Re-Establishing Perennial Vegetation in Cheatgrass Monocultures

Abstract

Humans have had a significant impact on shrublands of the western United States. The introduction of large numbers of livestock into native plant communities that had evolved without grazing pressure has greatly altered vegetation composition. Overgrazing resulted in the loss of perennial grasses and facilitated the widespread invasion by annual species such as cheatgrass (Bromus tectorum). With a herbaceous understory dominated by the short-lived, highly flammable cheatgrass, shrublands became prone to frequent wildfires. Cheatgrass persists under this fire regime because it germinates, grows, flowers, and sets seed before environmental conditions become conducive to wildfires. However, frequent wildfires greatly hinder natural regeneration of long-lived shrubs and complicate efforts to repair the structure and function of western shrublands. Although this scenario of shrubland conversion to annual grasses has been the focus of scientific research efforts for many decades, few land-management options exist that are capable of re-establishing perennial vegetation in fire-prone regions of the Great Basin and Intermountain West. Establishment of perennial vegetation in cheatgrass-dominated landscapes is difficult because the rapid growth rate of cheatgrass, especially under cool temperature, makes it extremely competitive for limited soil water and nutrients compared to slower growing perennial species. Even if management efforts successfully revegetate small areas, persistent seedbanks of cheatgrass and a high probability of wildfire undermine the persistence of perennial species. Consequently, to break cheatgrass dominance, wildfire frequency must first be reduced before persistent, perennial vegetation will successfully establish and begin the process of stabilizing landscapes. Planting fuel-breaks or 'greenstrips' of less flammable perennial vegetation (e.g., Monsen 1994) in strategic locations may provide a feasible option to reduce wildfire frequency (Pellant 1994). Greenstrips are an attractive option because a relatively small area is managed to protect a much larger area. Greenstrips will be most successful if the perennial vegetation can rapidly establish in cheatgrass-dominated areas, tolerate occasional wildfires, and be capable of reducing fine-fuel loads so that additional perennial vegetation can be incorporated back into the landscape.