Investigating the impacts of thinning treatments on Penstemon personatus on the Plumas NF Michelle Coppoletta, Colin Dillingham, and Kyle Merriam 30 March 2012 Introduction Penstemon personatus (closed‐throated beardtongue) is a rare species that is presently known from four counties in the northern portion of the Sierra Nevada mountain range. Most of the P. personatus occurrences (74 percent) are found within the boundary of the Plumas National Forest (NF) where this rhizomatous perennial occurs in 23 large but localized populations that vary in size from thousands of individuals to less than 10. P. personatus is currently designated as a Sensitive species by the USDA Forest Service (USDA Forest Service 2006). The California Native Figure 1. Penstemon personatus flower
Plant Society lists P. personatus as a 1B.2 species, which indicates that it is fairly endangered in California (California Native Plant Society 2010). Past observations suggest that P. personatus may tolerate or even benefit from management activities that open up the forest canopy if ground disturbance is minimized (Hanson 1987, Urie, Tausch and Hanson 1989). In the past, these types of lower impact activities have included selective removal of scattered large trees, reduction of the canopy by 30 percent or less, and cable logging. In contrast, this species does not appear to tolerate high impact activities, which result in high levels of soil displacement or compaction (Hanson 1987, Coppoletta et al. 2010). In 2006, Plumas NF botanists and Sierra Cascade Province ecologists developed objectives to guide the P. personatus monitoring effort. The intent was to define management triggers (i.e. actions resulting from monitoring), which would guide the future management of P. personatus on the Plumas NF. The objectives and management response were defined as follows: 
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Management Objective: To maintain P. personatus frequency or percent cover of at least half of the pre‐treatment mean and to evaluate the significance of declines in P. personatus cover relative to untreated controls. Sampling Objective: To detect a 50 percent change in the frequency or percent cover of P. personatus with a 90 percent confidence that our estimated mean is within 10 percent of the true value. Management Response: If sampling detects a decline of greater than 50 percent in P. personatus cover or frequency after treatment, the treatment would be considered detrimental to P. personatus occurrences and would not be advised. We will also evaluate the significance of declines in P. personatus cover in comparison to untreated control plots. The following summary presents the results of an analysis of P. personatus percent cover data collected between 2006 and 2010. The objective of this monitoring effort and analysis was to determine the effects of different types of timber harvest activities on P. personatus cover and to assess whether the 2006 management objectives were met. To frame the analysis, we focused on the following questions: 1. Were the management objectives for P. personatus met? If not, are management actions required? 2. Do timber harvest treatments result in a decline in P. personatus cover? 3. Are environmental variables, such as overstory canopy and duff and litter depth, associated with P. personatus cover? Methodology In 2006, permanent monitoring transects were established at eleven sites within the HFQLG project area. Within sites, four to six parallel transects (200 feet in length) were positioned at a minimum of 50 feet apart, along a randomly located baseline. Pilot sampling conducted in 2006 (within the Waters 29 Unit) indicated that six transects were sufficient to meet our sampling objective, which was to detect a 50 percent change in the mean cover of P. personatus with a 90 percent confidence interval. Along each transect, P. personatus cover was measured using a line intercept methodology (described in Elzinga, Salzer and Willoughby 1998). Overstory canopy and duff/ litter depth were also measured at 20 foot intervals. All data were input into the QLG effectiveness monitoring database. Figure 2. Colin Dillingham in a group selection monitoring unit To date, pre and post‐treatment monitoring have been conducted at eight sites. Treatments at these sites have included hand‐thinning and pile burning (n=1); mechanical thinning (n=2); and group selection (n=2). Three P. personatus monitoring sites have received no treatment and are used as controls (see Table 1). Table 1. Results of P. personatus line intercept monitoring. The one‐sided 90% confidence interval is included in parentheses. The threshold of concern is a decline of 50 percent from the pre‐treatment cover. Treatment Group Selection Mechanical Thin Hand thin/Pile Burn Control Units Percent Change in PEPE Cover Years in which Confidence Interval includes Threshold Value (decrease 1 yr post‐
3 yrs post‐
of 50%) treatment treatment Guard 442 (n=6) ‐57% (‐73%) 21% (‐28%) Guard 845 (n=6) 184% (34%) 240% (105%) Guard 15 (n=4) 81%(‐21%) Guard 16h (n=6) 33% (6%) 4% (‐26%) Waters (n=6) 60% (20%) 134% (58%) Guard Control (n=5) 297% (46%) Lotts Control (n=5) 240% (46%) 1 year post Treatment Units Faggs Control (n=5) Percent Change in PEPE Cover Years in which Confidence Interval l d
h h ld l (d
281% (‐109%) 204% (‐103%) 1 and 3 years post Statistical Analysis The percent change in cover was investigated by comparing pre and post‐treatment cover values over two time periods: (a) one year after treatment and (b) three years after treatment. For the control units, the change in cover was calculated using the first measurement value for comparison, rather than a pre‐treatment value. One‐sided 90 percent confidence intervals were calculated to investigate whether decreases in cover exceeded our stated management threshold (i.e. a decline of 50 percent from pre‐treatment cover). The management objectives did not specify the level of analysis; therefore we evaluated changes within individual units as well as within treatment types. A generalized linear mixed model was used to analyze the effect of the different treatments on P. personatus cover within the first three years following treatment. Multiple linear regression was used to investigate the relationship between environmental variables (canopy cover and duff/litter depth), treatment, and P. personatus cover. Cover data were logit transformed for analysis. A value equal to half of the smallest non‐zero value was added to all cover values to allow for the transformation of zero values. Data were analyzed using the statistical software programs SAS 9.3 (SAS Institute 2010) and R version 2.14.1 (The R Foundation for Statistical Computing 2011). Results Were the management objectives met? If not, are management actions required? Our stated management objective was to maintain P. personatus percent cover of at least half of the pre‐treatment mean, and to evaluate the significance of declines in P. personatus cover relative to untreated controls. As seen in Figure 3, our management objective was met for all of the treatment units when analyzed over the entire monitoring period, which extended up to three years after treatment. The only treatment unit to show a decline greater than our stated management objective was group selection unit Guard 442. The percent cover of P. personatus within this unit dropped by an estimated 57 percent in the first year following group selection thinning; however three years after treatment, the percent cover had rebounded to an estimated 21 percent more than the cover prior to treatment. This result corresponds with both past observations (Castro 1991, Zebell, Castro and Dwerlkotte 1991, Dwerlkotte 1990) and recent P. personatus data analyses (Coppoletta et al. 2010); these observations and analyses found that P. personatus frequency tended to drop in the first year after logging and then rebound in year three to levels similar to pre‐logging. This result is not surprising considering that plants can be directly impacted by equipment during treatment implementation or indirectly impacted by changing light conditions. These impacts may result in an initial decline in plant cover or frequency; however because P. personatus is rhizomatous, it is most likely able to recover to pre‐treatment levels by re‐sprouting a few years after treatment. PercentChangeinPEPECover
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Figure 3. The percent change in P. personatus cover within units one and three years after treatment. The red line represents the management threshold, which is a decrease of 50% from the pre‐treatment cover estimates. The error bars represent one‐sided 90 percent confidence intervals. PercentChangeinPEPECover
The management objective was also met when the individual units were pooled and changes within treatments analyzed (Figure 4); none of the means (representing the estimated amount of change in cover) or 90 percent confidence intervals dipped below the threshold of concern, which represents a decrease of 50 percent from pre‐treatment cover. 275%
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Figure 4. The percent change in P. personatus cover one and three years after treatment. The red line represents the management threshold, which is a decrease of 50% from the pre‐treatment cover estimates. The error bars represent one‐sided 90 percent confidence intervals In the figure above, the confidence intervals for group selection (one year after treatment), mechanical thinning (three years after treatment), and the control (in the second year of monitoring) all include zero. This suggests that the difference between the percent cover of P. personatus at that time period and the pre‐treatment cover was not significantly different (α=0.1). In contrast, all of the other estimates of change were significantly different from zero. Conclusions: 
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Sampling did not detect declines of greater than 50 percent in P. personatus cover three years after treatment; therefore treatments are not considered detrimental to this species and no management action is required at this time. P. personatus cover within units may decline in the first year or two following treatment; however it has shown the ability to rebound after year three to pre‐treatment levels. Do timber harvest treatments result in a decline in P. personatus cover? Thinning treatments did not result in a significant decline in P. personatus cover over time (p=0.06, α=0.1). The percent cover of P. personatus within treatments and controls did not differ significantly from their pre‐treatment values one or three years after treatment (Figure 5). AveragePercentCoverofPEPE
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Figure 5. Percent cover of P. personatus prior to treatment and one and three years after treatment. Error bars represent standard error. Are environmental variables, such as overstory canopy and duff and litter depth, associated with P. personatus cover? P. personatus cover was significantly and positively related to overstory canopy cover (p= 0.004, α=0.05) when variables such as duff and litter depth were included in the model and held constant. This result suggests that within areas of similar duff and litter depth higher canopy cover will generally be associated with higher P. personatus cover. The partial regression plots in Figure 6 below allow us to investigate the association between P. personatus cover and each of the two explanatory variables, after accounting for the effects of the other 1.5
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variable. These plots show a positive and relatively linear relationship between overstory canopy and P. personatus cover. In contrast, duff and litter depth does not appear to have a significant effect on P. personatus cover, when canopy cover is held constant. 0.5
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Figure 6. Partial regression plots showing the relative effect of (a) duff/litter and (b) canopy cover on P. personatus cover. Duff and litter values were log transformed. P. personatus and overstory canopy cover were logit transformed. It is important to note, that treatment (i.e. whether a site was treated or not) was significantly correlated to canopy cover (p=0.016, α=0.05); as we would expect, treated areas were associated with lower overstory canopy cover. Because of this correlation, this variable was not included in the final model. The R² value measures the amount of total variation in P. personatus cover that is described by its linear relationship with canopy cover or duff/litter depth. In our case, less than five percent of the total variation in the data were explained by the two habitat variables that we measured. This suggests that while overstory canopy and duff and litter depth may explain some of the variation that we see in P. personatus cover, there are likely other factors that we did not measure that may explain more of the variability in our data. Recommendations: 
Refine management objectives to add time dimension and to clarify the level of analysis. The current management objective states the following: Previous Management Objective: To maintain P. personatus frequency or percent cover of at least half of the pre‐treatment mean and to evaluate the significance of declines in P. personatus cover relative to untreated controls. Refined Management Objectives: 
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Evaluate the effect of management activities on P. personatus frequency and percent cover;  Within treatments, maintain an average of at least half of the pre‐treatment mean value (frequency or percent cover) over the first five years following treatment; and  Evaluate the significance of declines in P. personatus relative to untreated controls. Complete post‐treatment monitoring in order to achieve our goal of at least three sites within each treatment type; this will likely improve the experimental power of our design. Evaluate the line‐intercept cover method as a viable method for detecting change in cover for P. personatus. The low percent cover of P. personatus makes the design extremely sensitive to very small changes; for example, if one plant is missed, it may result in a decrease of 25 percent of the total cover along the transect. Line‐intercept is generally effective for species with dense canopies (i.e. shrubs or matted plants), but may not be as effective for species with sparse canopies such as P. personatus. The low percent cover of P. personatus also makes the design more susceptible to observer error (i.e. because the sighting line is not perpendicular to the tape or if wind causes the tape to shift). References California Native Plant Society. 2010. Inventory of Rare and Endangered Plants. February 11, 2010). Castro, B. 1991. Hardquartz Monitoring: Penstemon personatus; Analysis of data 1983‐1990. USDA Forest Service, Plumas National Forest. Coppoletta, M., K. Merriam, C. Dillingham & L. Hanson. 2010. The effect of timber management activities on Penstemon personatus on the Plumas National Forest. USDA Forest Service. Dwerlkotte, R. 1990. 1990 Penstemon personatus monitoring summary for the Quincy Ranger District. USDA Forest Service, Plumas National Forest. Elzinga, C. L., D. W. Salzer & J. W. Willoughby. 1998. Measuring and Monitoring Plant Populations. BLM Technical Reference 1730‐1, Denver, Colorado. Hanson, L. 1987. Species Management Guide for Penstemon persontaus. Urie, S., R. Tausch & L. Hanson. 1989. A Statistical Analysis of Penstemon personatus. USDA Forest Service. 2006. 2006 Sensitive Plant List, Pacific Southwest Region, Region 5. Letter from Regional Forester Weingardt. File Code: 2670. Dated July 27, 2006. Zebell, R., B. Castro & R. Dwerlkotte. 1991. Penstemon personatus frequency monitoring, 1980‐1990 ‐‐ Summary. USDA Forest Service, Plumas National Forest.