Land Bird Conservation Plan Colorado  

Executive Summary
Overview of Colorado
Physiographic Region 36
Physiographic Region 62
Physiographic Region 87

  • Cliff/Rock
  • Lowland Riparian
  • Mountain Shrubland
  • Pinyon-Juniper
  • Ponderosa Pine
  • Sagebrush Shrubland
  • Semidesert Shrubland
  • Wetlands


  • Implementation Strategies
    Literature Cited
    Appendices

    Physiographic Region 87: Colorado Plateau

    Sagebrush Shrubland

    Description and Ecology: In Colorado, sagebrush is found at elevations of approximately 1200 to 3050 m (4,000-10,000 ft). On moist sites it may reach 3 m (10 ft) tall, but more typically it is under 1.5 m (5 ft). It exists in a variety of climatic conditions, including low-elevation semidesert habitats and moist, cool, mountainous areas. Sagebrush species common in Colorado include big sagebrush and mountain sagebrush. Plants found in association with sagebrush shrublands include rabbitbrush, bitterbrush, snowberry, mountain mahogany, pinyon pine, juniper, and aspen. Grasses, especially bunchgrasses, are common components of sagebrush shrublands, including wheatgrass species, Junegrass, Arizona fescue, and Idaho fescue.

    Immense stands of sagebrush, interspersed with small openings of native bunchgrasses, formerly covered hundreds of thousands of hectares in the West (Vale 1975). Little is known about the natural disturbance regimes that shaped this ecosystem, although presettlement sagebrush shrublands probably experienced at least occasional wildfires. Given the slow recovery rate of sagebrush (it will not resprout after fire, but must come back from seed, a process that can take 15-30 years), these wildfires probably sculpted a landscape mosaic of sagebrush stands of varying age interspersed with grassy open areas, on the scale of tens to thousands of hectares.

    Importance and Conservation Status: Sagebrush birds evolved in this mosaic, a generally contiguous habitat with comparatively small openings. Consequently, some sagebrush bird species exhibit area sensitivity, i.e., they will not occupy otherwise suitable habitat patches unless the patches exceed some minimum size, often much larger than the home range. This contiguous habitat has been heavily fragmented by removing sagebrush shrubs, leaving small stands separated by large openings. Such fragmentation by anthropogenic causes is a recent phenomenon in evolutionary history. In other habitat types, researchers have documented higher rates of predation and nest parasitism in fragmented habitat than in more contiguous habitat, but these patterns have not been studied extensively in sagebrush.

    The primary use of sagebrush shrublands by humans has been for livestock grazing. Historically, sagebrush was cleared to increase forage and to allow a higher stocking rate of domestic animals or to support more grazing wildlife. Where little or no sagebrush removal has occurred, heavy grazing sometimes leads to the elimination of native perennial grasses, which are replaced by exotic annual grasses. In some cases, the herbaceous cover is lost entirely and is replaced by shrubs, which prompts land managers to remove the shrub cover through plowing, burning, chaining, or herbicide treatment. The land is then reseeded for forage, often with exotic grass species.

    Sagebrush shrublands that are converted to another cover type have limited potential to revert to sagebrush. Instead, they are usually maintained in those other cover types via increased frequency of fire, distance to seed sources, loss of symbiotic mycorrhizal fungi, and competitive exclusion by other plants.

    Much sagebrush has been removed in the interest of improving forage productivity on grazing lands. Perhaps 30% of Colorado's sagebrush had received some treatment between 1900 and 1974 (Braun et al. 1976). Other factors compromising the ecological integrity of sagebrush shrublands include invasion by exotic (e.g., cheatgrass) or native (e.g., pinyon-juniper) plant species, conversion to agricultural, residential and other developed land types, and changes in natural fire regimes.

    Priority Species Accounts: Four species are identified as high priority in sagebrush shrubland habitats in Physiographic Area 87: Northern Sage Grouse, Gunnison Sage Grouse, Brewer's Sparrow, and Sage Sparrow.


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