• Disturbance and Revegetation of Sonoran Desert Vegetation in an Arizona Powerline Corridor

      Hessing, M. B.; Johnson, C. D. (Society for Range Management, 1982-03-01)
      Rates and patterns of revegetation were studied during and after construction of the 500 kV Navajo Project Southern Transmission Line at two sites in the Arizona Sonoran Desert from 1972 through 1977. Herbs were reduced temporarily during the construction phase of the study. Perennial herbs did not return in the 5-year post-construction period. Annual herbs invaded immediately after disturbance. In one case annual herb density and diversity was higher after disturbance due to removal of larger woody plants. The tree and shrub community exhibited dynamic changes in cover, diversity, and richness, presumably in response to the climate. However, colonization by new species was not observed during the 5 years of study. Colonization by previously existing species seemed to be limited to Ambrosia deltoidea, probably due to its ability to reproduce vegetatively and to annual herbs. Annuals which were also on two control plots were probably a colonizing sere of plants.
    • Factors Influencing Development of Cryptogamic Soil Crusts in Utah Deserts

      Anderson, D. C.; Harper, K. T.; Holmgren, R. C. (Society for Range Management, 1982-03-01)
      The relation of some physical and chemical soil characteristics to cryptogamic crust development was determined from sites in semidesert regions of southern Utah. The effects of grazing on cryptogamic crust development also was examined. Electrical conductivity, percentage silt, and soil phosphorus were found to be correlated with well-developed cryptogamic crusts. Both total cryptogamic cover and the number of cryptogamic species decreased under grazing pressure. The management of rangelands, especially in arid regions, would be strengthened by understanding the role of cryptogamic crusts and considering them in range management decisions.