• Nutrient Availability in Rangeland Soils: Influence of Prescribed Burning, Herbaceous Vegetation Removal, Overseeding with Bromus tectorum, Season, and Elevation

      Blank, R. R.; Chambers, J.; Roundy, B.; Whittaker, A. (Society for Range Management, 2007-11-01)
      Soil nutrient availability influences plant invasions. Resin capsules were used to examine soil nutrient bioavailability along 2 sagebrush-grassland elevation transects in the east Tintic Range (Utah) and Shoshone Range (Nevada). In the fall of 2001, treatments were applied to 3 replicate plots at each site, which included prescribed burning, herbaceous vegetation removal, and controls. Cheatgrass (Bromus tectorum L.) was overseeded in small subplots within each treatment. Following treatments in each plot, resin capsules were installed at 15-cm depth in a shrub interspace and a B. tectorum-overseeded area. Nutrient availability was integrated during late fall to spring and spring to late fall for 2 years. Herbaceous vegetation removal increased availability of nitrate (Nevada and Utah) and Ca and Mg (Nevada only) but only during the second sampling period (growing season). Availability of K and ortho-P (Nevada and Utah) and nitrate (Nevada only) was greater on prescribed burned plots. For Utah, availability of ortho-P, K, Ca, Mg, and Fe generally increased with increasing elevation. Availability of Ca, Mg, K, and Fe was greatest during late fall to spring integration periods for Nevada. Overseeding with B. tectorum interacted with the burn treatment to influence availability of Ca, Mg, and Fe (Nevada sites only). Patterns of nutrient availability can be explained by a combination of decreased root uptake in relation to mineralization, differences in soil water content with season and elevation, and nutrient release from vegetation and soil as a consequence of prescribed burning. Herbaceous vegetation removal and burning can raise nitrate availability and increase risk of invasion by nitrophilic species such as B. tectorum. Nutrient availability can be out of phase with plant growth; plants capable of taking up nutrients during cold periods may have a competitive advantage. Resin capsules have utility in quantifying the effects of treatments on the availability of many soil nutrients. 
    • Prediction of Cheatgrass Field Germination Potential Using Wet Thermal Accumulation

      Roundy, Bruce A.; Hardegree, Stuart P.; Chambers, Jeanne C.; Whittaker, Alison (Society for Range Management, 2007-11-01)
      Invasion and dominance of weedy species is facilitated or constrained by environmental and ecological factors that affect resource availability during critical life stages. We compared the relative effects of season, annual weather, site, and disturbance on potential cheatgrass (Bromus tectorum L.) germination in big sagebrush (Artemisia tridentata Nutt.) communities. Soil water status and temperature in the seedbed were measured continuously for 4 years on 9 big sagebrush sites in Nevada and Utah. Field plots at lower-, middle-, and upper-elevation sites were either undisturbed, or were burned, sprayed with herbicide, or both sprayed and burned. Spraying removed perennial herbaceous vegetation, whereas burning removed sagebrush. We used thermal-germination data from laboratory incubation studies of 18 cheatgrass seedlots and field soil moisture and temperature measurements to model and predict potential germination in the field plots for periods when seedbeds were continuously wet (above –0.5, –1, or –1.5 MPa) and across intermittent wet and dry periods. Season had the greatest effect on potential cheatgrass germination, followed by annual weather, and site variables (elevation and location); the effects of disturbance were minimal. Potential germination was predicted for most sites and years in spring, a majority of sites and years in fall, and few sites or years in winter. Even though disturbance has limited effects on potential germination, it can increase cheatgrass invasion and dominance by reducing perennial herbaceous species resource use and allowing increased cheatgrass growth and reproduction. 
    • Salt-Lick-Induced Soil Disturbance in the Teton Wilderness, USA

      Walters, D. K.; DeLuca, T. H. (Society for Range Management, 2007-11-01)
      Manmade salt licks on public lands throughout the Rocky Mountain West have been created to attract large game for hunting purposes. This practice is both illegal and controversial, but is of particular importance in otherwise pristine wilderness landscapes. The impact of widespread saltlicks on public lands has never been quantified. This study was undertaken to examine the degree of change in soil physical and chemical properties caused by approximately 10-60 years of salt application in the Teton Wilderness of Wyoming, USA. A total of 27 sites were identified, surveyed, and paired with non-salt-affected control areas. Three replicate sampling points were located within each salt site and in each of the paired control areas. Soil samples from each site were analyzed for soil bulk density, soil salinity as electrical conductance (EC), pH, organic matter content, sodium absorption ratio (SAR), and exchangeable concentrations of sodium (Na+), potassium (K+), calcium (Ca2+), and magnesium (Mg2+). Salt-treated site centers were found to have elevated EC, bulk density, pH, SAR, and Na+ concentration compared to the no-salt controls. Salt-affected sites also contained decreased organic matter contents and decreased concentrations of Ca2+ and Mg2+. Observed differences were due to the addition of Na+ to the soil solum as well as direct effects of ungulates. Soil compaction appears to have a greater impact on plant establishment than the actual presence of NaCl. Salt licks established in wilderness areas habituate animals to localized zones causing extensive soil trampling and consumption of surface soils by grazing ungulates. 
    • The Effects of Forest Residual Debris Disposal on Perennial Grass Emergence, Growth, and Survival in a Ponderosa Pine Ecotone

      Law, Darin J.; Kolb, Peter F. (Society for Range Management, 2007-11-01)
      Soil surface conditions can have profound effects on plant seedling emergence and subsequent seedling survival. To test the hypothesis that different soil-surface treatments with logging residue affect range grass seedling emergence and survival, 6 alternative forest-residual treatments were established in the summer of 1998 following thinning of mature trees from approximately 500 to 133 trees ha-1. The treatments included 1) whole logging debris, hand-piled; 2) whole logging-debris piles that were burned; 3) whole logging-debris piles that were chipped; 4) whole logging-debris piles that were chipped and burned; 5) scattered debris followed by a broadcast burn; and 6) zero debris, not burned. The influences of the debris treatments on grass seedling emergence and survival were tested by seeding with native and exotic perennial grass species. Three plots per treatment were seeded with a mix of 4 native grass species, and another 3 plots per treatment were seeded with a mix of 4 exotic grass species. Two plots per treatment were left unseeded. Subsequent grass emergence, growth, and establishment were measured as seedling emergence, cover, density, height, and biomass for 3 growing seasons. Grass cover, density height, and biomass increased on the burn treatments during the study. Less-significant results were obtained for the nonburned woody- debris treatments. In addition, important abiotic factors, such as soil moisture and soil surface temperature, were not adversely affected by the woody debris disposal practices tested in this study. Results indicate that scattered woody debris that is broadcast burned is the best mechanism for disposing of woody debris, increasing grass emergence and survival, and preventing ponderosa pine recruitment and exotic invasion.
    • The Potential for Horses to Disperse Alien Plants Along Recreational Trails

      Wells, Floye H.; Lauenroth, William K. (Society for Range Management, 2007-11-01)
      Plant invasions are rapidly becoming an important threat to the conservation of wildlands. Understanding how potentially invasive plants are dispersed to new habitats is a critical step in the process of understanding such invasions. Our objective was to characterize the potential for long-distance transport of plant species in the digestive tract of horses along recreational trails. We sampled horse dung along the first 4 000 m of the Lower Piney River trail in the White River Forest of western Colorado. We evaluated the seed content of each sample by applying standard methods for soil seed bank analysis. We found 20 species and 564 seedlings. Twelve of the species were graminoids, 6 were forbs, 1 was a shrub, and 1 was a tree. The species were evenly divided between natives and aliens, but 85% of the seedlings were aliens. An average of 47 seedlings emerged per sample, but the range was from 4 to 192. Our results make it clear that horses, and very likely all pack stock used on recreational trails, represent a potentially important dispersal vector for alien plants into western wildlands.