• Biodiversity of rangelands

      West, N. E. (Society for Range Management, 1993-01-01)
      Biodiversity is a multifaceted phenomenon involving the variety of organisms present, the genetic differences among them, and the communities, ecosystems, and landscape patterns in which they occur. Society will increasingly value biodiversity and influence the passage of laws and writing of regulations involving biodiversity which rangeland managers will have to abide by over the coming decades. Even private and developing world rangelands will be affected. While taxonomic knowledge of vertebrates and vascular plants and their abundance, rarity, and distribution, in the developed nations is generally adequate, the same cannot be said of the developing world. Furthermore, adequate knowledge of invertebrates, nonvascular plants, and microbes is deficient everywhere. Although the basis of variation at all higher levels, genetic variation within rangeland species, even the major ones, has barely been assessed. Obtaining statistically adequate data on populations of rare species that are small and secretive is well nigh impossible. We have many means of measuring community diversity, but all of them are value laden. That is, choice of variables to measure and how they are indexed betrays what we consider are important. We should be more forthright in stating to the users the biases of these methods. There are many other, more useful ways to describe community-level diversity besides the traditional focus on species. Ungulate grazing is an important process in many ecosystems. Thus, removal of grazing destabilizes some systems. Livestock grazing will actually increase the chances of survival of some species. Moderate livestock grazing can also enhance community and landscape-level diversity in many instances. Attention is now shifting from "charismatic" species to defensively managing larger tracts of land with habitat or ecosystems holding suites of sensitive species. Since some accelerated extinction of isolated populations and species is inevitable, we need to know which species and ecotypes are most valuable. Understanding of modular, guild, and functional group structure would also help us identify keystone or critical link species and better focus our attention on truly important tracts of land where they live. It is probably more important to sustain soils and ecosystem processes than any randomly selected species, especially if functionally redundant species can be identified. Similarly, not all introduced, alien, or exotic species are equal threats; it depends on how they fit into ecosystems. Sustainable development will depend on finding balance between use and protection, from range sites 10 landscapes, and even on a global basis.
    • Dynamics of vegetation along and adjacent to an ephemeral channel

      Smith, M. A.; Dodd, J. L.; Skinner, Q. D.; Rodgers, J. D. (Society for Range Management, 1993-01-01)
      Ephemeral channels may be greater contributors to nonpoint sediment loads than perennial channels because of their abundance and lower vegetative cover. This study examines above- and belowground standing crop responses of selected vegetation classes and density of shrubs to grazing use and yearly weather variation along an ephemeral stream in northcentral Wyoming. Aboveground biomass standing crop was determined yearly in channel, floodplain, and upland habitats in ungrazed and grazed pastures during the 4-year study. Belowground biomass and shrub densities were determined yearly in the channel habitat only. Perennial grass standing crop in channels did not respond to grazing but decreased up to 73% with decreases in frequency and amount of precipitation. In floodplains, perennial grasses were not responsive to grazing; annual grasses were twice as abundant in grazed pastures. Vegetation standing crop in uplands was not influenced by grazing. Over the study period in all pastures, standing crop of blue grama (Bouteloua gracilis (H.B.K.) Lag. ex Griffiths) declined 4 fold while cool-season grasses increased 5 fold. Shrub density did not increase as much in grazed as in ungrazed pastures. Root biomass of the channel decreased 23% in years with less precipitation but was greater by 24% on concave than convex bank types. Location on channels influenced root biomass but grazing did not. Lack of general negative grazing influences on vegetation suggest short periods (10 days) of grazing as used in this study represent a sustainable management alternative for grazing in the cold desert.