Land Bird Conservation Plan Colorado  

Executive Summary
Overview of Colorado
Physiographic Region 36
Physiographic Region 62

  • Alpine Tundra
  • Aspen
  • Cliff/Rock
  • High Elevation Riparian
  • Lowland Riparian
  • Mixed Conifer
  • Mountain Shrubland
  • Ponderosa Pine
  • Sagebrush Shrubland
  • Spruce-Fir
  • Wetlands


  • Physiographic Region 87
    Implementation Strategies
    Literature Cited
    Appendices

    Physiographic Region 62: Southern Rocky Mountains

    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 a slow recovery rate (sagebrush 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 mostly contiguous habitat, where openings were comparatively small. Consequently, some sagebrush-obligate bird species exhibit area sensitivity, i.e., they will not occupy otherwise suitable habitat patches unless the patches exceed some minimum size, which is often much larger than their home range. Much of this contiguous habitat has been fragmented by removing sagebrush shrubs, leaving small stands separated by large openings. Such fragmentation by anthropogenic causes is a recent phenomenon in terms of evolutionary history. In some other habitat types, higher rates of predation and nest parasitism have been documented in fragmented habitat than in more contiguous habitat, although this has not been studied extensively in sagebrush.

    The primary use of sagebrush shrublands by humans has been for livestock grazing. Historically, large expanses of sagebrush have been 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 has been removed, heavy grazing sometimes has led to the elimination of native perennial grasses, which have been replaced by exotic annual grasses, especially cheatgrass. In some cases, the herbaceous cover has been lost entirely and replaced by shrubs. This replacement in turn has prompted land managers to remove the shrub cover by plowing, burning, chaining, or herbicide treatment and then reseed the land for forage, often with exotic grass species.

    Sagebrush shrublands that are converted entirely to another cover type have limited potential to revert to sagebrush. Factors such as increased frequency of fire, excessive distance to seed sources, loss of symbiotic mycorrhizal fungi, and competitive exclusion by other plants combine to maintain the new cover type.

    Perhaps 30% of Colorado's sagebrush received some treatment between 1900 and 1974 (Braun et al. 1976), and the ecological integrity of sagebrush shrublands has been widely compromised by the invasion of 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: Three species are identified as high priority in sagebrush shrubland habitats in Physiographic Area 62: Northern Sage Grouse, Brewer's Sparrow, and Sage Sparrow.


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