Vegetation Classification and Mapping Project Report - USGS

Appendix C: Global and local plant community descriptions
Distribution:
Globally. This riparian shrubland association is common along waterways of all sizes at lower
to middle elevations in the Great Basin, Colorado Plateau and Rocky Mountains extending
out into the western Great Plains along major rivers.
Petrified Forest National Park. Salix exigua / Barren Shrubland occurred at two relevés
within Petrified Forest National Park on bajada, playa, and talus landforms. Both these relevés
were sampled from the same area in the central neck area of the park. The relevés were located
south of the railroad tracks on the northern edge of the Puerco River, east of the park road,
and along the corridor of Dead Wash.
Environmental summary:
Globally. This riparian shrubland is common in the Rocky Mountains, Colorado Plateau,
and Great Basin. Elevation ranges from 780-2600 m. This association occurs within the annual
flood zone of rivers on point bars, islands, sand or cobble bars, and on streambanks occurring
along a wide variety of stream reaches, from moderately sinuous and moderate-gradient
reaches. It can form large, wide stands on mid-channel islands in larger rivers or narrow
stringer bands on small, rocky tributaries. Substrates are typically coarse alluvial deposits of
sand, silt and, cobbles that are highly vertically stratified from flooding scour and deposition,
often consisting of alternating layers of finer textured soil with organic material over coarser
alluvium. Occasionally, this association occurs on deep pockets of sand. The lack of soil development
and high ground cover of coarse alluvial material are key indicators for this association.
Petrified Forest National Park. This association occurred at 1630 and 1640 m (5330-5370 ft)
elevation. Slope was none to slight (0-1%).
USFWS wetland system: Palustrine.
Vegetation description:
Globally. This riparian association is characterized by a sparse to dense, tall-shrub (1.5-3
m) canopy composed of Salix exigua, with ground cover of exposed gravel, cobbles, or sand.
Salix exigua may be the only shrub in the community, or other shrubs and trees may be present
with relatively low cover, including Alnus incana, Ericameria nauseosa, Rhus trilobata, Salix
monticola, Salix ligulifolia (= Salix eriocephala var. ligulifolia), Salix irrorata, Salix lucida, Abies
lasiocarpa, Acer negundo, Populus angustifolia, Populus deltoides, Populus fremontii, and Salix
gooddingii. A sparse herbaceous layer may be present among the bare soil, gravel, cobbles, or
boulders, consisting of a wide variety of forbs and graminoids. Mentha arvensis and species of
Carex, Eleocharis, Juncus, Schoenoplectus, and Equisetum are often present. Introduced species,
such as Elaeagnus angustifolia, Tamarix spp., Bromus tectorum, Bromus inermis, Elymus
repens (= Elytrigia repens), Poa pratensis, Agrostis stolonifera (and other exotic forage species),
Taraxacum offcinale, Conyza canadensis, and Lepidium latifolium have been reported from
some stands.
Petrified Forest National Park. Two relevés were classified as Salix exigua / Barren Shrubland,
with total vegetation cover of 25 and 32%. This vegetation cover consisted of low tree
cover (0.5%) in one relevé and none in the other, a dominant shrub cover with 20 and 30%
cover, and a low herbaceous cover of 2 and 5% within the herbaceous stratum. The species
diversity for the association was 20 and 24 species. The vegetation in the shrub layer was dominated
by Salix exigua, which had 18 and 22% cover. Ericameria nauseosa had some cover in
both relevés with 3 and 4% cover.
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