• Crude Terpenoid Influence on Mule Deer Preference for Sagebrush

      Personius, T. L.; Wambolt, C. L.; Stephens, J. R.; Kelsey, R. G. (Society for Range Management, 1987-01-01)
      Samples of current year's growth of leaves and stems were collected in February 1983 from basin big sagebrush (Artemisia tridentata Nutt. tridentata), Wyoming big sagebrush (A.t. wyomingensis Beetle and Young), mountain big sagebrush (A.t. vaseyana [Rydb.] Beetle), and black sagebrush (A. nova Nels.) on a mule deer (Odocoileus hemionus hemionus) winter range near Gardiner, Montana. Samples were from both lightly and heavily used plants (form classes) within each taxon. Crude terpenoids were separated into 3 groups: headspace vapors, volatile, and nonvolatile crude terpenoids. Compounds in each group are thought to stimulate the sensory organs of mule deer. Individual compounds were identified and quantified for comparison with preference ranks among taxa and between utilization form classes. Seven compounds were selected by discriminant analysis as indicators among the 4 taxa, with methacrolein + ethanol, ρ-cymene, and the sesquiterpene lactones the most probable preference determinants. Seven other compounds were found useful for separating plants within taxa into form classes. Chemical differences between the 2 form classes, however, were less distinguishable than were those among the 4 taxa.
    • Shrub Litter Production in a Sagebrush-Steppe Ecosystem: Rodent Population Cycles as a Regulating Factor

      Parmenter, R. R.; Mesch, M. R.; MacMahon, MacMahon. J. A. (Society for Range Management, 1987-01-01)
      This study examines the impact of long-tailed vole (Microtus longicaudus) and deer mouse (Peromyscus maniculatus) population changes and their feeding behavior on shrub populations and the resulting litter production in a shrub-steppe ecosystem in southwestern Wyoming. Rodent populations were monitored on 3 replicate plots over a 3-yr period. Populations peaked in autumn 1983 and declined to lower levels in 1984-86. Damage to shrubs (in the form of bark-stripping and girdling) was observed after the winter of 1983-84, but not after the winters of 1984-85 and 1985-86. We assessed damage to shrubs on 4 sites. Extent of damage, mortality, and biomass-to-litter transformations were quantified. We found that: (1) 21% of all shrubs and 28% of the big sagebrush (Artemisia tridentata) sustained rodent damage; (2) 1% of all shrubs were killed as a result of girdling; (3) mean biomass lost from shrubs that suffered damage was 36%; (4) total aboveground biomass loss occurring on big sagebrush was 231 kg/ha or 4% of the standing crop. These results indicate that rodents feeding on big sagebrush can periodically increase annual rates of litter production by as much as 69% above "normal." Rodents in the sagebrush-steppe ultimately influence ecosystem-level nutrient cycles by accelerating shrub litter production, and may affect plant species composition via feeding-induced shrub mortality.