Vegetation Classification and Mapping Project Report - USGS

Vegetation Classification and Distribution Mapping Report: Petrified Forest National Park
NatureServe conservation status:
Global rank. G3Q (9-Apr-1998). The number of occurrences is unknown. The community
is reported from Arizona, Colorado (S3), Kansas, New Mexico (S2), Texas, Utah, and Mexico
and may occur in California. The community is found on slight to moderately saline, nearly
level bottomland and terraces with alluvial silty clay soils.
Distribution:
Globally. This alkali sacaton mesic grassland community is found in the southwestern Great
Plains, Colorado Plateau, and elsewhere in the southwestern United States and Mexico, ranging
from Kansas and Colorado south to Texas, New Mexico and west to Arizona, Utah, and
possibly California.
Petrified Forest National Park. Sporobolus airoides Southern Plains Herbaceous Vegetation
was identified from two relevés within Petrified Forest National Park. They were located
in a drainage channel and on a sand dune/sandsheet. These two relevés were sampled east
of Lithodendron Wash and west of Lacey Point and east of Newspaper Rock and east of the
main park road.
Environmental summary:
Globally. This grassland community occurs on alluvial toeslopes and flats, terraces, floodplain
depressions, and sandy streambanks and washes in bottomlands throughout the southern
Great Plains and Colorado Plateau. Additional moisture from washes and sheetflow runoff
are important for most stands. Elevations range from below 1000 m (3050 ft) to over 2000 m
(6100 ft). Sites are typically flat to gently sloping but may be as steep as 30% slope. Soils are
shallow to moderately deep, moderately well- to poorly drained, alkaline, and often saline with
sandy, silty or clay soils (Francis 1986, Johnston 1987, Kittel et al. 1999a, Lauver et al. 1999,
Von Loh et al. 2002). Other parent materials include lavaflow, cinders, relict Pleistocene river
cobbles, and sandstone.
Petrified Forest National Park. This association was sampled at 1640 and 1650 m (5360-5400
ft) elevation. Both stands had no slope.
USFWS wetland system: Not applicable.
Vegetation description:
Globally. This association is characterized by a sparse to moderately dense (15-75% cover),
medium-tall graminoid layer dominated by Sporobolus airoides. Associated species include
Achnatherum hymenoides, Symphyotrichum subulatum (= Aster subulatus), Buchloe dactyloides,
Distichlis spicata, Hordeum jubatum, Bouteloua gracilis, Panicum obtusum, Pleuraphis jamesii,
Sphaeralcea spp., Sporobolus cryptandrus, and Pascopyrum smithii (Francis 1986, Johnston
1987, Kittel et al. 1999a, Lauver et al. 1999, Von Loh et al. 2002). Scattered shrubs may be
present, such as Atriplex canescens, Atriplex confertifolia, Ephedra spp., Ericameria nauseosa,
Gutierrezia sarothrae, or Sarcobatus vermiculatus. Total shrub cover is low (