Vegetation Classification and Mapping Project Report - USGS

Appendix C: Global and local plant community descriptions
NatureServe conservation status:
Distribution:
Global rank. GNR (26-Jul-2001).
Globally. This association is described from Utah and northern Arizona, but is likely more
widespread throughout the semi-arid western U.S.
Petrified Forest National Park. Gutierrezia sarothrae - (Opuntia spp.) / Pleuraphis jamesii
Dwarf-shrubland was identified from two relevés in Petrified Forest National Park. One relevé
was sampled on a sand dune/sandsheet and the other on a midslope with talus. One of the
relevés was sampled south of Interstate 40 and south of the northern headquarters offce and
the other was sampled in the southwestern corner of the northern wilderness area, west of
Wildhorse Wash.
Environmental summary:
Globally. This association is described from Utah and northern Arizona where it occurs on
level to gently sloping hillslopes, plateaus, and bluffs. Elevations range from 1350 to 2000 m.
Aspects are reported from the southeast, south, and southwest. Soils are variable, but tend to
be fine-textured and may occur over gravel and cobbles. Disturbance may be important in
maintaining this vegetation community as some stands may have been created by chaining of
trees and improper grazing by livestock.
Petrified Forest National Park. This association occurred at elevations of 1700 and 1720 m
(5650 and 5590 ft). The slopes of these relevés were moderate at 3 and 13%.
USFWS wetland system: Not applicable.
Vegetation description:
Globally. This broadly defined association is characterized by an open dwarf-shrub canopy
(10-30% cover) dominated by Gutierrezia sarothrae, frequently with Opuntia spp. and an herbaceous
layer with Pleuraphis jamesii present to abundant (0-30% cover). Some stands have
a diverse woody layer that includes low cover of Artemisia nova, Atriplex canescens, Atriplex
confertifolia, Chrysothamnus viscidiflorus, Coleogyne ramosissima, Ephedra spp., Eriogonum
spp., Grayia spinosa, Lycium pallidum, Purshia tridentata, or occasional Pinus edulis or Juniperus
osteosperma trees. The herbaceous layer is typically dominated by graminoids with several
species present including Pleuraphis jamesii, Achnatherum hymenoides, Aristida purpurea,
Bouteloua gracilis, Elymus elymoides, Hesperostipa comata, or Pascopyrum smithii. There is usually
only sparse cover of native forbs like Chamaesyce spp. or Sphaeralcea coccinea; however,
introduced species such as Bromus tectorum, Erodium cicutarium, Sisymbrium altissimum, or
Salsola kali may dominate the herbaceous layer of some disturbed stands.
Petrified Forest National Park. Two relevés were classified Gutierrezia sarothrae - (Opuntia
spp.) / Pleuraphis jamesii Dwarf-shrubland with total vegetation cover of 16 and 28%. The
vegetation cover consisted of the shrub stratum with 11 and 16% cover and the herbaceous
stratum with 5 and 12% cover. Species diversity was 26 and 34 species. The vegetation in the
shrub layer was dominated by Gutierrezia sarothrae with 3 and 14% cover. The Opuntia sp.
shrubs covered just 0.5% in both relevés. Pleuraphis jamesii was a significant species in the
herbaceous layer with 3% cover in both relevés.
Most abundant species:
Stratum Global species PEFO species
Short.shrub/ Gutierrezia sarothrae Gutierrezia sarothrae
sapling
Herb.(field) Pleuraphis jamesii Pleuraphis jamesii
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