winter). Time was significant; total cover initially increased following release from uncontrolled grazing and improvement of climate (1935-58, P < 0.001), remained unchanged over the following dry interval (1958-69, P = 1.000), increased over a drier interval (1969-75, P < 0.001), and then decreased dramatically over the final wet period (1975-94, P < 0.001). Grazing was also significant (P < 0.001), but cover of ungrazed plots exceeded that of grazed plots only in 1975 and 1994 (P less than or equal to 0.033). The 6 dominant species showed varying responses to grazing and time, with some responding primarily to grazing (e.g., budsage, Artemisia spinescens D.C. Eaton in Wats.) and others responding primarily to time (climate, longevity, etc., e.g., Indian ricegrass, Oryzopsis hymenoides R. &S.). Similarly, seasonal effects were not universal. Shrub cover initially increased and then declined dramatically while grass cover monotonically increased. Results suggest that release from uncontrolled grazing coupled with improving climatic conditions were responsible for initial recovery of the community, but that over time, climate and inherent plant traits (e.g., longevity, establishment ecology, etc.) became relatively more important. For total cover and for many individual species, continued grazing affected the rate more than the direction of vegetation change.
    • Spring burning: Resulting avian abundance and nesting in Kansas CRP

      Robel, R. J.; Hughes, J. P.; Hull, S. D.; Kemp, K. E.; Klute, D. S. (Society for Range Management, 1998-03-01)
      Spring burning is used to control invasion by woody vegetation of rangelands in eastern Kansas and also of Conservation Reserve Program (CRP) fields planted to native grasses. We measured the effects of spring burning of CRP fields on vegetation structure and avian populations in northeastern Kansas during the summers of 1992 through 1995. Several vegetation characteristics differed between burned and unburned CRP fields in May, but few differed in July. Mean avian abundance on burned CRP fields was 5.6 birds km-1 of survey transect, significantly less (P < 0.01) than the 8.6 km-1 on unburned fields. The avian-assemblages on burned and unburned fields differed more in May/June [Morisita's Index to Similarity (MIS) = 0.86] than in June/July or July/August (MIS = 0.98 and 0.97, respectively). Avian species richness ranged from 12 to 21 on burned fields and from 10 to 19 on unburned fields. A total of 27 nests was found on burned fields, significantly less (P < 0.01) than the 372 found on unburned fields. The 22.2% nesting success on burned fields was not significantly different (P = 0.205) than the 34.1% success on unburned fields. Spring burning reduced bird-nest numbers in the summer of the same year, but did not reduce significantly (P = 0.235) the number of nests found in those fields the following summers nor the abundance of birds or nesting success. Avoidance of annual burning would reduce adverse impacts on bird populations relying on CRP fields for nesting habitat.
    • Tallgrass prairie response to grazing system and stocking rate

      Gillen, R. L.; McCollum, F. T.; Tate, K. W.; Hodges, M. E. (Society for Range Management, 1998-03-01)
      Grazing system and stocking rate effects on standing crop of species and relative species composition of tallgrass prairies in north-central Oklahoma were evaluated from 1989 to 1993. Twelve experimental units, consisting of pastures dominated by big bluestem [Andropogon gerardii Vitman], little bluestem [Schizachyrium scoparium (Michx.) Nash], and indiangrass [Sorghastrum nutans (L.) Nash], were arranged in a completely randomized design with either a short duration rotation or continuous grazing system and stocking rates ranging from 51.5 animal-unit-days/ha (AUD/ha) to 89.8 AUD/ha. Yearling steers grazed the pastures from late April to late September. Cumulative precipitation was above average during the study period. Continuous and rotation grazing affected the major herbage components similarly over time. Standing crop of all major herbage components declined as stocking rate increased. The standing crop of the major herbage components also declined from the first to the last year of the study. The decrease in standing crop of big bluestem, indiangrass and forbs over years was greatest at lighter stocking rates. Relative composition of switchgrass [Panicum virgatum L.] increased at the lower stocking rates over time in both grazing systems. The relationship between shortgrasses and stocking rate was different between grazing systems at the start of the study but became similar between grazing systems over time. After 5 years, short-grasses were positively related to stocking rate under both grazing systems. Favorable growing conditions and the high seral state of the vegetation in the experimental pastures may have tempered the response to grazing treatments.
    • Technical Note: Measuring moisture content of small seeds

      Booth, D. T.; Bai, Y. (Society for Range Management, 1998-03-01)
      An accurate determination of moisture content in hydrated or partially hydrated seeds is fundamental to understanding early physiological processes in seeds, and the associated environmental interactions that affect seedling vigor, establishment, and survival. One difficulty encountered while measuring the moisture content of imbibed seeds is that water evaporates from the seed during weighing. This is particularly significant for small seeds because they have a large surface area to volume ratio. We developed a procedure using a standard tin capsule and microbalance which was simple, inexpensive, facilitated precise measurement of moisture in hydrated seeds, and provided reliable results with a minimal amount of seeds. The method is recommended as a means for increasing the accuracy of seed weight and seed moisture measurements.
    • The deterioration of tall wheatgrass pastures on saline sodic soils

      Taboada, M. A.; Rubio, G.; Lavado, R. S. (Society for Range Management, 1998-03-01)
      The deterioration of sown tall wheatgrass (Elytrigia elongata) growing on 3 sodic saline soils was investigated in the Laprida basin, in the center of the Buenos Aires province of Argentina. These soils are known to have poor drainage and high saline levels and support different species associations. On each soil type the native grassland was compared to sown wheatgrass, in terms of plant density and cover and soil physical and chemical characteristics. The 3 soil types reacted differently to tillage. Tillage had little impact on soil type A (typic Natraquoll), a poorly drained soil with a loamy A horizon (14 cm) overlying a silty clay loam. Soil type B (typic Natraquaf), a wet texture contrast soil with bleached horizons has characteristics that are likely to severely limit plant growth. The sowing of wheatgrass increased ground cover by live vegetation on this soil type. This contrasted with soil type C (typic Natralboll), a saline soil with an organic matter-rich but thin (8 cm) A horizon. In this soil, the plant density declined and other components such as pasture cover also declined with time. This pasture deterioration was attributed to several soil factors including decreased organic matter content and increased soil bulk density. It was concluded that the varied performance of wheatgrass sown pastures was a function of the different inherent characteristics of the soils.
    • Using a grazing pressure index to predict cattle damage of regenerating tree seedlings

      Pitt, M. D.; Newman, R. F.; Youwe, P. L.; Wikeem, B. M.; Quinton, D. A. (Society for Range Management, 1998-03-01)
      This research investigated the potential for using cattle grazing pressure (AU Mg-1 ha-1) and stocking rate (Animal Unit Days ha-1) for predicting basal scarring and browsing of lodgepole pine (Pinus contorta Dougl.) seedlings on cutblocks in southern British Columbia from 1989 to 1992. Cattle browsing on lodgepole pine seedlings occurred almost exclusively during the first 2 years of grazing. Browsing increased (P < 0.05; r2 = 0.71) with increasing stocking rate only during the first year of grazing. Browsing increased with increasing grazing pressure in 1989 (P < 0.05; r2 = 0.38) and 1990 (P < 0.05; r2 = 0.39). Basal scarring peaked during the second year of grazing, but was correlated (P < 0.05; r2 = 0.79) with stocking rate only during the first year of grazing. Increasing grazing pressure was associated with higher (P < 0.05) basal scarring during all 4 years of the study, and likely better predicts trampling damage than does stocking rate, particularly during the first year of grazing. Basal scarring during 1989 generally increased to > 10% of sample trees when grazing pressure exceeded 12.0 AU Mg-1 ha-1. This threshold grazing pressure value of 12.0 AU Mg-1 ha-1, however, cannot likely be extrapolated directly to other sites. Grazing pressure values and associated basal scarring are unquestionably influenced by many factors (e.g., pasture size, kind of grazing animal, forage species, tree height, water availability, topography, and weather patterns during the grazing period). Nonetheless, our work provides evidence that grazing pressure provides a useful index for predicting the potential for trampling damage of lodgepole pine seedlings by cattle.
    • Viability of weed seeds in feed pellet processing

      Cash, S. D.; Zamora, D. L.; Lenssen, A. W. (Society for Range Management, 1998-03-01)
      Federal and state agencies in several western states now require the use of noxious weed-free or noxious weed seed-free forage to hinder the spread of noxious weeds. Forage can be certified as noxious weed-free through state administered programs. Processed feeds such as pellets or cubes made from noncertified hay and uncleaned grain are some of the forage products that may be potential sources of weed infestations. This study was conducted to determine levels of weed seed contamination in alfalfa hay/grain feed pellets manufactured with commercial-grade equipment. Seeds of whitetop [Cardaria draba (L.) Hand.], spotted knapweed (Centaurea maculosa Lam.), Canada thistle [Cirsium arvense (L.) Scop.], leafy spurge (Euphorbia esula L.), and common yellow sweetclover [Melilotus officinalis (L.) Lam.] were added in known quantities to alfalfa/grass mixed hay and to barley. The hay was ground in a hammermill through a screen with 7.9-mm diameter perforations, and the barley was ground to pass through a 2.4-mm screen. In a second experiment, uncertified 'Ladak 65' alfalfa (Medicago sativa L.) seeds were ground with alfalfa/grass mixed hay in a hammermill and extruded through a pellet die before being ground in another hammermill with barley grain followed by extrusion through a pellet die. The Montana Department of Agriculture collected pelleted feed from various manufacturers in the state during 1993 and 1994 to estimate potential weed contamination frequency. Grinding of weed seeds with alfalfa hay or barley grain reduced emergence by 98 to 100%. Grinding and pelleting reduced emergence of alfalfa seed by over 99%. Weed seedlings emerged from 11% of random feed pellet samples collected from Montana manufacturers. Rigorous processing such as occurs when manufacturing hay/grain pellets reduces the risk of disseminating weed seeds from pelleted feed.
    • Viewpoint: Sustainability of piñon-juniper ecosystems—a unifying perspective of soil erosion thresholds

      Davenport, D. W.; Breshears, D. D.; Wilcox, B. P.; Allen, C. D. (Society for Range Management, 1998-03-01)
      Many piñon-juniper ecosystems in the western U.S. are subject to accelerated erosion while others are undergoing little or no erosion. Controversy has developed over whether invading or encroaching piñon and juniper species are inherently harmful to rangeland ecosystems. We developed a conceptual model of soil erosion in piñon-juniper ecosystems that is consistent with both sides of the controversy and suggests that the diverse perspectives on this issue arise from threshold effects operating under very different site conditions. Soil erosion rate can be viewed as a function of (1) site erosion potential (SEP), determined by climate, geomorphology and soil erodibility; and (2) ground cover. Site erosion potential and cover act synergistically to determine soil erosion rates, as evident even from simple USLE predictions of erosion. In piñon-juniper ecosystems with high SEP, the erosion rate is highly sensitive to ground cover and can cross a threshold so that erosion increases dramatically in response to a small decrease in cover. The sensitivity of erosion rate to SEP and cover can be visualized as a cusp catastrophe surface on which changes may occur rapidly and irreversibly. The mechanisms associated with a rapid shift from low to high erosion rate can be illustrated using percolation theory to incorporate spatial, temporal, and scale-dependent patterns of water storage capacity on a hillslope. Percolation theory demonstrates how hillslope runoff can undergo a threshold response to a minor change in storage capacity. Our conceptual model suggests that piñon and juniper contribute to accelerated erosion only under a limited range of site conditions which, however, may exist over large areas.