• Plant Water Potential for Shrubs in Argentina

      Pelaez, D. V.; Bóo, R. M. (Society for Range Management, 1987-01-01)
      Water relations of Prosopis flexuosa, P. caldenia, Condalia microphylla, Larrea divaricata, and Chuquiraga erinacea, 5 shrub species of a temperate semiarid region of Argentina were analyzed by periodic measurement of soil water potential, plant water potential, and air humidity. Water potential in all species showed recovery during the night, the values obtained early in the morning being higher (less negative) than those recorded in the afternoon. Plant water potential showed higher correlation with soil water potential than with the other environmental variables considered. Results indicate that these species have the capacity to adjust to summer drought conditions.
    • 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.