Details - CALS Networking Lab - University of Arizona

species was encountered along the entire length
of the transect divided by effort (in most cases a
maximum of 300 intercepts per height category)
and multiplied by 100. We calculated percent
composition of each species in each height
category as the number of times a species was
encountered divided by the number of times all
other species were encountered. If there was at
least a single species encountered along a transect
(in each height category), the total percent
composition equaled 100 percent.
Community Types
We sought to identify plant communities within
the district and to compare characteristics among
them. We did not use the original stratification
of random transects for this analysis because we
were more interested in classifying communities
than drawing inference to a larger area. To group
transects, we used Ward’s hierarchical cluster
analysis using data from point-intercept transects.
Cluster analysis is a multivariate technique that
groups like entities (in our case transects) that
share similar values. We used the total number
of point intercepts by the most common plant
species in all four height categories for this
analysis. A detailed summary of point-intercept
data will be available along with other archived
materials (see Chapter 1).
Results
We collected 741 specimens representing 523
species from the Rincon Mountain District
of Saguaro National Park (Appendix A). We
found 39 species that had not previously been
documented in the district, almost one-half of
them (n = 19) during the course of surveying
at point-intercept and/or modified-Whittaker
plots. The list of new species that we found
included five non-native species, most notably
African sumac (Rhus lancea). Native species of
note that we added to the flora included cleftleaf
wildheliotrope (Phacelia crenulata), Arizona
dewberry (Rubus arizonensis), and American
black nightshade (Solanum americanum).
Based on a thorough review of past
studies, floras, and collections located at the
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University of Arizona, there have been a total of
1,170 specific and intraspecific taxa documented
at the district, of which 78 (6.7%) are non native.
Excluding eight species in the UA collection that
Bowers and McLaughlin (1987) cite as likely
extirpated from the district, there have been
1,120 species (1,162 including intraspecific taxa)
documented since the early 1980s (Appendix
A). Of these species, six were thought to be
extirpated by Bowers and McLaughlin (1987) but
were found by other studies: purple scalystem
(Elytraria imbicata), Lemmon’s hawkweed
(Hieracium lemmonii), alderleaf mountain
mahogany (Cercocarpus montanus), Baltic rush
(Juncus balticus), poverty rush (J. tenius), and
common barley (Hordeum vulgare) (Appendix
A).
Community Types
Based on our interpretation of the cluster analysis
using data from point-intercept transects, there
are four communities (i.e., clusters) represented:
• Sonoran Desertscrub. Five lowelevation
transects (112, 115, 130, 138,
and 139) and one middle elevation
transect (121). Mixed cacti and
paloverde (Parkinsonia spp.), with some
velvet mesquite (Prosopis velutina),
especially in the dry washes.
• Oak Savannah. Four middle-elevation
transects (101, 106, 189, and 111). Open
areas dominated by perennial grasses
with scattered trees, mostly oaks.
• Pine-oak Woodland. Two middle
(125 and 120) and three high (107,
155, and 128) elevation transects.
Most transects had dense stands of
manzanita (Arctostaphylos spp.) and
oaks, interspersed with some pine trees,
mostly pinon and ponderosa pine (Pinus
ponderosa).
• Conifer Forest. Two high elevation
random transects (113 and 191). Tall
forests of ponderosa pine, Douglas fir
(Pseudotsuga menziesii), and some
oaks, especially Gambel oak (Quercus
gambelii).