Vascular Plant and Vertebrate Inventory of Saguaro ... - USGS

General Botanizing
Methods
We collected species opportunistically and when
we thought we had found a species not on the
district list (derived principally from Bowers
and McLaughlin [1987]). We also searched
specifically for species that were listed as
possibly extirpated from the district (in Bowers
and McLaughlin 1987). Whenever possible we
collected at least one representative specimen
with reproductive structures for each plant
species that we encountered. We also maintained
a list of species observed but not collected.
When we collected a specimen, we assigned it a
collection number and recorded the flower color,
associated dominant vegetation, date, collector
name(s), and UTM coordinates. We pressed and
processed the specimens on site. Specimens
remained pressed for two to three weeks and
were later frozen for 48 hours or more to prevent
infestation by insects and pathogens. Mounted
specimens were accessioned into the University
of Arizona Herbarium.
Effort
We collected specimens during 38 days of
fieldwork between 10 April and 24 September
2001 and 4 and 5 May 2002. We collected
specimens from 41 locations throughout the
district (Fig. 3.1) and many of the collections
were made in the course of traveling to and from
focal points.
Analysis
We present a variety of summary statistics
including total number of species found and
number and percent of native and non-native
species.
Modified-Whittaker Plots
We used modified-Whittaker plots to characterize
the plant community at a single area associated
with focal points. Each plot was 20 x 50 m
(1000 m²) and contained 13 subplots of three
different sizes (see Stohlgren et al. 1995a): 0.5
x 2 m (10 subplots), 2 x 5 m (2 subplots), and 5
x 20 m (1 subplot) (Fig. 3.2; Shmida 1984). We
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estimated the coverage (m2 ) of each plant species
for the entire 1000 m2 plot. For all subplots we
simply noted the presence of each species. For a
more detailed explanation of the data collection
method, see Shmida (1984). We deviated from
the methods outlined in Shmida (1984) by not
surveying against the contours in steep areas,
because of safety reasons.
Effort
We used modified-Whittaker plots at 13 of the 17
focal points (Fig. 3.3). We excluded four plots
(numbers 120, 121, 125, and 155) because of
logistical constraints. We used a single observer
(Patty West) to estimate percent cover in the 20
x 50 m plot, but other observers occasionally
assisted with noting presence of plants in
subplots.
Analysis
We note patterns of species richness among plots
and community types. In this report we do not
present a complete summary of the data, but
instead will archive these summaries (see Chapter
1 for archive locations).
Point-intercept Transects
Methods
We used the point-intercept method (Bonham
1989) to sample vegetation along 50-m transects
located along each focal-point transect (Fig.
3.4). Point-intercept transects began at 25, 125,
425, 525, 825 and 925 m from the beginning of
the transect (i.e., focal point). For example, the
first transect started at 25 m from the focal point
and went to the 75-m mark. We placed a 50-m
transect tape along the length of each transect
section. In each of four height categories (4 m) we recorded the
species of the first plant intercepted by a vertical
line every 1 m along the transect line (n = 300
points for most transects). We created the vertical
line using a graduated pole and extrapolated
contacts in a fourth height category (>4 m),
which was rarely used in the desert areas. We
classified groundcover as rock, bare ground,
annual forb, grass or woody debris.