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

    Pinyon-Juniper

    Description and Ecology: Pinyon-juniper habitat extends over large areas in Utah, Colorado, Arizona, Nevada, and New Mexico (Tueller et al. 1979, Figure 1; Balda and Masters 1980). The estimates of total area range widely, between 17 and 40 million ha (43-100 million ac) depending on the definition of pinyon-juniper woodland; the high figure includes juniper of western North America outside the range of pinyon pines. In Colorado, there are approximately 2,000,000 ha (5 million ac) of pinyon-juniper habitat (Brown 1994). Seventy percent of Colorado's pinyon-juniper woodland is in Physiographic Area 87, the Colorado Plateau.

    Pinyon-juniper habitat type is a cold-adapted evergreen woodland situated above desert or grassland vegetation and below mountain shrub and pinyon-juniper zones (Pieper 1977); elevations range from 1400 to 2300 m (4,500-7,500 ft; Brown 1994). Colorado pinyon occurs in the eastern two-thirds of the pinyon pine range, and singleleaf pinyon predominates in Nevada. Several species of juniper are dominant or co-dominant, including Rocky Mountain juniper, Utah juniper, one-seed juniper, alligator juniper, California juniper, and redberry juniper. In Colorado, Rocky Mountain juniper grows predominately on the east side of Physiographic Area 62 and in southeast Colorado; farther west it becomes an increasingly rare mesic site species. Eastern red cedar and one-seed juniper enter eastern and southeastern Colorado. Utah juniper grows in the western third of the state.

    Proportions of juniper and pinyon within the habitat vary greatly, and pure stands of either tree may occur. Typically, as elevation increases pinyon dominance increases, juniper density decreases, total tree density increases, and trees become larger (Pieper 1977, LaRue 1994). Pinyon pines drop out completely at the lowest elevations. Depending on site variables, pinyon-juniper may range from an openly spaced savanna to a closed forest. Pinyon-juniper understories vary from completely open to quite dense, the densest understories occurring in open canopy woodland/sagebrush communities and where Gambel oak is encroaching.

    Soils underlying pinyon-juniper often are shallow, rocky and low in fertility (Pieper 1977). The relative resistance to fire of these soil types favors pinyon-juniper growth. Deep soil sites that are burned tend to revert to open "parks," often sagebrush, and resist returning to pinyon-juniper cover.

    Importance and Conservation Status: Pinyon-juniper habitat supports the largest nesting bird species list of any upland vegetation type in the West. Lowland riparian habitats will, across an entire year, harbor more species of birds due to their importance to migrants. A single ponderosa pine stand typically supports more species than a single pinyon-juniper stand. Aspen stands may hold a higher density of birds. However, the richness of the pinyon-juniper vegetation type is collected across its broad range and due to its middle elevation (Balda and Masters 1980). Survey tallies in pinyon-juniper are similar in species diversity to the best riparian and other types.

    Human activities have affected the distribution of pinyon-juniper habitat. Wide-scale programs designed to convert pinyon-juniper woodlands to grasslands for grazing began in earnest after World War II. By the mid 1960s about three million acres had been razed throughout the West (Terrell and Spillett 1975). Seeding with grass to improve forage has met with mixed results, and large conversion projects have proven to be minimally useful to native wildlife (Swenson 1977). In spite of these conversions, human activity has generally increased pinyon-juniper coverage. Fire suppression in grasslands adjacent to pinyon-juniper woodland has allowed the woodlands to advance by out-competing grasses (Little 1977).

    Today human activities in pinyon-juniper woodlands are diverse and increasing. Big game hunting and firewood, fence post, and pine nut harvesting are currently stabilized; however, recreational pursuits are burgeoning. Many of these pursuits include all-terrain vehicles which can rapidly turn paths and trails into roads. Oil and gas development has also increased the quantity and quality of roads in the pinyon-juniper zone. The esteem of land managers and users for the pinyon-juniper vegetation type is generally low. The low benefit/cost ratio of conversion projects has served to protect much of what exists today.

    Priority Species Accounts: Eight species are identified as high priority in pinyon-juniper habitats in Physiographic Area 87: Black-chinned Hummingbird, Gray Flycatcher, Cassin's Kingbird, Gray Vireo, Pinyon Jay, Juniper Titmouse, Black-throated Gray Warbler, and Scott's Oriole.


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