Vegetation Classification and Mapping Project Report - USGS

Vegetation Classification and Distribution Mapping Report: Petrified Forest National Park
Distribution:
Globally. This association is known from Arches National Park but likely is widespread in the
canyonlands of the Colorado Plateau in eastern Utah.
Petrified Forest National Park. Rhus trilobata - Ephedra (viridis, torreyana) Talus Shrubland
was identified at three relevés on talus slopes within Petrified Forest National Park. The relevés
were located on talus slopes. This association was recorded from two main locations: one location
south of Blue Mesa near the Blue Mesa Road and the other north of Jasper Forest in the
southwestern corner of the park.
Environmental summary:
Globally. This Colorado Plateau mixed shrub assemblage occurs on steep, rocky colluvial
slopes and bedrock canyon rims associated with mesas, canyons, benches, ravines, hills,
hogbacks, escarpments, and valley sides. Slopes are typically moderate and range from level
to steep (0-70%), occur between 1238 and 1700 m (4000-5580 ft) elevation, and tend to occur
on southerly to westerly aspects (less often east-facing slopes). Soils are shallow and range
from rapidly drained clay loams to sandy loams. Parent materials include shales (Moenkopi
and Chinle) and sandstones (Cedar Mountain, Navajo, and Wingate). Most of the unvegetated
surface is covered by gravel, talus, bedrock and large rocks, and occasionally petrified wood.
There is little dead wood, biological soil crust, or litter. It tends to be slightly more mesic than
most other talus type vegetation.
Petrified Forest National Park. Elevation ranged from 1680 to 1700 m (5500-5580 ft). All of
the relevés were sampled on steep slopes that varied between 45 and 50% (average 47%), with
variable aspects ranging from an easterly to a southwestern direction. The talus in all of the
relevés was composed of sandstone. One relevé also had a low cover of surface rocks consisting
of petrified wood.
USFWS wetland system: Not applicable.
Vegetation description:
Globally. This shrubland association has sparse to low cover of vegetation, not exceeding
25% total cover. It is characterized by a scattered mixture of shrubs, among which Rhus
trilobata var. trilobata and Ephedra torreyana or Ephedra viridis are conspicuous and either
dominant or codominant. As many as ten other species of shrubs may also be present, including
Amelanchier utahensis, Artemisia bigelovii, Atriplex confertifolia, Brickellia microphylla,
Chrysothamnus viscidiflorus, Coleogyne ramosissima, Ericameria nauseosa, Eriogonum corymbosum,
and Philadelphus microphyllus. Fraxinus anomala is absent or has trace cover, and if
Pinus edulis or Juniperus osteosperma are present, cover is less than 1%. The herbaceous layer
may include many species but never provides more than a few percent cover. Achnatherum
hymenoides, Aristida purpurea, Elymus elymoides, Pleuraphis jamesii, Leymus salinus, and
exotic annual grasses Bromus rubens or Bromus tectorum are common grasses. Forb compositions
are variable with frequent species including Artemisia ludoviciana, Chaetopappa ericoides,
Cryptantha crassisepala, Stanleya pinnata, and Plantago patagonica. Biological soil crust
formation is rare on these active slopes.
Petrified Forest National Park. Three relevés were classified as Rhus trilobata - Ephedra (viridis,
torreyana) Talus Shrubland, with total vegetation cover ranging from 8 to 21% (average
15%). This vegetation cover consisted of a shrub layer with 6-12% cover (average 9%) and
an herbaceous layer with 2-9% cover (average 6%). The species diversity ranged from 19 to
31 species (average 26 species). The vegetation was composed of three indicator shrub species:
Rhus trilobata, Ephedra viridis, and Ephedra torreyana. Each of these shrub species may
or may not be present, and their relative proportions to one another varied depending on the
environmental conditions. In these three relevés, Rhus trilobata ranged from 0 to 2% cover
(average 1%), Ephedra viridis ranged from 1 to 4% cover (average 3%), and Ephedra torreyana
ranged from 0 to 0.5% cover (average