• Acute toxic plant estimation in grazing sheep ingesta and feces

      Cid, M. S.; Lopez, T. A.; Yagueddu, C.; Brizuela, M. A. (Society for Range Management, 2003-07-01)
      'Romerillo' (Baccharis coridifolia DC), 'duraznillo negro' (Cestrum parqui L'Hérit.), and 'sunchillo' (Wedelia glauca (Ort.) Hoff.) are highly toxic species producing important economic losses of livestock in Argentina. This study assessed the accuracy and precision in the estimation of the percentage and the mass of these species in the ingesta and feces of sheep experimentally poisoned. This study also evaluated whether the quantified percentage and the calculated mass of each toxic species in the rumen+reticulum, the easiest region to sample, are good estimates of their relative consumption. Results indicate that if species fragment density is quantified, and the percentages of non recognized fragments of the toxic species in their in vitro digestion residues are accounted for (attributing some proportion of the unidentified fragment pool to the target species), estimations are accurate, but their precision differ among species. For a 3 sheep sample, the average mass estimated by microhistological analysis represented 92.3 +/- 5.8 (romerillo), 96.5 +/- 17.3 (duraznillo negro), and 92.0 +/- 12.5% (sunchillo) (P < 0.10) of the actual amount of each species consumed. The percentages of the toxic species in the total ingesta plus feces produced since the intoxication did not differ (P > 0.05) from those in the rumen+reticulum. For the evaluated species, the microhistological analysis of the rumen+reticulum not only confirmed the ingestion of the toxic species, but also adequately estimated the percentage in which they were ingested.
    • Bowen ratio versus canopy chamber CO2 fluxes on sagebrush rangeland

      Johnson, D. A.; Saliendra, N. Z.; Walker, J. W.; Hendrickson, J. R. (Society for Range Management, 2003-09-01)
      Because of their expansiveness, sagebrush (Artemisia spp.)-steppe rangelands could contribute significantly to the global carbon budget. However, it is important to determine if there are differences between methods for determining CO2 fluxes on these rangelands. The objective of this study was to compare the Bowen ratio-energy balance and canopy chamber techniques for measuring CO2 fluxes in a sagebrush-steppe ecosystem. A Bowen ratio-energy balance system was installed at a sagebrush-steppe site near Dubois, Ida., U.S.A to continuously measure the vertical gradients of air temperature, water vapor, and CO2 concentration in conjunction with associated micrometeorological characteristics. The canopy chamber technique, which employed a 1-m2 (1,020 liter) clear plexiglass/plastic film chamber in combination with a portable gas exchange system, was used periodically during May through August across 4 years (1996-1999) to obtain instantaneous measurements of CO2 fluxes across 3 replicate blocks during a 2-min. measurement period. For the same measurement dates and times across the 4 years of study, CO2 fluxes ranged from -0.22 to 0.55 mg m-2 sec-1 for the Bowen ratio-energy balance technique and from -0.18 to 0.48 mg m-2 sec-1 for the canopy chamber technique. Estimates of CO2 fluxes by the 2 techniques were not statistically different (P > 0.05) for the early (May) and mid-season (June to mid-July) portions of the growing season; however, fluxes measured by the 2 techniques were significantly different (P 0.05) for the late-season period (late-July to late-August). Despite this difference during the hot-dry, late-season period, flux estimates from the 2 techniques were significantly and positively correlated during the early (r2 = 0.71), mid- (r2 = 0.88), and late- (r2 = 0.72) season periods. Thus, both techniques showed similar patterns of CO2 fluxes at our sagebrush-steppe study site across 4 years of study, although caution should be used when the canopy chamber technique is used during hot, dry conditions.
    • Calibrating fecal NIRS equations for predicting botanical composition of diets

      Walker, J. W.; McCoy, S. D.; Launchbaugh, K. L.; Fraker, M. J.; Powell, J. (Society for Range Management, 2002-07-01)
      The objectives of this study were to investigate the use of near infrared spectroscopy (NIRS) of fecal samples for predicting the percentage of mountain big sagebrush (Artemisia tridentata Nutt. ssp. vaseyana (Rydb) Beetle) in sheep diets and to quantify the limitations of using NIRS of fecal samples to predict diet composition. Fecal material from a sheep feeding trial with known levels of sagebrush and several background forages was used to develop fecal NIRS calibration equations validated with fecal material from 2 other sheep feeding trials with known levels of sagebrush in the diets. The 1996 calibration trial varied the level of sagebrush, alfalfa, and grass hay in the diets. The 1998 trial compared frozen to air-dried sagebrush. The Wyoming trial was a metabolism study using frozen sagebrush. Trials used different levels of sagebrush varying from 0 to 30% of the diet in increments of 4 to 10 percentage points. Internal validation of the 1996 trial with a subset of the samples not used for calibration showed that when predicted samples are from the same population as the calibration samples, this procedure can accurately predict percent sagebrush (R2 = 0.96, SEP = 1.6). However, when predicted samples were from a different population than calibration samples, accuracy was much less, but precision was not affected greatly. Low accuracy was caused by a compression of the range of data in the predicted values compared to the reference values, and the predicted sagebrush levels in the diet should be considered to represent an interval scale of measurement. Modified partial least squares regression resulted in better calibration than stepwise regression, and calibration data sets with only high, low, and no sagebrush resulted in calibrations almost as good as data sets with several intermediate levels of sagebrush. High values of the H statistic were related to low precision but did not affect the accuracy of predictions. We believe the interval scale of measurement will contain sufficient information for the purpose of addressing many questions on rangelands.
    • Evaluation of USLE and RUSLE estimated soil loss on rangeland

      Spaeth, K. E.; Pierson, F. B.; Weltz, M. A.; Blackburn, W. H. (Society for Range Management, 2003-05-01)
      The Universal Soil Loss Equation (USLE) and the Revised Universal Soil Loss Equation (RUSLE 1.06) were evaluated with rainfall simulation data from a diverse set of rangeland vegetation types (8 states, 22 sites, 132 plots). Dry, wet, and very-wet rainfall simulation treatments were applied to the study plots within a 2-day period. The rainfall simulation rate was 65mm/hr for the dry and wet simulation treatments and alternated between 65-130 mm/hr for the very-wet treatment. Average soil loss for all plots for the representative simulation runs were: 0.011 kg/m2, 0.007 kg/m2, and 0.035 kg/m2 for the dry, wet, and very-wet simulation treatments, respectively. The Nash-Sutcliffe Model efficiencies (R2eff) of the USLE for the dry, wet, very-wet simulation treatments and sum of all soil loss measured in the three composite simulation treatments (pooled data) were negative. This indicates that the observed mean measured soil loss from the field rainfall simulations is better than predicted USLE soil loss. The USLE tended to consistently overpredict soil loss for all 3 rainfall simulation treatments. As the USLE predicted values increased in magnitude, the error variance between predicted and observed soil loss increased. Nash-Sutcliffe model efficiency for the RUSLE was also negative, except for the dry run simulation treatment [R2eff = 0.16 using RUSLE cover management (C) subfactor parameters from the RUSLE manual (C(table)), NRCS soil erodibility factor (K); and R2eff = 0.17 with C(table) and K estimated from the soil-erodibility nomograph]. In comparison to the USLE, there was less error between observed and RUSLE predicted soil loss. The RUSLE error variances showed a consistent trend of underpredicted soil loss among the 3 rainfall simulation treatments. When actual field measured root biomass, plant production and soil random roughness values were used in calculating the RUSLE C subfactors: the R2eff values for the dry, wet, very-wet rainfall simulation treatments and the pooled data were all negative.
    • Point sampling for leaf area index in sagebrush steppe communities

      Clark, P. E.; Seyfried, M. S. (Society for Range Management, 2001-09-01)
      Although point sampling has been used for more than 30 years to quantify leaf area index (LAI), this field technique has not been rigorously evaluated in sagebrush steppe plant communities. Leaf area index estimates obtained using different sampling pin inclinations or combinations of pin inclinations were evaluated in Wyoming big sagebrush (Artemisia tridentata Nutt. ssp. wyomingensis Beetle and Young), low sagebrush (Artemisia arbuscula Nutt.), and mountain big sagebrush (Artemisia tridentata Nutt. ssp. vaseyana [Rydb.] Beetle) communities within the Reynolds Creek Experimental Watershed near Boise, Ida. Leaf area index values determined by clipping and processing green foliage through a leaf area meter were used as evaluation standards. Pins inclined at 13 degrees from the horizontal, used alone or in combination with pins of 52 degrees and/or 90 degrees inclinations, performed poorly for estimating LAI in the Wyoming big sagebrush and low sagebrush communities. Estimating total LAI with either the combination of 52 degrees and 90 degrees angle pins or with 52 degrees or 90 degrees pins alone explained at least 96% of the variability in LAI standard values from the Wyoming big sagebrush and mountain big sagebrush communities. Using 52 degrees angle pins alone produced model fits similar to those obtained when the combination of 52 degrees and 90 degrees angle pins were used to estimate shrub, graminoid, and forb LAI across all 3 communities (P > 0.1). Collecting point data using 52 degrees angle pins often provided better or similar model fits with LAI standards compared to other pin angles but using 90 degrees angle pins offers a better compromise between practicality, efficiency, and accuracy.
    • Using Very-Large-Scale Aerial Imagery for Rangeland Monitoring and Assessment: Some Statistical Considerations

      Karl, Jason W.; Duniway, Michael C.; Nusser, Sarah M.; Opsomer, Jean D.; Unnasch, Robert S. (Society for Range Management, 2012-07-01)
      The availability of very-large-scale aerial (VLSA) imagery (typically less than 1 cm ground-sampling-distance spatial resolution) and techniques for processing those data into ecosystem indicators has opened the door for routinely using VLSA imagery in rangeland monitoring and assessment. However, for VLSA imagery to provide defensible information for managers, it is crucial to understand the statistical implications of designing and implementing VLSA image studies, including consideration of image scale, sample design limitations, and the need for validation of estimates. A significant advantage of VLSA imaging is that the researcher can specify the scale (i.e., spatial resolution and extent) of the images. VLSA image programs should plan for scales that match monitoring questions, size of landscape elements to be measured, and spatial heterogeneity of the environment. Failure to plan for scale may result in images that are not optimal for answering management questions. Probability-based sampling guards against bias and ensures that inferences can be made to the desired study area. Often collected along flight transects, VLSA imagery lends itself well to certain probability-based sample designs, such as systematic sampling, not often used in field studies. With VLSA image programs, the sample unit can be an entire image or a portion of an image. It is critical to define the sampling unit and understand the relationship between measurements and estimates made from the imagery. Finally, it is important to statistically validate estimates produced from VLSA images at selected locations using quantitative data of the same scale and more precise and accurate than the VLSA image techniques. The extent to which VLSA imagery will be useful as a tool for understanding the status and trend of rangelands depends as much on the ability to build the imagery into robust programs as it does on the ability to quickly and relatively easily collect VLSA images over large landscapes./La disponibilidad de imágenes aéreas a gran escala (IAGE) (normalmente menos de un cm de de distancia de resolución espacialen el terreno) y técnicas que procesen esos datos dentro de indicadores del ecosistema han abierto la puerta para que de manera rutinaria se use IAGE en pastizales en monitoreo y evaluación. Sin embargo, para IAGE proveer información defendible para administradores es crucial para entender las implicaciones estadísticas para diseñar e implementar estudios de IAGE que incluyan consideraciones de escala de la imagen, limitaciones en el diseño de muestreo y la necesidad de validación de los estimadores. Una ventaja significativa de IAGE es que el investigador puede definir la escala (ejm. resolución espacial y extensión) de la imagen. Los programas de IAGE deberían planear escalas que empaten preguntas de monitoreo, el tamaño delos elementos del paisaje a ser medidos y la heterogeneidad espacial del medioambiente. Fallas en planear la escala puede resultar en imágenes que no son optimas en resolver las preguntas del administrador. Muestreos basados en probabilidad protegen contra sesgo y aseguran que la inferencia puede ser hecha para la area de estudio deseada. Seguido, recolección a lo largo de vuelos en transectos, IAGE permite bien a cierto diseño de muestra basado en probabilidad como diseño sistemático nousado a menudo en estudios de campo. Con programas IAGE la unidad de muestreo puede ser la imagen completa o una porción de ésta. Es fundamental definir la unidad de muestreo y entender la relación entre medidas y estimaciones hechas de la imagen. Finalmente, es importante validar estadísticamente los estimadores producidos de IAGE es lugares seleccionados usando datos cuantitativos de la misma escala y más precisos y certeros que las técnicas de IAGE. La amplitud a la cual IAGE será de utilidad como herramienta para entender el estatus y tendencia de los pastizales, depende en gran medida en la habilidad para construir imágenes en programas robustos sino también con la habilidad de recolectar imágenes IAGE rápidamente y relativamente fácil sobre grandes paisajes.
    • View Points: Improving the Scientific Integrity of Nontechnical Publications

      Maestas, Jeremy D.; Hughes, John; Toombs, Theodore P.; Davies, Kirk W.; Gregg, Michael A.; Johnson-Nistler, Carolyn; Gilgert, Wendell C.; Petersen, Steven L. (Society for Range Management, 2006-10-01)