December 2012 Number 1 - Utah Native Plant Society

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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- 116
Calochortiana December 2012 Number 1 ation to species richness, soil moisture, and sagebrush density. The NMS used a Sorenson distance matrix and the presence or absence of plant species for the primary data matrix. The secondary matrix consisted of species richness per plot, categorical values for the ratio of Penstemon to Artemisia densities, and a dummy variable designating within which site the data are associated. Multi-Response Permutation Procedures (MRPP) provided a non-parametric statistical method to test for differences between groups (study sites) by comparing the heterogeneity within groups against the probability of occurrence by random chance. This type of randomization or permutation test provides an ‘A’ statistic and a ‘P’ value that is used to determine if the two study sites are statistically significant from each other based on species compositions. Both NMS and MRPP were conducted in PC-Ord version 5.0 software (MjM Software 1999). Linear regression and correlation coefficients (R 2 ) were determined between penstemon and sagebrush densities, soil moisture, and species richness using Microsoft Excel. RESULTS Long-term Demographic Study The 13 years of monitoring documented statistically significant variation in the number of rosettes per quadrat using a repeated measures ANOVA (Between subjects: P
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December 2012 Number 1 - Utah Native Plant Society

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