• Plant-animal interactions affecting plant establishment and persistence on revegetated rangeland

      Archer, S.; Pyke, D. A. (Society for Range Management, 1991-11-01)
      The role of ungulate grazing in shaping rangeland ecosystems is well known relative to other important plant-animal interactions such as pollination, seed dispersal, granivory, and belowground herbivory. Successful rangeland revegetation may be enhanced by strategies that favor certain groups of animals and discourage others. Many perennial forbs and shrubs require animals for successful pollination, reproduction, and subsequent maintenance of species on a site; however, pollination biology of many rangeland plants and pollinator abundances at potential revegetation sites are largely unknown. Granivory may be significant in some locations and planning and design of revegetation areas may be improved by implementing principles of seed escape mechanisms, such as predator satiation, seed escape in space (low perimeter-to-area ratio for revegetation site), and seed escape in time (synchronous or staggered timing for nearby revegetation sites). Seedling establishment may be associated with invertebrate population levels which need to be considered in future revegetation projects. Timing and site preparation are important in limiting belowground herbivory. Animals can serve as dispersal agents of seeds. Livestock dosed with desirable seeds can disperse them in their dung across the landscape, thereby creating patches of desirable plants. If revegetation sites will be grazed by livestock, then managers should choose plant species that tolerate rather than avoid grazing and should apply adequate management to establish and maintain plant populations. Seeds inoculated with mutualistic species such as mycorrhizae, nitrogen-fixing bacteria, or actinomycetes may enhance establishment, productivity, and nutrient quality of rangeland species while increasing rates of succession.
    • Plant-plant interactions affecting plant establishment and persistence on revegetated rangeland

      Pyke, D. A.; Archer, S. (Society for Range Management, 1991-11-01)
      Restoration and revegetation of rangeland ecosystems is based on knowledge of abiotic and biotic interactions that affect plant establishment. Once plants become autotrophic, interactions within and between plant species may occur and then interactions may range from antagonistic to mutualistic. This full range of potential interactions needs to be considered to ensure successful revegetation. At the intraspecific level, we propose the development and use of density-yield diagrams for rangeland species. These diagrams would be based on the self-thinning principle, that aboveground biomass is related to plant density and to the dynamic process of density-dependent mortality. The proposed approach would be used to determine optimum seeding rates, and to predict future biomass of revegetated rangeland. At the interspecific level, competitive relationships of species used to reseed rangelands need to be identified to enhance the probability that species will coexist and thereby facilitate greater species diversity on the site. A diversity of species and growth forms may provide a more stable cover and productivity than a monoculture on sites characterized by environmental variability while potentially enhancing nutrient status for the site.