• Vegetal recovery following wildfire in seeded and unseeded sagebrush steppe

      Ratzlaff, T. D.; Anderson, J. E. (Society for Range Management, 1995-09-01)
      Following an August wildfire, sagebrush (Artemisia L.)/grass benchlands adjacent to Pocatello, Ida., were seeded with a mixture of exotic wheatgrasses and forbs by rangeland drill in November 1987. The effects of seeding on vegetation development in the immediate postfire years were evaluated by comparing plant density, vegetal cover, species composition, species diversity, and standing crop in seeded areas to that in unseeded control plots in 1988 and 1989. We also examined cover of bare ground, litter, and growth form between treatments and between sampling periods. Twenty paired 10-m transects were established in seeded and unseeded areas on each of 3 plots on the burned benches. Plant density, vegetal cover, and species diversity were lower in the seeded areas than in the unseeded areas in 1988 and 1989. Species composition, species richness, and standing crop were similar between treatments. Establishment of seeded species was poor, probably as a result of drought conditions in 1987 and 1988. Most plants observed in seeded and unseeded areas in the spring of 1988 sprouted from established perennials. Even though the first postfire season was a drought year, plant cover in the unseeded areas (18.3%) approached that estimated by a U.S. interagency task force as needed to stabilize soils on that site. In the following year, which had average precipitation, plant cover in both treatments exceeded the task force's estimate of prefire cover. Because the indigenous plant species recovered rapidly, seeding of this burn was unnecessary to establish plant cover and counterproductive in terms of erosion potential. These results serve to emphasize that objective criteria should be established for evaluating the necessity of postfire seeding.
    • Viewpoint: The state and transition model applied to the herbaceous layer of Argentina's calden forest

      Llorens, E. M. (Society for Range Management, 1995-09-01)
      The ecological trends in the vegetation of the caldén (Prosopis caldenia Burk.) forest of central Argentina have generally been explained with a model that assumed a unique equilibrium state or "climax." This model does not adequately explain the ecological changes that occur in the understory of the caldén forest. Recently, models that present different stable states of vegetation have been suggested. These vegetation states do not change unless relatively drastic management or climatic actions occur. Observations of vegetation changes, grazing regimes, and other aspects of management permitted the development of a basic scheme to explain changes in the herbaceous layer in the caldén forest, based on the state and transition model. Five stable states and 9 transitions are proposed to account for current herbaceous associations and their origins. This model seems to more accurately explain transitions between the different vegetation states in the area, some of which could not be readily explained by the "climax" model.