December 2012 Number 1 - Utah Native Plant Society

Calochortiana December 2012 Number 1
Quemado; Cuellar: Catarina; Santa Margarita: Maverick,
eroded and Jimenez-Quemado (NRCS 2009). However,
soils maps for these areas lack precision and the
inclusion of P. thamnophila sites within Jimenez-
Quemado soil polygons is incorrect (see Discussion). In
some sites, fossil oyster shells or gypsum crystals were
conspicuous.
METHODS
Vegetation Data Collection
Vegetation data were collected once at Arroyo Ramirez,
Arroyo Morteros, and Santa Margarita and twice at
Cuellar in conjunction with intermittent censuses of the
study sites (Fowler et al. 2011). Cuellar vegetation was
sampled in 2002 and 2007, Arroyo Ramirez in 2003,
Santa Margarita in 2004, and Arroyo Morteros in 2007.
Due to limitations of time and personnel, we set up
study plots at one site each year in 2002-2005. In each
site, permanent circular plots marked with rebar were
located randomly along transects. Some of the Cuellar
census plots did not have vegetation data collected in
one or both years and were dropped from analyses.
At Cuellar, 30 plots were located in an uncleared
area and 30 plots in an area that had been brush-cleared
using a ‘Woodgator©’ (roller-chopper) in December
2000. This decreased shrub canopy (see Results) and
significantly increased herbaceous species richness and
grass abundance in the cleared area (Fowler et al. 2011).
A transect ran along the margin between the two areas,
with the plots on either side. In each of the other three
sites, transects were located to sample the entire Physaria
thamnophila population. The full extent of the
Santa Margarita population was unknown at the beginning
of this study, and the Arroyo Ramirez and Arroyo
Morteros populations were discovered in fall 2002 and
summer 2004, respectively. Therefore, we first conducted
reconnaissance surveys to map the populations’
extents using GPS. The two roughly linear populations
that followed rocky outcrops, Arroyo Ramirez and
Santa Margarita, were each sampled by running a discontinuous
transect (excluding unoccupied habitat)
along the long axis, through the approximate midline of
the population. The transect length was then divided
into 30 strata, with plots located within each stratum at
random distances either side of the transect line. There
were 30 plots at Santa Margarita (Figure 4) and 34 plots
at Arroyo Ramirez. At Arroyo Morteros, where the
population occupied a large, irregular polygon, we
placed 58 plots along ten parallel transects of different
lengths, spaced 38m apart. The initial plot in each transect
was located a random distance between 0.1 m to 10
m along the transect, with successive plots spaced 13.8
m apart.
By 2007, the cleared portion of Cuellar was quite
similar to the other three sites in herbaceous species
richness and grass abundance (Fowler et al. 2011). Arroyo
Morteros had on average somewhat greater herbaceous
species richness than the other sites (12 species
per plot, on average, versus 6 to 10 in the other sites;
Fowler et al. 2011).
Vegetation data from each plot were collected in five
circular subplots. Each subplot was 0.25m in radius.
One of these subplots was centered on the plot’s central
point, and the other four were centered around points
located on the circumference of the circle at the distal
ends of four radial lines emanating from the central
point (two parallel and two perpendicular to the transect).
In each subplot, the presence/absence of each species
was recorded in each of 4 height categories. These
categories were 0.0 to 0.5 m, 0.5 to 1.0 m, 1.0 to 2.0 m,
and 2.0 to 3.0 m above ground. No plants were taller
than 3 m. Species names follow USDA PLANTS database
(2012) with the exception of Physaria and Paysonia,
for which we follow the treatment of Al-Shehbaz
and O’Kane (2002). Most common species, particularly
woody dominants, were identified in the field. We collected
voucher specimens when species were encountered
in flower; specimens are being prepared for deposit
at the University of Texas herbarium (TEX-LL).
It was not always possible to definitively identify
species at the time when they were first observed. As a
result, in a few cases the interim identifications used for
unknown species were not consistent between years.
Therefore, for analysis we pooled (a) the two Chamaesyce
(Euphorbiaceae) species; (b) Chaetopappa bellioides
and Aphanostephus skirrhobasis (Asteraceae);
and (c) Chamaesaracha sordida and Physalis cinerascens
(Solanaceae). This reduced the number of 'species'
in the analyses from 150 to 147. For simplicity, each of
these three pairs of species is referred to simply as a
species. ‘Bare ground’ was recorded as a 148 th ‘species’.
A few plants could never be identified; almost all of
these were without fruits or flowers and many were
grasses. These have been left as unknown species 1,
unknown grass, etc. in Table 1.
The number of subplots in each plot in which the
species occurred was used to quantify the abundance of
each species. The abundance of a given species in a plot
therefore had a value between 0 and 5. For P. thamnophila
only, counts of numbers of individuals in each plot
were also available. However, censuses of P. thamnophila
were conducted in all sites in 2006 and 2007 only.
We calculated the density of P. thamnophila in each
plot by dividing the number of individuals in the plot by
the plot’s area, for each plot separately. P. thamnophila
densities in 2006 and in 2007 were then averaged, for
each census plot separately.
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