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Publications (8)3.08 Total impact

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    ABSTRACT: Auxinic herbicides, such as 2,4-D and dicamba, that act as plant growth regulators are commonly used for broadleaf weed control in cereal crops (e.g., wheat, barley), grasslands, and noncroplands. If applied at late growth stages, while cereals are developing reproductive parts, the herbicides can reduce seed production. We tested whether growth regulators have this same effect on the invasive annual grass Japanese brome. The herbicides 2,4-D, dicamba, and picloram were applied at typical field use rates to Japanese brome at various growth stages in a greenhouse. Picloram reduced seed production nearly 100% when applied at the internode elongation, boot, or heading stages of growth, whereas dicamba appeared to be slightly less effective and 2,4-D was much less effective. Our results indicate it may be possible to control Japanese brome by using growth regulator herbicides to reduce its seed production, thereby depleting its short-lived seed bank. Nomenclature: 2,4-D; dicamba; picloram; Japanese brome, Bromus japonicus Thunb.; barley, Hordeum vulgare L.; wheat, Triticum aestivum L.
    Invasive Plant Science and Management 03/2010; · 0.98 Impact Factor
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    ABSTRACT: Precipitation-use efficiency (PUE) is a key determinant of aboveground net primary production (ANPP). We used long-term datasets to contrast ANPP and PUE estimates between northern (southeast Montana) and southern (north Texas) mixed-grass prairies. Effects of varying amounts and temporal distribution of precipitation on PUE were examined at the Montana site, using a rainout shelter and irrigation. Results show that 1) ANPP was 21% less in Montana than Texas (188 g·m-2 vs. 237 g·m-2); 2) plant function type (PFT) composition varied between the two study locations, with cool-season perennial grasses (CSPG) dominating in Montana (52%) and warm-season perennial grasses (WSPG) dominating in Texas (47%); 3) production dynamics varied between the two sites with 90% of ANPP completed by 1 July in Montana as compared to 31 August in Texas; 4) average PUE estimates were greater in Montana (0.56 g dry matter·m-2·mm-1 of precipitation) than Texas (0.40 g·m-2·mm-1); and 5) contributions to PUE estimates varied among PFT and location, with CSPG estimates being greater in Montana than Texas (52% vs. 31%) and WSPG estimates being greater in Texas than Montana (47% vs. 27%). Seasonal droughts and supplemental irrigations at the Montana site substantially altered ANPP, PFT biomass composition, and PUE. Results show PUE was responsive to PFT composition relative to amount and seasonal distribution of precipitation. Therefore, one should expect changes in ANPP and PUE to occur with shifts in precipitation patterns until PFT composition becomes adjusted to the regime.
    01/2009;
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    Lance T. Vermeire, Matthew J. Rinella
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    ABSTRACT: Restoration of historic fire regimes is complicated by concerns about exotic plant invasions, yet little is known of how the two may interact. Seeds of Japanese brome, spotted knapweed, Russian knapweed, and leafy spurge were subjected to fire at six fuel loads (100 to 700 g m-2) and a nonburned control. Fires were simulated with field-cured grass and time-temperature profiles were developed from thermocouples at the soil surface. Emergence was determined by species and fuel load in growth chambers. Fuel load explained 98% of variation in mean heat dosage and emergence decreased with increasing fuel load across species. Emergence was reduced 79 to 88% relative to nonburned treatment with 100 g m-2 of fuel and at least 97% with 200 g m-2 of fuel. Emergence probabilities were less than 0.01 for all species but spotted knapweed with a 300 g m-2 fuel load. Results indicate high potential for fire to disrupt the life cycle of invasive species through direct seed mortality. The relationship between fuel load and seedling emergence provides good predictability of fire effects on surface-deposited seeds. A single fire is unlikely to eradicate many invasive species because they often produce abundant seeds and some will undoubtedly escape fire. However, abrupt reductions in seedling emergence with relatively light fuel loads indicate that fire may be an effective tool for increasing mortality of invasive plant seed across a broad range of habitats.
    01/2009;
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    ABSTRACT: Rangelands are complex systems that occupy more than 50% of the land area in the world. Carbon cycling on rangelands is generally understood, but details concerning agricultural management practices of prescribed fire and grazing are not well defined. Field experiments were conducted on northern mixed-grass prairie in eastern Montana with undisturbed, burned, and grazed treatments established in 2003. Designated plots were burned during the dormant season (December) in 2003. Grazing occurred in 2004 and 2005, removing 45-50% of then currently available leaf area. Responses were evaluated monthly from April to October of 2004 and 2005. Abiotic measurements included: precipitation, soil water content, photosynthetically active solar radiation, and temperatures of soil and leaves. Biotic responses were: standing crop, leaf area, root mass to a soil depth of 30cm, and CO₂ fluxes above the mixed-grass prairie canopy and bare soil. Moisture available to the northern mixed-grass prairie system at this location was the primary identifiable factor that either directly or indirectly controlled much of the CO₂ flux. Treatment effects on seasonal changes in soil water content were consistent across years, with grazed and undisturbed plots being similar. Burned plots had less soil water content than grazed or undisturbed plots in late spring and early summer with soil water content becoming similar across all treatments in late summer and into autumn. Despite differences in soil water content, CO₂ fluxes above either burned or undisturbed plots were dynamically similar. However, peak CO₂ flux of grazed plots was shifted one month earlier in 2004 and was decreased in 2005, relative to the undisturbed and burned plots. Over the course of this experiment, cumulative CO₂ flux on the grazed plots was 72% of that on the burned and undisturbed plots. Depending on conditions during the growing season, C removed from northern mixed-grass prairie rangeland may not be re-sequestered during the growing season immediately post-burning. We conclude that the studied ecosystem is unlikely to sequester considerable C, irrespective of imposed agricultural practices, due to the relatively low CO₂ flux and the small magnitude of treatment observed.
    01/2008;
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    ABSTRACT: Grazing systems may alter botanical composition and productivity of grasslands through differential use in time, space, or intensity. Seven simulated grazing treatments were applied six years in eastern Montana, USA to determine effects on plant community composition and standing crop. Treatments were moderate stocking (28.8AUDha⁻¹ year⁻¹) of cattle using 3-pasture summer rotation, season-long, high-intensity low-frequency, short-duration, 3-pasture winter rotation, and spring calving systems. The final treatment was severe growing-season grazing (108.2AUDha⁻¹ year⁻¹). Treatments were randomly assigned to 14, 6.1-ha pastures. Post-treatment grass and total standing crops were 54 and 58% of their pre-treatment measures because of extended drought. No single grazing system affected standing crop of any herbage component. Standing crops of Pascopyrum smithii Rydb. (Love) (674±186kgha⁻¹; P >0.69), other perennial C₃ grasses (102±156kgha⁻¹; P >0.77), perennial C₄ grasses (178±111kgha⁻¹; P >0.22), and shrubs (13±34kgha⁻¹; P >0.57) were similar across grazing treatments. Severe grazing produced more forbs (142±16kgha⁻¹; P <0.01) than moderate stocking (67±16kgha⁻¹). Annual C₃ grasses increased (P <0.01) from 131±55kgha⁻¹ on pastures grazed after May to 362±55kgha⁻¹ on pastures grazed before June. Cacti also increased (P <0.03) from 47 to 187±52kgha⁻¹ on early-grazed pastures. Greater total standing crop on pastures grazed before June (P <0.03) was accounted for by increases in annual C₃ grasses and cacti. Rotational and continuous grazing strategies produced similar effects on all vegetation components. Grazing systems were not effective in altering standing crop or functional group composition one year after six years of treatment. Standing crop changes over time and limited shifts in forbs, cacti, and annual C₃ grasses indicate northern mixed prairie is most responsive to weather, with stocking rate and timing of grazing contributing minor influences.
    01/2008;
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    R.K. Heitschmidt, L.T. Vermeire
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    ABSTRACT: Drought is an inherent trait of most rangelands and sound management necessitates managers address two fundamental questions when facing a drought situation. The first question is, "what is the probability that a useful amount of precipitation will be received over the period of concern?" and the second question is, "if it does rain, what will the impact be in terms of quantity and quality of herbage produced?" The objective of this study was to address the second question. Our hypothesis was that herbage growth response to above normal summer precipitation (i.e., 2x in July and August) would be limited in the northern Great Plains because of a general absence of productive warm-season species. Study plots were twelve 5 x 10-m non-weighing lysimeters. Treatments were: 1) simulated (i.e., rainout shelter imposed), severe spring drought (i.e., 1 May - 1 July) followed by ambient precipitation thereafter; 2) simulated, severe spring drought followed by ambient precipitation thereafter plus summer irrigation (i.e., July and August); 3) ambient precipitation only; and 4) ambient precipitation plus summer irrigation. Results indicated substantial herbage production can be expected in this region during summer when precipitation is well above average because of the positive growth response of blue grama (Bouteloua gracilis H.B.K. Lag. ex Griffiths), the dominant warm-season grass growing in this region. However, results also showed that level of production in the study situation (i.e., spring drought, wet summer) was only about 50% of that attained in a normal (i.e., wet spring/dry summer) year. Moreover, long-term weather data shows the probability of receiving 2x normal precipitation in both July and August (i.e., our irrigation treatments) is < 1%. Thus, although these rangelands possess the capacity to respond favorably to summer precipitation, the low probability of receiving substantial levels of summer precipitation ensures levels of ecological and economic risk remain high.
    01/2006;
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    R K Heitschmidt, L T Vermeire, E E Grings
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    ABSTRACT: The objective of this paper is to examine the sustainability of rangeland agriculture (i.e., managed grazing) on a world-wide basis, with a focus on North America. Sustainability is addressed on three fronts: 1) ecological, 2) economic, and 3) social acceptance. Based on previous and on-going research, we suggest that employment of science-based rangeland grazing management strategies and tactics can ensure ecological sustainability. The formidable challenge in employing such technology centers around the need to balance efficiency of solar energy capture and subsequent harvest efficiencies across an array of highly spatially and temporally variable vegetation growing conditions using animals that graze selectively. Failure to meet this fundamental challenge often accelerates rangeland desertification processes, and in some instances, enhances rate and extent of the invasion of noxious weeds. We also suggest that the fundamental reason that ecologically sound grazing management technologies are often not employed in the management of grazed ecological systems is because social values drive management decisions more so than ecological science issues. This is true in both well-developed societies with substantial economic resources and in less-developed societies with few economic resources. However, the social issues driving management are often entirely different, ranging from multiple-use issues in developed countries to human day-to-day survival issues in poorly developed countries. We conclude that the long-term sustainability of rangeland agriculture in 1) developed societies depends on the ability of rangeland agriculturalists to continually respond in a dynamic, positive, proactive manner to ever-changing social values and 2) less-developed societies on their ability to address the ecological and social consequences arising from unsustainable human populations before the adoption of science-based sustainable rangeland management technologies.
    Journal of Animal Science 02/2004; 82 E-Suppl:E138-146. · 2.09 Impact Factor
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    ABSTRACT: As public and scientific interest in black-tailed prairie dogs has grown, views about their ecological role have become polarized. We evaluated three claims frequently made concerning the status of black-tailed prairie dogs and their interactions with other species: (1) that black-tailed prairie dogs historically occupied 40 million to 100 million hectares (ha) and now occupy only 1 to 2 percent of their former range, (2) that large ungulates preferentially forage on prairie dog colonies, and (3) that prairie dogs do not reduce carrying capacity for large herbivores. The conclusion that prairie dogs historically occupied up to 100 million ha is not supported by the literature, and the more conservative figure of 40 million ha is based on estimates from the early 20th century, when prairie dog populations were artificially high as a result of human activities. Prairie dog activity is not unique in facilitating grazing by large herbivores; and selection of prairie dog colonies for foraging is limited to specific conditions, including colony age, proximity, and season of the year. Finally, prairie dogs reduce carrying capacity for large herbivores by consuming forage, clipping plants to increase visibility, building mounds, and changing plant cover and species composition.
    01/2004;