December 2012 Number 1 - Utah Native Plant Society

Utah Native Plant Society
METHODS
Plant Species
Penstemon harringtonii is a potentially long-lived
perennial forb in the Scrophulariaceae. A distinctive
characteristic of the species is the exsertion of the two
lower stamens from the blue to pink/lavender corollas
(Figure 1). Flower production and seedling recruitment
are thought to be episodic and probably related to seasonal
precipitation and available soil moisture (Panjabi
and Anderson 2006). The species is found in open sagebrush
(A. tridentata) and less commonly in pinyonjuniper
plant communities between 1951 and 2865m
elevation. All major threats are based on increased human
use and development in the region for housing, ski
areas, resource extraction, grazing, and recreation
(CoNPS 1997, Spackman et al 1997).
Study Sites
Two geographically and ecologically diverse populations
of P. harringtonii have been monitored since
1996. The Eagle study site is a sagebrush-steppe community
near the town of Eagle, CO and is at an elevation
of 2100m (Buckner and Bunin 1992). The site was
roller-chopped in the 1980s (BLM personal communication)
to decrease shrub cover and promote graminoid
forage for cattle grazing and has relatively low sagebrush
cover (6.99%). The Gypsum study area is located
near the town of Gypsum, CO at an elevation of 2200m
(Buckner and Bunin 1992). Relative to the Eagle site,
this area has much higher cover of sagebrush (25.57%)
and lower densities of P. harringtonii. Sagebrush cover
was determined using the line-intercept method on the
aerial cover of the shrubs and consisted of ten 60m transects
per site. Based on a two-sample t-test, the amount
of sagebrush cover was significantly different between
the two study sites (P < 0.0001, alpha = 0.05, n = 10).
Long-term Demographic Study
At each site a 40 x 60m macroplot was installed at a
location containing P. harringtonii and 1 x 60m quadrats
were sampled within the macroplot based on a
stratified random sampling method. The goal of the
monitoring was to be statistically capable of detecting a
20% change in the populations of P. harringtonii and
was designed with the analysis having a power of 95%
with a 1% chance of making a false-change error (Type
I). Sample size and power analyses were conducted on
the two initial years of data (1996 and 1997) to determine
the appropriate number of quadrats for each site
(Elzinga et al. 1998). The eight quadrats sampled at the
Eagle site and 12 at Gypsum were sufficient to meet the
desired power of the study. Within each quadrat the following
data were collected: x and y coordinates, number
of rosettes, and presence or absence of flowers, fruits
Figure 1. Penstemon harringtonii (Photo by Carol Dawson).
and herbivory. The quadrats were censused annually in
early to mid-June. Repeated measures Analysis of Variance
(ANOVA) and paired t-tests were utilized to determine
statistically significant differences in rosette numbers
over time or between years, respectively. Data were
log transformed for statistical analysis.
Plant Community Analysis
In the summer of 2005 additional sampling of the
macroplots was conducted as part of a Denver Botanic
Garden internship investigating the relationship between
A. tridentata density, soil moisture and the rare penstemon.
Species richness and the density of sagebrush and
Harrington’s penstemon were determined for 4 x 2m
plots randomly located within the existing macroplots at
the Eagle and Gypsum study sites. Sample size and
power analysis determined that 17 and 20 plots were
necessary for the Eagle and Gypsum study areas, respectively
(Elzinga et al. 1998). Sample size was estimated
using the 2005 data and a confidence level of
90%. Analysis of the plant community data was conducted
using Non-metric Multi-dimensional Scaling
(NMS), a non-parametric multivariate ordination technique
capable of detecting and describing vegetation
patterns between the sites and correlating this inform-
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