Vegetation Classification and Mapping Project Report - USGS

Vegetation Classification and Distribution Mapping Report: Petrified Forest National Park
and Grace 2002) to test if the allocated
NVC associations were different enough
between each other to be statistically
significant. MRPP is a nonparametric
test of the hypothesis that there is no
difference between groups and provides a
test statistic and a p-value.
2.1.2 Photo-Interpreter
Observations
One plant community, Sarcobatus
vermiculatus / Atriplex obovata Shrubland,
was identified from fieldwork associated
with photointerpretation. It was described
without quantitative analysis.
2.1.3 NVC Nomenclature
NatureServe reviewed the first iteration of
plant community names and reconciled
them with the NVC alliances and
associations in their Biotics (http://
www.natureserve.org/prodServices/
biotics.jsp) database. The SBSC and
NatureServe teams consulted on the NVC
nomenclature for each plant community
before the naming was finalized.
2.2 Results
The team used the results of the
reinterpretation of the 1996 classification
relevés, quantitative classification of 2003
relevés, and the one photointerpretation
observation to identify 39 plant
communities at PEFO (table 5). Appendix
B lists the strength of documentation for
all plant communities. Full descriptions
of these communities can be found in
Appendix C. Ancillary products related
to accuracy assessment include all species
on the classification relevés (as well as the
species found on accuracy assessment
sites) and are listed in Appendix D.
2.2.1 Plant Community
Characteristics
Thirty-two of the plant communities at
PEFO were associations. All but these
three had been described previously in
the NatureServe database and/or at other
locations: Calamovilfa gigantea Desert
Wash Shrub Herbaceous Vegetation,
Eriogonum leptophyllum Sparse Vegetation,
and Purshia stansburiana – Eriogonum
corymbosum Shrubland. Achnatherum
hymenoides Shrub Herbaceous Alliance,
observed and classified in 1996, was not
observed again in 2003. Since the 1996
data were insuffcient to classify it to the
association level, it was eliminated from
the current listing of plant communities
for the park. Persistent drought, especially
in the sampling year 2003, caused many
perennial grasses to remain dormant or
to die. As a result, these grasses were not
as abundant as they were during the 1996
sampling.
Seven plant communities were identified
as park specials (table 5). These plant
communities appear to be unique to the
park. Their uniqueness does not imply
rarity, but rather that they are assemblages
of plant species for which not enough data
exists to develop new NVC types.
The plant communities identified
represented four major physiognomic
types: woodland, shrubland, herbaceous,
and sparse. There were three woodland
associations within three alliances. These
three associations were reassigned to
the shrub grouping of relevés used in
quantitative classification, based on the
NatureServe description of the plant
community. Shrublands were represented
by 14 associations within 12 alliances, one
undifferentiated alliance, and four park
specials.
Relevés grouped as steppe in quantitative
classification were reassigned to
either shrubland or herbaceous based
on NatureServe description of the
plant community. Herbaceous plant
communities were represented by ten
associations within eight alliances and
by three park specials. Lastly, sparse
vegetation at the park was represented by
four associations within three alliances.
Some of the woodland, shrubland, and
herbaceous associations at PEFO were
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