Vegetation Classification and Mapping Project Report - USGS

Appendix C: Global and local plant community descriptions
NatureServe conservation status:
Global rank. G3 (14-Nov-2005). G2G4 (15-Oct-1999). Historically, most sites supporting this
association have been converted to dryland or to irrigated cropland in the plains. Overgrazing
by livestock has changed some of these grasslands to sparse desert grasslands or desert
scrubland. In addition, the reduction of fire frequency, either by livestock grazing the fine
fuels that carry fires or by active suppression, has allowed the invasion of trees and shrubs.
Loss to urban development has been significant in recent decades. Urban development and
transformation to pinyon/juniper woodlands or desert grassland/scrubland are continuing the
negative trend. More classification and survey work are needed to distinguish this type from
closely related grasslands over its relatively broad geographic range and to inventory its extent
and condition.
Distribution:
Globally. These grasslands are found in the southern shortgrass steppe of southeastern Colorado
and eastern New Mexico, and alluvial flats and mesas of the Colorado Plateau in New
Mexico and Utah, south to Sevilleta National Wildlife Refuge in central New Mexico.
Petrified Forest National Park. Bouteloua gracilis - Pleuraphis jamesii Herbaceous Vegetation
was identified from three relevés within Petrified Forest National Park. Sites occurred on
a plateau and on sand dunes/sandsheets in the central neck section of the park, south of Blue
Mesa along the main park road and Dry Wash, and northwest of Jim Camp Wash and the Giant
Logs.
Environmental summary:
Globally. These grasslands occur on alluvial flats, mesas, and plains in the semi-arid southwestern
Great Plains and the Colorado Plateau in southeastern Colorado, New Mexico,
northern Arizona and southern Utah. Elevation ranges from 1625-1890 m (5330-5654 ft) on
the Colorado Plateau and extends below 1525 m (5000 ft) in the southwestern Great Plains.
Sites are flat to undulating, with shallow to moderately deep, loam to silty clay loam-textured
soil.
Petrified Forest National Park. The association occurred between the elevations of 1664 and
1725 m (5459-5654 ft), with zero to moderate slope (0-16%, average 6%). Only one stand had
any surface rocks, including desert pavement and petrified wood.
USFWS wetland system: Not applicable.
Vegetation description:
Globally. This association is characterized by an open to moderately dense (20-80% cover)
herbaceous layer that is codominated by the graminoids Bouteloua gracilis and Pleuraphis
jamesii (= Hilaria jamesii). These short and medium-tall perennial bunch grasses may form
a sod-like ground cover with patches of bare ground, especially where grazing by livestock
encourages a prostrate growth form. Other grasses include Buchloe dactyloides, Muhlenbergia
torreyi, Sporobolus cryptandrus, Aristida spp., Achnatherum hymenoides (= Oryzopsis hymenoides),
Pascopyrum smithii, Hesperostipa comata (= Stipa comata), or Hesperostipa neomexicana
(= Stipa neomexicana). Forb cover is generally sparse but may be diverse. Characteristic species
include Sphaeralcea coccinea, Grindelia squarrosa, Cryptantha spp., Machaeranthera pinnatifida,
Ratibida spp., and Zinnia grandiflora. Scattered dwarf-shrubs, shrubs, and cacti, such
as Gutierrezia sarothrae, Artemisia bigelovii, Artemisia frigida, Krascheninnikovia lanata, Prosopis
glandulosa (southern stands), Yucca glauca, Opuntia imbricata, and Opuntia polyacantha,
are not uncommon. Codominance of Bouteloua gracilis and Pleuraphis jamesii distinguishes
this vegetation from several closely related grasslands.
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