Vegetation Classification and Mapping Project Report - USGS

2 Identification and Classification of Plant Communities
2.1 Methods
The classification team, consisting of
ecologists M.L. McTeague and A. Cully,
identified and classified plant communities
of Petrified Forest National Park (PEFO)
to the finest floristic level possible. They
used three approaches:
1. reanalysis of relevé data collected in
1996
2. new field data collection, analysis, and
quantitative classification
3. direct field observation during photointerpretation
for one-plant communities
(see section 3 Base Map Class
Development)
All plant communities, whether identified
through quantitative classification or
direct observation, were reconciled with
the current NatureServe Explorer registry
of NVC alliances and associations, and
reviewed for compatibility by K. Schulz of
NatureServe. New plant assemblages were
classified as park specials if they were not
supported by suffcient observation data
to be identified to an existing alliance or
association or to be identified as a new, or
provisional, plant community.
to the results of the quantitative analysis
of newly collected data and were
provisionally assigned plant communities
at the same time (see “Quantitative data
analysis” below).
2.1.1.2 Newly Collected Data
In 2003, a field team led by M. McTeague
collected plant-community data in the
form of cover/abundance values for
individual plant species in 149 relevé
plots (Mueller-Dombois and Ellenburg
2002) (see sample datasheet in the project
DVD). The sampling design stratified the
park landscape into unique biophysical
types for relevé allocation. This approach
assumed that environmental variables
drive vegetation patterns at PEFO and that
a stratification based on environmental
variables would assure adequate sampling
across the range of plant-community
variability. The biophysical types were
derived by layering spatial data for aspect,
elevation, watercourse presence, and
geology in a GIS environment (table 3)
and identifying each unique combination
as one type. The number of polygons
targeted for sampling within each
biophysical type was proportional to the
Table 3. Categories of environmental variables used to identify
2.1.1 Relevé Data unique biophysical units to sample at Petrified Forest National Park.
2.1.1.1 Existing Data
The team used relevés 2 from a 1996
vegetation sampling directed by Dr.
Kathryn Thomas (Thomas et al. 2003).
These relevés were collected throughout
the park in an effort to classify the
vegetation at PEFO. Previously, they had
been quantitatively analyzed and assigned
alliance-level classification. As the plant
communities were not expected to change
significantly in that time, the team was able
to use 186 relevés from the 1996 effort.
These data were compared qualitatively
2
A relevé is a vegetation sample using a quadrant that
can be square, rectangular, or circular. Size varies according
to the type of vegetation being sampled. Relevés are
usually placed non-randomly in a uniform and representative
sample of the vegetation being sampled. They are
distinguished from line-transects and completely random
sampling (Kent an Coker 1992).
Environmental variables
Categories
Aspect North facing (116-269°)
South facing (270-115°)
Elevation (Using 10 m DEM)
High elevation(1756-1890m)
Low elevation (1620-1755m)
Stream (Including 5m Buffer)
Streams
No Streams
Geology Map (Apache and Navajo
County)
Qal=alluvial/alluvium deposits
Qc=alluvium and sand sheets
Qd=eolian deposits
Ql=colluvial deposits
TR=Triassic
Tb=volcanic
bft=Black Forest Tuff
ss=sandstone
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