• A Method for Forecasting Potential Losses from Grasshopper Feeding on Northern Mixed Prairie Forages

      Hewitt, G. B.; Onsager, J. A. (Society for Range Management, 1982-01-01)
      Information on the potential loss of forage that might be expected from grasshopper feeding in a given season would benefit ranchers and land managers if the loss could be estimated in the spring before peak forage production. A method was developed for forecasting such losses on the northern mixed prairie when most species of grasshoppers are in the 3rd and 4th instars. The method is based on the assumptions that forage losses (forage consumed + destroyed) are directly proportional to grasshopper size and density and that during the period between the 3rd instar and death, which usually does not exceed 46 days, density decreases linearly to 0. Using feeding ratios (weight of forage destroyed/weight of adults), losses/day were calculated for each of 26 grasshopper species and for 3 groups of species separated by weight. Forecasted loss estimates for any population can be estimated if the density and species are determined, or a loss of 43 mg/grasshopper feeding day could be used as a general average if species cannot be identified. Forecasted losses are related to grasshopper density and to observed losses at one site in Montana during a 3-year period.
    • Effects of Two Years of Irrigation on Revegetation of Coal Surface-Mined Land in Southeastern Montana

      Depuit, E. J.; Skilbred, C. L.; Coenenberg, J. G. (Society for Range Management, 1982-01-01)
      Responses of reseeded vegetation in the first two growing seasons (1978 and 1979) to irrigation on topsoiled sodic mine spoils are presented. In terms of above-ground productivity and stand composition, irrigation significantly promoted growth of seeded perennial grasses and legumes in total. This stimulation was most pronounced in 1979 for the cool-season grasses, slender wheatgrass, smooth bromegrass and western wheatgrass and the invading cool-season legume yellow sweetclover. Other cool-season grasses and warm-season grasses were stimulated by initial irrigation, but were either unaffected or retarded (due to competitive relationships) by continued irrigation. Productivity of invading annual weeds was significantly curtailed by irrigation by 1979. Although differences in composition occurred, total stand productivity was similar for irrigated and nonirrigated plots in 1978, a year of above-average precipitation. In 1979, a drier year, total stand productivity was nearly three times higher under irrigation than nonirrigation. In the first year of study (1978), a higher measured index of stand structural diversity occurred under irrigation. This relationship became reversed in 1979, with higher structural diversity in nonirrigated plots. Root biomass was significantly higher in nonirrigated than in irrigated plots. This difference between irrigation and nonirrigation was most pronounced in the applied topsoil zone. Root distribution was skewed towards shallowest soil depths under irrigation to a far greater extent than under nonirrigation.
    • Identification of Subspecies of Big Sagebrush by Ultraviolet Spectrophotometry

      Shumar, M. L.; Anderson, J. E.; Reynolds, T. D. (Society for Range Management, 1982-01-01)
      The three subspecies of big sagebrush (Artemisia tridentata) are dominant shrubs over much of the Intermountain West. Because the subspecies differ in palatability and habitat requirements, researchers and resource managers have become increasingly concerned with their identification. Subspecies have been identified by leaf morphology, ultraviolet (UV) fluorescence, or chromatography. Fluorescence of leaf extracts under short-wave UV light provides a convenient technique for distinguishing between A.t. vaseyana and the other two subspecies, but this technique will not distinguish between A.t. tridentata and A.t. wyomingensis. Chromatographic techniques can differentiate between all of the subspecies, but the methods are tedious. We describe a technique for distinguishing all three subspecies by UV spectrophotometry. Alcohol leaf extracts of the three subspecies produce relative absorbance graphs that differ markedly from one another between 230 and 280 nm.